Here we overcome these challenges with a chalcogenide glass-on-CaF2 PIC architecture incorporating split-gate photothermoelectric graphene photodetectors. Our design extends operation to λ = 5.2 μm with a Johnson noise-limited noise-equivalent power of 1.1 nW/Hz1/2, no fall-off in photoresponse up to f = 1 MHz, and a predicted 3-dB bandwidth of f3dB > 1 GHz. This mid-IR PIC platform readily extends to longer wavelengths and opens the door to applications from distributed gas sensing and portable dual comb spectroscopy to weather-resilient free space optical communications.The development of compact and fieldable mid-infrared (mid-IR) spectroscopy devices represents a critical challenge for distributed sensing with applications from gas leak detection to environmental monitoring. Recent work has focused on mid-IR photonic integrated circuit (PIC) sensing platforms and waveguide-integrated mid-IR light sources and detectors based on semiconductors such as PbTe, black phosphorus and tellurene. However, material bandgaps and reliance on SiO μm. Here, the authors report the realization of photothermoelectric graphene photodetectors incorporated in a chalcogenide glass-on-CaF2 PIC operating at 5.2 μm, showing promising results for gas sensing applications.Mid-infrared photonic integrated circuits (PICs) are important for sensing and optical communications, but their operational wavelengths are usually limited below 4  To facilitate sensor deployment for greenhouse gas leak detection and other chemical sensor application areas, there exists a strong need to transition from co-packaged discrete components to compact and chip-integrated sensors.Mid-IR absorption spectroscopy is a critical tool for chemical sensing and analysis, especially for inert gases that evade detection by chemical reaction-based sensors. Many such gases derive their inertness from halogenated chemistries and thus exhibit global warming potential due to carbon-halogen stretching modes resonant in the thermal IR3 and volatile organic compound4 sensing, but required coupling to off-chip sources and detectors. However, integrating the detector on-chip is more compact and can improve sensitivity by reducing the volume of active material able to generate thermal noise. Su et al. achieved integration of a PbTe photoconductor and demonstrated methane sensing at a wavelength of λ = 3.31 μm5, but their platform is limited to λ ≲ 4 μm due to absorption in the SiO2 substrate6 and by PbTe’s absorption cutoff7. Waveguide-integrated detectors based on narrow-gap 2D materials black phosphorus8 and tellurene9 have also been demonstrated, but they too are bandgap-limited to λ ≲ 4 μm.To address this challenge, mid-IR photonic integrated circuit (PIC) platforms have been investigated to reduce optical gas sensors to the size of a chip. Recent work has demonstrated integrated optical methane10, the material’s advantages are magnified further at longer wavelengths due to the thermal nature of the photothermoelectric (PTE) response mechanism12 and due to the impact of optical plasmon scattering at short wavelengths13. Integrated photodetection with graphene has been demonstrated at wavelengths up to 3.8 μm6 and with chalcogenide glass waveguides14, but on SiO2 platforms. To access longer wavelength operation and achieve good sensitivity at zero-bias, we introduce a Ge28Sb12Se60 (GSSe)-on-CaF2 waveguide platform supporting gated PTE-based graphene photodetectors. These key changes allow us to extend operation to a wavelength of λ = 5.2 μm while achieving a Johnson noise-limited noise-equivalent power (NEP) of 1.1 nW/Hz1/2. By comparing the gate voltage maps of our device’s resistance, transmittance, and responsivity with a photothermoelectric model, we extract material quality parameters of the graphene channel, revealing a path to further reduce the device’s NEP by shrinking the optical mode size in tandem with the graphene channel.Here we exceed the wavelength limit of previous demonstrations using graphene-based detectors on an extended-transparency waveguide platform. While graphene integrated detectors have shown promise at telecom wavelengths2 as the gate dielectric and as an airtight capping layer. The device is fabricated on a CaF2 substrate, transparent up to λ = 8 μm. Figure λ = 5.2 μm.Figure λ = 5.2 μm QCL source into our chip’s input facet. Light exiting the chip is focused onto an InAsSb photodetector and amplified for transmission measurement. Supplementary Fig. f noise15. For the following low-frequency measurements we use a lock-in amplifier to measure the photovoltage directly with no preamplification.We use lock-in measurement to characterize our detectors, focusing light from a λ = 5.2 μm QCL source at 3.78 kHz with a guided “on” power of 11 μW at the detector input. From our photovoltage and resistance maps, alongside the power and waveguide loss calibrations described in Supplementary Note 1/2, respectively. The observed photovoltage gate map indicates a PTE response mechanism, evidenced by the six-fold sign change pattern around the graphene channel’s charge neutral point11. Figure 11.Figure 12 to calculate the electronic temperature distribution and Seebeck photovoltage in the graphene channel under illumination. Figure τeph are established a priori from fitting parameters extracted from the device transmittance and resistance maps, with only τeph obtained by matching the scales of the measured and modeled responsivities. The resemblance between Fig. Tel(x), as well as the source term To confirm our understanding of device operation and elucidate the prospects for performance improvement, we apply the formalism introduced in Song et al.τeph-limited frequency response with an assumed 12. We thus predict a 3-dB cutoff frequency of f−3dB ≈ 1.3 GHz, dominated by the capacitance between the graphene back-gates.Current modulation of our QCL source permits frequency response measurements up to its modulation bandwidth of 1 MHz. To account for the modulation response of our laser, we measure the photovoltage of Device A alongside that of a fast InAsSb photodiode. The comparison shown in Fig. To investigate our device’s noise performance, we modulate the QCL current at 30 kHz, amplify the photovoltage with a low-noise preamplifier and inspect using a signal analyzer. As shown in Supplementary Fig. 16:I0 is the source power, αbase is the waveguide attenuation coefficient in the absence of gas, a is the specific attenuation coefficient of the gas, ng is the guided mode group index, ΓE is the confinement factor of electric field energy within the gaseous medium, and λ = 5.24 μm and a specific attenuation of approximately a ≈ 70 m−1atm−1 at low concentrations17, we arrive at 18. Removing the slightly lossy HfO2 dielectric underneath the gas-light interaction waveguide could decrease 19.To demonstrate our device’s utility, we analyze its predicted gas-sensing performance, summarized from Supplementary Note λ = 5.2 μm by light source availability, the optical conductivity of our graphene inferred from the fitting parameters in Table λ = 10 μm and beyond, perhaps requiring a BaF2 substrate for extended transparency, with little reduction in performance owing to the PTE effect’s thermal nature. In Table 20. Additionally, the vacuum requirement of VOx bolometers may complicate co-packaging and introduce coupling losses, and the high cost of HgCdTe may preclude use in broadly deployed sensor networks.Although our demonstration is limited to 1/2 and a bandwidth exceeding f−3dB = 1 MHz. We have modeled the bandwidth to approach 1.3 GHz and we predict similar performance at longer wavelengths for scaled-up devices enabled by the transparency of GSSe beyond λ = 10 μm21. Finally, we have shown that our device and waveguide platform would enable NO detection at concentrations comparable to its REL. Substantial improvements are likely using metal-insulator-metal10 or dielectric slot waveguides to concentrate the optical mode to within a cooling length of the pn-junction, which would also increase the attenuation of the guided mode and thus decrease the device footprint needed to absorb an optical signal. Gapped bilayer graphene may also be investigated as an alternative to monolayer graphene to reduce thermal noise22. The PIC platform further promises to support a full toolkit of mid-IR active devices including on-chip quantum cascade light sources23, and may even leverage the same graphene material platform for devices such as graphene modulators14 and hot-electron-based24 or gapped bilayer graphene light sources. The platform could also be adapted to alternative mid-IR waveguide approaches, such as suspended Ge, as necessary to reach longer wavelength ranges25. Chalcogenide glass could then supplement such a platform by enabling designs where the graphene channel is sandwiched between the Ge and high-index glass to increase overlap with the optical mode. This research represents the first foray into waveguide-integrated detectors operating beyond λ = 4 μm, paving the way towards 2D-material-enabled integrated mid-IR microsystems for gas sensing, spectroscopy20 and free-space optical communications26.In conclusion, we have demonstrated a PTE-based graphene photodetector, integrated in a scalable chalcogenide glass waveguide platform with an NEP of 1.1 nW/Hz2 in a 1-inch-diameter quartz tube furnace under atmospheric pressure. The furnace was heated to 1060 ∘C over 30 min under 500 sccm of Ar flow; afterwards, 15 sccm of H2 and 10 sccm of dilute CH4 (1% in Ar) were introduced as reducing gas and carbon source, respectively, and flowed for 4 h to ensure the continuity of the graphene film. Finally, the furnace was allowed to cool to 100 ∘C without modifying the gas flow before the CVD graphene was removed from the chamber. Our devices were fabricated on a 1" diameter by 1.0 mm thick (111)-cut CaF2 substrate . We first coated our substrate with a PMMA bilayer for liftoff (495 PMMA A6 followed by 950 PMMA A2), which features a slightly re-entrant sidewall profile after developing. We then performed e-beam lithography using an Elionix FLS-125 125 keV electron beam lithography system to pattern alignment marks on our substrate, followed by room-temperature development in 3:1 isopropanol:methyl isobutyl ketone for 90 s and isopropanol rinse for 120 s (“development process”), e-beam evaporation of 5 nm Ti/100 nm Au  , and liftoff using a 4-h room-temperature acetone soak (“liftoff process”). To transfer the first layer of graphene, we first coated one side of the CVD graphene-on-Cu sheet with PMMA and removed the graphene from the other side using 90 s of oxygen RIE . We then etched away the Cu using a FeCl3-based etchant, followed by 2 DI water rinses, a 30-min clean in 5:1 DI water:HCl 37% in water to reduce metal ion contamination, and two more DI water rinses. After letting the graphene film sit overnight in the final evaporating dish of water, we scooped it out with our CaF2 substrate, blew N2 on the film to eliminate most of the trapped water, and then baked the sample at 80∘ for 30 min followed by 160∘ for 2 h (“graphene transfer process”). We then removed the PMMA from the graphene using acetone at room temperature, rinsed it in isopropanol and blew it dry , and baked the sample at 200 ∘C in N2 for 1 h to improve adhesion. To pattern the graphene back-gates, we spun on a layer of 950 PMMA A6, exposed the gates in the Elionix and developed using “development process”, etched away the exposed graphene using “oxygen RIE process” for 45 s, and removed the PMMA using “PMMA removal process”. We then spun on another 495 PMMA A6/950 PMMA A2 bilayer, exposed the metal contacts to the graphene gates using the Elionix FLS-125, and repeated “development process”, “metal evaporation process”, and “liftoff process”, but using a 2 nm Ti adhesion layer in the Ti/Au stack rather than 5 nm. After this, we evaporated 1.5 nm Al  as an ALD seed layer, allowed the thin Al layer to oxidize in ambient, and deposited 300 cycles ≈ 30 nm of HfO2 ALD at 200 ∘C (Cambridge Nanotech Savannah 200). To define the graphene channel, we performed another “graphene transfer process”, “PMMA removal process”, 1 h N2 ambient 200 ∘C bake, 950 PMMA A6 spin-coating, Elionix FLS-125 exposure of graphene channel pattern, “development process”, “oxygen RIE process” for 45 s, and “PMMA removal process”. To define the channel contacts, we spin-coated another 495 PMMA A6/950 PMMA A2 bilayer, exposed the graphene channel contacts using the Elionix FLS-125, and performed another “development process”, “metal evaporation process”, and “liftoff process”, but using a 2 nm Ti adhesion layer in the Ti/Au stack rather than 5 nm. We then evaporated another 1.5 nm Al seed layer using the Temescal VES2550 and 150 cycles of HfO2 ALD at 200 ∘C using the Cambridge Nanotech Savannah 200 to protect the graphene channel. Finally, to pattern the GSSe waveguides, we coated the chip with 495 PMMA A11, used the Elionix FLS-125 to define the waveguides, and developed in room-temperature 3:1 isopropanol:methyl isobutyl ketone for 120 s followed by an isopropanol rinse for 120 s. The longer development time is mandated by the thicker resist film. We then evaporated 750 nm of Ge28Sb12Se60 followed by a quick liftoff in boiling acetone (~20 min), IPA rinse and N2 blow-dry, and cleaving of the chip to expose waveguide facets.A continuous monolayer graphene film was grown on Cu foil  cut to a size of 15 × 2 cmThe maps in Fig. 27 to model graphene’s conductivity at DC and infrared frequencies :e is the elementary charge, kB is Boltzmann’s constant. As I will show below, graphene’s low-frequency conductivity σDC and infrared conductivity σIR affect various intermediate model parameters; σDC and σIR themselves depend strongly on EF, which features spatial variation due to the back-gates. For the graphene channel, we assume a constant Nc = N0,c  +  e−1CgVg in the region above each gate, where Nc is the carrier concentration in the channel , N0,c is the native carrier concentration at zero gate voltage, Cg is the capacitance per area of the gate dielectric, and Vg is the voltage applied to the gate in question  using ω = 2πc/λ instead of 0 and τIR instead of τDC. Finally, we have 28. Cel is obtained by convolving the heat capacity of pristine graphene with a Gaussian of standard deviation σN as in Eqn. , noting of course that σIR,g(x) = 0 for x within the gap between the gates where there is no graphene. Finally, We use a waveguide eigenmode solver to find the mode profile of our waveguide at κ(x), Cel(x), S(x), Π(x), αc, αg and ρΩ as a function of the gate voltages, as well as τDC, τIR, σn, EFc, EFg, τeph, αe, and ρc, we then solve for the increase in electronic temperature per guided power ΔTel(x)/P = (Tel(x) − T0)/P using the equation:κ is the 2D electronic thermal conductivity of the graphene, τeph is the electron-phonon cooling time, η is the conversion efficiency of absorbed optical power to electronic heat after initial electron-phonon scattering12, Jx is the line current density in the x-direction, and Π is the Peltier coefficient. We are approximating the electric field to run exclusively in the x-direction, valid for sufficiently gradual light absorption. We assume η = 1, as has been previously reported in pump-probe experiments at this wavelength range13. The thermal electromotive force (EMF) arising from the Seebeck effect is then given by:W = 5.4 μm is the channel width and S is the Seebeck coefficient. In Eqns.  are all dependent on the local Fermi level EF of the graphene, and thus have a gate-tunable x-dependence, which we account for in our calculations. Combining the equations, the V is the voltage across the contacts, αc is the component of the waveguide power attenuation coefficient arising from absorption in the graphene channel, P(z) is the guided power at a position along the waveguide, and ρΩ, ρΠ, ρc are the Ohmic, Peltier, and contact line resistivities (dimensions of Ω ⋅ m), respectively. Averaging over z along the length of the waveguide we obtain:I is the current produced by the photodetector, thus describing a Thévenin equivalent source. Here, αtot = αc + αg + αe is the total guided power attenuation coefficient within the detector, including contributions not only from the graphene channel but also from the graphene gates (αg), as well as a gate-independent excess loss αe associated with scattering and absorption from organic or metallic impurities attached to or trapped underneath the graphene sheets. Thus, the total device resistance is equal to R = RΩ + RΠ + Rc, and the voltage responsivity is given by:Having thus obtained expressions for mentclass2pt{minimSupplementary Information


Cryo-electron microscopy (cryo-EM) visualizes the atomic structure of macromolecules that are embedded in vitrified thin ice at their close-to-native state. However, the homogeneity of ice thickness, a key factor to ensure high image quality, is poorly controlled during specimen preparation and has become one of the main challenges for high-resolution cryo-EM. Here we found that the uniformity of thin ice relies on the surface flatness of the supporting film, and developed a method to use ultraflat graphene (UFG) as the support for cryo-EM specimen preparation to achieve better control of vitreous ice thickness. We show that the uniform thin ice on UFG improves the image quality of vitrified specimens. Using such a method we successfully determined the three-dimensional structures of hemoglobin (64 kDa), α-fetoprotein (67 kDa) with no symmetry, and streptavidin (52 kDa) at a resolution of 3.5 Å, 2.6 Å and 2.2 Å, respectively. Furthermore, our results demonstrate the potential of UFG for the fields of cryo-electron tomography and structure-based drug discovery. This paper shows that the uniformity of vitreous ice thickness relies on the surface flatness of the supporting film, and presents a method to use ultraflat graphene as the support for cryo-EM specimen preparation. For small biomolecules with molecular weight less than 100 kDa, low contrast in cryo-EM hinders successful reconstruction and lowers the resolution able to be achieved7, given that high-resolution structural determination requires thin ice to minimize the background noise. During the standard process of preparing thin ice in cryo-EM specimen preparation, a thin liquid film is normally obtained by wicking excess solution from a supporting film. The rough and heterogeneous liquid–solid interfaces during wicking have recently been found to be a fundamental limitation to the production of a reproducible and uniform ice thickness8. In 1990 the homogeneity and thickness of thin liquid film were found to be markedly influenced by the roughness of the underlying support. That is, the thinner the liquid film, the more dominant the effect of support roughness10. Thus, the production of uniformly thin vitreous ice would appear to be dependent on the development of an ultraflat supporting film.Cryo-electron microscopy (cryo-EM) has become a major tool in structural biology. As the resolution achievable by cryo-EM improves, the production of the uniformly thin ice required for high-resolution structural determination becomes increasingly important21. The height difference of the wrinkled surface can be up to dozens of nanometers   are inevitable even on thin graphene oxide nanosheets and graphene films grown on copper foil, although both have proven to be helpful for better cryo-EM specimen preparationET) Fig. .Fig. 1GrIn this Article we present a pre-tensioned ultraflat graphene (UFG) without wrinkling for uniform thin ice preparation Fig. , in whic23, that is, dense rolling lines of copper foil  of graphene on the wafer is only 0.28 nm, and no sharp step bunches or wrinkles are observed /sapphire wafer as a growth substrate Fig. . The Cu and Young’s modulus (E) of UFG were 145 ± 13 GPa and 933 ± 171 GPa, respectively, which are comparable to the values of near-ideal graphene exfoliated from graphite  and much higher than those of rough graphene  when the liquid film thickness approaches tens of nanometers for high-resolution cryo-EM8. Based on this, we constructed a theoretical simulation to investigate the influence of shear force on the suspended graphene. For the suspended UFG with a pre-tension of 0.2 N m−1, the suspended membranes remained ultraflat without any distortion under a shear stress of ~10–100 kPa , a thin liquid film is formed and then vitrified as the vitreous ice layer. Under cryo-EM, the vitreous ice on pre-tensioned UFG had evenly distributed intensities across the holes, indicating a uniform ice layer without wrinkles Fig. . In cont31. Consistent with the cryo-ET results, the ice was wave shaped with a thickness variation of 5–20 nm  and followed the standard data-processing workflow to achieve a 2.6 Å resolution reconstruction , due to the poor signal-to-noise ratio, remains a practical limit in cryo-EMion Fig. . In the ion Fig. , inset. ion Fig. 10. To ou0 kDa, dumap Fig. . Furthermap Fig. . For phemap Fig. . The 2.2We prepared suspended UFG using graphene grown on a Cu(111)/sapphire wafer via the face-to-face transfer method with a high yield. The UFG had superior mechanical strength compared with the commonly used graphene-based cryo-EM supports. Importantly, we show that the flatness of the support film significantly influences the uniformity of ice thickness and the height distribution of particles in cryo-EM specimens. The resistance of UFG to deformation enables better control of uniformly thin ice and improves the image quality. We generated a cryo-EM map of 67 kDa α-fetoprotein with no symmetry at a resolution of 2.6 Å and achieved a resolution of 2.2 Å for 52 kDa streptavidin using such UFG grids.41, for which tilted datasets are typically required. Moreover, UFG can provide a flat and uniform interaction surface with functional ligands, thus enabling a more controllable bioactive functionalization for high-affinity and bio-friendly recognition of the target biomolecules. As well as its use in atomic-resolution EM imaging, the design of UFG could be generalized to other 2D materials to further extend the applications to drug discovery, high-performance electronic devices and separation membranes.Given that the uniform and thin ice on UFG eliminated the wavy features at high-angle tilt, UFG is a promising supporting substrate for cryo-ET or cryo-EM analysis with regard to particle preferential orientationA step-by-step protocol is available in the 2 at atmospheric pressure for 1 h to seal the Cu(111) thin film to the sapphire substrate.The single-side polished C-plane (0001) sapphire wafers were purchased from Jiangsu Helios. The sapphire wafer had an ultraflat surface with an average roughness of <0.2 nm and a miscut angle of <0.5°. Before Cu film deposition, the sapphire wafers were annealed at 1,000 °C for 6 h in an oxygen atmosphere. Then, a 500-nm-thick Cu film was deposited onto the sapphire wafer by magnetron sputtering within 30 min using the physical vapor deposition method  with a radiofrequency power of ~300 W and a basal pressure of ~0.15 Pa. Subsequently, the wafers were annealed in a tube furnace at 1,000 °C with 500 standard cubic centimeters per minute (sccm) Ar and 10 sccm H2 at atmospheric pressure, and then 40 sccm CH4 (0.1% diluted in Ar) was introduced for graphene growth. Usually, it took 2 h for graphene to fully cover the surface of the Cu(111) wafer. CH4 gas flow was shut down as soon as the growth was completed, and the sample was then cooled to room temperature.The Cu(111)/sapphire wafer was placed on the surface of the other sapphire wafer  was used to grow graphene film. The Cu foil was first electrochemically polished in phosphoric acid and ethylene glycol solution (v/v 3:1) with a voltage of 2.4 V for 12 min. The polished copper foil was rinsed with deionized water and ethanol in sequence to remove the electrolyte. A nitrogen gun can be used to facilitate the drying process of polished copper foil. The copper foil was then annealed at 1,000 °C for 0.5 h in a tube furnace under a flow of 100 sccm H4)2S2O8 aqueous solution. To transfer UFG from the Cu(111)/sapphire wafer to the transmission electron microscopy (TEM) grids we placed a batch of TEM grids on the wafer. We then dropped a few droplets of isopropanol to cover the surface of these TEM grids. After the solution was volatilized, the TEM grids and UFG were combined  were used to prepare the graphene grids. Note that the grids with copper bars should be avoided because the copper bars can be etched by the (NH4)2S2O8 aqueous solution to etch the Cu(111) film away, to produce graphene grids with UFG covering the holey carbon film. For the etching of the copper foil, the grids/graphene/copper foil composite was floated on the surface of an (NH4)2S2O8 solution because the copper foil was light enough to be supported by the surface tension of the solution42.The grids/graphene/Cu(111)/sapphire composite was submerged in a 1 M  after the chamber was evacuated for 2 min.−1 as calibrated using the Sader method43. A constant deflection rate of 500 nm s−1 was used in all of the tests.The mechanical properties of suspended graphene membranes were measured in nanoindentation experiments using an Asylum Cypher ES system. A single-crystal diamond probe  with a tip radius of ~10 nm was used, and the cantilever stiffness was 30.85 N m44:F is the applied load, σ2D and E2D are the 2D pre-stress and Young’s modulus of the nanosheets, respectively, δ is the indentation depth and r is the radius of the microwells. The dimensionless constant q = 1/(1.05 − 0.15ν − 0.16ν2), in which ν = 0.165 is the Poisson ratio for graphene44. The breaking force and mechanical strength of suspended graphene were directly measured on the graphene grids (Quantifoil R1.2/1.3). Young’s modulus of suspended graphene and the pre-tension were directly measured on the rigid Si3N4 graphene grids (R1.2/1.3) to prevent the deformation of holey substrates during the nanoindentation.The pre-stress and elastic modulus were extracted from the indentation force versus depth data, using the previous model by Lee et al.E = 1,000 GPa, ν = 0.165 and thickness t = 0.335 nm. Two types of graphene models were prepared for comparison. For a UFG sheet, radial displacement is imposed on the circular boundary to impose a pre-stress σ2D = 0.2 N m−1. A rough graphene sheet is formed by squeezing the circular plate along x , which leads to buckling of the plate with a ripple amplitude of ~5 nm. Both graphene sheets then underwent uniform in-plane shear of 10–100 kPa in the x direction.Finite element simulations were performed in ABAQUS software. A circular monolayer graphene sheet with a diameter of 1.2 μm was modeled as a linear elastic isotropic plate using the four-node shell (S4R) element. The following parameters were adopted: Young’s modulus 32, the compressive stress will build up in the thin ice owing to the inhibited volume change when the liquid water cools rapidly and turns into vitreous ice. Naydenova et al. have shown that the largest volumetric strain in ice is Eice≈ 1 GPa and vice ≈ 0.3 as Young’s modulus and Poisson’s ratio of amorphous ice, respectively, there is a radial compressive stress of Nr ≈ −0.58 N m−1 in 2D stress form given that the ice layer thickness is 20 nm). Note that the negative sign means a compressive stress and strain.As noted by Naydenova et al.32, the critical compression for a clamped circular membrane to buckle can be approximated by Ec, hc and vc are the effective Young’s modulus, total thickness and effective Poisson’s ratio of the UFG–ice composite layer, respectively. Applying the rule of mixtures, we can estimate Ec ≈ 16.4 GPa and vc ≈ 0.3. Therefore, the critical compression for the UFG–ice layer to buckle is Nc ≈ −0.13 N m−1.According to the physical theory of ice bending−1. Thus, the maximum effective compressive stress in the UFG–ice composite layer is −0.58 + 0.2 = −0.38 N m−1. Therefore, the calculations above suggest that although the UFG–ice layer might still buckle eventually, the pre-tension in UFG can effectively delay the buckling, and the maximum compression in ice is also notably reduced (from −0.58 N m−1 down to −0.38 N m−1). In contrast, the rough graphene has no pre-tension to compensate for the compression in the ice layer, therefore the rough graphene–ice composite layer has much less resistance to buckling.For UFG, our nanoindentation tests have shown an average pre-tension of approximately 0.2 N mThe morphologies of graphene films on growth substrates and suspended graphene membranes on EM grids were characterized by atomic force microscopy (AFM) in tapping mode (Bruker Dimension Icon with Nanoscope V controller). The coverage of suspended graphene membranes on the graphene grid was collected using scanning electron microscopy (SEM) , and the aberration-corrected scanning transmission electron microscopy (STEM) images of graphene were carried out using a Nion U-HERMS200 microscope at 60 kV.13 we first constructed a plasmid containing the α and β subunits of the 20S proteasome, and the amino terminus of the β subunit was His-tagged. The plasmid was then transformed into Escherichia coli-competent cells and left overnight for expression. The cells were centrifuged and sonicated to obtain the cell lysates, which were finally loaded onto a nickel column  for affinity purification. For α-fetoprotein we first transfected the recombinant vector of pCAG-afp-His-Strep into HEK-293F cells. After transfection the cells were cultured for 2 days and then collected by centrifugation. The pellets were resuspended in lysis buffer and loaded onto Strep-Tactin XT for affinity purification. We then performed gel filtration to obtain the purified α-fetoprotein sample45.Streptavidin was purchased from New England Biolabs  and hemoglobin was purchased from Sigma-Aldrich . For 20S proteasome purification−1 hemoglobin or 1 μM human α-fetoprotein was pipetted onto graphene grids, which had been previously glow-discharged. The grids were transferred into an FEI Vitrobot with humidity at 100% and temperature at 8 °C and blotted for 1 s with a force of −2. Afterward, the grid was plunge-frozen into liquid ethane and kept in liquid nitrogen for further cryo-EM imaging.A 3 μl drop of a sample solution containing 0.2 μM 20S proteasome or 0.1 μM streptavidin or 6 mg ml46 written by J. Lei at Tsinghua University to automatically collect single-particle datasets on an FEI Titan Krios (300 kV), equipped with an energy filter and a Gatan K3 summit detector, with an accumulated dose of 50 e− Å−2. All of the movies contained 32 frames, which were motion-corrected using the MotionCor2 algorithm47. The contrast transfer function (CTF) values were estimated using CTFFIND448. We then used Relion3.149 to select the particles and performed iterative 2D classification to discard bad particles. The remaining good particles were imported for 3D classification and refinement. For hemoglobin, C2 symmetry was imposed in the 3D refinement with a final particle number of 105,000 (Supplementary Table 7VDE)50 was docked into the cryo-EM map and real-space refined in PHENIX51. For α-fetoprotein we collected 2,290 micrographs and used 354,264 particles in the final 3D reconstruction to obtain a 2.6 Å density map. For streptavidin, D2 symmetry was applied in the 3D refinement step. The resolution (2.2 Å) was determined using Fourier shell correlation (FSC) = 0.143 as the cut-off criterion, and the final particle number used here is 260,390  equipped with a Gatan K2 camera. At each tilt angle, we collected movies containing 8 frames, with a sum dose of ~3 e− Å−2 s−1, and the total dose for every tilt series (+60° to −60°) was 120 e− Å−2. The pixel size was 1.25 Å. The movies were first motion-corrected by MotionCor247 and then imported into Etomo54 for alignment and reconstruction. The position of protein particles inside the ice was manually identified and plotted13.Cryo-ET tilt series were acquired using SerialEM softwareThe experiments in Fig. Further information on research design is available in the Any methods, additional references, Nature Portfolio reporting summaries, source data, extended data, supplementary information, acknowledgements, peer review information; details of author contributions and competing interests; and statements of data and code availability are available at 10.1038/s41592-022-01693-y.Supplementary InformationSupplementary Protocols, Figs. 1–8 and Tables 1 and 2.Reporting SummaryPeer Review File


The numerical simulations, by the transfer matrix method (TMM), demonstrate the sensor has a maximum sensitivity of 282°/RIU, which is approximately 2 times greater than the conventional Au-based SPR sensor. The finite difference time domain (FDTD) indicates that the presence of MoS2 film generates a strong surface electric field and enhances the sensitivity of the proposed SPR sensor. In addition, the influence of the number of MoS2 layers on the sensitivity of the proposed sensor is investigated by simulations and experiments. In the experiment, MoS2 and graphene films are transferred on the Au-based substrate by the PMMA-based wet transfer method, and the fabricated samples are characterized by Raman spectroscopy. Furthermore, the fabricated sensors with the Kretschmann configuration are used to detect okadaic acid (OA). The okadaic acid–bovine serum albumin bioconjugate (OA-BSA) is immobilized on the graphene layer of the sensors to develop a competitive inhibition immunoassay. The results show that the sensor has a very low limit of detection (LOD) of 1.18 ng/mL for OA, which is about 22.6 times lower than that of a conventional Au biosensor. We believe that such a high-sensitivity SPR biosensor has potential applications for clinical diagnosis and immunoassays.We investigate a high-sensitivity surface plasmon resonance (SPR) biosensor consisting of a Au layer, four-layer MoS Surface plasmon resonance (SPR) is one of the most powerful optical-sensing technologies due to its high sensitivity, real-time, and label-free detection ,3,4,5,6.Many chemical methods are used to enhance the immobilization of bioreceptors. Among them, the self-assembly monolayer (SAM) has been widely proven to be particularly effective because of its simplicity of fabrication, reproducibility, and good temperature stability ,13,14. MIn addition to these chemical methods, many biosensors, based on metallic nanoslits  or nanoh2 carbon atoms well organized in the form of a honeycomb lattice. It provides better support for biomolecule adsorption due to its rich To solve this problem, a large-area thin graphene layer is used to cover the Au film surface to improve the sensitivity of the SPR sensor ,19. Grap sensing ,21. For  sensing  exploit  sensing  employ 12), have gained much attention for sensing applications. Monolayer MoS2 has many unique advantages, such as higher light absorption efficiency (5%), large direct bandgap (1.8 eV), and larger work function (5.1 eV), so it is widely used in the field of SPR sensing [2 on the surface of a sensor. They demonstrate that the highest sensitivity is about 1902+ for the sensor is 1.0 pM. In addition, the emergence of the chemical vapor deposition (CVD) technique makes the large-area growth of MoS2 possible, which further facilitates the development of MoS2-based SPR sensors [In addition to graphene, other 2D materials, such as molybdenum disulfide , shows that a maximum sensitivity ~282°/RIU is achieved, when the Au-based substrate is modified with four-layer MoS2 and monolayer graphene. The mechanism of sensitivity enhancement is discussed and explained theoretically. In the experiment, a PMMA-based wet transfer method is used to transfer MoS2 and graphene film on the Au-based substrate and the high-refractive-index (RI) sensitivity of the fabricated sensor is verified. In addition, the proposed biosensor is used to detect okadaic acid (OA) by the indirect competitive inhibition method. The experimental results demonstrate that the graphene–MoS2 hybrid structure can greatly reduce the LOD of the SPR biosensor.In this work, we propose a high-sensitivity SPR biosensor based on the graphene–MoS2, and monolayer graphene. In this structure, BK7 glass is used as a coupling prism and Au is used as a plasmonic material to excite the SPR effect. Few-layer MoS2 films are used to absorb more light energy and the monolayer graphene is used as the biological recognition component, which further improves sensor sensitivity. In the simulation, the thickness of the Cr layer is 5 nm and the thickness of the Au layer is 50 nm. The wavelength of the incident light source is 632.8 nm. At this wavelength, the RI of BK7 glass is 1.516 [G = L∗0.34 nm, where L is the number of graphene layers. The RI of the MoS2 layer is 5.9 + 0.8i [M = M∗0.65 nm, where M is the number of MoS2 layers.In is 1.516 . The RI is 1.516 . The RI is 1.516  and its 2-based sensor, and the graphene–MoS2 hybrid-structure sensor. TMM is used to calculate the reflectivity curves of various structures and the calculated results are shown in s changes from 1.330 to 1.335. Thus, the sensitivity of the Au-based sensor is 142°/RIU. In 2 to enhance the sensitivity and the sensitivity is calculated to be 256°/RIU. The high sensitivity is because the presence of the MoS2 layer increases the efficiency of light absorption of the sensor. Most of the incident light energy is transferred to free electrons on the sensor surface, so more surface plasmons are generated, which results in the higher sensitivity [2 layer to further improve the sensitivity. The resonance angle shifts by ∼1.41° and the sensitivity increases to 282°/RIU. Obviously, the monolayer graphene does not significantly enhance the RI sensitivity of the proposed sensor. This is due to the fact that the light absorption efficiency of graphene is lower than that of MoS2. The primary function of the monolayer graphene is used as a biomolecular recognition component. In biological experiments, the graphene provides a large surface area for adsorbing biomolecules, which lowers the LOD of the sensor [To evaluate sensing performance, we compare the RI sensitivities of three different structures: the conventional Au-based sensor, the MoSsitivity . In Figu2 layers on the sensitivity of the graphene–MoS2 hybrid-structure sensor, we calculate the reflectivity curves in a different sensing medium, as shown in 2 layers. This is due to the relatively high RI in the real parts of the MoS2 material, which produces excessive amount of damping in the plasmonic wave [2 layers. This can be explained that as the number of MoS2 layers continuously increases, the resonance angle will increase to 90°, but the detection angle cannot reach 90°, limiting the sensitivity of the SPR sensor [2 layers is four (M = 4), the highest sensitivity of 282°/RIU is obtained, which is significantly improved as compared to the other reported works [To study the influence of the number of MoSnic wave . FurtherR sensor . When thed works ,23,27.2 hybrid-structure sensor with four-layer MoS2 at resonance condition. The finite difference time domain (FDTD) method is used to simulate the electric field distribution and the calculated results are shown in 2 and graphene film. On one hand, the graphene–MoS2 hybrid structure improves the absorption of light energy. On the other hand, the absorbed light energy is transferred to the free electrons, resulting in strong coupling on the graphene surface, ultimately enhancing the surface electric field. The electric-field-enhanced region has a more sensitive response to the slight variation in RI of the sensing medium.In order to clearly demonstrate the electric field enhancement of the proposed sensor, we compare the electric field distribution in two configurations of the conventional Au-based sensor and the graphene–MoS2SO4, HCl, NaOH, H2O2, anisole, KOH, acetone, and poly (methyl methacrylate)  were obtained from Sinopharm Chemical Reagent Co., Ltd. . N-hydroxysuccinimide (NHS), 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC), ethanolamine and phosphate-buffered saline (PBS) were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Okadaic acid (OA) with >95% purity (HPLC-grade), the okadaic acid–bovine serum albumin bioconjugate (OA-BSA), and anti-OA monoclonal antibody (OA-mAb) were purchased from Anti Biological Technology Co., Ltd. . A 0.2 M NaOH solution was used as the regenerant. All reagents and solvents are analytical grade and were used without further purification. Deionized water (18.2 MΩ·cm) was used throughout the work.NaCl, H2 hybrid-structure sensor with different numbers of MoS2 layers are fabricated in this paper and the fabrication processes are shown in The conventional Au-based sensor and graphene–MoS2 film purchased from SixCarbon Technology was grown on SiO2/Si substrate by CVD technique. The few-layer MoS2 films were transferred onto the Au-based substrate by a PMMA-based wet transfer method [2 transfer process, first, MoS2 grown on SiO2/Si substrate was spin-coated with PMMA (4% in anisole) at 3000 rpm for 1 min and baked at 120 C for 3 min. Then, samples with the PMMA coating were then soaked in a 2 mol/L KOH solution for 2 h, in which the PMMA/MoS2 layer was separated from the Si substrate due to etching of SiO2. Next, the PMMA/MoS2 layers were washed in DI water, scooped using an Au-based substrate, dried under ambient conditions, and baked at 80 °C for 1 h. Finally, the acetone was used to dissolve the PMMA. We can complete the transfer of MoS2 to obtain the MoS2-based substrate  and 2679.1 cm−1 (2D-band). According to previous reports, the number of graphene layers depends on the intensity ratios 2 hybrid structure.The photograph of the fabricated graphene–MoStructure . In the 2. The Abbe refractive index meter was used to measure the RI of the NaCl solutions at room temperature (26 °C). The NaCl solution with concentration ranges of 0.1 g/L, 0.25 g/L, 0.5 g/L, 1 g/L, 2.5 g/L, 5 g/L, and 10 g/L were prepared, and their corresponding refractive indices are 1.33152, 1.33154, 1.33158, 1.33165, 1.33189, 1.33229, and 1.33308, respectively. In the experiment, deionized water was first injected into the sensor for a sufficient time to ensure the stability of the baseline. Then, the NaCl solution and deionized water were sequentially injected as a cycle, and the process was repeated to test different concentrations of NaCl solutions. Every concentration was measured three times, and the results were recorded in computer software. 2. The response spectra are shown in 2, respectively, and all the correlation coefficients (R2) are higher than 0.98. When the number of MoS2 layers is four, the maximum sensitivity is obtained, which is 1.85 times that of conventional Au-based sensor. A good agreement is observed between the experimental results and the theoretical calculation results.In this section, we compare the RI sensitivity of the Au-based sensor and the proposed sensor with different layers of MoSThe surface of graphene has abundant functional groups, which can be covalently bound to antigen or antibody molecules. For the pretreatment of the graphene-based SPR-sensing chip, the chip was rinsed thoroughly with plenty of water, and dried with nitrogen. Then, the carboxyl group of graphene was activated by NHS/EDC mixture solution  for 30 min, followed by washing in plenty of water. Afterwards, the OA-BSA conjugate (1 mg/mL) was dissolved in PBS buffer and was dropped onto the chip surface and incubated for 1 h. Finally, a 1 mol/L ethanolamine solution (pH 8.5) was used to block the nonspecific interaction on the biosensor surface.2 by an indirect competition inhibition method [The low-molecular-weight analyte OA was detected by the proposed SPR sensor with four-layer MoSn method ,42, and For the indirect competition inhibition method, the concentration of antibody is a key parameter affecting sensitivity. To obtain the appropriate antibody concentration, a series of concentrations of OA-mAb (1~60 μg/mL) were injected into the sensor chip. Firstly, the OA standard solutions were incubated with the 15 μg/mL OA-mAb solution for 30 min. Subsequently, the equilibrated mixtures, containing a series of OA concentrations (0.5~2048 ng/mL) and 15 μg/mL OA-mAb, were injected into the sensor chip. The reproducibility of the immune reaction was assessed by analysis of each concentration of OA mixture solutions three times. The obtained SPR response signal curves are shown in 2 and graphene is proposed, and its performance was investigated through a simulation and experiments. MoS2 films with a high light absorption efficiency were utilized to promote the transfer of electrons, which resulted in a significant enhancement of the electric field on the sensor’s surface. Monolayer graphene was employed as the biological recognition component to further increase the sensitivity of the sensors. The numerical results show that the maximum sensitivity ~282°/RIU is achieved, when the sensor is modified with four-layer MoS2 and monolayer graphene. In the experiment, the proposed sensor was used to measure the RI sensitivity and detect the OA concentration. The result of the RI experiments show that the RI sensitivity of the proposed sensor is approximately 1.85 times higher than the conventional Au sensor. In addition, the LOD of OA for the proposed sensor is 1.18 ng/mL, which is about 22.6 times lower than the conventional Au sensor. These results suggest that this device has the potential for clinical diagnostics and chemical detection.In this work, a high-sensitivity SPR biosensor composed of MoS


Applications of ionic liquids (ILs) for the modification physicochemical properties of porous materials have been extensively studied with respect to various applications based on the understanding and development of properties of ILs. In this review, IL–graphene composites are discussed and provided a perspective of composites of IL. IL has been used as a medium to improve the dispersibility of graphene, and the resulting composite material shows excellent performance in gas separation and catalysis during environmental treatment. The applications of ILs and IL–functionalized graphene are discussed in detail with the actual environmental issues, and the main challenges and opportunities for possible future applications are summarized. The unique physical and chemical properties of graphene make it an ideal adsorbent for adsorbates ..3O4) wer2 is currently the most commonly used photocatalyst for decomposing water, which provides better activity in removing organic pollutants and shows more favorable mineralization level, thus preventing the accumulation of harmful organic pollutants in water. Due to the surface limitations and inadequate adsorption capacity of TiO2 resulting from its nonporous nature, for more effective removal of PCBs from wastewater treatment plants, it is useful to incorporate photocatalysts into porous supports in order to facilitate the efficient absorption of target environmental pollutants  [PF6] from wastewater [Cl]) . Activatstewater . The str2O2.In addition to photodegradation, ultrasonic degradation, and Fenton/Fenton-like reactions, electrolytic degradation is an attractive choice . In the After a few years of development, the research on ILs and IL-modified graphene has become an intensively developing area . IL/grap6 and BMIMBF4, are not green. This might be ascribed to fluoride formation during the hydrolysis of [BF4] −, which enhanced the toxicity of these substances. Considering these studies, it is sugges.ted that the properties of ILs should be related to the environment and the production of non-toxic and biodegradable ILs for the environment.Initially, because of its extremely low vapor pressure and low toxicity, attention was paid to how ILs could be environmentally friendly reagents. On the basis of the literature, many of them, such as BMIMPFRegarding future research, IL/graphene-material composites provide a wide range of possibilities of functionalization and constitute a promising class of composites for further study. Hopefully, this review can provide some clues to support a great deal of future research on the application of ILs.


Idiopathic pulmonary fibrosis (IPF), characterized by progressive worsening of dyspnea and irreversible decline in lung function, is a chronic and progressive respiratory disease with a poor prognosis. Chronic or repeated lung injury results in inflammation and an excessive injury-repairing response that drives the development of IPF. A number of studies have shown that the development and progression of IPF are associated with dysregulated expression of several chemokines and chemokine receptors, several of which have been used as predictors of IPF outcome. Chemokines of the CC family play significant roles in exacerbating IPF progression by immune cell attraction or fibroblast activation. Modulating levels of detrimental CC chemokines and interrupting the corresponding transduction axis by neutralizing antibodies or antagonists are potential treatment options for IPF. Here, we review the roles of different CC chemokines in the pathogenesis of IPF, and their potential use as biomarkers or therapeutic targets. Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive respiratory disease characterized by excessive extracellular matrix (ECM) deposition, interstitial fibrotic lesions, and architectural distortion. Patients with IPF experience pulmonary function decline and progressive worsening of dyspnea; prognosis is poor, with death typically occurring within 3 to 5 years . Usual iWhen the pulmonary epithelium or endothelium is impaired by various insults, the coagulation pathway is triggered to prevent blood loss, followed by acute inflammation and activation of the innate immune system . Innate Chemokines  comprise a family of small soluble proteins originally discovered as mediators of directional migration of immune cells to sites of inflammation and injury . These sStudies of CX3C chemokines and XC chemokines in IPF have rarely been reported. However, accumulating evidence has shown that the development and progression of IPF are associated with the dysregulated expression of CC chemokines and CXC chemokines in lung tissues, suggesting that these chemokines may be involved in its pathogenesis . Some chCCL1, also known as I-309 in humans and TCA-3 in mice, is a small glycoprotein secreted by activated T lymphocytes, endothelial cells and activated monocytes. By interacting with the cell surface chemokine receptor CCR8, CCL1 has a chemotactic effect on Th2 cells, monocytes, natural killer (NK) cells, immature B cells and dendritic cells ,13,14,15Our recent work showed that expression of CCL1 is enhanced in lung tissues of PF patients and mice. CCL1 exerts its fibrogenic activity via interaction with autocrine motility factor receptor (AMFR) but not its classical receptor CCR8. This CCL1-AMFR interaction on the membrane of fibroblasts causes PKCα-mediated AMFR phosphorylation, through which AMFR acquires E3 ligase activity, followed by ubiquitination and translocation of the endogenous ERK inhibitor Spry1 to the plasma membrane. At the plasma membrane, Spry1 binds to RasGAP, relieving the inhibitory effect of Spry1 on Ras-ERK-p70S6K signaling activity and enhancing profibrotic protein synthesis in fibroblasts. Genetic and pharmacological inhibition of the CCL1 signaling pathway has potent therapeutic efficacy against PF. Our study revealed a mechanism through which CCL1 influences PF development, suggesting this chemokine as a potential target for treating fibroproliferative lung diseases .CCL2, also named monocyte chemoattractant protein-1 (MCP-1), exhibits chemotactic activity for monocytes, microglia, T cells, NK cells and fibrocytes by binding to the receptor CCR2 ,22,23. ANumerous studies have shown that CCL2 contributes to IPF through a variety of mechanisms. Apart from its major role as a chemoattractant of monocytes for immunological surveillance, new findings suggest its functional role in upregulation of ECM proteins. Indeed, CCL2 promotes upregulation of endogenous transforming growth factor beta 1 (TGF-β1) in pulmonary fibroblasts and stimulates collagen synthesis indirectly via autocrine and/or juxtacrine loops . StimulaCCL2 is expressed by various cell types. Strong expression of CCL2 has been detected on pulmonary alveolar epithelial cells (AECs) from IPF patients but not non-IPF subjects . In addiIn addition to AECs, pulmonary fibroblasts are another primary source of elevated CCL2 in IPF ,38. PulmBleomycin (BLM) injury increases CCL2 production in the lung by up to twofold, but it is reduced to basal levels after regulatory T (Treg) cell adoptive transfer therapy . The inhCCL3 (macrophage inflammatory protein (MIP)-1α) and CCL4 (MIP-1β), proinflammatory chemokines secreted by activated T cells, B cells, macrophages, monocytes, NK cells, neutrophils, epithelial cells, fibroblasts, and osteoblasts, induce recruitment of dendritic cells, neutrophils, monocytes, macrophages, NK cells and T cells to inflammatory sites. CCL3 is a ligand for the receptors CCR1 and CCR5; CCL4 is a ligand for CCR5 but has low affinity for CCR1. CCR5 is recognized as a shared cellular receptor in activated T lymphocytes and alveolar macrophages (AMs) . CCL3 prSeveral groups have shown involvement of CCL3 and CCL4 in the pathogenesis of IPF. Compared with that in the lungs of healthy controls, CCL3 and CCL4 expression is increased in the lungs of IPF patients and different animal models, including the BLM model, silica model and mustard gas model. CCL3 and CCL4 have been shown to be involved in the inflammatory process of IPF. CCL3 levels in IPF patients correlate significantly with both the percentage and total number of neutrophils and eosinophils. Although Bless et al.  observedIn a murine model of BLM-induced lung fibrosis, the time-dependent increase in CCL3 after a BLM challenge was associated with an increased number of leukocytes and elevated profibrotic factors ,51. TargCCL5, also known as RANTES, is widely expressed in a variety of immune and nonimmune cells. The most studied receptor of CCL5 is CCR5, but it also binds to CCR1, CCR3, CCR4, CD44 and GPR75. Interaction between CCL5 and its receptor CCR5 induces recruitment of different leukocyte types, including T cells, monocytes/macrophages, dendritic cells, eosinophils and basophils, to sites of injury.It has been reported that expression of CCL5 mRNA in BALF cells and levels of CCL5 protein in BALF are significantly increased in patients with distinct ILD compared with healthy volunteers . ElevateCCR5, the most studied interacting partner of CCL5, is expressed on various cell types, including T cells, macrophages, dendritic cells, eosinophils, and microglia. It is also the major coreceptor for human immunodeficiency virus (HIV) cell entry . FibroblAlthough CCL5 expression is upregulated in patients with IPF, this characteristic is not unique to IPF and occurs in other types of ILD, including sarcoidosis and IP-CVD. Although measurement of CCL5 expression in BALF cells is inadequate for distinguishing IPF from other ILDs, such data provide new evidence that CCL5 is involved in pulmonary fibrotic disease and that modulation of CCL5 is a potential therapeutic strategy for IPF. Although several studies have indicated that CCL5 participates in the inflammatory process of IPF , the exaCCL7 , first characterized from osteosarcoma supernatant, is a member of the MCP subfamily and also includes CCL2 and CCL8. CCL7 exhibits the broadest range in that it activates lymphocytes, monocytes, dendritic cells, NK cells, eosinophils, basophils and neutrophils . CCR1, CAs a member of the MCP subfamily, CCL8  plays key roles in allergic and inflammatory responses by attracting diverse immune cells, including eosinophils, basophils, mast cells, monocytes, T cells and NK cells. It is produced by many cell types and signals through interactions with CCR1, CCR2, CCR3, CCR5 and CCR8 ,63.A recent study reported CCL8 involvement in IPF development. A global transcriptome analysis revealed that CCL8 expression is higher in fibroblasts from IPF patients than in fibroblasts from controls . SubsequCCL17  and CCL22  are T helper type 2 (Th2)-type chemokines that share 37% identity at the amino acid level. CCR4, their shared receptor, is highly expressed in macrophages, dendritic cells, NK cells, monocytes, platelets, neurons, microglia and functionally distinct T-cell subsets, including activated T cells, Th2 cells and Treg cells. As development of IPF is a Th2-mediated process, there is growing evidence that CCL17, CCL22 and CCR4 are involved in its pathogenesis ,66,67,68Several studies have revealed the underlying mechanisms of CCL17, CCL22 and CCR4 in IPF development. Yurika Yogo et al. reported localization of CCL22 and CCR4 at CD68+ AMs, and an inverse correlation was observed between CCL22 levels in BALF and DLco/alveolar ventilation per minute (VA) values in IPF patients , suggestApart from macrophages, BAL CD4 T cells show higher expression levels of CCR4 in IPF patients than in controls ,75. DespCCL18 was originally discovered in the lung, and CCL18 expression was found to be induced in alternatively activated macrophages (AAMs); as such, CCL18 was initially named pulmonary and activation-regulated chemokine (PARC), alternative macrophage activation-associated CC chemokine-1 (AMAC-1), dendritic cell chemokine 1 (DC-CK1), and macrophage inflammatory protein-4 (MIP-4) ,78. CCL1Markedly enhanced CCL18 expression in the serum and BALF of IPF patients has been reported ,82. PrasHowever, according to a case–controlled study by Ganesh Raghu et al., there is no significant association between CCL18 concentration at baseline and the rate of disease progression in IPF patents, indicating that the baseline value of CCL18 cannot predict disease progression . In contCCL18 is primarily produced by myeloid cells, particularly AMs and follicular dendritic cells. Its expression is induced by Th2-associated cytokines, including IL-4, IL-13 and IL-10, whereas it is downregulated by interferon-γ (IFN-γ) and lipopolysaccharide (LPS) . CCL18 iCCL21, also known as 6-Ckine, exodus-2 and secondary lymphoid-tissue chemokine (SLC), is one of the major chemokines predominantly expressed in secondary lymphoid tissues. It exerts effects on target cells by binding to the chemokine receptor CCR7, which is expressed on different immune cells. CCL21-CCR7 interaction essentially contributes to the homing of various subpopulations of T cells and antigen-presenting dendritic cells to the lymph nodes.The CCL21-CCR7 axis plays important roles in several physiological and pathological processes, such as tissue homeostasis, the inflammatory response and immune surveillance. Several studies have identified involvement of CCR7 and CCL21 in progression of lung fibrogenesis. CCR7 expression is significantly increased in biopsies from patients with IPF compared with that in normal margins . However6 primary fibroblasts grown from IPF and other biopsies intravenously into CB-17 severe combined immunodeficiency (SCID)/beige (bg) mice [Several studies have verified the in vivo roles of CCL21 and CCR7 in IPF. Researchers injected 1 × 10bg) mice . Comparebg) mice . Immunonbg) mice  and suggbg) mice .CCL24 (eotaxin-2) is a member of the eotaxin family, which also includes CCL11 (eotaxin-1) and CCL26 (eotaxin-3). It acts as an attractant, inducing trafficking of eosinophils, basophils, neutrophils, and macrophages by binding to CCR3 . Both CC1κ monoclonal antibody that specifically binds to and neutralizes human CCL2, failed to provide benefit to patients with progressive disease [Based on the evidence that IPF is associated with upregulation of several CC chemokines and chemokine receptors, some studies in mouse models of PF have provided proof-of-principle evidence that targeting the CC chemokine system can reduce disease severity . For exa disease . Some imCompared with data from mouse models, data from clinical studies are limited. In a phase 2 trial, carlumab, a human antibody-neutralizing CCL2 , failed Chronic inflammation within the respiratory tract may arise from the combination of diverse environmental insults and genetic susceptibility, and this inflammation underlies the pathogenesis of numerous chronic pulmonary diseases, such as IPF . HoweverApart from their conventional role in recruiting immune cells to the site of inflammation, chemokines also mediate several cellular processes that are specific to IPF remodeling, such as promoting fibroblast trafficking, proliferation and activation. Therefore, chemokines act as a bridge between persistent inflammation and abnormal tissue repair in IPF pathogenesis. Fibroblasts isolated from patients with IPF exhibit distinct characteristics compared with those from healthy donors or patients with other ILDs. As the major effector cells in IPF, fibrotic fibroblasts are hyperresponsive to certain CC chemokines, such as CCL2. In addition, these cells have been proven to serve as a cellular source of some chemoattractants, such as CCL2, CCL7 and CCL8, suggesting a tight link between inflammation and fibroblast activation as well as mutual impact within regional niches. In addition to CC ligands, the multifunctional receptor CCR5 is strongly expressed in fibroblasts from fibrotic lobes, but this expression is less dramatic in ILDs other than IPF , furtherHighly expressed CC chemokines in serum or BALF, such as CCL2, CCL8, CCL18, CCL17 and CCL22, have been found to have potential diagnostic or prognostic value in IPF. In particular, CCL2 and CCL18 are recognized as diagnostic and prognostic biomarkers for chronic fibrosing ILDs with a progressive phenotype . NeverthCCLs exert profibrotic roles in IPF via CCRs and CCL-CCR transduction axes, including CCL21-CCR7, CCL17/CCL22-CCR4 and CCL-CCR5. Inhibition of CCRs or CCL-CCR transduction axes block the function of CCLs. For instance, treatment with PTX or CCR7-specific siRNA is capable of blocking the CCL21-mediated functional responses of IPF fibroblasts . The potIn summary, extensive in vitro and in vivo investigations have elucidated the crucial roles played by the CC chemokine system in the pathogenesis of IPF . The CC


The thermal conductive anisotropy and improvement in the through-plane thermal conductivity of the epoxy composite were attributed to the particular structure of cigarette filter-templated graphene in the epoxy matrix. The unique structure formed effective conductive pathways in the composite to improve the thermal transportation properties. The excellent thermal transportation properties allow the epoxy composite to be used as an efficient heat dissipation material for thermal management applications.Herein, a cigarette filter-templated graphene/epoxy composite was prepared with enhanced thermal conductive properties. The through-plane thermal conductivity of the epoxy composite was up to 1.2 W mK We report a facile method to prepare cigarette filter-templated graphene/epoxy composites with excellent thermal transport performance. Polymer materials are generally good candidate materials.3 Due to its excellent chemical resistance, high mechanical strength, and insulation, epoxy is considered an ideal material for electronic packing.4 However, its thermal conductivity is only 0.2 W mK−1, which enormously limits its widespread use as an electronic packing material.5 Therefore, multiple high thermal conductivity nanomaterials, such as boron nitride nanosheets, alumina, and graphene, have been introduced into epoxy resin to enhance its thermal transport properties.6–11 However, simple blending-processed epoxy-based composites commonly cannot achieve high thermal conductivity with a low nanofiller loading.12–14 Thus, the design and fabrication of effective heat conductive paths in the composites are crucial for the next-generation of electronic packing materials.With the development of modern electronic and electrical industries, cooling has become the main factor that affects the working stability and lifetime of devices.−1) among the materials known to date.15 With a two-dimensional (2D) nanostructure of sp2-bonded carbon atoms arranged in a honeycomb pattern, graphene has become one of the marvel carbon materials today.16,17 Because of its high thermal conductivity and large specific surface area, graphene is an ideal nanofiller to enhance the thermal conductivity of an epoxy matrix.18 When the composites were prepared through simple blending, graphene tended to aggregate and sedimentate in the epoxy matrix as its concentration increased.19,20 To avoid this problem, three-dimensional (3D) frameworks have been proposed to obtain a high thermal conductivity in polymer-based composites. Yang et al.21 fabricated a 3D cellulose/graphene-supported aerogel and encapsulated it with polyethylene glycol. The thermal conductivity of the composite was 1.35 W mK−1, which was 463% higher than that of the pristine polyethylene glycol. Chen et al.22 constructed a cellulose nanofiber-supported 3D interconnected boron nitride nanosheet aerogelskeleton via a sol–gel and freeze-drying process. Then, epoxy was impregnated into the 3D framework, with a 9.6 vol% boron nitride nanosheets content, and the thermal conductivity of the composite reached 3.13 W mK−1. However, among all the 3D structure-templated composites, few of them possessed an anisotropic structure. 3D-templated bulk composites with anisotropic thermal diffusivity have rarely been reported in the literature.Graphene is considered to have the highest thermal conductivity  composites, with anisotropic thermal diffusivity. At first, a graphene suspension was passed through a cigarette filter (CF) to obtain cigarette filter-templated graphene (CFTG). After several filtration cycles, the as-obtained CFTG was immersed in epoxy resin to obtain the CFTG/Ep composite. The aligned CFTG can form effective heat transport pathways in the composite and enhance the thermal diffusivity at a quite low graphene loading. The incorporation of CFTG into the epoxy matrix shows a significant enhancement in the thermal diffusivity, especially in the axial direction. The thermal conductivity in the axial direction was 1.2 W mK2.2.1.iii) acetylacetonate trihydrate (Nd(iii)acac) purchased from Aldrich Chemicals was used as the latent catalyst. All other chemicals were of analytical reagent grade and used without further purification.Cigarette filters (CFs) were purchased from Shanghai Zhengyou Industry and Trade Co., Ltd. (China). Commercial graphene nanoplatelet (GNP) powders were produced by the Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences (China). Cycloaliphatic epoxy resin (6105) and methylhexahydrophthalic anhydride (MHHPA) were obtained from DOW Chemicals (U.S.A.) and Shanghai Li Yi Science & Technology Development Co. Ltd. (China), respectively. Neodymium(2.2.iii)acac was added to a cycloaliphatic epoxy resin and subsequently stirred at 80 °C in a three-necked flask for 2 h. The resulting homogeneous solution was mixed with its curing agent (MHHPA) at a 100 : 95 ratio. The mixture was mixed using a speed mixer at a speed of 3000 rpm for 5 min. Then, the homogeneous mixture was infused into the assembled filter and then placed into a vacuum drier to remove the air bubbles from the solution. Finally, after the curing process, the samples were naturally cooled down to the room temperature and then diced using a low speed diamond cutter for different characterizations. The preparation process of the epoxy composite with cigarette filter-templated graphene (CFTG) is illustrated in A solution method was adopted to prepare the GNP dispersion. At first, the GNP powder was dispersed in ethanol by applying tip sonication for 5 min at room temperature. Then, the paper cover wrapped on the CFs was removed. The pristine CF was filled in a flexible pipe to ensure that the GNP dispersion only flowed through the CF using an injection syringe. The CF turned into black after several cycles of injection and ejection. In addition, the surface of the CF was assembled with the GNP after the drying process. A quantity of Nd(2.3.via a Kratos AXIS Ultra DLD spectrometer using Al Kα excitation radiation (hν: 1253.6 eV). Raman spectroscopy was conducted employing a laser wavelength of 532 nm . The thermal diffusivity of the composites was determined using an LFA 447 Nanoflash apparatus  at room temperature. The thermal conductivity λ (W mK−1) was calculated as a multiplication of the density , specific heat , and thermal diffusivity , namely, λ = ρ × Cp × α. The samples were prepared with a square shape, 10 mm in lateral size, and a thickness of about 1.2 mm. The IR images were obtained using an infrared camera .The microstructures of the samples were obtained using a JEOL JEM-2100  instrument at an acceleration voltage of 200 kV. The optical microscopy (OM) images were obtained using an optical microscope . The fractured surface of the composites was examined using field emission scanning electron microscopy  at an acceleration voltage of 10 kV. The samples were broken, and the fractured surface was coated with a thin gold layer to avoid the accumulation of charge in SEM. X-ray photoelectron spectroscopy (XPS) was carried out 3.3.1.23 An obvious precipitation was observed in the GNP dispersion before washing and tip sonication due to the distinct agglomeration of graphene. However, the washed GNP suspension was visually observed as a homogeneous solution, indicating that its 2D plane structure and large specific surface area effectively prevented aggregation. The SEM image of the washed GNPs powder is shown in −1 corresponds to the first-order scattering of the E2g mode.24The inset of −1) intensity is related to disordered, sp3-hybrided carbon, which can be activated at the edges.24 The ID/IG ratio reflects the impurities and defects in the GNPs structure, and its low value predicts a high intrinsic thermal conductivity.25,26 The 2D band (2708 cm−1) is known to be very sensitive to the graphene layers in a flake. From the position and shape of the 2D peak, we can draw a conclusion that the GNP flakes are constituted by few-layer graphene.26 This fact is further confirmed using TEM analysis. TEM was employed to determine the morphology and thickness of the GNPs. As shown in 27 In In addition, the D-band (1345 cmXPS was used to explore the chemical character of the GNPs, as shown in 3.2.Like CF, the CFTG also exhibited a typical anisotropic structure with a high aspect ratio, as can be seen in 3.3.−1, which was about 3 times higher than that of pure epoxy. In addition, the thermal conductivity in the radial direction was only 0.261 W mK−1, and only slightly enhanced. This anisotropic thermal conductivity can be ascribed to the anisotropic structure of the CF. After one filtration cycle, the GNPs could be coated on the surface of CF and construct an effective heat conductive pathway in the axial direction; however, the GNPs could not build a continuous graphene network between the different CFs in the axial direction. Continuous GNPs networks can form effective heat conductive pathways and greatly improve the thermal conductivity of a composite. After five filtration cycles, the thermal conductivity of the composite in the axial direction increased up to 1.2 W mK−1; however, the thermal conductivity in the radial direction only reached 0.298 W mK−1. With an increase in the number of filtration cycles, more GNPs were coated on the surface of the CF, but the low thermal conductivity in the radial direction indicated that the GNPs did not build a continuous GNPs thermal conductive pathway in the radial direction. In addition, epoxy between the discontinuous graphene networks will also result in more phonon scattering and influence the thermal conductivity in the radial direction. In the axial direction, heat can be effectively transferred through the continuous graphene networks. The improvement in the thermal conductivity in the axial direction upon increasing the number of filtration cycles can also be attributed to the increase in the content of the GNPs.To visually verify the enhanced and anisotropic heat dissipation performance of the CFTG/Ep composite, we used an infrared camera to determine the variation in temperature in the composite and neat epoxy, as shown in As shown in 4.−1 after 5 filtration cycles, whereas the thermal conductivity in the radial direction was only 0.298 W mK−1. The thermal conductive anisotropy can be ascribed to the anisotropic structure of the cigarette fiber-templated graphene. The excellent thermal transportation properties allow the epoxy composites to be used as an efficient heat dissipation material for thermal management applications.A CFTG/Ep composite with significant anisotropic thermal diffusivity was fabricated using a facile filtration method. The thermal conductivity of the composite in the axial direction was 1.2 W mKThere are no conflicts to declare.


As a chronic and multisystemic granulomatosis of unknown origin, sarcoidosis can affect multiple organs throughout the body with variable progression and prognosis. Sarcoidosis may present with a battery of symptoms and signs, such as dyspnea, non-productive cough, uveitis, and erythema nodosum. Although the lungs and mediastinal lymph nodes are almost affected in sarcoidosis, involvements of the pleurae remain uncommon. Herein, we report a case of sarcoidosis with both pleural effusions and pleural nodules as confirmed by thoracoscopic pleural biopsy. Sarcoidosis is a multisystem disease characterized by non-caseating granulomatous inflammation and its exact etiology remains unknown . It can A 69-year-old female was admitted to our hospital in Oct 9, 2019 because of dry cough, dyspnea on exertion and fatigue for a month. She had no night sweats or weight loss. The patient was a nurse and she had neither previous disease nor history of smoking. She also had no history of exposure to foreign antigens inorganic particulates. In addition, she had no family history of rheumatologic or autoimmune diseases. On admission, temperature, pulse, respiratory rate, and blood pressure were 36.6°C, 79 beats/min, 21 breaths/min, and 126/88 mm Hg, respectively. Serum levels of electrolytes, brain natriuretic peptide, and liver & kidney function were normal. The levels of serum carcino-embryonic antigen (CEA), neuro-specific enolase (NSE), CYFRA 21-1, squamous cell carcinoma antigen (SCCA), and pro-gastrin-releasing peptide (Pro-GRP) were 1.24 ng/ml (0–5.0 ng/ml), 17.78 ng/ml (0–16.3 ng/ml), 1.54 ng/ml (0.1–3.3 ng/ml), 0.9 ng/ml (0–1.5 ng/ml), and 34.19 pg/ml (0–63 pg/ml), respectively. A computed tomographic (CT) scan of the thorax demonstrated left pleural effusions and linear opacity . The exuThe clinical features of pleural involvements in our patient seem to be interesting for several reasons. Firstly, this case of sarcoidosis is presented with both pleural effusion and pleural nodules. Pleural involvement in sarcoidosis was first recognized by Schaumann in 1933 and it can be manifested by pleural effusion, pleural nodules, pleural thickening, pneumothorax, hydropneumothorax, and chylothorax , 5. The Secondly, pleural involvement is the initial manifestation of sarcoidosis. Pleural manifestations caused by sarcoidosis may arise at the onset of this disease which is first diagnosed, as the case we have described, or at any time during the course of the known sarcoidosis . The devFinally, the pleural involvement of sarcoidosis responds well to corticosteroids. Systemic corticosteroids are the mainstay of treatment of sarcoidosis and also the most commonly used first-line therapy . CorticoThe diagnosis of sarcoidosis involving the pleura is based on the histologic evidence of non-caseating granuloma, the hallmark of sarcoidosis, and on excluding other granulomatous diseases, such as tuberculosis, fungal disease, and granulomatous polyvasculitis . In addiMedical thoracoscopy, a relatively less invasive and more efficient diagnostic method, plays a significant role in the diagnosis of pleural involvement in sarcoidosis, especially of pleural effusions and pneumothorax. By thoracoscopy, physicians can directly access and assess the pleural cavity, including the parietal, visceral and diaphragmatic pleura, and obtain adequate tissue sampling. Additionally, pleural fluid can be aspirated without complications during thoracoscopy. Therefore, thoracoscopy, an appropriate alternative technique, can provide doctors with important evidences to convince pleural sarcoidosis . AlthougIn summary, this case illustrates an unusual form of pleural involvement of sarcoidosis with pleural effusion plus pleural nodules. A definitive diagnosis of pleural sarcoidosis relies on the histological identification of non-caseating granulomas in the pleurae and on the exclusion of all other possible causes. Although rare, pleural involvements in sarcoidosis should be considered in the differential diagnosis of pleural effusion and pleural nodules. As is the case with other forms of pulmonary involvement in sarcoidosis, these manifestations respond well to corticosteroids. It is believed that careful evaluation and vigorous treatment of pleural involvement in sarcoidosis is imperative.The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.The studies involving human participants were reviewed and approved by the First Affiliated Hospital of Shandong First Medical University . The patients/participants provided their written informed consent to participate in this study. Written informed consent was obtained from the individual(s) for the publication of any potentially identifiable images or data included in this article.XJ, JL, and DL: conception and design. XJ, JL, HP, and FS: collection and assembly of data. XJ, JL, AZ, and DL: data analysis and interpretation. All authors: manuscript writing and final approval of manuscript.


Graphene doped with different transition metal (TM) atoms, namely, Co, Ni, Cu, Zn, and Au, have been investigated through first-principles calculations. The TM atom forms a substitutional defect, replacing one carbon atom in the graphene basal plane, which considerably can be obtained through wet or dry chemical processes as reported elsewhere. The calculation results showed that TM atom substitution leads to the opening of a band gap and the emergence of mid-gap states with the Fermi energy in the middle of it. The effects on optical properties were seen from the calculated optical absorption and Electron Energy Loss Spectroscopy (EELS) spectra. Two EELS bands are seen in the far UV region corresponding to the π and (π + σ) plasmons but the influence of the substituted TM effects on the plasmon frequency is small. On the other hand, as the Fermi energy level appears in the middle of the mid-gap state band while the real part of its dielectric permittivity at low photon energy is negative, these TM-doped graphene have a metal-like characteristic. Hence, plasmon wave excitation can be expected at the THz region which is dependent on the dopant TM atom. The plasmon excitation in these TM-doped graphene is thus principally similar to the plasmonic excitation in pure graphene by electric or magnetic fields, where the Fermi energy level is shifted from the graphene Dirac point leading to the possibility of an intraband transition. Doping graphene with a single transition metal atom results in bandgap opening and partial filling of the mid-gap states, leading to the possibility of plasmon excitation with plasmon frequency depending on the TM dopant. This Dirac cone is formed from a cross-section point of the valence and conduction bands, resembling the stacking of two cones in opposite orientations, creating a zero bandgap and zero density of states (DOS) at the cross-section point. Because the Fermi energy is located at the cross-section point, i.e., the Dirac point, graphene is a semi-metal with zero-bandgap semiconductor properties. As already reported elsewhere, these unique properties have led to diverse applications of graphene.1–7 Initially, benefitting from the electric field effect in 2D materials, graphene was used in transistor-like devices that attracted much attention.1,2 Subsequently, other physical properties of graphene have also been reported and used for different potential applications. Among others, owing to its high electron mobility and catalytic properties, graphene has been applied as an electrode material in supercapacitors, batteries, solar cells, and electrochemical-based sensors.2,8–10Graphene is a two-dimensional (2D) carbon allotrope possessing an sp11–14 Graphene has advantages as a plasmonic material because of its low losses and large electromagnetic field confinement.15,16 However, in pristine (undoped) graphene, being a perfect semi-metal, plasmonic wave cannot be generated directly due to zero charge carriers at its Dirac point. It should be noted that the real part of the dielectric permittivity of pristine graphene is negative in the mid-infrared (mid-IR) to THz frequency region. In general, the real part of the dielectric permittivity must be negative for metal-based plasmonic materials. Several methods have been proposed and applied to attain plasmonic excitation and resonance tuning in graphene, such as by using multilayer structuring, in order to match the momentum between incident light and the electrons in graphene, and other different approaches through electric and magnetic fields, mechanical strain, and impurities/defects insertion, in order to shift the Fermi energy from the Dirac point.17–26 Most studies on the utilization of surface plasmon polariton (SPP) waves in graphene are performed in the mid-IR to terahertz (THz) frequency range. THz sensors and detectors are important in THz spectroscopy that have found a wide range of applications in biomedical imaging, biochemical sensing, environmental monitoring, etc.27,28 Using THz spectroscopy, one could investigate low-energy molecular vibrations, crystal-lattice or phonon vibrations and intermolecular vibrations of macromolecular structure hydrogen-bonded network structure.29 Zheng et al. have investigated both experimentally and computationally the vibrational spectra of benzene-1,2-diol, in which they concluded that the spectrum peaks in the mid-infrared range can be associated with intramolecular vibration whereas the peaks in THz range can be associated with intermolecular vibrations.30The plasmonic properties of graphene have also been intensively studied because of its strong light–matter interactions.et al. have performed EELS on carbon nanotubes, reporting a π plasmon at either 5.2 or 6.4 eV and a (π + σ) plasmon at 22–24.5 eV.31 Reed et al. then investigated isolated single-walled carbon nanotubes and reported spectral bands associated with π plasmon at approximately 4.5–5.5 eV and (π + σ) plasmon at 13–27 eV.32 By the same principle, EELS has also been employed to investigate the plasmon characteristics in graphene, in which two broad plasmonic bands were detected at around 5 eV and 10–35 eV for the π and (π + σ) plasmons, respectively.33–35 The π plasmon originates from the π–π* transition, while the (π + σ) plasmon originates from higher photon energy transitions, such as σ–σ*, π–σ*, and σ–π* transitions. Besides experimental investigations, numerous efforts have been also devoted to predicting the plasmonic properties of pristine graphene through first-principles calculations.26–28,36In addition to the plasmon at low energy in mid-IR to THz frequency range as mentioned above, there is another plasmon with much higher photon energy, in the far UV region, that also becomes a subject of interest. Experimentally, the presence of plasmons in several materials has been extensively investigated using electron energy loss spectroscopy (EELS). Kuzuo et al. demonstrated the formation of Ni single-atom bonding with a defect vacancy in a 2D graphene sheet, in which the defect was created through an impregnation method with acid leaching.37 Jiang et al. reported direct evidence of the coordination bonding formation of Ni single atoms with graphene vacancy defects using scanning transmission electron microscopy (STEM).38 Besides the synthesis via a wet chemical process, another approach via a dry chemical process has also been reported. Dyck et al. then demonstrated the formation of Ni-doped graphene by using an electron beam, where the Ni adatom can be selectively and precisely inserted into a graphene vacancy defect.39 Single-atom B or N-doped graphene achieved by low-energy ion implantation has been reported by Hage et al., in which a dampening or enhancement of the characteristic interband π plasmon was observed.40 The defect resembles a substitutional defect where the metal atom replaces a carbon atom in the basal plane. Motivated by those reports, we have performed first-principles calculations based on density functional theory (DFT) methods to investigate the effects of the substitution of different TM atoms  on the electronic structure, optical properties, and plasmon characteristics of 2D graphene sheets . The results demonstrate that TM doping leads to bandgap opening and Fermi energy shift in their electronic structures as well as the possibility and modification of THz plasmon excitation.Recently, Zhang 2.41,42 which was implemented in the Quantum Espresso package.43 The generalized gradient approximation (GGA) along with the Perdew–Burke–Ernzerhof (PBE) exchange-correlation functional and the projected augmented wave (PAW) pseudopotentials were used.44,45 The cut-off energy was set to 525 eV. The transition metal atoms considered as dopants in this study were Co, Ni, Cu, Zn, and Au. Each dopant was substituted at the center of a graphene supercell consisting of 8 × 8 unit cells (127 carbon atoms and 1 dopant atom), as shown in z-direction to eliminate the interaction between layers. A k-point mesh of 9 × 9 × 1 was used for the calculations.Electronic structure computations were conducted using the DFT method,−8 Ry. The lattice constant for graphene was 1.42 Å, as reported in the literature.46 The relaxation of atomic position in the unit cell was performed by using the Broyden–Fletcher–Goldfarb–Shanno (BFGS) algorithm. Relaxation was allowed in the x and y directions. A slightly larger k-point mesh of 11 × 11 × 1 was applied for the calculation of DOS and PDOS, and 20 points along the Γ–M–K–Γ high symmetry k-path were considered to obtain the band structures. Optical properties were calculated using the optimized norm-conserving Vanderbilt (ONCV) pseudopotential with Γ-centered calculation.47–49First, each TM-doped graphene structure was optimized until the change in energy was lower than 10From those calculated electronic structures, the optical properties were then calculated in a sequential step initiated from the calculations of the dielectric function, absorption spectra, and finally the EELS spectrum calculation.3.3.1.dC–TM) after structure optimization for these TM-doped graphene are presented in ρTM-doped graphene, ρgraphene, and ρTM are the charge densities of TM-doped graphene, pristine graphene with vacancies, and TM atoms, respectively.18,57,58 As shown in The optimized lattice structures were obtained after the structure relaxation calculations converged, that is, when the minimum energy for each calculation has been reached. Our structure optimizations confirm that a single TM atom can form bondings with the three nearest C atoms, as depicted in Γ–M–K–Γ path on the Irreducible Brillouin Zone (IBZ). The calculated electronic structures provided information regarding the electron states at a particular wavenumber (k) and energy in the TM-doped graphene. The calculated electronic structures and the corresponding DOS for graphene and TM-doped graphene are shown in i.e., without dopant  level is located at the Dirac point. This result was in agreement with that reported in the literature, demonstrating the calculations' validity herein.22,43,50 Significant changes in the electronic structures of TM-doped graphene can be seen in The electronic structures were calculated along the high-symmetry t dopant , the calThe PDOS curves demonstrate the contribution of specific orbitals to the electronic band. The PDOS presented in For Au-doped graphene, the contribution of Au orbitals in the mid-gap state band δ is very little, similar to the Zn dopant, because the formed bonds do not involve the Au 3d orbitals but likely other orbitals with much lower energies than the Fermi energy. In this case, the mid-gap band is then formed merely due to the structural/bond alteration of the graphene units surrounding the TM atoms. As the mid-gap states also involve valence electrons from carbon atoms of this graphene, the band structure now forms a metal-like band structure, where the states below the Fermi energy are filled but states above it are empty. Despite the number of free electrons will be small, we may still expect metal-like properties and hence plasmonic characteristics, where the plasmonic frequency will be determined by this free electron density.51–54 In systems with low electron delocalization, the valence electrons from both TM and the ligand or surrounding atoms may form a bonding through several possible hybridization schemes leading to a typical trigonal bipyramidal or octahedral local coordination. In such cases, analysis of the ligand field effect should be carefully undertaken, which may determine the orbital level splitting as well as the spin multiplicity.55 For the cases discussed here, the PDOS for these TM-doped graphene and the electric charge difference ΔρTM indicate that the bonding is also formed from a hybridization scheme which involves involving the 3d, 4s, and 4p orbitals of the TM atom and the 2p orbitals from surrounding C atoms. However, in contrast to the previous studies,51–54 electrons in these TM-doped graphene are much more delocalized, as implied by the local charge in each atom. Tables S1–S6 of ESI56 Tables S1–S6 of the ESI51–54 For the TM-doped graphene considered in this work, it seems that spin multiplicity has a minor role in the electronic structure and the subsequence optical properties  is calculated as a result of a response function that comes from a perturbation theory with adiabatic approximation. This imaginary part of the dielectric function εi(ω) is given by:61e is the electron charge, m is the electron mass, Ω is the primitive cell volume, and ω is the incident light frequency. Ek,n′ is the final state energy (empty CB) and Ek,n is the initial state (filled VB), whereas f and fare Fermi–Dirac distribution functions for both bands. Mα,β is the moment of transition from n  to transition n′ . The real part of the dielectric function is then calculated using the well-known Kramers–Kronig transformation. The EELS spectrum is proportional to the imaginary of the inverse dielectric tensor, which is computed by using the following relationship61In general, a dielectric function is a complex number given byTherefore, as seen from those equations, the calculation of the EELS spectrum in this method only includes the plasmons originating from interband transitions and does not include the plasmon from intraband transitions.ε1), the imaginary part of the dielectric permittivity (ε2), and EELS spectra for Co- and Au-doped graphene are presented. As similar as seen in the absorption coefficient spectra above, the EELS spectra also exhibit two bands at different photon energies, in which the π plasmon band appears at approximately 5.9 eV, and a wider (π + σ) plasmon band appears at around 17–22 eV. This result is in good agreement with the reported values in the literature.58 Typically, the plasmon frequency for metallic materials can be determined considering a condition in which both the real (ε1) and imaginary parts (ε2) of the dielectric permittivity intersect the horizontal axis. Here, the EELS peak can also be used as a complementary parameter to determine the possibility of plasmon excitation, for which the EELS peak may appear at the same frequency (photon energy) as the intersection of ε1 and ε2 on the horizontal axis.60 However, in the case of plasmon excitation that undergoes damping due to interband transition, the plasmon frequency (photon energy) may exhibit a slight shift from the ε1 and ε2 intersection frequencies.61 This is the case in ε1 and ε2. The substitution of TM atoms caused a slight alteration in both plasmon frequencies, as depicted in In The π plasmon frequency of pristine graphene  is almos62ngraphene is the electron density inside the mid-gap states at the Fermi energy level; e is electron charge; me is electron mass, and ε0 is the vacuum permittivity. In the present stage, as a simple approximation, the electron density was obtained by integrating the mid-gap states band δ band at the Fermi energy level according to the following formula:EF is the Fermi energy level, δE is the onset bottom energy level of the mid-gap states band, where the integral boundaries are from EF − δE to EF, as indicated by two vertical dash lines in ωp, using λ), wavelength (λ), and energy are listed in −1 in wavenumber.Since the EELS calculation method cannot calculate the intraband transition, it is not seen in the calculated EELS spectra above. This intraband transition does not require large photon energy because this mid-gap states band δ behaves like a metallic band characteristic. However, as seen in DOS, only a very small number of electrons are available for this intraband transition in comparison to metals. To predict the possibility of plasmon excitation at small photon energy (∼0 eV or in the THz region) owing to this intraband transition, the following theoretical plasmon frequency was used as a rough estimation:12,65,66 In those previous reports, graphene plasmonics are realized through Fermi energy shift by applying external electrical or magnetic fields. By adjusting the Fermi energy or the chemical potential, one can control the free electron density and electrical conductivity of graphene as well as its plasmon frequency.67–71 In the present work, our calculation results show that the plasmon frequency in THz range, as seen in This estimated plasmon frequency range seems almost in the same range as reported by several pioneer groups who experimentally investigated and developed graphene plasmonics in the THz region.−1. As a comparison, we may look at the following several cases. The vibration modes of water clusters in pentamer structure, involving intramolecular vibrations of H2O, symmetric stretching and bending as well as asymmetric stretching, appear at the THz region. The vibrational modes of water are observed at 450–780 cm−1, the O–H⋯O stretching vibrations are observed at 167 cm−1 and the O–H⋯O bending vibrations at 53 cm−1.72 Böhm et al. reported that in an aqueous solution the trivalent Fe cation has a different feature of THz spectra in comparison to its divalent cation. Trivalent Fe cation exhibits two absorption peaks at 180 and 260 cm−1, while divalent Fe cation exhibit only one absorption peak at 200 cm−1.63 The same group has also reported the same behavior for Mn and Ni.64 Therefore, by choosing TM-doped graphene with a plasmon frequency that matches the frequency of a specific vibration mode of a substance, a resonance between plasmon and vibration mode can be expected and possibly applied in molecular sensing or detection applications.Although the range of these plasmon frequency shifts seems small, in terms of molecular vibration energy those shifts are actually quite large. 4.Ab initio calculations based on the DFT method were performed to study the structural, electronic, and optical properties of TM-doped graphene. The TM atom evaluated herein is Ni, Co, Cu, Zn, and Au, which is substituted into an 8 × 8 graphene supercell replacing one carbon atom. The structure resembles a substitutional defect by a single TM atom in the basal plane of graphene as reported elsewhere. The substitution of these TM dopants leads to a bandgap opening at the Dirac point, shifting the Fermi energy downward inside the mid-gap states band that forms the half-filled valence band top, where it varies depending on the TM atom. Such electronic-band structure changes are originated from structural/bond deformation surrounding the TM dopant along with the bond hybridization between the TM dopant and the nearest carbon atoms. In the TM-doped graphene, the absorption peaks just shift slightly toward low energies in comparison to pure graphene. The EELS calculations results confirm a plasmon frequency at approximately 5.86 eV, which is associated with the interband excitation of π electrons.The TM-doped graphene, however, exhibit negative numbers for the real part of dielectric permittivity, which resembles metal material properties. As EELS calculations cannot predict the plasmon originating from intraband photo-excitation, by using the number of electrons in the mid-gap states band δ, the plasmon frequencies of these TM-doped graphene can be predicted to appear at the THz region around 5–7.5 THz. Although the plasmon excitation in these TM-doped graphene here is caused by a substitutional defect, which could be achieved such as by the aforementioned wet chemical process, the plasmon excitation mechanism seems principally similar to plasmonic excitation of pure graphene induced by electric or magnetic fields reported elsewhere, in which the Fermi energy shifting from Dirac cone point level leads to the possibility of intraband transition. In addition, the plasmon frequency range matches the intermolecular vibration frequencies, which is useful in THz spectroscopy for generating plasmon resonance with a particular vibration mode of a substance, the present calculation results might be beneficial for optoelectronic and molecular sensing applications in the THz region.D. U. D. investigation, formal analysis, and writing – original draft. R. H. conceptualization, formal analysis, writing – review & editing, funding acquisition. A. M. P. and K. N. methodology and writing – review & editing. All authors confirmed the final manuscript.There are no conflicts to declare.RA-013-D2RA06446D-s001