By analyzing the GH variation, the index sensitivity of such configuration can reach as high as 8.02 × 105 λ/RIU, which is 293.24 times of the Au-ITO structure and 177.43 times of the Au-ITO-graphene structure. The proposed SPR biosensor can be widely used in the precision metrology and optical sensing.In order to improve the performance of surface plasmon resonance (SPR) biosensor, the structure based on two-dimensional (2D) of graphene and transition metal dichalcogenides (TMDCs) are proposed to greatly enhance the Goos-Hänchen (GH) shift. It is theoretically proved that GH shift can be significantly enhanced in SPR structure coated with gold (Au)-indium tin oxide (ITO)-TMDCs-graphene heterostructure. In order to realize high GH shifts, the number of TMDCs and graphene layer are optimized. The highest GH shift (−801.7 λ) is obtained by Au-ITO-MoSe Surface plasmon resonance (SPR) is a kind of highly sensitive real-time spectral phenomenon, which can be used to measure the refractive index change on the surface of the metal film . The optAs we know, when total reflection occurs at the interface of two kinds of media, a small lateral displacement occurs between the incident light and the reflected light, which is called the Goos-Hänchen (GH) shift ,13. Artm2O3 (commonly used doping ratio is: In2O3:SnO2 = 9:1), and substituting Sn4+ atom for in3+ atom, it has the characteristics of high band gap and degeneracy [2, TMDCs, and direct band gap semiconductor in detail [2 are considered [2 heterojunction, the GH shift is significantly enhanced to 235.8 λ [Indium tin oxide (ITO) is a new kind of semiconductor material . Pass thgeneracy . It is cgeneracy ,23,24,25generacy ,27, trangeneracy ,29, blacgeneracy ,31, and generacy ; secondlgeneracy ; finallygeneracy ,35. Grapgeneracy . Howevergeneracy . Therefogeneracy . The hargeneracy ,40. Wu egeneracy . Comparen detail . The spinsidered . In the  235.8 λ .2/MoS2/MoSe2/WSe2) and graphene on GH shift in current literatures. Moreover, the combination effects of metal and ITO on GH shift has yet been reported, while in this paper, the GH shifts of TMDCs and graphene are compared, and the maximum GH shift is 801.7 λ for Au-ITO-MoSe2-graphene heterostructure. The optimum sensitivity based on GH shift is 8.02 × 105 λ/RIU, which is 293.24 times of Au-ITO structure and 177.43 times of Au-ITO-graphene structure. These results will provide a helpful guidance for the scholars who study 2D-materials-based GH shift.Although TMDCs and graphene are recognized as promising approaches to enhance the GH shift, there is no comparative analysis of various TMDCs n1=1.ollowing :(2)n2=1.According to the Drude–Lorentz mode, the third layer is the Au film with refractive index as following :(3)n3==1The fourth layer is the ITO film with refractive index as :(4)n4=3.The fifth layer of TMDCs with the refractive index and thickness of monolayer at λ = 632.8 nm is shown in 1 ≈ 5.446 μm−1. The thickness of monolayer of graphene is 0.34 nm. For the last layer, the sensing medium is water. In the λ = 632.8 nm, the refractive indices are n1 = 1.7786, n2 = 1.5151, n3 = 0.181 + 3.068i, n4 = 1.858 + 0.058i, n6 = 3.000 + 1.149i, n7 = 1.330 [bion. The dielectric constant of each layer is set to kε . The thickness (kd) of SF11 glass, BK7 glass, and sensing medium are 1d = 200 nm, 2d = 100 nm, and d7 =100 nm, respectively. For this SPR biosensor, we use the thickness of Au (3d) 50 nm and ITO (4d) 10 nm to excite the SPR. It is reasonable to take the individual graphene sheet as a non-interacting monolayer if the number of layers N ≤ 5 [In the sixth layer, the refractive index of graphene at visible range is obtained by the relation :(5)n6=3. = 1.330 , respectM is the characteristic TM of n-layer composite structure, which is obtained from the following relation of P-polarized light [kM is expresses as:kp and kα are written as:kd is the thickness of the kth layer. The matrix of the total reflection polarized light (pγ) can be expressed as [p1 and Np are the corresponding terms for the first layer and the Nth layer. The reflectivity (Rp) and phase (pψ) is shown as:In order to study the changes of the GH shift and reflectivity in SPR biosensors, we use the transfer matrix method (TMM) and the Fresnel equation based on N-layer model to perform a detailed analysis. The ed light :(6)M=∏k=essed as :(10)γp=S=−1The curve of reflectivity changing with incident angle is called SPR curve, once SPPs are excited, there will be a reflection angle and a corresponding sharp change of reflection phase. According to Equations (11)–(13), we can know that the SPR reflectivity (Rp), phase (ψp), and GH shift of Au-ITO film coated BK7 and SF11 glass, as shown in S = 63.89 λ. For bilayer and 3 layers, the GH shifts of this Au-ITO-graphene structure are 89.06 λ and 168.5 λ, respectively. For 4 layers, the minimum reflectivity is 1.9829 × 10−6 a.u. at resonance angle of 61.01°, the phase change to Lorentzian-like at resonance angle, and the highest GH shift of SPR biosensor structure is −241.2 λ. Therefore, when the phase change is Lorentzian-like, the GH shift is negative, and the greater the change of phase, the larger the value of GH shift. The GH shift of −134.7 λ is obtained by 5 layers. Hence, when the thickness of graphene is 4 layers, the GH shift reaches the maximum value S = −241.2 λ. Subsequently, different layers of MoSe2 are added to the Au-ITO structure, as demonstrated in −5 a.u. at resonance angle of 63.02°. The phase change to Lorentzian-like at resonance angle, and the highest GH shift of SPR biosensor is S = −492.6 λ. From 3 layers to 5 layers, the GH shift is −53.41 λ, −28.01 λ, and 20.14 λ, respectively. Therefore, the maximum GH shift of −492.6 λ is obtained by the MoSe2 bilayer. From 2 layer, the SPR resonance angle will show a larger GH shift, and the GH shift of MoSe2 is larger than that of graphene. Secondly, the bandwidth of the reflection curve will be broadened rapidly with the increase of the number of MoSe2/graphene layers, because the electronic energy loss of MoSe2 layer is related to its imaginary part of dielectric function. The increment of MoSe2 layer leads to a large electron energy loss [Then, the different layers of graphene and TMDCs are used to increase GH shift. First, the different layers of graphene are added to the Au-ITO structure. In rgy loss .2. In 2 (monolayer) hybrid structure change with angle of incidence. For monolayer, the GH shift of this structure is S = 186.4 λ at resonance angle of 61.53°. For the bilayer of graphene, the minimum reflectivity is 3.29 × 10−5 a.u. at resonance angle of 61.97°, the phase change to Lorentzian-like at resonance angle, and the highest GH shift of SPR biosensor is S = −801.7 λ. For the 3, 4, 5 layers, the GH shift is −114.1 λ, −58.14 λ, and −37.68 λ, respectively. Therefore, when the graphene and MoSe2 are bilayer and monolayer, respectively, the maximum GH shift of −801.7 λ is obtained by Au-ITO-MoSe2-graphene hybrid structure. Secondly, the different number of MoSe2 layers added to the Au-ITO-graphene (monolayer) structure. In 2 from layer 2 to layer 5, the lowest point of the reflection curve is more and more far away from zero, and the phase change is smaller, which shows that the light absorption is gradually weakened, and the SPR excitation are also weakened.In order to enhance the GH shift, the different layers of graphene and TMDCs are used to increase GH shift. Firstly, we investigate the angle of incidence for different number of graphene layers with monolayer of MoSe2/WS2/WSe2) are added to the monolayer of graphene. As shown in 2 monolayer, the highest GH shift is 409.9 λ. With the increment of MoS2 layers, the GH shift changes from positive to negative. However, the GH shift that become negative are smaller, which are −56.57 λ, −24.23 λ, −16.12 λ, and −13.03 λ, respectively. Therefore, the maximum GH shift of 409.9 λ is obtained with both monolayer of MoS2 and graphene. In 2 is from monolayer to 5 layer, the GH shift is 43.09 λ, 29.92 λ, 21.82 λ, 17.0 λ, and 14.28 λ, respectively. In 2.Subsequently, different number of other TMDCs  can be obtained. With WS2, the highest GH shift 382.4 λ is gained by WS2 monolayer and graphene 5 layers. Finally, the largest GH shift of −454.3 λ is obtained when the WSe2 is monolayer and graphene is 5 layers.With the increase of layers of TMDCs/graphene, the GH shift increases gradually. However, further increasing the layers, the absorbed energy will not be completely transferred to the enhanced evanescent field, which leads to the decrease of GH shift. This can be analyzed from the depth and width of the SPR curve. The closer the reflectance to zero the higher the modulation depth, and the greater the loss the broader the resonance . Therefon7), the GH shift will appear with a large variation. Hence, the structure can be used as a high sensitivity biosensor by monitoring the change of GH and the sensitivity (PS) is defined as [n7 is the change of refractive index of sensing medium. In n7 is plotted. When the n7 increases from 1.330 to 1.332, the maximum of GH shift reaches ΔGH = 5.47 λ . Therefore, we can calculate the sensitivity to be PS = 2735 λ/RIU. Similarly, in PS = 4520 λ/RIU. In 2 (monolayer)-graphene (monolayer) structure, so the sensitivity is PS = 2.142 × 104 λ/RIU. In 2 (monolayer) -graphene (bilayer) offers the maximum of GH shift ΔGH = 160.4 λ, when the n7 increases from 1.3300 to 1.3302, resulting in the highest sensitivity of 8.02 × 105 λ/RIU, which is 293.24 times larger than the Au-ITO structure and 177.43 times larger than the Au-ITO-graphene (monolayer) structure.We found that when we change the refractive index of sensing medium (fined as :(14)SP=ΔFor comparison, the performances of previously reported 2D-material-assisted GH shift sensors based on SPR sensors are summarized in 2 and bilayer of graphene. The maximum displacement is 801.7 times of the incident wavelength. Compared with the traditional SPR structure, the shift of the structure is increased by more than 2 orders of magnitude. Moreover, the GH shift can be positive or negative depending on the layer number of TMDCs and graphene. The sensitivity corresponding to the maximum GH shift can reach as high as 8.02 × 105 λ/RIU, which is 293.24 times of the Au-ITO structure and 177.43 times of the Au-ITO-graphene structure. Such configuration could pave the way to high precision optical sensing.In this paper, the high GH shift in SPR biosensor based on Au-ITO-TMDCs-graphene hybrid structure is analyzed. We theoretically prove the influence of the number of graphene and TMDCs layers on the GH shift, and a large GH shift is obtained by using the mixed structure of monolayer MoSe


We obtained and minutely analyzed the relevant parameters of each most stable adsorption configuration to explore the microscopic mechanism during gas adsorption. Theoretical results reveal that Pd3-graphene shows great adsorption capacity and sensitivity toward those decompositions. High adsorption energies and abundant charge transfer amounts could guarantee a stable adsorption structure of decomposition gases on Pd3-graphene surface. The complex change of density of states verifies a strong chemical reaction between the gases and the surface. Moreover, the conductivity of Pd3-graphene would improve due to the decrease of energy gap, and the sensitivity was calculated as SOF2 > H2S > SO2 > SO2 F2. This work provides an effective method to evaluate the operation status of SF6 gas-insulated equipment.In this study, we investigate Pd To date, several methods such as gas chromatography, mass spectrometry and Fourier transform infrared spectroscopy, are suggested to detect SF6 products [6 decomposition products.Owing to its outstanding insulation and arc-extinguishing properties, SFar (GIS) ,2. Howev(GIS) [6 ,4. Simul2 F2 gas ,6,7. The2 F2 gas ,9. Thereproducts ,11. Howe2 reduction reaction and found that a single Mo embedded on nitrogen-doped 555–777 graphene shows eminent catalytic performance [6 decomposition product detection have been reported.In recent years, the gas sensor method has been used in various fields due to its advantages such as high sensitivity, rapid response and small size. Graphene is a 2D material with a unique 2D monoatomic layer structure and an electronic energy band structure. Its excellent characteristics—including high electron mobility, high thermal conductivity, brilliant mechanical properties and large specific surface area—make it a promising gas sensor material ,15,16,17formance . Arokiyaformance . Ma et aformance . Despiteformance ,23,24,252 hybrid orbital network but forms a stable topological hole. Thus, 555–777 graphene has a more stable electronic structure compared with other defective structures. Previous studies showed that doping transition metal elements on graphene surface can improve its electrical conductivity and enhance its capacity to adsorb gas molecules [6 decompositions on Pd (111) surface and found that Pd (111) would have great adsorption capacity on absorbing those products. Thus, doping Pd element on 555–777 graphene may be a potential method to improve its adsorption properties [3-doped 555–777 graphene (Pd3-graphene) is carried out to detect SF6 decomposition products . Different adsorption structures of each gas are obtained to find the most stable adsorption structure. Furthermore, adsorption energy, charge transfer, density of states (DOS) and deformation charge density (DCD) of Pd3-graphene surface before and after gas adsorption are calculated to reveal the gas response mechanism. Overall, our work aims to provide some theoretical basis for developing a novel graphene sensor.555–777 graphene is a double-vacancy defect graphene sheet . The absolecules ,28,29,303 package based on density functional theory (DFT) [−6 Ha and spin polarization is considered due to the magnetic properties of Pd atoms. Additionally, total energy of convergence tolerance, maximum force and maximum displacement are set as 1 × 10−5 Ha, 2 × 10−3 Ha/Å and 5 × 10−3 Å, respectively.In this work, all calculations are carried out using Dmolry (DFT) . Generalry (DFT) ,33. DFT ry (DFT) . Double ry (DFT) . The sme3 cluster is a triangular structure composed of three Pd atoms. Through DFT calculations, various parameters of stable adsorption structures can be acquired, including adsorption energy (Ead), charge transfer amount (QT), adsorption distance (D) and energy gap (Eg). The definition of these parameters are the same as the previous study [Intrinsic 555–777 graphene surface consists of a 6 × 6 supercell, and the lattice parameter is 14.760 Å × 14.760 Å. The vacuum area is set as 20 Å to avoid the interaction of neighboring slabs. The Pdus study .2S, SO2, SOF2, SO2 F2 and Pd3-graphene. The optimized structures are shown in 3 cluster at the defect center of graphene to form a stable anchored structure. 3 cluster is parallel to the graphene surface, indicating that the force of the crystal plane on the three Pd atoms is almost equal. Bond lengths between the Pd atoms are 2.714, 2.714 and 2.812 Å. Millikan charge analysis shows that 0.16 electrons transfer from the Pd3 cluster to the graphene sheet after geometric optimization, showing an evident orbital hybridization between C and Pd atoms. The electronic structure of the graphene surface will be greatly changed, which may substantially improve gas adsorption capacity.We apply geometric optimization to minimize their energy and obtain the most stable status of H2S molecule is placed in different distances and angles to approach the Pd3-graphene surface and obtain the most stable adsorption structure of H2S gas. Considering the symmetry of H2S molecule, its two typical stable adsorption structures are acquired through H and S atoms approaching the Pd3-graphene surface, as shown in Ead, QT and D are listed in The H2S molecule approaches the surface by the S atom and forms a stable interaction between the S and Pd atoms. The D of M1 is 2.338 Å, revealing that the reaction is relatively strong. When the adsorption energy is greater than 0.6 eV, the adsorption is generally considered chemical. The corresponding Ead of M1 is −1.211 eV; hence, the adsorption is chemical, and the process is spontaneous. The positive value of QT of M1 (0.286) demonstrates that 0.286 electrons transfer from the H2S molecule to the Pd3-graphene.2S molecule approaches the Pd3-graphene by H atom, forming a new ionic bond with the Pd atom. The length of the H–Pd bond is 1.868 Å, indicating a strong chemical interaction between H and Pd atoms. Similar to system M1, 0.279 electrons transfer from the H2S molecule to the sheet during optimization. The Ead of system M2 (−1.185 eV) is smaller than that of M1 (−1.211 eV), which means that system M1 releases more energy than M2 after H2S adsorption. Above all, according to the greater Ead and QT of configuration M1, M1 is the most stable adsorption structure of H2S on Pd3-graphene surface.In 2S adsorption further, as shown in 2S adsorption, respectively. Several distinct changes are observed in DOS after H2S adsorption, which mainly reflect in the increase of DOS from −8 eV to −4 eV. The DOS at the Fermi level rises slightly, revealing that electrons can more easily transfer from the valence band to the conduction band, which may have a substantial effect on improving its conductivity. The PDOS in DOS and partial density of states (PDOS) of the most stable adsorption structure (M1) are calculated to analyze the mechanism of H2 on Pd3-graphene surface, various initial positions of SO2 molecule are set to investigate the most stable adsorption system. After geometric optimization, two typical stable adsorption configurations are obtained. 2 molecule forms a stable adsorption structure by building a chemical bond between S and Pd atoms. The length of the S–Pd bond is 2.192 Å, declaring a strong interaction between them. The two O atoms are far from the sheet; thus, no direct interaction may exist between them and the crystal plane. In 2 molecule approaches the Pd3 cluster by O atoms, forming two chemical bonds with the Pd atoms. The length of both O–Pd bonds is 2.131 Å, which is shorter than that of the S–Pd bond in system M3. Thus, the chemical reaction in system M4 may be stronger than that in M3.For the adsorption of SOEad are negative, manifesting that the adsorption is exothermic and proceeds spontaneously. By contrast, the Ead of system M4 is greater than that of system M3, implying that the SO2 molecule absorbed on the Pd3-graphene surface through two O atoms is the most stable structure. Given the strong reaction between O and Pd atoms in system M4, 0.283 electrons transfer from the sheet to SO2 molecule. For system M3, the small QT means that the ionic S–Pd bond is relatively easy to break.2 on Pd3-graphene. 2 adsorption at around −8, −6 and −4 eV. PDOS shows that the new peaks mainly result from the 2p orbit of O atom and the 3p orbit of S atom. The small increase of DOS at fermi level demonstrates an increase of the conductivity of Pd3-graphene. In addition, a large overlapped area between the 2p orbit of O atom and the 4d orbit of Pd atom ranges from −5 eV to −3 eV, reflecting a complex hybridization of those orbits. Therefore, the chemical reaction between O atoms and Pd atom is strong enough to form a stable adsorption configuration.The DOS and PDOS of M4 are intensively calculated to analyze the adsorption mechanism because M4 is the most stable adsorption configuration of SO2 molecule in different directions and distances approaching the sheet to explore the most stable adsorption structure. 2 molecule is absorbed on Pd3-graphene surface by S, F and O atoms. Related parameters are listed in Subsequently, we place the SOF2 molecule approaches the surface by the S atom and forms a stable adsorption structure ultimately. The S atom is trapped by the Pd atom and builds a new chemical bond with a bond length of 2.170 Å. The Ead of system M5 listed in 2 molecule to the sheet, so their electronic structure may change slightly. For system M6 shown in 2 molecule absorbs on the Pd3-graphene surface by forming an ionic bond length of 2.124 Å between F and Pd atoms. The Ead of M6 (−0.284 eV) is smaller than that of M5 (−1.230 eV), revealing that M5 is more stable than M6. In system M7, the SOF2 molecule absorbs directly above the hollow position of Pd3 cluster. The length of the O–Pd bond is 2.299 Å, which is longer than that of M5 and M6. However, the specific Ead of M7 (−1.282 eV) is greater than that of M5 (−1.230 eV), implying that system M7 is more stable. Opposite to system M5, 0.132 electrons transfer from the sheet to SOF2 molecule after absorbing on Pd3-graphene. Hence, the SOF2 molecule tends to be absorbed on the Pd3-graphene surface in the form of M7, establishing an adsorption system with the lowest energy.2 on the Pd3-graphene surface. The DOS of M7 structure increases distinctly in the range from −9 eV to −7.5 eV and −6 eV to −3 eV after SOF2 adsorption. These changes are mainly caused by the 2p orbit of O atom and the 2p orbit of F atom. A slight increase of DOS near the fermi level is observed, signifying that SOF2 adsorption can improve the conductivity of Pd3-graphene. The PDOS displaces the hybridization of individual atoms during adsorption. The 2p orbit of O atom, the 2p of F atom and the 4d orbit of Pd atom overlap from −6 eV to −1 eV, suggesting that the chemical reaction between them is considered strong, and the electronic structure of the SOF2 molecule is active.2 F2 molecule approaches the Pd3-graphene surface in various directions and distances to find the most stable adsorption structure. After adsorption structure optimization, two typical adsorption systems are obtained, as shown in Eventually, the SO2 F2 molecule approaching the Pd3-graphene surface by F atom. The Pd atom builds a chemical connection with the F atom during the approaching process and forms an F–Pd bond with length of 2.014 Å ultimately. The S–F bond is stretched to 2.40 Å due to the radial force of the Pd atom. In system M9, the SO2 F2 molecule approaches the sheet by O atom. Similarly, the O atom forms a chemical bond with the Pd atom, but the length of the O–Pd bond (2.181 Å) is longer than that of the F–Pd bond (2.014 Å), implying a stronger interaction in configuration M8. The Ead of M8 (−0.920 eV) is greater than that of M9 (−0.804 eV), demonstrating that the M8 structure is more stable than the M9 structure. Additionally, 0.705 electrons transfer from the sheet to the SO2 F2 molecule in M8, which is 2.4 times of M9, confirming a stronger oxidation of the F atom. Thus, configuration M8 is supposed to be the most stable adsorption structure of SO2 F2 on the Pd3-graphene surface.3-graphene is expected to improve after SO2 F2 adsorption. According to the PDOS, a large hybridization is observed between the 2p orbit of F atom and the 4d orbit of Pd atom from −5 eV to −1 eV, implying that these orbits are relatively active, while SO2 F2 approaches the surface.3-graphene sensor can be utilized in GIS, we further calculated the adsorption of SF6 gas on Pd3-graphene surface to eliminate the interference of SF6 gas. Same as other gases, SF6 approaches the graphene surface at different angles and distances. After the geometric optimization, we obtained the most stable adsorption structure of SF6 on Pd3-graphene surface shown in 6 molecule approaches the Pd3-graphene surface by F atom and forms a weak interaction with the Pd atom. The adsorption distance of SF6 is 4.060 Å, which is longer than other gases. Moreover, the Ead of SF6 is calculated to be–0.124 eV, reflecting that the adsorption the adsorption system is not stable enough. During the adsorption, 0.162 electrons transfer from the Pd3-graphene to SF6 molecule. In conclusion, the Pd3-graphene can be a potential sensor applied in the SF6 gas-insulated equipment.In order to ensure that the Pd3-graphene and the four most stable adsorption systems is calculated to investigate the difference in electronic structure before and after modifying or gas adsorption. As presented in 3 cluster decreases, revealing that the defect of 555–777 graphene has a strong oxidation during the doping process. Although the absence of carbon atoms do not give rise to dangling bonds, the reconstruction of the graphene structure results in the change of bond lengths. Meanwhile, the defect would cause a rehybridization of the sigma and pi orbitals of carbon atoms, which would enhance the electron activity near the defect. When the transition metal approaches the defect, its special d electrons form a strong chemical interaction with the defect. 3 cluster after adsorption. Therefore, the adsorption reaction is concentrated between the S atom and the Pd atom. In 2 gas changes prominently. As for SOF2 gas, the charge density neighboring the O atom increases to a certain degree, and the charge density of the Pd atom decreases. In principle, the O atom performs as an electron acceptor during SOF2 adsorption. In 3 cluster behaves as an electron donator during gas adsorption and leads to a violent chemical reaction in the vicinity, certifying that the Pd3 dopant can substantially enhance the adsorption capacity of intrinsic 555–777 graphene.The deformation charge density of pure Pd3-graphene after SF6 product adsorption, the sensitivity and selectivity for application of chemical gas sensor must be further investigated. As a resistor-type gas sensor, the change in conductivity is an important factor in detecting SF6 decomposition products. The conductivity  and LUMO (EL) and obtain the specific Eg, which the difference between them.According to the evident effect on the electronic structure of Pd formula :σ ∝ e, and the calculation results are as follows:In this work, we propose Pd2S, SO2, SOF2 and SO2 F2 are −1.211, −1.591, −1.282 and −0.920 eV, respectively, demonstrating that the four gases could be absorbed on Pd3-graphene surface by chemisorption. Charge transfer makes various atoms form ionic bonds during adsorption. In addition, the change of DOS and PDOS verifies high hybridizations of different atomic orbits.(I) Adsorption energies of the most stable adsorption systems of H3-graphene would be improved without exception due to the decrease of Eg after gas adsorption. SOF2 gas adsorption leads to the largest increase, whereas SO2 F2 is the smallest. According to the reduced value of Eg, the sensitivity of the four gases follows the order SOF2 > H2S > SO2 > SO2 F2.(II) The conductivity of Pd3-graphene can absorb SF6 decomposition products, and the Pd3-graphene sensor can be employed to evaluate the insulation condition of GIS by detecting these decompositions.Thus, we confirm that Pd


The genitourinary syndrome of menopause (GSM) is a collection of signs and symptoms related to estrogen decline that involves physical changes to the vulva, vagina, and lower urinary tract. GSM signs and symptoms may occur during any reproductive stage but are most common during menopause. Vaginal microbiota, particularly Lactobacillus spp., protect the female genital tract from multiple conditions; however, Lactobacillus spp. abundance declines during menopause. We aimed to determine the longitudinal association of vaginal microbiota with GSM signs and symptoms across reproductive stages. In a two-year cohort study comprising 750 women aged 35-60 years who contributed 2111 semiannual person-visits, low-Lactobacillus spp. vaginal microbiota communities were observed at 21.2% (169/798), 22.9% (137/597), and 49.7% (356/716) of person-visits among pre-, peri-, and post-menopausal women, respectively (p<.001). After covariate adjustment, low-Lactobacillus spp. communities characterized by high Atopobium and Megasphaera relative abundance were associated with vulvovaginal atrophy relative to high-Lactobacillus spp. communities dominated by L. crispatus  among post-menopausal, but not among peri- or pre-menopausal women. Also, post-menopausal women with low-Lactobacillus spp. communities reported decreased libido  and vaginal dryness  more frequently than their counterparts with high-Lactobacillus spp. communities, but not among peri- or pre-menopausal women (p for interaction<.05). Specifically, low-Lactobacillus spp. communities characterized by high Atopobium and Megasphaera relative abundance were related to both decreased libido  and vaginal dryness  compared with high-Lactobacillus spp. communities dominated by L. gasseri/L. jensenii. Vaginal microbiota, particularly Lactobacillus spp., and menopause may synergistically influence GSM.


We propose and demonstrate a temperature and humidity sensor based on a fluorinated polyimide film and fiber Bragg grating. Moisture-induced film expansion or contraction causes an extra strain, which is transferred to the fiber Bragg grating and leads to a humidity-dependent wavelength shift. The hydrophobic fluoride doping in the polyimide film helps to restrain its humidity hysteresis and provides a short moisture breathing time less than 2 min. Additionally, another cascaded fiber Bragg grating is used to exclude its thermal crosstalk, with a temperature accuracy of ±0.5 °C. Experimental monitoring over 9000 min revealed a considerable humidity accuracy better than ±3% relative humidity, due to the sensitized separate film-grating structure. The passive and electromagnetic immune sensor proved itself in field tests and could have sensing applications in the electro-sensitive storage of fuel, explosives, and chemicals. Humidity monitoring and regulation are of great significance in pharmacy, semiconductors, and costly facility maintenance and explosive storage ,2,3. RelOptical fiber sensing, as a passive and electromagnetism-immune method, provides a safe and reliable approach to temperature and humidity monitoring for such electro-sensitive storage ,6. Howev3 modification in the monomer of the polyimide reduces its moisture capacity, restrains its humidity hysteresis, and provides a short moisture breathing time less than 2 min. Another cascaded FBG temperature sensor is used to exclude its thermal crosstalk, with a temperature accuracy of ±0.5 °C. Experimental monitoring over 9000 min revealed a relative humidity accuracy better than ±3% RH, while field testing for tobacco storage proved its stability and practicability as designed. The passive and electromagnetism-immune sensor with an accurate and fast response can be applied for the electro-sensitive storage of explosives, chemicals, and fuels.In this paper, a fluorinated polyimide-film-based temperature and humidity sensor utilizing fiber Bragg grating is proposed and demonstrated. The sensor was constructed with an FBG and a 20 μm-thick fluorinated polyimide film by direct manual gluing. Moisture-induced film expansion or contraction causes an extra strain, which is transferred to the FBG and leads to a humidity-dependent wavelength shift. Compared with the coating method, the separate film-grating structure provides a large surface area for moisture exchange, an improved dynamic range, and considerable sensitivity. The –CFFor common polyimide films, the vapor in the air is easily captured by the hydrophilic hydrogen bonds and porous surface. The strong absorption causes a slow moisture release and may even lead to humidity hysteresis and agglomeration. Thus, chemical modification is necessary to improve the surface properties of the polyimide film. The fluorinated polyimide film was synthesized and provided by the group of Pro. L. Fan, Institute of Chemistry Chinese Academy of Sciences, and is commercially available with excellent hysteresis resistance . As can As the moisture capacity is significantly reduced in a fluorinated polyimide film, the sensitivity to humidity declines sharply along with the insufficient expansion. The conventional coating method is no longer suitable for practical use, with which it is hard to achieve a fast response, a low hysteresis, and considerable sensitivity simultaneously.Thus, a separate film-grating structure was specifically designed to maintain the dynamic range and the humidity sensitivity, as a result of the large cross-sectional ratio between the functional film and fiber grating. As shown in Once the humidity changes, the film self-rebalances by exchanging moisture with that in the air. In this way, the expansion or contraction leads to an axial strain change transferred to the FBG. Finally, the humidity variation is visualized by tracing the wavelength shift, which indicates dynamic moisture absorption and release. Moreover, εpi (εG) and Epi (EG) refer to the strain and the elastic modulus of the film (grating), respectively. Wpi and dpi describe the transverse section of film, while RG denotes the radius of the bare fiber. Besides, the polyimide film expansion strictly equals the contraction in the FBG, fixing an isolated length at a constant temperature in Equation (2).The humidity sensing mechanism is further discussed below. According to the equal stress in a rigid connection as in Equation (1), the strain transferred to the FBG is strictly associated with the expansion and contraction of the polyimide film,αpi and H represent the hygroscopic expansion coefficient and the humidity variation, and LG and Lpi stand for the lengths of the fiber grating and film available, respectively. After derivation calculus on Equation (2) and simplification with Equation (1), we deduce the differential sensitivity HS as the humidity-dependent wavelength shift,k is defined as the transfer coefficient between the axial strain and wavelength shift, and ε0 refers to the initialized strain in the FBG. The negative expression indicates a blue-shift direction with an alterable sensitivity, which can be enhanced by increasing the cross-sectional ratio and the length ratio between the film and FBG. A slight nonlinearity in the sensitivity is introduced at different humidity, which can be well corrected with a second-polynomial coefficient.2), 60% (NaBr), 75% (NaCl), and 98% (K2SO4). The wavelengths measured at humidity of 10.4%, 34.2%, 57.6%, 76.1%, and 96.2% at 25 °C were distributed near the calibration fitting curve, similar with those at other temperatures.The temperature and humidity sensors were calibrated with a highly accurate Humidity Generator , and their sensing performance was validated in humidity-mimicking enclosures created with different saturated solutions. As shown in As assumed in theoretical analysis, the polynomial fitting curves exhibit an approximately linear dependence between the humidity and the wavelength shift. Additionally, the slight nonlinearity can be estimated with a second coefficient as the humidity varies from 12% RH to 98% RH. Its central wavelength shift towards the blue direction from 1535.1 to 1534.6 nm agrees well with the looseness of the polyimide film and decrement in axial strain. The temperature and humidity sensitivities were obtained as +5.033 pm/°C and −6.09 pm/%RH, respectively, providing opposite spectral responses to better exclude the thermal crosstalk.2SO4 (98% RH) solutions, as well as in the lab (62% RH). The red line above indicates the humidity recorded by CE314, while the blue line represents the wavelength shift determined with the FBG humidity sensor. As the humidity changes among 12% RH, 98% RH, and 62% RH, the central wavelength of the FBG exhibits a red-shift or blue-shift in response to a decrement or increment in the humidity, respectively. Due to the fluoride doping in the polyimide film, a short breathing time less than 2 min is observed with low hysteresis. Besides, the considerable sensitivity and accuracy are preserved, as a consequence of the separate film-grating structure. Thus, the humidity sensor is experimentally proved to be feasible with considerable sensitivity, a fast response, and low humidity hysteresis.The spectral response to humidity change is compared with that of a CE314 electronic sensor, and the humidity hysteresis is discussed in In the experiment as shown in Moreover, as shown in We propose and demonstrate a fluorinated-film-based FBG temperature and humidity sensor. The fluoride doping resolves the humidity hysteresis and provides a short breathing time less than 2 min. The calibrated sensors show different humidity corresponding to enclosures created with saturated solutions and good stability during 9000 min of monitoring in the lab. Additionally, the field tests prove the outstanding performance and practicability of the humidity sensors, but the consistency, size, weight, and cost of the humidity sensors can be further improved in the future, revealing potential for pharmacy, semiconductors, facility and equipment protection, and chemical and explosive storage.


The purpose of this review is to critically evaluate current sarcoidosis models and assess their potential to progress the field toward the goal of improved therapies in this disease. We conclude with the potential integrated use of preclinical models to accelerate progress toward identifying and testing new drugs and drug combinations that can be rapidly brought to clinical trials.The inability to effectively model sarcoidosis in the laboratory or in animals continues to hinder the discovery and translation of new, targeted treatments. The granuloma is the signature pathological hallmark of sarcoidosis, yet there are significant knowledge gaps that exist with regard to how granulomas form. Significant progress toward improved therapeutic and prognostic strategies in sarcoidosis hinges on tractable experimental models that recapitulate the process of granuloma formation in sarcoidosis and allow for mechanistic insights into the molecular events involved. Through its inherent representation of the complex genetics underpinning immune cell dysregulation in sarcoidosis, a recently developed  Significant progress toward improved therapeutic and prognostic strategies in sarcoidosis hinges on tractable experimental models that recapitulate the process of granuloma formation in sarcoidosis and allow for mechanistic insights into the molecular events involved. The purpose of this review is to critically evaluate current sarcoidosis models and assess their potential to progress the field toward these goals. Selected sarcoidosis models described in the following sections have been summarized in Sarcoidosis is a complex immune disease with genetic susceptibility and environmental factors playing important roles. The disease occurs in about 15–40 per 100,000 people in the United States . Severe Studies of diseased patient biopsy tissue are the foundation of sarcoidosis research. The original description of sarcoidosis in 1877 was based on the characteristic appearance of biopsied skin lesions and histological features that discriminated sarcoidosis from tuberculosis (TB) and other infectious granulomatous disorders . DespiteSarcoidosis granuloma formation is considered to be environmental antigen-mediated , and thePropionibacterium acnes are consistent with hypersensitivity pneumonitis in that, unlike sarcoidosis granulomas, they are poorly formed, transient, and surrounded by prominent lymphocytic pneumonitis , which normally represses the activity of mammalian target of rapamycin complex 1 (mTORc1)  . The Tsctivation . HoweverA major barrier to developing a viable sarcoidosis model is the inability to identify a specific sarcoidosis disease-causing antigen. However, pulmonary sarcoidosis is clinically and histologically very similar to berylliosis, a human disease linked to genetic variability of T cell receptors for divalent beryllium molecules . Given t+ T cells derived from sarcoidosis BAL samples induced fibroblasts to produce increased amounts of collagen in a STAT3-IL17A dependent manner, thus clarifying signaling events upstream of fibrotic tissue changes  naïve sarcoidosis patients and healthy controls. No difference in PBMC gene expression profiles was observed between M.tb naïve sarcoidosis patients and healthy controls at baseline  as reflected by >1,000 differentially expressed (DE) genes  genes . While tanulomas  and prodanulomas . These ranulomas .in vitro granuloma model holds promise in providing detailed mechanistic insight into sarcoidosis–specific disease regulating pathways at play during early stages of granuloma formation. This was demonstrated through the common stimulation of PBMCs derived from M.tb naïve sarcoidosis patients and individuals with latent TB infection (LTBI) with M.tb-derived antigens. Both groups produced granuloma-like structures following stimulation, albeit the structures derived from LTBI individuals had a denser lymphocytic cuff. However, gene expression differences were vast between the groups revealing divergent mechanisms of granuloma formation that once again were dependent on antigen stimulation (+-ATPase (V-ATPase), a multisubunit proton pump that actively acidifies lysosomal compartments. In addition to this role, V-ATPase forms a signaling complex with mTORc1 that promotes its activation when phagolysosomes are acidified  inhibition  into human trials to effectively inhibit the cycle of pathological granuloma formation (As cell-based laboratory models continue to advance, the use of mathematical models will act in concert with them to accelerate the pace of discovery , 56. A cver time . We enviormation .in vitro human granuloma models as complementary platforms for testing new therapies and evaluating pharmacokinetic and toxicity aspects ahead of human trials (As we look toward the future of therapeutic development in sarcoidosis, the role of animal models is currently unclear. Undoubtedly animal models have proven valuable for defining new aspects of disease pathogenesis and pre-clinical testing of new therapeutics. Relevant to sarcoidosis, novel imaging techniques can be performed in mice to enable powerful visual insights into the interplay of immune cells and tissue stroma . The futn trials .in vitro human granuloma model could be leveraged to screen novel therapies and determine the contribution of specific genes to granuloma formation using siRNA or CRISPR technology (in vitro human granuloma model is that it can be used to better understand the dynamic, multicellular mechanisms underpinning distinct granulomatous immune responses that occur in humans and is not restricted to sarcoidosis (In addition to the providing greater insights into granuloma formation in sarcoidosis, the chnology . Becausechnology , the modcoidosis . For exain vitro cell culture models to address. For example, the in vitro human granuloma model is likely not capturing the entire spectrum of disease due to the absence of a tissue-mimicking environment. Recent advances in organ-on-a-chip technology are beginning to provide new opportunities in in vitro cell culture models such as the modeling of more complex cell interactions involving extracellular matrix components and stromal cells, although to date most of these models lack immune cells (There are some caveats of current ne cells . Enablinne cells . Organ-oin vitro granuloma model allows for the interrogation of antigen-immune cell interplay and related cell-cell interactions driving the various stages of granuloma formation in sarcoidosis and underpinned by the complex and, as yet, undefined genetic features of this disease. The in vitro human granuloma model provides a powerful approach to addressing critical knowledge gaps in sarcoidosis, and we envision its complementary use with other pre-clinical models will likely accelerate progress toward identifying and testing new drugs and drug combinations that can be rapidly brought to clinical trials.The failure to effectively model sarcoidosis in the laboratory or in animals continues to hinder the discovery and translation of new, targeted treatments. Preclinical models that are capable of clarifying the significant knowledge gap surrounding the triggers and mechanisms driving granuloma formation and self-perpetuation in sarcoidosis will be key to this cause. Compared to modeling approaches that study only a single cell type, the patient-derived PBMC-based EC, LS, and LL wrote the article. EC and LL contributed to designing the figures and table for the article. All authors contributed to the article and approved the submitted version.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


High quality opal‐like photonic crystals containing graphene are fabricated using evaporation‐driven self‐assembly of soft polymer colloids. A miniscule amount of pristine graphene within a colloidal crystal lattice results in the formation of colloidal crystals with a strong angle‐dependent structural color and a stop band that can be reversibly shifted across the visible spectrum. The crystals can be mechanically deformed or can reversibly change color as a function of their temperature, hence their sensitive mechanochromic and thermochromic response make them attractive candidates for a wide range of visual sensing applications. In particular, it is shown that the crystals are excellent candidates for visual strain sensors or integrated time‐temperature indicators which act over large temperature windows. Given the versatility of these crystals, this method represents a simple, inexpensive, and scalable approach to produce multifunctional graphene infused synthetic opals and opens up exciting applications for novel solution‐processable nanomaterial based photonics. Graphene‐infused photonic crystals are fabricated using evaporation‐driven self‐assembly of soft polymer colloids. The crystals can be deformed mechanically or can reversibly change color as a function of temperature. Their sensitive mechanochromic and thermochromic properties are demonstrated for application areas ranging from time‐temperature indicators to security devices. One of the major limiting factors for the realization of colloidal photonic crystals requiring color perceptibility is their opaque nature. The origin of the opacity is structural disorder causing strong incoherent scattering that generates diffuse light in the presence of a low refractive index contrast. A possible method to counteract these issues is to embed nanomaterial dopants in the dielectric opal matrix. For example, Aguirre et al. incorporated carbon black micro‐particles into poly(methyl methacrylate) (PMMA) to produce powdered pigments for coating applications. In other reports, chromatic sensors were fabricated using core‐shell particles infused with sub‐50‐nm‐diameter carbon particles. More recently, Huang et al. fabricated photonic inks made of polystyrene‐based colloidal crystals containing graphene quantum dots. A hydrogel colloidal crystal made of silica nanoparticles and graphene oxide (GO) has also been reported for smart sensing and counterfeiting applications.Nature offers incredible examples of functional materials. Structural color, as found in butterfly wings or opal gem stones, is particularly fascinating.1 Mimi For instance, the high carrier mobility enables ultrafast extraction of photo‐generated carriers at significantly low light intensities leading to high‐bandwidth operation. Moreover, graphene has a wide absorptive spectral range from the ultraviolet to the infrared, with the optical absorption being proportional to the number of monolayers per nanosheet. Recent developments to produce liquid exfoliated, defect‐free pristine few‐layered graphene in large quantities have opened up new exciting avenues for applications. However, incorporating pristine graphene into ordered polymer matrices in a controllable manner has proven rather challenging, and as a consequence, heavily functionalized graphene oxide (GO) is often used instead. Consequently, very little is known about water‐based functional composites enhanced with pristine graphene.A particularly interesting dopant candidate is graphene. Graphene has extraordinary electronic and optical properties.27 For we have developed an evaporation‐driven self‐assembly method to fabricate highly ordered conducting polymer composites and photonic crystals containing pristine graphene. Using a polymer colloid template, a segregated distribution of graphene is achieved with periodicities comparable to the wavelengths of visible light. The resulting composites possess a low electrical percolation threshold. Furthermore, through careful control of the drying conditions, these composites form colloidal crystals which exhibit strong angle‐dependent structural color and a stop‐band that can be repeatedly shifted in the visible spectral range. We show that our opalescent colloidal crystals can be made to any size and thickness and can be crystallized on various substrates or be made freestanding. Importantly, the resulting photonic crystals (PCs) are free of cracks, and the stop band and mechanical deformability can be dialed in during the fabrication stage by changing the lattice parameters and the polymer glass transition temperature, respectively. Finally, we demonstrate the use of the graphene doped photonic crystals for a range of applications from strain gauges to time‐temperature indicators. Ultimately, this simple assembly process could be generalized to fabricate tunable crystal structures using a range of 2D crystals as the active filler, thus opening up a plethora of potential applications.Guided by our work on fabricating ordered polymer colloid assemblies containing carbon nanotubes (CNTs),42 we 22.1 we achieved solids with long‐range particle ordering resulting in opal‐like crystals containing pristine graphene.The polymeric latex used in this study produced through emulsion polymerization, is comprised of a random copolymer of methyl methacrylate (MMA), butyl acrylate (BA), and methacrylic acid (MAA) in the form of a charge‐stabilized colloidal suspension of polymer spheres. Polymer latex can undergo self‐ordering during sedimentation and compression under gravitational forces. Because of their highly ordered structure, distinct optical characteristics (photonic stop bands) can be achieved leading them to exhibit unique structural color. By carefully controlling the self‐assembly of the colloidal particles and taking into account the interplay between particle diffusion, inter‐particle forces, and settling dynamics,43 we Figure and disorder‐to‐order transitions. These observed structures indicate that the evaporation rates are slow enough in our experiments to avoid jamming in a non‐crystalline structure. the capillary forces resulting from the receding water/air interface  for the colloidal polymer system are ≈10−7 N, whereas the forces resulting from the proceeding capillary liquid bridge forces are one order of magnitude smaller (≈10−8 N). Graphene is present throughout the crystal formation process. During drying, the graphene is trapped at interstitial spaces between polymer particles and is subjected to the same capillary forces acting on the particles. As the film forms, at each contact surface between particles there is a localized distribution of both compressive and tensile stresses resulting from capillarity. In order to bend graphene flakes and conform them to the particle curvature, the superposition of forces must be large enough to overcome the graphene's resistance to bending  can be bent and efficiently fit at the particle boundaries and interstitial spaces. Additionally, the viscosity of the polymer near its glass transition temperature is very high and any flow is very slow.As shown in our previous work,46 theThe photonic crystals presented here are assembled using a technique we refer to as evaporation‐driven self‐assembly. During water evaporation, the top surface descends at a constant velocity, which will have the effect of accumulating particles at the air/water interface. Brownian diffusion re‐distributes the particles to diminish concentration gradients. Finally, sedimentation has the potential to accumulate particles at the bottom of the suspension in a highly ordered manner. we use dimensionless numbers to determine which effect is dominant. To determine the relative importance of evaporation in relation to diffusion, we use the dimensionless Péclet number (Pe) which is written asE is the experimentally obtained water evaporation rate in units of velocity (E = 1.1 × 10−7 m s−1), H0 is the initial thickness of the suspension, and D0 is the Stokes–Einstein diffusion coefficient for the particles. For spherical particles, D0=kT6πηr, where k is the Boltzmann's constant, and T is the temperature, η is the viscosity of the liquid (water), and r is the particle radius. When Pe >>1, evaporation is dominant and particles will accumulate at the top descending interface, but for Pe <<1 diffusion will dominate and particles will be uniformly distributed during drying. The value of Pe for the polymer particles (PPe) and for the graphene (GPe) is high because of the large height (H0 = 0.5 cm) of the colloidal suspension. Using a standard approximation for the diffusivity of a 2D plate‐like particle with a diameter of 350 nm, we estimate GPe to be ≈150, whereas for the 255 nm polymer particles, PPe ≈320.Following the arguments of Cardinal et al.,43 we U0) invoking the Stokes' drag force, is:pρ is the particle density (ρp = 1.1 g cm−3), Lρ is the liquid (water) density, and g is the gravitational acceleration. U0 for our 255 nm diameter polymer particles is calculated to be 3.5 × 10−9 m s−1. We find a distribution of diameters for the graphene platelet with the center of the distribution at 350 nm . Using this size, and considering the relatively high density of graphene, U0 is estimated to be 3 × 10−7 m s−1 for graphene flakes, which is considerably faster than the polymer particles. The relative importance of sedimentation and evaporation is given by the sedimentation number, NS=U0E. We find SN ≈ 0.03 for the polymer particles and SN ≈3 for the 350 nm graphene flakes. It is worth noting that this simple model ignores the effect of increased particle concentration and its associated effect on slowing the sedimentation velocity. Regardless, it is clearly valid in the initial stages of self‐assembly when the solids content of the system is still relatively low.The settling velocity of spherical particles under gravitation at room temperature U0 invokinPe and SN) to characterize the crystal formation process. As shown in Figure while the partial break‐up of the particle membranes and subsequent partial chain interdiffusion leads to the mechanical robustness of the crystals.We invoke Cardinal et al.'s map of parameters .It is worth noting that conventional sedimentation of particles under gravity in a closed system without evaporation58 is 2.2FigureThe PC‐Gs possess the necessary ordering to satisfy the Bragg condition, and hence exhibit a distinct stop band positioned at approximately twice the particle diameter (≈520 nm), which is shifted upward by 17 nm with respect to the pristine crystal, as is shown in neff. From the resulting analysis, the neff of PC and PC‐G crystals are 1.26 ± 0.01 and 1.34 ± 0.01, respectively, which are in reasonable agreement with the neff values obtained using other methods as described in the Supplementary Information 1. Additionally simulations calculating the stop band positions  . Water that diffused into the polymer crystal forms nanometer sized domains of heterogeneous water. Such water domains possess a different refractive index than the polymer particles and hence acts as light scattering centers.The fitting of the Bragg equation shown in the inset of Figure s Figure  of both s Figure , even ths Figure  indicateIn natural opals, various internal imperfections give rise to incoherent scattering events and part of the transmitted spectrum is diffusely reflected. In the presence of graphene, the likelihood of absorption of the diffuse transmitted light is strongly enhanced as the incoherent scattering increases its effective optical path inside the opal. Hence, the parasitic reflections are reduced and the light Bragg‐scattered by the stop band dominates the reflection spectrum.p‐ over the s‐ polarization) and Δ (corresponding difference in phase changes) as a function of wavelength at θ = 20°, are presented in the inset of Figure In order to characterize the optical reflectivity and confirm the modifications to the refractive index in the presence of graphene, spectroscopic ellipsometry was performed at angles‐of‐incidence, θ ranging from 20° to 60°. As the PC has very weak reflectivity, it was not possible to obtain a spectrum. For the PC‐G, representative ellipsometric spectra, showing Ψ .2.3Interestingly, due to the recoverable deformability of the crystals, notable changes in the position of the stop band can be achieved by mechanical modulation using lateral compression, stretching, in‐plane pressure or bending. The crystals are mechanically robust but can be deformed cyclically with no hysteresis in their performance . At the same time, the stop band of the deformed PC‐G can be controlled mechanically, and a significant blueshift or redshift is observed, depending on the type of deformation applied. The ability to tune or modulate the optical properties makes the PC‐Gs attractive candidates for a wide variety of sensing applications with the output directly observable by the naked eye.FigureFor example, the stop band of a stretched colloidal crystal shifts to shorter wavelengths as a result of a decrease in the spacing parallel to the crystal surface with increasing extension ratio. Consequently there is a visible change in the sample color from green to blue. As shown in Movie S1, Supporting Information, when the stress is released, the sample returns to its original shape. A schematic representation of the deformation of a crystal lattice is shown in the inset in 0/100 = 5.2 nm/%, which is verified experimentally for the applied strain and wavelength shift above. This sensitivity is competitive with mechanochromic sensors reported in the literature and could be further increased by modifying the size of the latex particles and thereby the initial stop band position. Bending of the PC‐G crystals results in a rainbow‐like color variation along the cross‐section, effectively producing a microscopic 2D strain field that is related to varying degrees of particle deformation from top to bottom  value. Each time the crystal experiences elevated temperatures, it gradually relaxes back to the initial shape configuration while at the same time exhibiting gradual structural color change as the stop band returns to its original value pre‐deformation. This striking thermochromic effect of the crystals can be used for non‐invasive characterization of shape‐memory effects.The crystals can also act as smart shape‐memory polymers that can memorize and recover their shape and color after experiencing an external stimulus, for example, heat . The temperature of PC‐G crystals can be repeatedly shifted above and below their glass transition temperature  for intelligent packaging to offer a visual indication of whether perishables, such as food, pharmaceuticals, chemicals, inks, paints or coatings have experienced undesirable time‐temperature histories. If the crystals are subjected to elevated temperatures, they act as sensitive visual TTIs that function over a broad temperature range (from room temperature to 100 °C). The crystals contain up to 10% of water locked within their crystalline structure, and when they are exposed to atmospheric conditions, they lose their distinctive green color turning either transparent or opaque  . The distinct but gradual color change with time is associated with the loss of refractive index contrast when polymer/polymer boundaries are formed when intervening water is lost. The thermal expansion of polymer particles and interfacial water (both increasing the lattice constant) with increasing temperatures produces a redshift of the stop band, which is extremely sensitive to even a small rise in temperature. A time–temperature phase diagram Figure6d shows The gray‐shaded region in Figure  The periodicity disappears, and thus Bragg's diffraction does not apply anymore. The loss of the stop band can be treated as a diffusion driven process where the time for the transition is defined by the time needed for the polymer chains to diffuse across the interfaces between particles.Because of the presence of a network of pores as well as hydrophilic functional groups at the particle boundaries, the water diffusion will proceed along the interstitial sites allowing for good permeability.66 The written ask is the reaction rate constant, Z is a temperature independent pre‐exponential factor, aE is the activation energy describing the temperature sensitivity of the quality loss reaction, R is the universal gas constant. Briefly speaking, it is important that the activation energy of the TTI device does not differ by more than 20 kJ mol−1 from the activation energy of the product of interest.When developing a visual monitoring TTI device to maintain product quality it is essential that the TTI accurately mimics the product's kinetic reactions related to the product's shelf‐life defined by the Arrhenius equation68 wrigR across particle interfaces (where Rg is in the polymer melt). The diffusion coefficient (D) is related to the distance of diffusion, x and the time, t asgR is given as ≈Rg2D. Important for this model is the concept that diffusion is thermally activated and that temperature significantly affects D and hence can be described by the Arrhenius relationship of the form:D0 is a constant for a given diffusing system (m2 s−1). Substituting in for D we see that:ln t) that is required to achieve optical clarity and irreversible coalescence against the reciprocal temperature of the experiment, then there is a linear relationshipIn our case, the irreversible nature of the TTI is related to the complete coalescence of particles during thermal reactions, while coalescence of particles requires the diffusion of polymer chains a distance on the order of their radius of gyration, me, t asD~x2t ~ R−1, which falls within the range of aE of food‐related chemical reactions leading to its spoilage and pathogenic microbial growth, which is between 30 and 140 kJ mol−1.The activation energy found for PC‐G is 65 kJ molkJ mol−1.702.4Composite formation is achieved through direct mixing of surfactant stabilized aqueous dispersions of pre‐exfoliated graphene and the latex. The mixed dispersion is cast onto a substrate (such as glass slide or a free‐standing mold) and dried.Figure−1) of the same sample area, it is clear that graphene is only positioned at the polymer's interstitial sites as shown in Figure  A significantly higher critical exponent of 3.81 than the most accepted universal value of t = 2 can be attributed to the tunneling conduction previously witnessed in other composite systems.As can be seen in  Existing models show that there is a negative capillary pressure associated with the curved meniscus of water between the particles at the top surface. This negative pressure pulling particles together exerts compressive forces on the particles in the packed array below. At later stages of drying, the models show that pendant water present at the contacts between the particles presses them closer together, thereby leading to the elimination of interstitial voids. Finally, particles undergo coalescence through the inter‐diffusion of polymer chains across particle boundaries, ultimately forming a cohesive film.To understand the segregated composite formation mechanism, it is necessary to examine the deformation of polymer particles during the film formation process. In the first stage of drying, evaporation of water leads to the reduction of average inter‐particle distance, forcing colloidal particles into a hexagonal close‐packed (HCP) configuration.73 ExiTg) of 38 °C, while the Tg of the composite containing 0.4 wt% of graphene is reduced to 31 °C. As we have shown previously, some of the surfactant can be adsorbed onto the nanomaterial surface, while the remaining free surfactant is confined in the interstitial spaces between the particles. Such free surfactant acts as a traditional plasticizer, softening the outer regions of polymer particles (mimicking core‐shell particles). It is likely that the softer polymer shell facilitates the formation of long‐range petal‐like ordering of graphene.It is interesting to note that, as produced, the pristine polymer latex has a glass transition temperature Tg of 38 °3The study presented here provides the first experimental demonstration of mechanically robust, free‐standing, flexible, and thick synthetic opal containing pristine graphene locked in a colloidal polymer crystal lattice. The graphene‐enhanced colloidal crystals were, for the first time, fabricated using a novel inexpensive method of evaporation‐driven self‐assembly and have a range of applications as mechanochromic and thermochromic sensors. The presence of graphene enhances the structural color because of its wide spectral absorbance and higher refractive index. Importantly, the effects happens at significantly lower weight fractions compared to other carbon‐based fillers, such as carbon black. The versatile fabrication process can employ different particle sizes and glass transition temperatures, which allows property tuning. The color is responsive to pressure and stress, temperature and time and is fully lost when particles coalesce during exposure to high temperatures for prolonged times. These properties were demonstrated for application areas ranging from TTI sensors to security devices. The inclusion of a higher amount of graphene leads to the formation of conducting segregated network graphene‐based composites with a low electrical percolation threshold.2, WS2), boron nitride sheets, etc. within the photonic crystals to achieve a plethora of potential novel sensing functionalities.Ultimately, our method represents a generic way to assemble a broad range of 2D nanomaterials, such as transition metal dichalcogenide monolayers  to give an initial graphitic concentration of 25 mg mL−1. This mixture was sonicated using a sonic tip (Sonics VX‐750 ultrasonic processor with flat head tip) for 4 h. The dispersion was left to stand overnight. The top 50 mL of the suspension was decanted into two 28.5 mL vials and centrifuged (Hettich Mikro 22R) for 90 min at 1500 rpm. The top 14 mL was then decanted into a 14 mL vial. The final concentration of graphene in water was 0.57 mg mL−1 as determined using UV–vis spectrophotometry.Graphite powder (2.5 g) purchased from Sigma Aldrich (product number 332461) was added to 100 mL of aqueous surfactant solution (0.5 mg mLTg) is 38 °C, and the initial solids content is 55 wt%. The latex dispersion was prepared by semi‐batch emulsion polymerization.The latex polymer used as a template for graphene assembly, provided by DSM Coating Resins , is based on a random copolymer of butyl acrylate (BA), methyl methacrylate (MMA) and methacrylic acid (MAA). The polymer particle size is 255 nm, its dry glass transition temperature  was used. For measurements, polymer films were prepared by casting the composite dispersion using a metallic cube applicator with a nominal 150 µm gap width onto a ceramic substrate and dried for 24 h at room temperature. After drying, two 10 nm thick top gold electrodes of 3.5 × 3.5 mm area each were prepared by thermo‐evaporation of gold using an Edwards Evaporator. Dark current‐voltage characteristics have been obtained using a Keithley 487 picoammeter/voltage source. The final specific conductivity was calculated from the resistance and thickness of the film. All sample thicknesses were measured using a profilometer ., the same amount of surfactant was added to the latex dispersion for the fabrication of pristine PCs. This step was necessary to ensure that both, pristine and graphene‐enhanced PCs possess the same gT.To grow photonic crystals, evaporation‐driven self‐assembly was successfully used. 2.5 mL of latex dispersion, containing 0.01 wt% of graphene, was left in an open glass beaker at room temperature for 4–6 days to induce the self‐assembly of the particles combined with drying of the suspension from above. The crystals were formed under a relative humidity of ≈65%. Since we have shown previously that the Triton X‐100 surfactant has a plasticizing effect on the polymer particles46, thFor topographic studies, an atomic force microscope (AFM) , using semi‐contact mode, was employed. In order to study the cross‐section, the PCs were fractured in liquid nitrogen. In order to obtain AFM images of the crystals under deformation, the crystals were first immersed in hot water (80 °C) for 3 s, deformed and then quickly immersed in an ice cold water bath in order to “freeze” the structure for imaging.Microstructural investigations of composite materials were carried out using a Hitachi S‐4000 scanning electron microscope (SEM) at an accelerating voltage of 7 kV. A latex dispersion containing 0.4 wt% of graphene was deposited a onto silicon dioxide/silicon wafer by drop casting and subsequently left to dry for 48 h at room temperature (≈23 °C). A sample was freeze‐fractured after immersion in liquid nitrogen, in order to investigate the cross‐sectional area. Samples were imaged without sputtering a metal onto their surface.gT of the latex composites was determined using a differential scanning calorimeter (DSC) . Samples were deposited onto poly(tetrafluoroethylene) (PTFE) molds by drop casting and subsequently left to dry for 48 h at room temperature before being loaded into the DSC. A standard heating rate of 10 °C min−1 and cooling rate of 10 °C min−1 were used for all samples. The value of gT was taken in the first heating scan at the midpoint step‐wise increase of the specific heat associated with the glass transition.The The optical transmission measurements were carried out using a computer controlled double beam UV–vis spectrophotometer . The angle of incidence in the transmission measurement was changed from 0° to 55° by rotating the sample by means of a made‐in‐house sample holder. The absorption spectra were recorded from 200 to 900 nm.In order to take the UV–vis spectra as a function of applied pressure, the crystals were immersed in hot water (≈80 °C) for 3 s, then placed into a glass beaker and a sample of known mass was placed on top of the crystals for 5 s. With the known weight still on top of the crystal, the beaker was filled with ice‐cold water in order to freeze the structure under compression. The crystal was then quickly transferred to the UV–vis spectrometer for measurement.The standard ellipsometric quantities, Ψ and Δ which describe the changes in the amplitude and relative phase of the polarized light, respectively, were measured as a function of angle of incidence ranging from 20° to 55° at wavelengths ranging from 385 nm to 700 nm using a variable‐angle spectroscopic ellipsometer . For this measure, free‐standing photonic crystal samples were attached to the silicon dioxide/silicon wafer.cSAXS  experiments were performed at the Paul Scherrer Institute, Switzerland. A sample‐detector distance of 7160 mm (using a 7 m evacuated flight tube) and X‐ray energy of 8.9812 keV was used for measurements; the spot size was approximately 0.7 mm × 0.7 mm. The PILATUS 2M detector was used to capture scattering patterns from the mounted samples; this detector has 1475 × 1679 pixels which are 172 mm × 172 µm (an active area of 253.7 mm × 288.8 mm). Captured scattering patterns were integrated through the azimuthal angle to obtain radial scattering profiles.The authors declare no conflict of interest.Supporting InformationClick here for additional data file.Supporting Movie 1Click here for additional data file.Supporting Movie 2Click here for additional data file.


N = 70 ALS patients (N = 4 carrying TARDBP mutations), N = 40 age-comparable healthy controls (CTRL), N = 20 motor neuron disease mimics (MN-m), N = 20 Alzheimer’s disease (AD) and N = 15 frontotemporal lobar degeneration (FTLD) patients. Anti-TDP-43 NAb were found to be significantly increased in ALS patients compared to all the other groups (p < 0.001). On the other hand, the distribution of serum levels of TDP-43 protein was highly variable among the various groups. Levels were increased in ALS patients, albeit the highest values were detected in MN-m patients. NAb and protein serum levels failed to correlate. For the first time, we report that serum anti-TDP-43 NAb are detectable in human serum of both healthy controls and patients affected by a variety of neurodegenerative disorders; furthermore, their levels are increased in ALS patients, representing a potentially interesting trait core marker of this disease. Further studies are needed to clarify the exact role of the NAb. This information might be extremely useful for paving the way toward targeting TDP-43 by immunotherapy in ALS.Amyotrophic Lateral Sclerosis (ALS) patients express significant clinical heterogeneity that often hinders a correct diagnostic definition. Intracellular deposition of TDP-43, a protein involved in RNA metabolism characterizes the pathology. Interestingly, this protein can be detected in serum, wherein cognate naturally-occurring auto-antibodies (anti-TDP-43 NAb) might be also present, albeit they have never been documented before. In this exploratory study, we quantified the levels of both anti-TDP-43 NAb and TDP-43 protein as putative accessible markers for improving the ALS diagnostic process by using ELISA in  TARDBP gene whose mutations are known to cause ALS. TDP-43 inclusions are typically found in affected neurons, even in non-genetically mediated cases1.Amyotrophic lateral sclerosis is a relentless neurodegenerative disorder that preferentially affects motor neurons. TAR DNA-binding protein 43 (TDP-43) is a protein coded by the 4, raising suspicion of a potential functional derangement of immune cells in a disorder for which the contribution of neuroinflammation has been repeatedly reported5. Abnormal inflammatory responses are directly sustained by protein aggregates  of ALS patients9.Presumably, the adaptive immune response against TDP-43 inclusions contemplates the production of polyclonal antibodies, as already demonstrated in DAMPs associated to a variety of neurodegenerative disorders, such as beta-amyloid for Alzheimer’s disease (AD) and alpha-synuclein for Parkinson’s disease11.Although the presence of naturally occurring anti-TDP-43 auto-antibodies (NAbs) could be hypothesized, it is unknown whether ALS patients express a different quantity of NAb as compared to healthy controls and whether they play a pathogenic role in ALS onset and progression. Notably, the hypothesis that a decrease of anti-DAMP serum NAb could be related to an increased protein aggregation has already been formulated to explain neurodegeneration12, although the diagnostic value of this observation is scarce13. One may hypothesize that increased levels of soluble TDP-43 in serum could contribute to an increased production of specific NAb.On the other hand, besides intracellular aggregates, serum (and CSF) levels of soluble TDP-43 have been previously reported to be moderately increased in ALS patientscore biomarkers of TDP-43 pathology.To verify these hypotheses, we assessed the presence of anti-TDP-43 NAb and TDP-43 protein in the serum of n = 165 subjects, represented by both patients affected by ALS, frontotemporal lobar degeneration (FTLD), AD and other motor neuron disorder mimics (MN-m), and healthy controls. Then, we quantified the serum levels of anti-TDP-43 NAb and TDP-43 protein and we investigated the putative clinical correlate of these serum N = 70 ALS outpatients diagnosed according to El Escorial criteria were recruited at the NEMO center ; among them, N = 4 ALS patients were carrier of a TARDBP mutation  [N = 1]; c.1144G>A (p.Ala382Thr) [N = 2]; c.1147A>G  [N = 1]). None of the other patients were carrying mutations in other major ALS causative genes , with the exception of one patient carrying a SOD1 mutation (p.Ile150Thr). For this preliminary study, full-blown dementia was suspected based on the clinical interview with the ALS patient and the respective caregiver, and eventually defined according to DSM-V criteria. N = 40 sex- and age-comparable healthy controls (CTRL) were recruited as well. Furthermore, we included the following consecutive outpatients: N = 20 typical Alzheimer’s disease (AD) patients according to IWG-2 criteria 14; N = 15 FTLD patients according to current criteria for bvFTD15, with a CSF profile that excluded AD and without clinical evidence of motor neuron disease (MND); N = 20 MND mimics . FTLD patients were age- and sex-comparable to ALS, whereas both AD and MN-m patients were significantly older (~ 10 years) than ALS patients and more representative in females (+ 20%). Patients with dementia were recruited if either (a) a legal representative was available or (b) if they were able to express informed consent .The study was approved by San Gerardo Hospital ethical committee (protocol: Anti Abeta AD 21/04/2011), patients and controls voluntarily agreed to participate in the study and informed consent was obtained from all subjects. Patients and controls gave their consent for publication. Exclusion criteria for all groups were the use of steroid or immunosuppressive drugs, recent infection or surgery, cancer or autoimmune/inflammatory diseases. See Table Blood samples (5 ml) were collected after overnight (O/N) fasting. Serum was obtained by centrifugation (2800 g 20 min) and stored at − 80 °C until blind-coded assay. The concentration of anti-TDP-43 NAb was determined by indirect ELISA, specifically developed for the target. Different setting regarding protein coating concentration , blocking buffer , calibration curve range (3000 to 6.25 ng/ml) and sample dilution (from undiluted to 1:300) were tested. Eventually, 96-well plates (Greiner Bio One) were coated at 4 °C O/N with 25 µg/ml human TDP-43 full length protein (Abcam) in 50 mM carbonate buffer (pH 9.6), blocked with SmartBlock (CANDOR Bioscience) (200 µl/well) for 60 min at room temperature (RT) with shaking and washed 3 times with PBS. A standard curve was generated using an affinity-purified mouse  anti-TDP-43 antibody (Santa Cruz Biotechnology), at different concentrations, ranging from 400 to 6.25 ng/ml . Blank wells were included to subtract out the non-specific binding of serum antibody. Coated plates were incubated at 4 °C O/N with standard curve and serum samples (1:200 dilution). After washing with PBS-T , plates were incubated for 2 h with HRP conjugated goat anti-mouse IgG antibodies (Sigma-Aldrich) 1:12,000 for the standard curve and HRP conjugated goat anti-human IgG antibodies 1:10,000 (Sigma–Aldrich) for samples at RT with shaking. Then, plates were washed with PBS-T and incubated for 10 min with TMB (Sigma–Aldrich); after adding the stop solution, the absorbance at 450 nm was read. The concentration of serum NAb was determined from the standard curve and read in triplicate.Precision: two samples of known concentration were tested 20 times on a single plate to assess intra-assay precision and in 20 separate assays to assess inter-assay precision. Inter- and intra-assay variability was lower than 5 and 10% respectively. Sensitivity: the lower limit of quantification (LLOQ) was calculated based on the signal and SD of 16 blank samples (10 SDs above the mean blank sample). LLOQ of the assay is 34.5 ng/ml.Total IgG serum content was measured by an automated immunoturbidimetric analysis on Modular P analyzer (Roche Diagnostics). Serum samples were also analyzed for the presence of TDP43 protein by a commercially available ELISA kit (LSBio) following manufacturer’s instructions.All methods were carried out in accordance with relevant guidelines and regulations.R-test was used for correlative analyses.Statistical analysis was performed using Graph Prism 7.04 . Data are shown as mean ± SD. ANOVA, followed by Tukey post hoc test, was used to assess differences among the groups. Two-tailed Pearson's N = 4 TDP-43 + ALS patients presented NAb levels and ratio similar to those expressed by TDP-43 negative ALS patients  in ALS patients compared to CTRLs, and they were two-to-threefold increased in ASL patients compared to AD and FTLD patients. Notably, serum anti-TDP-43 NAb levels were about fourfold lower in MN-m than in ALS patients  was found. No correlations between biological data and any other clinical and demographic variable were found.No correlation between TDP-43 and cognate NAb serum levels in any group p = 0.14 for ALS) was found. A positive correlation between TDP-43 serum levels and the disease progression index . Serum TDP-43 protein levels resulted to be increased as well, confirming the results of previous observations12; however, their distribution showed a positive asymmetry, plausibly making it less useful for the purpose of developing a diagnostic biomarker, as previously noted by other Authors16.We report for the first time the presence of immunoreactivity suggestive for the existence of anti-TDP-43 NAb in human serum samples, whose levels resulted to be significantly high in a consistent number of ALS patients, apparently regardless of the presence of LATE”17)—and FTLD that could, at least in some cases, share a TDP-43 pathology. The group of MN-m allowed to further underline the potential clinical usefulness of this finding, since MN-m patients displayed very high (and variable) serum levels of TDP-43 protein, despite very low levels of cognate NAb. Certainly, sample size at this time is limited, at least for the pathological control groups, but this is a preliminary report and we are currently recruiting for a larger confirmatory study. In particular, more data regarding ALS clinical phenotype are going to be collected, in order to analyze further any putative relationship of blood-based TDP-43 biomarkers with disease signs, progression, and with the degree of cognitive impairment (not included at the moment).The disease specificity of the NAb increase was here magnified by the inclusion not only of healthy controls, but also of patients affected by a variety of neurodegenerative disorders, such as AD—wherein an altered TDP-43 proteostasis is not expected, although this consideration has been recently challenged, as reported inthe case of “In fact, many points need to be clarified. The NAb increase in the ALS cohort was apparently unrelated to clinical and demographic parameters and, albeit target-specific (see the IgG ratio), it did not correlate with the serum levels of the cognate protein. As a trait/core marker of TDP-43 pathology, the NAb could be extremely useful for the differential diagnosis, but the absolute confirmation of their presence and the understanding of their exact physiological role need to be further investigated; future studies should also include the analysis of the CSF compartment.20. Against this interpretation, one may point out the fact that MN-m displayed a strong dissociation between NAb and protein levels. Further data is necessary to draw any conclusions, since pronounced inflammatory conditions, such as some ALS mimics, exhibit different modalities of immune system involvement as compared to neurodegenerative disorders like ALS. Similar issues have been deeply debated in other neurological disorders; for example, anti-beta-amyloid NAb are typically found in both AD and in healthy controls21, and they are also detectable in patients with the inflammatory form of cerebral amyloid angiopathy22.Concerning the physiological role of the NAb, it could be hypothesized that NAb might prevent excessive TDP-43 accumulation, in accordance with several recent experimental evidences23. These findings fit well with the hypothesis that the generation of toxic protein affecting the immune-surveillance may apply to the TDP-43 pathology and they could be the ground for designing novel probative experiments. Meanwhile, a variety of specific NAb have been described in the neurodegenerative field, raising more questions than answers regarding both methodology and significance of these findings25.Besides some methodological issues related to the acid-dissociation of immunocomplexes before NAb assessment—that introduced a variable that has not been completely understood—some evidences suggest an increased immunoreactivity towards toxic Abeta speciesA possible limit of this exploratory study consisted in having tested serum immunoreactivity (NAb) against the full-length form of TDP-43, since phosphorylated (and other) species could potentially be more toxic and, therefore, elicit a more robust immune response. Nevertheless, we should not forget that we are marking a polyclonal immunoreactivity against TDP-43 that presumably would have been captured also in case we had designed our assay using the phosphorylated full-length form of the same protein (work in progress). In any case, uncertainty remains regarding the toxic potential of modified or truncated species of TDP-43, such that the choice of a potentially “meaningful” NAb a priori is challenging. Moreover, future studies will be also necessary to discriminate which immunoglobulin subspecies are involved.26.In spite of these limits, we are planning to test serum anti-TDP-43 NAb levels in a larger cohort of carefully phenotyped ALS patients to better elucidate the real usefulness of this marker for ALS diagnosis and clinical follow-up. This data would also be potentially useful to develop anti-TDP-43 immunotherapies for ALS patientsSupplementary Figure 1.


A dual-functional ultraviolet (UV) photodetector with a large UV-to-visible rejection ratio is presented, in which interdigitated finger-type two-dimensional graphene electrodes are introduced to an AlGaN/GaN heterostructure. Two photocurrent generation mechanisms of photovoltaic and photoconductive dominances coexist in the device. The dominance of the mechanisms changes with the induced bias voltage. Below a threshold voltage, the device showed fairly low responsivities but fast response times, as well as a constant photocurrent against the induced bias. However, the opposite characteristics appeared with high bias voltage. Specifically, above the threshold voltage, the device showed high responsivities with additional gain, but slow rise and recovery times. For instance, the responsivity of 10.9 A/W was observed with the gain of 760 at the induced bias voltage of 5 V. This unique multifunctionality enabled by the combination of an AlGaN/GaN heterostructure with graphene electrodes facilitates the development of a single device that can achieve multiple purposes of photodetection. As demand and expectation have begun to exceed the performance of conventional UV photodetectors, the development of novel UV photodetectors with special functions or multiple functions has become necessary6. Smart, flexible, and self-powering characteristics, as well as intelligence, are expected to be essential for next-generation UV photodetectors in the internet-of-things (IoT) era8.Semiconductor-based ultraviolet (UV) photodetectors with very high sensitivity, stability, speed, and signal-to-noise (S/N) ratio have attracted much attention in recent years for their potential applications in environmental monitoring and security systems. Such applications include flame monitoring, missile plume detection, ozone layer monitoring, biological and chemical analysis, and secure optical communication in outer space10. First, regarding materials, GaN and its alloys with Al and In are highly promising for both visible-blind and solar-blind UV detection without requiring bulky optical filters or cooling systems, unlike Si-based UV photodetectors11. Special attention has been paid to AlGaN ternary semiconductors, in which, by tuning the Ga and Al compositions, the bandgap energy can be varied from 3.4 eV (GaN) to 6.2 eV (AlN), thereby covering the UVA to UVC spectral region. In addition to the use of a single layer of nitride semiconductors for photodetector applications, an AlGaN/GaN heterostructure can provide additional benefits of high-speed and high-gain operation. Such a heterostructure intrinsically forms a two-dimensional electron gas (2DEG) at the interface between AlGaN and GaN; this simultaneously provides both high carrier density and mobility14. In fact, AlGaN/GaN heterostructures are essential platforms for high-electron-mobility transistor technology for next-generation high-power and high-frequency devices16.In order to develop high-performance UV photodetectors, various material- and structure-based approaches have been investigated and published20. Previous studies have confirmed that the graphene/GaN contact is stable under high-temperature and high-radiation operations, indicating that graphene electrodes are appropriate for applications in fire alarms and space exploration devices, which operate in extremely harsh conditions21. Our previous studies demonstrated the successful implementation of graphene and reduced graphene oxide as transparent electrodes on AlGaN layers with various Al mole fractions, showing sharp cut-off wavelengths at the energy bandgaps of AlGaN23. In this regard, the combination of graphene electrodes and AlGaN/GaN heterostructures may yield an excellent UV photodetector, considering the high transparency of graphene in the UV spectral region and the high electrical conductivities of graphene and 2DEG, which would benefit efficient charge collection in the photodetector.Graphene, a two-dimensional (2D) hexagonal lattice array of carbon atoms, is attractive for applications as transparent conductive electrodes because of its high electrical and thermal conductivities, transparency, and mechanical strength24. Among them, the MSM structure with back-to-back Schottky contacts provides a low dark current, high S/N level, fast response speed, and compatibility for integration with other circuit components, particularly via simple fabrication methods26. The MSM-type structure can be fabricated in one step of electrode deposition on a semiconductor material without any deteriorations of device performance from the complicated processes of etching and diffusion, as well as those from the asymmetric traveling lengths of electrons and holes before reaching an electrode.Secondly, in structural approaches, various photodetector structures have been employed, including a metal–semiconductor–metal (MSM) photodiode, p–n and p–i–n photodiodes, an avalanche photodiode, a photoconductor, and a phototransistorIn this study, we present a dual-functional  UV photodetector comprising an AlGaN/GaN heterostructure and a graphene electrode . The photodetectors presented here have an MSM-type structure, as shown schematically in Fig. 2/V·s and the sheet carrier density of 5.6 × 1012 cm−2 at room temperature. Figure −1, respectively27. The peak intensity ratio of I2D/IG is less than 1, indicating the presence of multilayered graphene28. The final MSM-like device structure of Gr/AlGaN/GaN stacks has eight pairs of interdigitated finger electrodes of 10 µm in width, 10 µm in spacing, and 300 µm in length, as shown in the scanning electron microscope image of Fig. The transmission electron microscopy (TEM) image in Fig. Figure 29:D is the dark current, IP is the photocurrent, and Φ is the incident optical power, all of which are easily measurable values. Measurements of responsivity as a function of wavelength are performed at various bias conditions, as shown in Fig. 29:As a representative figure-of-merit of a photodetector, the responsivity (R) was calculated by using the relation29. First, a junction of two dissimilar materials can yield the photovoltaic effect, in which the dissimilarity can be different dopant types (homojunction), different materials themselves (heterojunction), and the contact between metal and semiconductor (Schottky-type)30. As photons impinging on the junction are absorbed, the absorbed photons produce free charge carriers within the depletion region. The existing electric field then causes the charge carriers to move apart, resulting in current flow in an external circuit. The most common photovoltaic-effect-based photodetectors are photodiodes and phototransistors. Second, photoconductivity  occurs when photons impinge on semiconducting materials, causing the excitation of electrons from the valence band to the conduction band, and thus affecting the material conductivity32. This photoconductive effect is widely utilized in electromagnetic radiation sensors, photoconductors, light-dependent resistors, and photoresistors. CdS and CdSe are typical semiconductors used in photoconductive-effect-based photodetectors and sensors34. Generally speaking, photodetectors in these two categories have certain strengths and weaknesses. For example, in comparing a photodiode and a photoconductor, a photodiode operated under the photovoltaic effect has device characteristics as follows36: (1) relatively low responsivity limited by the wavelength [refer to Eq.  shows how much minimum signal can be detected by the photodetector. The detectivity can be calculated by using the simplified equation nm see “. AlthougIn conclusion, a dual-functional Gr/AlGaN/GaN UV photodetector with a clear UV-to-visible rejection ratio is presented. The photodetector shows two photocurrent generation mechanisms in a single device; the mechanisms can be selected by the induced bias voltage. Under low bias conditions, i.e., below the threshold voltage, the device showed relatively low responsivities, but fast response times and constant photocurrent against the induced bias. At high-bias conditions, i.e., above the threshold voltage, the device showed high responsivities with additional gain, but a slow response time and a strong dependency of the photocurrent on the induced bias. Depending on the bias voltage induced on the photodetector device, the dominant device features of the photodetector can be easily tuned; thus, a single device can be adjusted to meet any purpose of UV photodetection. This unique multifunctionality enabled by the combination of an AlGaN/GaN heterostructure and a 2D graphene electrode is expected to be highly useful to the development of UV photodetectors for the coming IoT era.40. In brief, PMMA was spin-coated on a graphene-coated Cu foil and subjected to soft baking at 180 °C for 5 min. The PMMA/graphene/Cu stack was then treated with ammonium persulfate solution for 7 h to etch away Cu. In sequence, the separated graphene/PMMA stack was transferred to the surface of the AlGaN/GaN heterostructure sample. To improve the adhesion between the graphene and AlGaN semiconductor, the sample was baked at 200 °C for 3 h on a hot plate. Next, PMMA was removed by an acetone treatment at 60 °C. After a 100-nm-thick SiO2 layer was deposited by a plasma-enhanced CVD system, an interdigitated finger structure was introduced by using a standard photolithographic technique and wet-etching of buffered oxide etchant. Probing metal electrodes of Ni/Au were deposited by electron-beam evaporation and the graphene layer in unnecessary areas was etched away by O2 plasma.Devices were fabricated on an AlGaN/GaN heterostructure grown on a Si substrate by metalorganic chemical vapor deposition (MOCVD). In detail, after a 5-μm-thick layer of undoped GaN underlayer was grown on a p-type 6-in. Si (111) substrate, a 21-nm-thick AlGaN layer with a 20% Al mole fraction and a 3-nm-thick GaN cap layer were subsequently grown on the GaN underlayer. Multilayered CVD-grown graphene was transferred by a polymethyl methacrylate (PMMA)-assisted wet transfer methodThe I–V characteristics of the Gr/AlGaN/GaN photodetectors were measured by a source measurement unit  equipped with a dark-room probe station. The wavelength-dependent and temporal responsivities were measured by combining a Bentham switching monochromator and the SMU. The illumination power of the switching monochromator was calibrated by a Newport optical power meter. All presented measurements were taken at room temperature.Supplementary information.