Ion implantation is a superior post-synthesis doping technique to tailor the structural properties of materials. Via density functional theory (DFT) calculation and ab-initio molecular dynamics simulations (AIMD) based on stochastic boundary conditions, we systematically investigate the implantation of low energy elements Ga/Ge/As into graphene as well as the electronic, optoelectronic and transport properties. It is found that a single incident Ga, Ge or As atom can substitute a carbon atom of graphene lattice due to the head-on collision as their initial kinetic energies lie in the ranges of 25–26 eV/atom, 22–33 eV/atom and 19–42 eV/atom, respectively. Owing to the different chemical interactions between incident atom and graphene lattice, Ge and As atoms have a wide kinetic energy window for implantation, while Ga is not. Moreover, implantation of Ga/Ge/As into graphene opens up a concentration-dependent bandgap from ~0.1 to ~0.6 eV, enhancing the green and blue light adsorption through optical analysis. Furthermore, the carrier mobility of ion-implanted graphene is lower than pristine graphene; however, it is still almost one order of magnitude higher than silicon semiconductors. These results provide useful guidance for the fabrication of electronic and optoelectronic devices of single-atom-thick two-dimensional materials through the ion implantation technique. Ion implantation is a widely used technique to modify the structural and electronic properties of various materials in the semiconductor industry. For bulk materials, such as silicon-based semiconductor, the alien species can be introduced into the near-surface region of target material under irradiation of accelerated ion beams, and the concentration and depth distribution of doping atoms can be controlled by adjusting the flux and kinetic energy of incident ions. Similarly, the ion implantation technique could be applied in the modification and fabrication of two-dimensional materials ,2,3. In In spite of a variety of incident ion species, only the implantations of boron (B) ,8,9,10, In this work, spin-polarized density functional theory (DFT) calculation, ab-initio molecular dynamics simulations (AIMD) combined with stochastic boundary conditions (SBC) model are used to investigate the structural and electronic properties of implanted Ga/Ge/As-graphene systems at the atom-scale level. The kinetic energy ranges of incident Ga/Ge/As atoms are calculated to be successfully implanted into graphene through head-on collisions without inducing any vacancies, in agreement with available experimental results . The widTo simulate the energy exchange between a non-equilibrium system and the surrounding environment, it is essential to apply a reasonable heat bath. As proposed by Kantorovich and Rompotis , the colMolecular dynamics simulations based on spin-polarized DFT are carried out by Vienna Ab initio Simulation Package  with the projector augmented wave (PAW) potential method . The eleFirstly, we optimize the structures of orthorhombic 5 × 8, hexagonal 4 × 4 and 8 × 8 supercells, as well as the structures of Ga/Ga/As-doped graphene by DFT calculations. The calculated lattice constant of graphene is 2.465 Å, which agrees well with the experimental value of 2.47 Å . The finTo avoid the effect of thermal disorder on the results, the optimized orthorhombic 5 × 8 supercell by DFT calculation is used to quantify the kinetic energy ranges of the incident Ga/Ge/As atoms implanting into graphene lattice. During the process of implantation, Langevin thermostat is used to mimic energy dissipation at 300 K. The incident atom is initially placed at 10 Å above graphene layer, and the given incident energies range from 1 eV to 50 eV with 1 eV interval, corresponding to the initial velocity of ~ 0.1 Å/fs that is able to approach the graphene surface after about 100 fs. Only head-on collisions are considered since the energy transfer from an incident atom to a lattice C atom is maximal. In order to quantify the kinetic energy range of incident atom implanting into graphene, we performed dozens of independent AIMD simulations.An incident Ga/Ge/As atom collides head-on with a C atom in the graphene lattice, so only incident Ga/Ge/As atom with the appropriate kinetic energy can be introduced into the graphene lattice without producing defects. Our AIMD simulations show that a single Ge atom with 22 to 33 eV initial kinetic energy can directly implant into graphene by head-on colliding with a C atom of graphene, and the impacted C atom is sputtered, while the incident Ge atom with lower than 21 eV cannot be inserted into graphene, with higher than 34 eV can penetrate through the graphene layer with leaving a C vacancy defect. The minimal kinetic energy of implanting Ge atom into graphene is 22 eV, consistent with previous experimental results . SimilarAs shown in Our results show that Ge and As atoms have a wide range of kinetic energy for implantation, while Ga is relatively difficult to be inserted into graphene lattice, and the minimum kinetic energies Ga, Ge and As for implantation decrease with increasing atomic number. To verify the differences of implantation between Ga, Ge and As atoms, we analyze the kinetic energy transfer between the incident atom and the sputtered C atom as well as the corresponding atomic-scale snapshots of 26 eV Ga/Ge/As atoms implanted into graphene. As shown in Similarly, the kinetic energy transfers and the corresponding atomic-scale snapshots of 26 eV Ge and As atoms implanting into graphene are shown in As shown in +m2)2Ek1 . The cal3, Ge-C3 and As-C3 are 2.9–3.2 Å, 2.8–2.9 Å and 2.4–2.5Å, respectively. Obviously, the charge transfer from Ge/As atom to C atoms in distorted graphene lattice is greater, and there is a more significant charge accumulation among Ge-C3 and As-C3 than Ga-C3, which indicates that the interactions of Ge-graphene and As-graphene are stronger than that of Ga-graphene. Furthermore, there are hybridization peaks between Ge/As-4p and C-2p orbitals at about 1.5 eV above Fermi level, while the hybridization peaks between Ga-4p and C-2p orbitals appear at 1.0 eV. In brief, the differences in interactions of Ga/Ge/As and distorted graphene are mainly attributed to their different number of 4p electrons. As a result, as shown in As known, the zero-energy bandgap of pristine graphene has limited its applications for further electronic and optoelectronic applications. According to our AIMD simulations and DFT calculations as shown in ε2) and real parts (ε1) of dielectric function can be obtained by the momentum matrix elements between the occupied and unoccupied virtual wave functions and Kramers–Kronig dispersion relation, respectively [ε1 and ε2, the absorption coefficient, electron energy-loss (EELS) spectrum function, refractive index, extinction coefficient and optical reflectivity could be obtained by the equations: To investigate the optical properties of Ga/Ge/As-graphene, DFT calculation within the random phase approximation approach is applied . The optectively ,36,37. Bectively ,39,40.ε1) of ion-implanted Ga/Ge/As-graphene is similar to pristine graphene, while the peaks of ε2 shift to lower energy. As shown in Next, we demonstrate the optical properties of pristine and ion-implanted graphene. As shown in Similarly, ion-implantation can modify the refractive index, optical reflectivity and optical conductivity, as shown in To evaluate the carrier mobility, the effective mass method is used to calculate the transport properties of pristine and ion-implanted graphene. The carrier mobility can be obtained by |m*|2E12 ,45, wher5 cm2 V−1·s−1 as described in 4 cm2 V−1·s−1) as compared to that of pristine graphene. Interestingly, we find that the hole mobility of Ge-graphene is roughly three times larger than that of the electron, while the hole mobility of Ga/As-graphene is about two times smaller than that of the electron. The reason mainly comes from the different hybridization between implanted ions and graphene, which produces different dispersion shapes of valence and a conduction band near the Fermi level (as shown in 3 cm2 V−1 s−1 and ~4.5 × 102 cm2 V−1 s−1 at 300 K, respectively [Due to the nature of the zero-energy bandgap and linear dispersion relation near Fermi level, and the electron and hole mobility of pristine graphene at room temperature is very high up to 10ectively . These uThe control of structural and electronic properties of graphene and other atom-thick two-dimensional materials is a core issue in practical applications . On the In summary, systematic DFT calculations and AIMD simulations based on the SBC model are performed to study structural and electronic properties of implanted Ga/Ge/As-graphene systems at the atom-scale level. The dynamical process of ion implantation, as well as energy transfer and chemical interaction between incident ions and graphene, are investigated. The electronic, optical and transport properties of ion-implanted graphene are analyzed and discussed for possible applications in optoelectronic devices through the coupling with other Van de Waals 2D materials and substrates. The present work will accelerate and broaden the applications of graphene through ion implantation in ultrafast and low power electric and optoelectronic devices, gas sensing devices, single-atom catalysis, as well as a single-photon emitting system, etc.


Herein we report a unique structure design of graphene-isolated Pt from CoNi nanoparticles (PtǀCoNi) for efficiently catalytic CO oxidation in an oxygen-rich atmosphere. CoNi alloy is protected by ultrathin graphene shell from oxidation and therefore modulates the electronic property of Pt-graphene interface via electron penetration effect. This catalyst can achieve near 100% CO conversion at room temperature, while there are limited conversions over Pt/C and Pt/CoNiOx catalysts. Experiments and theoretical calculations indicate that CO will saturate Pt sites, but O2 can adsorb at the Pt-graphene interface without competing with CO, which facilitate the O2 activation and the subsequent surface reaction. This graphene-isolated system is distinct from the classical metal-metal oxide interface for catalysis, and it provides a new thought for the design of heterogeneous catalysts.Achieving CO oxidation at room temperature is significant for gas purification but still challenging nowadays. Pt promoted by 3 Achieving CO oxidation at room temperature is significant for gas purification but remains challenging to perform. Here, the authors report design of graphene-isolated Pt from cobalt-nickel nanoparticles for efficiently catalytic CO oxidation in an oxygen-rich atmosphere. Moreover, as a probe reaction in surface science, it promotes the development of heterogeneous catalysis2. It is well documented that CO adsorbs more strongly on bare Pt surfaces than O2. Therefore, the activation of O2 on Pt is difficult due to the saturated coverage of CO and is the rate-determining step of the reaction4. An approach to facilitate this step is to construct an active interface between Pt and 3d TMs oxides5, at which O2 can preferentially adsorb and dissociate into atomic O for reaction. However, such an interface usually requires a hydrogen-rich atmosphere to keep TMs oxides in the coordinatively unsaturated state, such as FeOx1−6, CoOx1−8, or NiOx1−10, otherwise, it will be deactivated by the deep oxidation of TMs in an oxygen-rich atmosphere.Pt-catalyzed CO oxidation to CO12. It has been found that graphene encapsulating iron-based catalysts exhibit high activity and stability in electrocatalytic oxygen reduction14, oxygen or hydrogen evolution18, and other reactions20 under harsh conditions . Their excellent catalytic performances are derived from the unique electron penetration effect13, that is, TMs in the metallic state do not need to directly contact the reactants but only employ their electrons to activate the outer graphene for reaction. Inspired by this, herein we design a unique graphene-isolated Pt from CoNi nanoparticles (PtǀCoNi) catalyst, of which CoNi can be protected by graphene from oxidation in an oxygen-rich atmosphere and thus effectively trigger the interface activity of Pt–graphene for CO oxidation at room temperature.Recently, a general strategy of graphene encapsulating TMs has been developed to protect TMs from oxidation and corrosion3CN or CH4 on CoNi nanoparticles (NPs). The obtained samples are labeled as CoNi@NC and CoNi@C, respectively, according to the carbon sources of CH3CN and CH4. Then, Pt NPs were synthesized in the form of sol and deposited on them and two control samples, commercial carbon nanotube (CNT) and carbon black (CB), with the same Pt loading amount of 4 wt%. The correspondingly obtained catalysts are labeled as Pt/CoNi@NC, Pt/CoNi@C, Pt/CNT, and Pt/CB, respectively.Graphene encapsulating CoNi alloy was prepared by chemical vapor deposition from CHThe morphology of these catalysts was characterized by a transmission electron microscope (TEM). As shown in Supplementary Fig. III edge (2p → 5d transition) for Pt/CoNi@NC, Pt/CoNi@C, Pt/CNT, and Pt/CB , indicating that electrons of CoNi NPs can penetrate through graphene to Pt NPs.To verify the electron penetration effect of this composite catalyst, the electronic structure of Pt in each catalyst was detected by synchrotron-based X-ray absorption near edge structure spectroscopy (XANES). Figure yst Fig.  was calc4 on the hollow graphene cage exhibits a positive Bader charge of +0.15 due to the electron transfer from Pt to C, whereas the Pt4 on the graphene cage with CoNi NPs inside exhibits a negative charge of −0.08, indicating that CoNi does indeed transfer electrons to Pt through graphene. Benefiting from the electron penetration effect, the binding energy between Pt4 and graphene is strengthened from −2.17 to −2.74 eV when encapsulating CoNi NPs into the graphene cage. This can explain the selective deposition of Pt NPs on the surface of graphene encapsulating CoNi alloy shown in Fig. Two comparable catalyst models were established to further confirm the electron penetration effect Fig. . The Pt4s + 2p orbitals of C in Pt4/CoNi@C and Pt4/C 22 shown in Supplementary Fig. 4/CoNi@C and Pt4/C 7, and the activity can be fully recovered after H2 reduction  Co and Ni can be rapidly oxidized even at near room temperature. Therefore, the intact graphene layer is essential to keep CoNi in the metallic state.To check the role of graphene in protecting CoNi NPs from oxidation, NAP-XPS was applied to monitor the valence states of Co and Ni in Pt/CoNi@NC during an in situ reaction in a flow of 0.067 mbar CO and 1.13 mbar OTo directly observe the break of graphene, TEM characterization on Pt/CoNi@NC samples Fig.  after tex/C catalysts  was applied. The detection depth of LEIS is only two atomic layersses Fig.  were per2 on Pt4/CoNi@C and Pt4/C. For both models, the adsorption energy of CO on Pt site even with a saturated coverage  calculations were carried out to further reveal the surface reaction mechanism of CO oxidation over Pt on graphene encapsulating CoNi alloy and the promotion mechanism of the electron penetration effect. Figure i@C Fig.  without 4/CoNi@C. The energy profile starts from model I with 4CO adsorbed on Pt4/CoNi@C. Then, a gaseous CO adsorbs on model I preferentially than O2 with a decrease of ∆G. On the 5CO-saturated adsorption structure (model II), O2 can still adsorb at the Pt–graphene interface (model III) with a slight increase of ∆G (0.44 eV) due to the loss of entropy. By contrast, O2 cannot adsorb at the interface of Pt4/C but would competitively adsorb on the CO-saturated Pt site with a huge increase of ∆G (1.61 eV). During the transition state (model TS-1), the activation of O2 is assisted by the adsorbed CO, and then CO2 is formed with a moderate barrier of 0.66 eV. The remaining adsorbed O atom will react with another re-adsorbed CO to form CO2 with a similar barrier of 0.63 eV. Therefore, the graphene encapsulating TMs can avoid the CO poisoning of Pt by providing additional sites for O2 adsorption  by urea co-precipitation with equimolar Co(NO3)2·6H2O (Alfa Aesar) and Ni(CH3COO)2·4H2O (Alfa Aesar). In detail, 1.06 g of Co(NO3)2·6H2O, 0.90 g of Ni(CH3COO)2·4H2O, and 1.8 g of urea were dissolved into 100 mL of water. After adding 6.0 g of 30% SiO2 sphere colloidal dispersion, the mixture was refluxed at 100 °C for 12 h with continuous stirring. The precipitate was washed with deionized water to neutral and then dried at 100 °C for 12 h. Secondly, the obtained CoNiOx/SiO2 solid (200 mg) was heated from 30 to 700 °C at a rate of 10 °C/min in a 100 mL/min of 30% H2/Ar to obtain CoNi metallic alloy. After reaching 700 °C, H2 was switched off and CH3CN (bubbling with 70 mL/min of Ar) or CH4  was introduced as carbon sources to form graphene on CoNi NPs. Finally, the cooled sample was immersed into an aqueous solution of 10 wt% HF at room temperature for 12 h and then washed and dried at 40 °C in a vacuum (~0.1 kPa) for 12 h. The obtained samples were labeled as CoNi@NC and CoNi@C corresponding to the carbon sources of CH3CN and CH4.First, CoNi layered double hydroxides were deposited on SiO24. In detail, 50 mg of NaOH and 50 mg of H2PtCl6·6H2O were successively dissolved into 5 mL of ethylene glycol, and then it was refluxed at 160 °C for 3 h with continuous stirring under the protection of Ar flow (50 mL/min) to obtain the Pt colloid. Next, the Pt colloid was added into the ethanol dispersion of CoNi@NC or CoNi@C at room temperature. After ultrasonic oscillation for 0.5 h, an aqueous solution of 1 mol/L HCl was added into the mixture to precipitate Pt NPs on CoNi@NC or CoNi@C. Finally, they were thoroughly washed and dried at 40 °C in a vacuum (~0.1 kPa) for 12 h to obtain Pt catalysts for use.First, a colloidal solution of Pt NPs (1–2 nm) was prepared by glycol reduction3 at 110 °C for 5 h. CB was directly used without further purification. The same preparation processes were conducted to obtain Pt/CNT and Pt/CB as those for Pt/CoNi@NC and Pt/CoNi@C. The loading amount of Pt for each catalyst was confirmed to be around 4 wt% by inductively coupled plasma–optical emission spectrometry.Commercial CNT  and CB (Vulcan XC-72) were used for comparison. CNT was pretreated in an aqueous solution of 37 wt% HNO23, which allows the reduction and reaction of catalysts with the same parameters of temperature and pressure as for the actual testings described below.Transmission electron microscopy (TEM) images were acquired on an FEI Tecnai F20 microscope operating at 200 kV. Aberration-corrected HAADF-STEM images were acquired on a JEOL ARM200F microscope equipped with a probe-forming aberration corrector operating at 200 kV. XRD measurements were conducted on a Rigaku Ultima IV diffractometer with Cu Kα radiation at 40 kV and 30 mA. X-ray absorption near edge structure spectroscopy (XANES) was measured at the BL14W1 beamline of the Shanghai Synchrotron Radiation Facility. NAP-XPS measurement was carried out by a PHOIBOS 150 NAP 1D-DLD analyzer using monochromatic Al Kα radiation (1486.6 eV). LEIS was obtained using an ion-TOF Qtac100 instrument with helium as an ion source. There is an in situ reaction chamber connecting with the chamber of LEIS2, and 79% He (Messer). A 20 mL/min of mixed gas flowed through 20 mg of catalyst  to achieve a space velocity of 60,000 mL g−1 h−1. The tail gas was analyzed online by gas chromatography equipped with a packed column (TDX-01) and a methane converter in front of a flame ionization detector (FID). The methane converter is a micro high-temperature furnace (330 °C) with Ni-based catalyst that can fully convert CO and CO2 into CH4 for FID detection. Before reactions, all catalysts were pre-reduced in high-purity H2  flow at 240 °C for 2 h. After cooling to room temperature in high-purity Ar  flow, temperature-dependent CO oxidation was performed from 25 to 240 °C (or to 120 °C) at a rate of 1 °C/min.CO oxidation was carried out in a quartz tube (6 mm outer diameter and 4 mm inner diameter) reactor. The temperature was measured with a thermocouple on the external surface of the quartz tube right next to the catalyst bed. The reaction gas consisted of 1% CO, 20% O27. The exchange-correlation functional was described as Perdew–Burke–Ernzerhof generalized gradient approximation28. The interactions between ionic cores and electrons were described using projector augmented-wave pseudopotentials29 with kinetics cut-off energy of 400 eV. The vacuum region was set to 15 Å between the clusters. The models of metal clusters encapsulated into graphene (Co27Ni28@Gr) consist of C240 encapsulating 55 atoms. All structures were fully relaxed to the ground state and spin-polarization was considered in all calculations. The convergences of energy and force were set to 1 × 10−4 eV and 0.05 eV/Å, respectively. The free energies of the intermediates were obtained by ΔG = ΔE + ΔZPE − TΔS, where ΔE is the binding energy of adsorption species, and ΔZPE, ΔS is the zero-point energy changes, entropy changes, respectively. Totally, 298.15 K was chosen as the temperature according to the experimental condition. The transition states were identified via automated relaxed potential energy surface scans method recently developed by Philipp N. Plessow30.DFT calculations were performed on the Vienna ab initio simulation package (VASP)Supplementary InformationPeer Review File


In this work, an easy, green, noncovalent surface modification of pristine graphene (GR) was carried out using a single-step method between sodium carboxymethyl cellulose (CMC) and pristine GR, resulting in the formation of a modified CMC–GR (CGR) dispersion with 15% nanosheet content, the first reported in water. Results obtained from thermogravimetry analysis (TGA), Raman spectroscopy, and atomic force microscopy (AFM) confirm that the CMC modifier is successfully decorated on the pristine GR surface. Analyses of transmittance spectrum, zeta potential and transmittance electron microscopy (TEM) images reveal that the modified CGR has a high degree of dispersion. More importantly, the pristine GR is insoluble, while the modified CGR-3, mixed with 1.1 wt% CMC modifier, is easily well dispersed in water and has good flowability, and no sedimentation is observed after more than 3 months. An easy, green, noncovalent surface modification of pristine graphene (GR) was carried out by using a single-step method, resulting in the formation of a modified CMC-GR dispersion with 15% nanosheet content, the first reported in water. Thus, waterborne coatings with good corrosion resistance are urgently needed to be developed.Waterborne coatings have gained much attention for metal protection on account of their reduced emission of volatile organic compounds (VOCs), avoiding serious workplace accidents.2,3 montmorillonite,4,5 boron nitride,6–8 and graphene,9,10 are considered more efficient materials that enhance the corrosion resistance of coatings by improving their barrier properties. Graphene, a promising two-dimensional (2D) nanosheet with only one-atom thickness, has a series of preeminent characteristics, such as high barrier performance, good mechanical properties, outstanding thermal stability and high chemical stability.11–14 At present, it has received increasing attention in the field of anticorrosion coatings for ultralight metals, and it has been used in waterborne anticorrosion coatings to enhance anticorrosion performance.15,16 However, graphene is not easy to disperse in water due to its high surface area, strong van der Waals forces, and intrinsic hydrophobicity. One effective method is to gain hydrophilic graphene oxide (GO) using chemical oxidation modification. Unfortunately, the defect sites introduced during the process can affect the long-term anticorrosion performance. Furthermore, many studies have been done to improve the wettability of graphene in matrix through facile noncovalent modification. Chang et al.17 constructed polyaniline/graphene waterborne epoxy coatings to enhance the corrosion resistance of steel against O2 and H2O. He et al.18 used tannic acid (TA) as intercalator to disperse graphene in water via π–π noncovalent bonds, forming graphene–TA hybrids and obtaining highly efficient anticorrosive epoxy coatings. Yu et al.19 prepared waterborne epoxy coatings combined with dispersed sandwiched polyvinyl butyral@graphene@polyvinyl butyral composites to improve the corrosion resistance of commercial aluminum alloys, and the effect can last 120 days even when exposed to simulated seawater.Polymer nanocomposites, including nanofillers such as silica,In recent years, most works have only focused on graphene dispersion through covalent and noncovalent modification using a low graphene content, between 0.1% and 5%. However, it is difficult to use this kind of graphene dispersion as a corrosion resistance additive for industrial waterborne coatings. Based on the demand for corrosion resistance and mass production requirements, graphene dispersions with high solid content and good dispersibility in water need to be designed and developed.In this paper, we report an easy, green modification of graphene by using a noncovalent strategy between CMC and graphene, as shown in This method for green surface modification of pristine GR can be used to prepare GR/waterborne polymer nanocomposites. The entanglements between the long chains of CMC and the polymer matrix substantially enhance the interactions between them and accordingly improve their compatibility. Importantly, this strategy is available and economical due to its easy operation in industry. We also believe that this work will accelerate the development of industrial anticorrosion coatings for ultralight metals.2.2.12 g−1) were obtained from Sixth Element (Changzhou) Materials Technology Co. Ltd Sodium carboxymethyl cellulose  was purchased from Hefei Aigo Additives Technology Co. Ltd. Deionized water was prepared using the appropriate equipment.Pristine graphene (GR) nanosheets  g) and CMC modifier (n g) water were added to a three-necked flask and stirred with a high-speed stirrer at 900 rpm for 15 minutes. Then, crude GR (15 g) was added to the preprepared mixture and sonicated for 1 hour to obtain a uniform CGR dispersion. For the sake of comparing different CGR dispersions, four different contents of CMC modifier  were designed to prepared CGR-x , correspondingly. Then, the products were purified after each modification by ultrafiltration. The resulting CGR solid powders were dried overnight at 80 °C in vacuum.First, deionized water . The transmittance of the graphene dispersion was investigated with an ultraviolet spectrophotometer (UV2600). Morphology of the graphene dispersion was investigated by field emission scanning electron microscopy  and transmittance electron microscopy . Atomic force microscopy  was used to characterize the thickness of the GR nanosheets.Thermogravimetry analysis (TGA) of pristine GR and CGR was performed under nitrogen on a STA409PC thermogravimetric analyzer (Netzsch instruments) with a temperature range of 25–1000 °C at a heating rate of 10 °C min3.3.1−1, respectively. The first stage of mass loss terminates at approximately 180 °C, which is due to the rejection of the adsorbed water from the interlayers of the materials. The TGA plot of CMC indicates a gradual mass loss of around 58.4% as the temperature reached 600 °C. Furthermore, we noted that CGR showed a significant weight loss in the range of 260–600 °C, corresponding to pyrolysis of the CMC modifier. The results indicate that the CMC modifier can be adsorbed on the surface of graphene.Supporting evidence for the noncovalent attachment of CMC modifier on the pristine GR surfaces comes from the thermogravimetry analysis (TGA). 3.218 The D band and G band are represented in the in-plane vibration of sp2 carbon atoms and the vibration of sp3 carbon atoms from the functional groups, respectively. It can be seen from −1 (D band) and 1586 cm−1 (G band), ID/IG = 1.03. The ID/IG ratio presents a slight increase from 1.03 for pristine GR to 1.06 for CGR-4, indicating that no more defects are introduced after the modification of pristine GR with CMC modifier, and the graphene preserves its basic structural properties.Raman spectroscopy is usually employed to distinguish the ordered and disordered carbon structures of graphene.3.3The diluted dispersions of pristine GR and CGR with obvious Tyndall effect in water were prepared through mechanical dispersion for 15 min. On the basis of the dynamic light scattering (DLS) principle, the average diameter and size distribution of the graphene dispersions were analyzed using a zeta potential analyzer, as shown in 50) is about 4560 nm, as shown in According to the result, the pristine GR was dispersed poorly in water, and serious agglomeration was formed because of the high surface area, strong van der Waals forces, and intrinsic hydrophobicity of GR. Its average diameter (D3.4For quickly evaluating the dispersion effect of graphene, it is necessary to compare the optical transmittance. 3.5The most important parameter defining surface properties of electrostatically stabilized nanomaterials in aqueous solutions is the zeta potential value. The relation between zeta potential and CMC modifier content in the GR nanosheets is shown in The inset photo in 3.618,20 which is attributed to the poor dispersion of GR nanosheets (The surface morphologies of pristine GR and modified GR dispersed in water were examined by SEM, as shown in nosheets . In compFurthermore, TEM results confirmed the dispersibility of pristine GR and modified CGR-3 with the best dispersion stability in 4.In summary, a CMC-modified CGR dispersion was successfully prepared in aqueous solution by single-step noncovalent functionalization technique. The results show that the optimum content of CMC modifier coated on the surface of graphene is 1.1 wt%. The modified CGR possesses good dispersibility and good flowability in water. The prepared CGR-3 dispersion, with no sedimentation after more than 3 months, has potential application as a functional corrosion resistance additive for waterborne coatings, providing a new strategy for the high-value-added use of graphene.There are no conflicts to declare.


Stretchable optical fiber sensors (SOFSs), which are promising and ultra-sensitive next-generation sensors, have achieved prominent success in applications including health monitoring, robotics, and biological–electronic interfaces. Here, we report an ultra-sensitive multi-functional optical micro/nanofiber embedded with a flexible polydimethylsiloxane (PDMS) membrane, which is compatible with wearable optical sensors. Based on the effect of a strong evanescent field, the as-fabricated SOFS is highly sensitive to strain, achieving high sensitivity with a peak gauge factor of 450. In addition, considering the large negative thermo-optic coefficient of PDMS, temperature measurements in the range of 30 to 60 °C were realized, resulting in a 0.02 dBm/°C response. In addition, wide-range detection of humidity was demonstrated by a peak sensitivity of 0.5 dB/% RH, with less than 10% variation at each humidity stage. The robust sensing performance, together with the flexibility, enables the real-time monitoring of pulse, body temperature, and respiration. This as-fabricated SOFS provides significant potential for the practical application of wearable healthcare sensors. At present, the research and application of flexible wearable electronics are reflected in various aspects of human life ,2,3,4, sIn addition to traditional electrical sensing, combining optical sensing with soft and stretchable packaging may provide an alternative means of developing cheap but reliable wearable sensors ,23. WithTo address this issue, we propose a method to fabricate multi-functional stretchable fiber sensors by using a PDMS membrane embedded with MNFs. Based on the transition from guided modes to radiation modes of the waveguiding MNFs upon external stimuli, the as-fabricated MNF sensors are demonstrated to have outstanding sensitivity and repeatability when used in strain and temperature sensing. Moreover, by taking advantage of the water-absorbing ability of tin oxide, a wide detection range and highly sensitive humidity sensing are realized.In order to fabricate the MNFs, we used an electricity-heated mechanical stretching technique to draw a standard silica optical fiber into a biconical tapered fiber. In this method, a 3 cm-long section of the standard fiber was stripped of its cladding layer and fixed onto the MNF translation platform. When the fiber was heated to an optimal temperature, it was drawn into the horizontal plane until the diameter was reduced to the desired value. The entire MNF fabrication process was controlled by a computer program. To obtain uniformity among MNFs with different diameters, the temperature distribution in the drawing region and the speed of the stepper motors could be adjusted.To fabricate an SOFS, we developed a sandwich-like structure to encapsulate the as-fabricated MNFs, which involved a three-step process: (1) 25 um of PDMS was prepared on a thin polyethylene (PET) flake to support the MNFs, which was firmly held in position using van der Waals forces and electrostatic interactions between the MNFs and the PDMS membrane; (2) 1 mL of degassed PDMS  was slowly poured onto the PDMS/PET substrate, waiting for several seconds to ensure the substrate was covered with the fluid PDMS and that the MNFs were enclosed in the liquid; and (3) another thin PDMS/PET flake was placed on the substrate, followed by curing at 80 °C for 30 min, forming a 500 um-thick PDMS thin film. As for humidity sensing, a humidity-sensitive layer (tin oxide) was deposited using the magnetron sputtering method on the as-fabricated MNFs; the thickness of the tin oxide layer was about 20 nm for the sake of optimal sensing performance. According to the requirement of various sensing applications, the as-fabricated SOFS was peeled from the PET sheet.Computer-controlled stepper motor translation platforms, which precisely control different step movements (including single step movement and periodic step movement), were prepared to measure the strain sensing performance of the SOFS. Before strain sensing, the as-fabricated SOFS was fastened onto the translation platforms with standard clamps and coupled with a 1550 nm wavelength fiber laser at one end. The optical output was detected by a spectrometer at the other end. The sensing process can be divided into two main parts: the first is a micro-strain measurement which contains several micron dimension step movements, and the other is an endurance test with hundreds of cycles of movements. Finally, in order to demonstrate the capability for health monitoring, the detection of cardiopalmus was conducted.A constant temperature heating facility was used to test the temperature sensing performance of the SOFS, which could provide a stable temperature environment (ranging from 30 to 60 °C). During the temperature sensing process, the as-fabricated SOFS was positioned within the facility at all times and was always in a closed environment. Moreover, in order to demonstrate the capability of the SOFS for health monitoring, the detection of body temperature was conducted. A humidity generator and a detector were prepared to support the measurement of the SOFS’s humidity sensing capability, which provided a continuous standard humidity atmosphere (ranging from 10 to 90% RH). Furthermore, for the duration of the humidity sensing process, the as-fabricated SOFS was placed in an airtight chamber. In order to demonstrate the capability for health monitoring, the detection of respiration was conducted.An optical fiber laser  and an optical fiber spectrometer  were used as a light source and a detector, respectively. A humidity generator  and a humidity detector  were used to generate standard humidity and measure the unknown environmental humidity, respectively. When a single-mode optical fiber  was coupled with the fiber laser, the input optical power of the MNF was about 16 mW, with a stability of less than 0.05%. The stepper motors of the optical fiber drawing platform  and the translation stage  were used to investigate the strain response of the sensor. A home-made system consisting of multiple channels was used for monitoring the response of the optical sensor to humidity, maintaining a relatively long recording period. A constant temperature heating facility  with a temperature resolution of 0.1 °C was provided to maintain a stable temperature in the range of 30 to 60 °C.Although the conventional PDMS embedding method has been widely employed ,33, demoExperimentally, highly uniform MNFs are fabricated through the tapered drawing of silica glass optical fibers, which allows for a guiding light at the micrometer scale. However, the as-fabricated MNFs, with a large proportion of evanescent fields exposed to the surroundings ,35, are −4 per °C), and thus the guided modes of the MNFs are sensitive to the surrounding variation of RI owing to the large fractional evanescent fields outside the MNF, ensuring the SOFS’s responsiveness to the change in temperature. Moreover, a wider expansion of aspects of sensing media could be compatible with the as-fabricated SOFS. Tin oxide, as a humidity-sensitive material, has already been used in humidity sensing [Bending a flexible SOFS embedded with PDMS can lead to a bending-dependent transmission, which includes large-scale winding and tiny vibrations, enabling strain sensing. The RI of PDMS is a function of the temperature due to its large negative thermo-optic coefficient  as a function of strain leads to a gauge factor (GF), where the gauge factor is defined as GF = (∆I/I0)/strain. Meanwhile, the detectivity of the SOFS was shown to be highly sensitive, with a gauge factor of 118 and higher compared to conductive core–shell aramid nanofibrils (GF:18.8) [To investigate strain sensing, firstly, the SOFS embedded with a 1 um-diameter MNF was fastened to a computer-controlled stepper motor translation platform for bending sensing. By taking advantage of the high-precision moving stage, we designed each step to correspond to a replacement of 1 um, 2 um, and 5 um with 10 times bend and 10 times recover. As shown in GF:18.8) , and silGF:18.8) . ConsideGF:18.8) . To demoThe long-term reversibility and stability of the SOFS were further investigated by automatically bending and recovering the sensor over 250 cycles using a computer-controlled moving platform. After the cycles, the sensor maintained a steady baseline intensity with a slight decrease of 5% d, which I/∆T, where ∆I is the increase in the output intensity, and ∆T is the change in the temperature, the sensor achieved a sensitivity as high as 0.02 dBm per °C, which is similar to that of wearable temperature sensors based on metal oxides [In addition to strain sensing, the refractive index characteristics of PDMS are promising for temperature sensing; it has a large negative thermo-optic coefficient, while the silica MNF shows a negligible change compared with that of PDMS. The SOFS with a 1 um-diameter MNF embedded in a 500 um-thick PDMS film was placed on a computer-controlled constant temperature heating facility, which provided a stable temperature in the range of 30 to 60 °C. The transmission spectra of the SOFS at different temperatures were recorded using a spectrometer a. The prl oxides . The decBesides the excellent stretchability and temperature response, an ultra-sensitive optical sensor with a wide range of humidity detection was obtained according to the Materials and Methods section. Interestingly, when we started to study the effect of different diameters on the humidity response, SOFSs with diameters that were too small or too large under the same thickness of the sensitive layer were demonstrated to be unresponsive. The phenomena of guided light scattering and optical absorption  close to the most sensitive area in order to ensure wet air penetrated into the humidity-sensitive material. Tin oxide, a promising humidity-sensitive material, has not only been widely used in the field of humidity sensing but also popularized in the field of opto-electronics for decades [I/∆H, where ∆I is the increase in the output intensity, and ∆H is the change in the relative humidity, the as-fabricated sensor exhibits a peak sensitivity of 0.5 dB/% RH, which is far better than a humidity sensor based on a hetero-core optical fiber [Compared to the above sensors, the pattern of encapsulation was discriminating to some extent, which included a spindly silt , the humidity response curve presents quite a sharp peak and an excellent reverting capacity. In addition, the as-fabricated SOFS possesses a better response speed (of a few seconds) compared with its electronic counterpart  under a wide humidity range.To exclude the disturbance of continuous humidity measurement and demonstrate the effect of the SOFS under all humidity conditions, the humidity stages from 30% to 90% RH were conducted individually. As shown in In summary, we have demonstrated an ultra-sensitive multi-functional optical micro/nanofiber embedded with a flexible encapsulation of PDMS, which possesses great potential in the field of wearable optical sensors. By taking advantage of the character of its strong evanescent field, the as-fabricated MNF embedded with a PDMS membrane is highly sensitive to weak bends, enabling a robust durability within hundreds of measurements and high sensitivity with a peak gauge factor of 450. At the same time, taking the large negative thermo-optic coefficient of PDMS into account, a temperature response in the range of 30 to 60 °C was realized, resulting in a resolution of 0.02 dBm/°C. In addition, a humidity measurement within a broad detection range from 30% to 90% RH was demonstrated, with a sensitivity of 0.5 dB/% RH, and less than 10% variation at each humidity stage. Moreover, the as-fabricated highly sensitive sensing performance with flexibility enables the real-time monitoring of pulse, body temperature, and respiration. The above results may pave the way towards future wearable optical sensors for health monitoring including real-time monitoring of pulse, respiration, and other aspects of life signs.


The graphene and TiO2 hybrid nanoparticles are dip-coated on a biodegradable thermoplastic poly(lactic acid) (PLA) substrate. The thermoplastic PLA is approved by the Food and Drug Administration (FDA), and is widely utilized in medical devices. The graphene/TiO2 coating is substantiated to transform the hydrophilic PLA film into superhydrophobic biomaterials that can help to reduce hazardous medical-device complications. The surface wettability of the graphene/TiO2 nanoparticle-coated PLA surface was evaluated by measuring the apparent water contact angle. The surface chemical composition and surface morphology were analyzed via Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The graphene/TiO2-coated PLA film achieved superhydrophobic properties by demonstrating a water contact angle greater than 150°. The water contact angle of the graphene/TiO2 coating increased along with the concentration of the nanoparticles and the ratio of TiO2 to graphene. Moreover, the graphene/TiO2 coating exhibited excellent durability, whereby the contact angle of the coated surface remained unchanged after water immersion for 24 h. The duration of the effectiveness of the superhydrophobic coating suggests its suitability for medical devices, for which a short duration of administration is involved. This study reports an easy-to-replicate and cost-effective method for fabricating superhydrophobic graphene/TiO2-coated surfaces, which additionally substantiates a potential solution for the manufacturing of biomaterials in the future.Materials with superhydrophobic surfaces have received vast attention in various industries due to their valuable properties, such as their self-cleaning and antifouling effects. These promising superhydrophobic properties are taken into high priority, particularly for medical devices and applications. The development of an ideal superhydrophobic surface is a challenging task and is constantly progressing. Various strategies have been introduced; however, a minority of them are cost-effective. This work presents a facile fabrication of the superhydrophobic surface by using graphene and titanium dioxide (TiO Superhydrophobic biomaterials have been commonly employed in various applications due to their non-wettability. The superhydrophobic effect of these materials is generally indicated by a high contact angle >150°) 2]. The f2) nanoparticles onto a poly(lactic acid) (PLA) substrate. This method is substantiated to be employed in the large-scale production of superhydrophobic biomaterials, particularly targeting medical devices.Developments of functional superhydrophobic surfaces are mostly inspired by nature, for example, by the hierarchical structure of the lotus leaf, which provides the infamous lotus leaf effect, as well as the water-repellent surfaces of insects ,12,13. V2 are introduced as the coating materials due to their tendency to improve hydrophobicity, and their high corrosion resistance and low toxicity [2 nanocomposite materials exhibit enhanced antibacterial activities by suppressing the growth of both gram-negative and gram-positive bacteria via photocatalytic activity and suppressing the generation of reactive oxygen species [Graphene and TiOtoxicity ,19,20,21 species ,24,25,26 species . The Foo species . Previou species ,30.2 coating that was fabricated in this work aims to target applications, particularly medical devices, that require self-cleaning properties. The rough topography of the graphene/TiO2 surface provides protrusions that trap an adequate amount of air layers within the surface structure and promote resistance to bacterial adhesion. This mechanism induces the inhibition of biofilm formation [2 have shown superior bactericidal effects and antifouling abilities [2 coating on PLA film via the dip-coating method. Herein, we propose that the artificial superhydrophobic surface fabricated via a simple step is appropriate for imparting into medical devices, for which self-cleaning and antimicrobial properties are desirable.The superhydrophobic graphene/TiOormation ,32. In abilities ,35,36,37bilities ,39. The bilities . The pre2/g) and titanium dioxide  were obtained from Sigma–Aldrich, MO, USA. Polydimethylsiloxane (PDMS) prepolymers and curing agents were purchased from the Dow Corning Corporation, Lansing, MI, USA. Poly(lactic acid) (3052 D) was purchased from Natureworks LLC, Saint Paul, MN, USA. Chemicals, including n-hexane  and chloroform (CHCl3), were obtained from Merck, Darmstadt, Germany, and were used as received.Graphene nanoplatelets  (PLA) film was prepared using PLA grade 3052 D. PLA pellets of 5 weight % were used to produce a transparent and resilient PLA film. The PLA pellets were dissolved in 30 mL of chloroform by stirring for 1 h at 50 °C. The clear PLA solution was cast onto a glass petri dish and dried at room temperature for 24 h.2 coating solution was prepared with different concentrations of nanoparticles  in 30 mL of hexane. Each concentration of the coating solution contained graphene nanoplatelets and TiO2 nanoparticles with ratios of 10:0, 9:1, 7:3, 5:5, 3:7, 1:9, and 0:10. Prior to mixing, 0.3 g of PDMS (10:1 ratio of base to curing agent) was added into the solution. The suspension was then stirred for 10 min, followed by ultrasonication for 15 min. Poly(lactic acid) film (2 cm × 4.5 cm) was dip-coated with the graphene/TiO2 solution, at a withdrawal speed of 2 mm/s, and dried at ambient temperature. The dip-coating process was repeated 3 times. The final product was cured in the oven at 50 °C for 1 h.The graphene/TiOThe static water contact angles on the surfaces were measured by using a goniometer . A droplet of distilled water with a volume of 10 µL was applied onto the surface of the films. The contact angle of the water droplet was measured immediately after droplet stability. The sessile water contact angles on both sides of the droplet were measured and the average value was recorded. The test was performed in triplicate.−1 with a resolution of 4 cm−1, and analyzed with LabSolutions IR Software (version 2.2). The surface morphology was assessed by using the scanning electron microscope .The surface chemical compositions were determined by using Fourier-transform infrared spectroscopy . The FTIR spectra were collected over a spectrum range of 400–4000 cm2-coated film to water exposure over a prolonged time. The graphene/TiO2-coated film was immersed in distilled water at room temperature for 24 h. The contact angle measurements were performed immediately after the samples were dried.A water immersion test was used to evaluate the resistance of the graphene/TiO2 coating on PLA film was successfully fabricated via dip coating. The graphene/TiO2 nanocomposites coating achieved superhydrophobic properties, as shown in 2 is illustrated via the high apparent water contact angle. The hydrophilic PLA film, with a contact angle of 77 ± 5°, transformed into a superhydrophobic surface (contact angle of >150°) upon the application of the graphene/titanium dioxide coating.The superhydrophobic graphene/TiO2 nanoparticles concomitantly improves the non-wettability of the surface. This result is in concordance with the statement mentioning that superhydrophobic properties are influenced by surface roughness and the chemical composition of the surface. In addition to the low surface energy, the graphene and TiO2 nanoparticles provide the hierarchical structure to the surface of PLA film and thus endow the modified surface with low wettability. The surface roughness, attributed to the micro/nano structures on the graphene/TiO2 surface, entrapped a sufficient air layer on the surface. Hence, high water contact angles are observed, due to the reduction of the contact point between the water droplet and the coated surface.This phenomenon suggests that the enhancement of the surface roughness by the graphene and TiO2 coating on the surface increased from 0.1% to 0.5%. Thereafter, the contact angle of the graphene/TiO2-coated PLA surface slightly decreased when the concentration rose to 0.7%, followed by a surge at 0.9%. In other words, the graphene/TiO2 coating alters the surface structure of the PLA film and transforms the surface-wetting properties from hydrophilic to hydrophobic, and later to superhydrophobic, as the concentration of graphene/TiO2 nanocomposites increases  was obtained when the ratio of graphene to TiO2 was equal. In concordance with previous studies [2 provided surface roughness to the coated surface. The addition of graphene further enhanced the textured surface by establishing the hierarchical nanostructure on the superhydrophobic surface. Therefore, both graphene and TiO2 exert a synergistic effect to produce a surface with superhydrophobic properties.It is noteworthy that, for the 0.5% hobicity . Howeverct angle . The sur studies ,25, the 2 solution increased, the contact angle of the graphene/titanium dioxide-coated PLA surface increased  − 1, where sf indicates the total area of the solid–liquid interface and θc represents the contact angle of the coated PLA surface, whereas θ represents the contact angle of the smooth PLA surface. By substituting 77°, which is the contact angle of the smooth unmodified PLA film, and the contact angles of the respective coated surface into the equation, the result for sf can be determined (sf value for the superhydrophobic surface is less than 0.1, which is in agreement with the previous studies reported by Karapanagiotis et al. and Basu et al. [2 allowed for a sufficient amount of air entrapment on the surface, thereby lowering the wettability and endowing the graphene/TiO2-coated surface with superhydrophobic properties.The hierarchically structured surface attributed to the graphene and TiOequation , cos θc termined . The resu et al. ,43 The s2 coating are characterized via FTIR, as illustrated in −1 to 3600 cm−1 represent the O−H stretching. The peaks around 1000 to 1200 cm−1 represent the C–O−C stretching of PLA. The peaks of ester are depicted at 1083 cm−1, belonging to the C–O−O stretching vibration, and circa 3000 cm−1, which belongs to the CH3 stretching band. Moreover, the asymmetric and symmetric C−H deformations in CH3 bending are depicted by the peaks at 1454 cm−1 and 1365 cm−1. The carbonyl C=O stretching is depicted as the peak at 1751 cm−1. The bands between 1630 cm−1 to 1800 cm−1 represent the C=C bond [2 produces an intensified peak at 1454 cm−1. The Ti−O stretching band can also be observed at 890 cm−1 and 750 cm−1 [−1 and 1253 cm−1, attributed to the in-plane and out-of-plane bending of the Si−CH3 [−1 and 3000 cm−1 represent C−H stretching, while the peaks between 1000 to 1400 cm−1 represent C−O stretching. The peaks around 1000 cm−1 to 1130 cm−1, which represent the Si–O–Si bands of PDMS, is suggested to be overlapped with the C−O-stretching bands.The chemical functional groups of the graphene/TiOC=C bond ,45,46,47750 cm−1  The peak2-coated film are illustrated in 2-coated surface shows a homogenous distribution of graphene and TiO2 nanoparticles. The uniform coverage of graphene and TiO2 nanoparticles provides a roughness to the surface, which is accountable for the low surface wettability. The graphene nanoplatelets are irregular in shape, whereas the TiO2 nanoparticles appear to have a nanoscopic particle size of less than 50 µm. The hierarchical structure on the coated surface is attributed to the graphene/TiO2 nanoparticles acting as protrusions. The interspacing between the protrusions allows for an adequate amount of air pockets to be entrapped on the surface. As depicted in the 3D images in 2 coating provides protrusions with different heights and interspacing, which help to minimize the contact point of liquid on the surface. This result correlates with the aforementioned porosity factor in 2 nanoparticles. The graphene/TiO2 hybrid nanocomposite confers a higher degree of surface roughness, therefore manifesting a greater reduction in the total surface area of the solid–liquid interface. The mixture of graphene and TiO2 nanoparticles offers an optimal surface roughness, which allows for a sufficient amount of air-layer entrapment, thus furnishing the coated surface with superhydrophobic properties. We suggest that the Cassie–Baxter regime be used for this scenario. The minimal solid–liquid interface, consequently, results in the high-water contact angle, and hence, the superhydrophobic properties.The surface morphologies of the non-coated PLA film and the graphene/TiO2-coated films are evaluated via the water immersion method, according to ASTM D870 [2-coated film (2-coated film decreased by approximately 2° after being immersed in water for 5 h. An additional period of water immersion, up to 24 h, further decreased the contact angles by approximately 5°. Nonetheless, the contact angles of the three different ratios of the graphene/TiO2-coated films remained above 150° at the end of the water immersion test. This indicates that the immersion of graphene/TiO2-coated film in water for a prolonged period does not result in a significant degradation of the coating. In the practical setting, it is not uncommon for medical devices to be in direct contact with body fluids for less than 8 h. The result validates the effectiveness of the graphene/TiO2-coated surface to be utilized for ample time. Hence, this study asserts the durability and robustness of the superhydrophobic graphene/TiO2-coated PLA film and substantiate it to remain functional in the long run.The durability of the graphene/TiOSTM D870 . The rested film . The con2 nanoparticles composite. This study reports the effectiveness of the graphene/TiO2 nanoparticles for fabricating the superhydrophobic surface. The water-repelling effect exhibited by the graphene/TiO2 coating shows a promising antifouling and self-cleaning effect. The strategy herein is proposed as an ideal manufacturing method for superhydrophobic surfaces that are suitable for employment in medical devices. Further investigation is required to study the antibacterial activity, as well as the cytocompatibility, of the graphene/TiO2-coated PLA surface. Nonetheless, this study offers a simple, time-saving, and eco-friendly method of fabricating a durable superhydrophobic graphene/TiO2-coated surface.The PLA films demonstrated superhydrophobic properties upon modification with the graphene/TiO2 with a minimal concentration of 0.5% w/v, via a simple dip-coating method. The graphene/TiO2 coating showed superhydrophobic properties by exhibiting a high apparent contact angle. The apparent contact angle increased with the concentration of nanoparticles. Moreover, the coating of graphene and TiO2 hybrid exerted a synergistic effect by providing an enhanced surface roughness on the PLA surface. It is implied that the structured surface allowed for the entrapment of air pockets, which reduced the direct contact point between the water and graphene/TiO2-coated surface. Therefore, the graphene/TiO2-coated PLA film demonstrated low wettability. Additionally, the ratio of graphene to TiO2 influenced the wettability of the coated surface. In brief, a superhydrophobic surface was achieved by using a minimal amount of graphene and TiO2 nanoparticles. In addition, the graphene/TiO2 coating possesses significant durability and stability by demonstrating low degradation after overnight water immersion. This study shows a promising nanoparticles composite, prepared with graphene and TiO2, that is suitable for introduction into medical devices, where they can deploy their antifouling properties.A superhydrophobic surface was successfully fabricated by using graphene and TiO


The expression of TDP-43, the main component of neuronal intracellular inclusions across a broad spectrum of ALS and FTD disorders, is developmentally regulated and studies in vivo have shown that TDP-43 overexpression can be toxic, even before observation of pathological aggregates. Starting from these observations, the regulation of its expression at transcriptional level might represent a further key element for the pathogenesis of neurodegenerative diseases. Therefore, we have characterized the human TARDBP promoter, in order to study the transcriptional mechanisms of expression. Mapping of cis-acting elements by luciferase assays in different cell outlined that the activity of the promoter seems to be higher in SH-SY5Y, Neuro2A, and HeLa than in HEK293. In addition, we tested effects of two SNPs found in the promoter region of ALS patients and observed no significant effect on transcription levels in all tested cell lines. Lastly, while TDP-43 overexpression did not affect significantly the activity of its promoter (suggesting that TDP-43 does not influence its own transcription), the presence of the 5′UTR sequence and of intron-1 splicing seem to impact positively on TDP-43 expression without affecting transcript stability. In conclusion, we have identified the region spanning nucleotides 451–230 upstream from the transcription start site as the minimal region with a significant transcription activity. These results lay an important foundation for exploring the regulation of the TARDBP gene transcription by exogenous and endogenous stimuli and the implication of transcriptional mechanisms in the pathogenesis of TDP-43 proteinopathies. After initial implication in the pathogenesis of monosymptomatic forms of cystic fibrosis7, it has been discovered a direct association between TDP-43 abnormalities and neurodegenerative diseases, and in particular with Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Degeneration (FTD)9 was discovered. Over the last years, TDP-43 immunoreactive inclusions have also been reported in 70% of patients with hippocampal sclerosis, 30% of patients with Alzheimer's disease, 33% of patients with Pick's disease and in a subset of patients with Lewy-body related disease17. Whereas many efforts have been expended in characterizing TDP-43 pathophysiological functions, a contentious debate ensued and is still ongoing over the possible mechanisms whereby TDP-43 triggers neurodegeneration. It has been proposed both that cytoplasmic aggregates might be neurotoxic ("gain of function" hypothesis) and that the sequestration of the factors in aggregates might induce a functional deficiency resulting in alteration of the TDP-43-regulated processes ("loss of function" hypothesis)22. Of course, the two hypotheses are not necessarily mutually exclusive, and studies with animal models have shown that TDP-43 overexpression can be neurotoxic, even without presence of inclusions in worms23, flies26, mice33, and monkeys34. Importantly, mice expressing the mutant A315T TDP-43 mice show a dose-dependent degeneration of cortical and spinal motor neurons, without evidence of cytoplasmic TDP-43 inclusions32. These studies suggest that even an increase in TDP-43 can contribute to neurodegeneration without occurrence of aggregation. In addition, elevated levels of TDP-43 has been found in the cerebrospinal fluid37 as well as in plasma of ALS40, FTD and Alzheimer42 patients, and in FTD patients carrying C9orf72 expansion or GRN mutations, plasma phosphorylated TDP-43 levels have been found to be higher than in healthy controls43. On the other hand, it is now well established TDP-43 levels are tightly controlled: in fact, it has been demonstrated that TDP-43 can regulate its own expression through a negative feedback loop51. Altogether these observations suggest that regulation of TDP-43 expression at transcriptional level might also be implicated in the pathogenesis of neurodegenerative diseases.TAR DNA-Binding Protein 43 (TDP-43) is an ubiquitously expressed and highly conserved nuclear protein encoded by the human TARDBP gene, and it is involved in several cellular mechanisms, including transcription, pre-mRNA processing, splicing and translation52. However, no functional studies have been so far carried out.The study of the TARDBP gene promoter is therefore useful to shed further light on the pathogenesis of TDP-43 proteinopathies. Interestingly, two SNPs were found within the promoter sequence of TARDBP gene in ALS patientsIn this work, we have characterized the cis-acting elements important for TARDBP gene regulation and evaluated its cell-type specificity. Subsequently, we have characterized the possible impact of some cis-acting elements (SNPs and 5′UTR), trans-acting factors (TDP-43 itself) and events (splicing) on the transcriptional activity of TARDBP promoter.TARDBP gene sequence (Ensembl gene ID: ENSG00000120948) was initially performed by a bioinformatic analysis using the UCSC Genome Browser (GRCh37/hg19). The TARDBP gene, mapped to chromosome 1p36.22 region, spans 12870 bp from position 11,072,679 to 11,085,548 on the forward DNA strand. Figure http://dbtss.hgc.jp54), most of transcription start sites (TSS) mapped at the corresponding positions indicated in the Reference Sequence NM_007375  failed to detect the main core promoter elements. These observations suggest that the expression of the human TARDBP gene is driven by a TATA-less promoter.Subsequently, by querying the Eukaryotic Promoter Databasehttp://www.ensembl.org/). Alignments were performed using MUSCLE software57. Among primates, we compared the genomic sequences of the putative TARDBP promoter region from Hominoidea , from of New World monkey  and from Old World monkey . In general, this comparison highlighted that the relative degree of similarity among all three species increases significantly with respect to the proximity of the TSS. Then, in the region spanning from nucleotide -1316 to -1000 upstream from TSS, the hominoid sequences seem to be closer to each other than with that of New and Old World monkeys. On the other hand, in the region spanning the 1000 nucleotides upstream from TSS, the sequences from all primates show a high degree of identity , without outlining regions evolutionary conserved between these two species (data not shown).In order to study the evolutionary conservation of TARDBP promoter, the 1316 nucleotides upstream of the TSS of TARDBP transcripts from human and other species were retrieved using GenBank and Ensembl Genome Browser  to 1316, 927, 451, 380, 320, 280, 230 and 180 nucleotides upstream from the TSS  and the luciferase activity of each construct was normalized versus the 1316 construct .Intracellular analysis showed that most of the promoter activity was retained in the fragments spanning from 1316 to 451 nucleotides upstream from the TSS within all tested cell lines  and in HeLa cervical carcinoma cell line than in HEK293 embryonic kidney cells  has revealed two promoter variants (c.1-562t>c and c.1-100t>c) with a different frequency in patients than in controls 52. The c.1-562t>c single nucleotide substitution  was found in homozygosity (C/C) at higher frequency and in heterozygosity (T/C) at lower frequency in sALS patients, as compared to controls . On the other hand, the c.1-100t>c polymorphism  was present only in heterozygosity (T/C) at higher frequency (0.2 vs 0.1) than in controls52.The analysis of pathogenic mutations found in the Therefore, we sought to test the impact of these SNPs on the transcription of TDP-43, in order to find a possible functional correlation with the manifestation of ALS. In order to analyze the SNP effects alone or in combination, we created three variants of our 927 original pGL4 construct , so reproducing all the possible alleles ,  and  Fig. A. The co62 and was used as it allows a more homogenous TDP-43 expression from a Tetracycline inducible expression vector.After characterizing the sequence of the promoter of TARDBP gene and its activity in different cell lines, we wished to evaluate the ability of TDP -43 to influence, directly or indirectly, the synthesis of its own transcript. For transfections of these constructs, a stable HEK293-flp-in cell line carrying a single copy of flag-tagged wild type human TDP-43 (HEK-TDP43wt) was used. This cell line was generated in our laboratoryThe HEK-TDP43wt cells were transfected with the constructs 451, 927, and 1316 . Subsequently, TDP-43 expression was driven by Tetracycline induction (48 h) and its levels were probed by Western blotting  and the first 12 bp of exon 2, separated by intron 1 (972 bp). In order to explore the presence of additional elements able to modulate TDP-43 expression, the functional impact of the 5′ UTR (construct 451 + Ex1Ex2) and intron 1 (construct 451 + Ex1-IVS1-Ex2) of mid Fig. A. A firs63. Considering the higher mRNA levels derived from the intron-containing construct (451 + Ex1-IVS1-Ex2 wt), to prevent the possibility that the decay machinery might be saturated by the spliced mRNAs, we used proportionately less of this construct, while keeping constant the amount of total transfected DNA. While it was not possible to determine the half-life of the 451 + Ex1-IVS1-Ex2 mut mRNA (whose expression was negligible), the mRNA species of both the 451 + Ex1-IVS1-Ex2 wt and the 451 + Ex1Ex2 constructs exhibited half-lives of ∼ 7 h, indicating no significant differences in mRNA stability dependent on splicing  outlined how, in most TDP-43 transcripts, transcription starts from the TSS indicated in the main transcript isoform NM_007375. Regarding the spatio-temporal expression pattern, TDP-43 is a developmentally regulated protein64, while its distribution in adult tissues seems to be ubiquitous64. These observations are consistent with the hypotheses supported by recent studies reporting that TATA box is present in only a minority of promoters67, often with tissue-specificity such as liver and muscle70.We have experimentally characterized the promoter region of the human TARDBP gene. A previous prediction indicated that the core regions of the TARDBP promoter could be located between 500 nucleotides upstream of exon 1 and 66 nucleotides downstream of exon 1 and in two regions of intron 1 (212 and 613 nucleotides)From an evolutionary perspective, it is interesting to note that, among primates, the greatest degree of evolutionary conservation encompasses the 600nts upstream of the TSS. On the other hand, the alignment of human and rodents sequences highlights the 200nts upstream of the TSS as the region of higher homology. These observations suggested that the region in-between plays an important role in directing transcription of the TARDBP gene. Indeed, this hypothesis is consistent with the experimental mapping performed in this study that has outlined the region spanning nucleotides 451–230 as necessary for the minimal promoter activity in all the tested cell lines  cellular toxicity or alteration of the TDP-43-regulated gene expression. Understanding the factors that control TDP-43 expression within cells will certainly provide a better insight into disease origin and progression. Indeed, it has been observed that an increase of TDP-43 protein levels can activate the aggregation process in both cytoplasmic and nuclear compartmentsLooking for potential modifiers of the TARDBP promoter activity, we have focused the attention on two SNPs  previously identified within the TARDBP promoter of SALS patients. Although the variants do not change any transcription factor binding site, we have functionally tested their transcriptional impact. Although, in our system, we did not find statistically significant differences in the promoter activity of each haplotype, we can hypothesize that the potential regulatory SNPs do not lead to variation of TARDBP promoter activity directly, but cannot exclude that other possibilities of how these may affect transcription levels do exist. The variants might affect transcription at endogenous copy numbers, but not for overexpressed exogenous constructs. In addition regulatory elements, outside the promoter region included in our reporter plasmid and might interplay with the variants and modulate the activity of the promoter.75, we verified if there are transcriptional effects of TDP-43 on its own promoter activity and it does not modulate its own transcription.Subsequently, since TDP-43 autoregulates its own expression through a negative feedback mechanism via direct interaction with its own 3′UTR76, we next sought to test the possible effects of the TARDBP 5′UTR and intron 1 splicing on the expression of the associated reporter gene  indicated that this element can positively influence gene expression. Consistently, recent studies have shown that approximately 35% of human 5′UTRs are annotated as harboring introns64, in a cell specific fashion, and, through aging, these fluctuations are evolutionary conserved at least in mice and flies59. Notwithstanding there are no clear data of age-related changes in TDP-43 in human83, altogether these observations suggest that a better understanding of the mechanisms and factors involved in controlling the activity of the TARDBP promoter and, consequently, TDP-43 expression will give clues to uncover novel processes implicated in the onset and progression of the TDP-43 proteinopathies.In conclusion, growing lines of evidence suggest that the pathophysiology of ALS, FTD and other neurodegenerative diseases might be the consequence of the convergence of multiple risk factors acting also on changes of TDP-43 levels. Indeed, TDP-43 expression can be modulated during developmentThe 1316 bp region upstream of the TARDBP TSS was amplified by PCR and cloned in pGEM-T easy vector. The 1316 bp insert was digested with the restriction enzymes KpnI and HindIII (these sites were designed into the primers used in PCR) and subcloned into the pGL4.1 vector  digested with the same restriction enzymes. Other 7 deletion-mutants of TDP-43 promoter  were then generated by PCR using gene-specific forward primers and the pGL4-1316 construct as template. Deletion-mutant inserts were KpnI-HindIII-subcloned in the pGL4.1 vector. TARDBP promoter SNPs were generated by PCR mutagenesis. The identity of all constructs was verified by DNA sequencing. Primer sequences are available.The cell lines used for transfections were the following: HEK293, HeLa, Neuro2A, and SH-SY5Y. Each construct was transfected in duplicate, 600 ng of DNA was diluted in a final volume of 100 µl with Opti-MEM I Reduced Serum Medium . To normalize for transfection efficiency, the cells were co-transfected with 20 ng/well of pRL-TK  plasmid along with the promoter constructs. In parallel, 98 µl of Opti-MEM were added to 2 µl Lipofectamine 2000 Reagent . After 5 min. at room temperature, the two solutions were combined and mixed, and 20 min later, the growth medium was removed from the cells and replaced with fresh DMEM containing 5% FBS. Then, the transfection mix was added to each well.44.Total cell lysate was prepared from cells 48 h post transfection and firefly luciferase activity was assayed using the Beetle-Juice KIT  and a Turner Design 20/20 Luminometer . Control transfections with pGL4.1 empty vectors were used as negative controls. Data presented are mean ± Standard deviation (SD) of at least three independent experiments and given as fold expression overexpression indicated in the Figures set arbitrarily at 1. Statistical analysis was performed using Student’s T or ANOVA tests. In order to verify the possible influence of TDP-43 on its own promoter, we used the previously generated human stable cell line Flp-In HEK293 -TDP-43 wild type, carrying the human TDP-43 transgene locus-specific-integrated, whose expression is driven by an inducible version of the Tetracycline (Tet) promoterOne day before transfection, Flp-In HEK293 -TDP-43 wild type (wt) cells were seeded at 60% confluence. Lipofectamine reagent was used for transfection with 300 ng of the reporter plasmids and 20 ng of pRL-TK vector. After 12 h, the medium was changed, and the cells were incubated further for 24 h. Flag-tagged TDP-43 expression was induced with 1 µg/ml tetracycline. The luciferase/renilla activities were then assayed and statistical analyses were performed using Anova one-way followed by Tukey's test.In order to quantify the mRNA levels of the 5′UTR TDP-43 constructs, co-transfections of luciferase constructs and pRL-TK were carried out as described in the section "Transfections and Luciferase assays".84 and the expression levels were numerically expressed as the ratio of applicant density of the target amplicons over that of GAPDH.Relative expression of constructs 451, 451 + Ex1Ex2, 451 Ex1-IVS1-Ex2 wt and 451 Ex1-IVS1-Ex2 mut constructs was performed by semi-quantitative RT–PCR and by quantitate Real Time PCR. Forty eight hours after transfection, cultures were terminated and RNA was extracted with Trifast reagent , according to manufacturer’s instruction. In the semi-quantitative RT–PCRs, GAPDH was used as internal control. The sequences of primers were (5′–3′): GAPDH_Ex1s, 5′-CGCTCTCTGCTCCTCCTGTT-3′; GAPDH_Ex2as, 5′-CCATGGTGTCTGAGCGATGT-3′; TDP-43 Ex1 + 9 (277 bp)_s, 5′-AGCTTGCGCCATTTTGTGGGAGCGA-3′; Luc ATG + 155(277 bp)_as, 5′-GTAATGTCCACCTCGATATGTGCGT-3′. Optical density of amplicons was calculated using the ImageJ image processing programQuantitation of the 5′UTR TDP-43 mRNAs by Real Time PCR, co-transfections of luciferase constructs and pRL-TK were carried out as described in the section "Transfections and Luciferase assays". The extracted RNA (1 µg) was DNAse-treated and reverse-transcribed using the M-MLV reverse transcriptase , and oligo-dT (0.2 µg/reaction as primer), in a final volume of 40 µl, essentially as indicated in the manufacturer's instructions. The CFX96 real-time PCR detection system  was used for all qPCRs. SYBR green assays were optimized  with the iQ SYBR Green Supermix (Bio-Rad), according to the manufacturer's instructions, using tenfold serial dilutions of cDNAs. The amplification mixture consisted of 0.2 μM primers, 5 μl of SYBR Green Supermix, and 4 μl template DNA in a total volume of 10 μl. Samples were amplified with the following program: initial denaturation at 95 °C for 2 min, followed by 40 cycles of denaturation for 15 s at 95 °C and annealing/elongation for 30 s at 60 °C. The expression of the co-transfected renilla orf was used to normalize the luciferase qPCR data.Primer sequences were: Luciferase (62 bp), forward 5′-CACAAAGCCATGAAGCG-3′ and reverse 5′-ATATGTGCGTCGGTAAAG-3′; Renilla (140 bp), forward 5′-CAGAACAAAGGAAACGGATGA-3′ and reverse 5′-CGCGTTACCATGTAAAAAA-3′.85.Melting curves were examined to determine the specificity of each product and relative expression data were calculated with the ΔΔCT method85.For experiments with actinomycin D, SH-SY5Y cells were transfected with 3000 ng of no-intron constructs  or of the 451 Ex1-IVS1-Ex2 mut plasmid or 600 ng of the 451 Ex1-IVS1-Ex2 mut construct in a p100 plate. Total DNA was normalized to 3000 ng by adding an appropriate amount of pUC18 vector. Twelve hours later, cells deriving from each transfection were harvested and plated in different wells (one for each actinomycin incubation time point). Twenty-four hour after plating, actinomycin D (5 μg/ml) was added. The relative levels of the indicated mRNAs were assessed at the designated time points, following shutoff of transcription using qRT-PCR. Samples were collected at the indicated times using TRIzol. Total RNA from these samples was analyzed via qRT-PCR using the abovementioned Luciferase primers and normalization was carried out versus the housekeeping gene RPII . Relative transcript abundances were determined using the ΔΔCt methodCells extracts were prepared in PBS containing 1 × protease inhibitor . Proteins were separated by SDS-PAGE and transferred to nitrocellulose  and protein detection was carried out with standard Western blotting techniques. After transfer, membranes were incubated for 10 h in blocking solution  to prevent non-specific binding. Subsequently, membranes were incubated for 1 h at room temperature with specific primary antibodies diluted in blocking solution. Expression levels of both endogenous and flag-tagged human wild-type TDP-43 was monitored by using a commercially available polyclonal anti-TDP-43 antibody . Endogenous tubulin was used as a loading control, using an in-house made mouse monoclonal antibody. Immunoblots were developed by using the ECL Star Enhanced Chemiluminescent Substrate .Supplementary Figures.