Photothermal therapy is an emerging method of cancer treatment in which tumors are ablated by heating agents using near-infrared light (700–1000 nm). A semiconductor with a band gap between 0.3–0.7 eV would therefore efficiently emit near-infrared light. The new “magic” material graphene has a band gap of zero, which is advantageous with regard to designing a new material with a suitable band gap for the emission of near infrared light. In our investigations, using the first principles density functional theory calculation method, we aimed to and successfully designed graphene-based materials with a direct band gap of 0.68 eV. They have the potential to be optimal and efficient near-infrared light sources, due to their narrow yet fitting band gap. The present results open up a new avenue for the application of graphene-based materials to assist in photothermal therapy. Biomedical engineering; Materials chemistry; Materials science; Oncology; Physical chemistry; Photothermal therapy; Band gap; Graphene; First principle calculation. The Photothermal therapy (PTT) is less damaging among other cancer treatment methods largely due to its creative use of heat . This apin vitro drug delivery as well as in vivo cancer treatment using a near-infrared laser source [Graphene has various potential applications in the biomedical field . In recer source . Moreover source , 20.This indicates that graphene oxide is an effective photothermal agent with an absorbance ability which is comparable to that of gold nanoparticles and carbon nanotubes . HoweverIn this research, we used first-principles calculations to tune the band gap of graphene-based materials using the method of doping with different elements. In order to achieve the band gap within the aforementioned range to emit near infrared light , we depoOur first-principles calculations, based on the density functional theory (DFT) method, are discussed in Section 2We performed first-principles calculations based on the DFT , 26, 27 The ABINIT  package −10 Hartee/Bohr. Structural optimization was performed using.The convergence criterion for total energy calculations in the self-consistent field (SCF) iterations were set to 10−6 Hartree/Bohr.Broyden-Fletcher-Goldfarb-Shanno method (BFGS)  and the First of all, we needed to perform convergence for kinetic energy cutoff, k-point mesh and vacuum height. The convergence criterion for the total energy were less than 0.0001 Hartree for two consecutive SCF cycles. In order to deposit impurities on top of a graphene sheet, we used the above mentioned converged kinetic energy cutoff, k-point mesh and vacuum height values to perform optimization. The atom position and the size of the unit cell were relaxed until the equilibrium state was reached. In the next step, we used all the above-mentioned converged parameters and optimized the atom position and unit cell to calculate the converged charge density for the future band structure calculations.1, a2, a3 are the real space lattice vectors.The 3D Bravais lattice is expressed using the real space translational vector:1, b2, b3 are the reciprocal space vectors.The corresponding reciprocal space translational vector G can be expressed using:In order to perform band structure calculations, the first step was to compute the self-consistent total energy so all k-point sets could be calculated automatically with the.Monkhorst-Pack scheme . The resWe first have performed calculations of the atomic structure and band structure of pure graphene with the slab model and converged vacuum height. We used 2 × 2 supercell to calculate graphene doped with oxygen , boron , nitrogeGraphene was interstitially doped using oxygen, boron and nitrogen. Each element was deposited on three typical doping sites, with either the doping element located directly on top of a carbon atom (T-site), at the center of a hexagonal (H-site) or the midpoint of a C–C bond (B-site); all three positions are shown in Additionally, graphene was substitutionally doped using germanium, tin, and silicon elements.λ represents wavelength and c is the speed of light. For a given frequency, the band gap is represented by Eλ. In near-infrared light, the wavelength is 700–1000 nm and the corresponding band gap is 0.34–0.73 eV.The relationship between band gap and the color of light is given by the following equation:3Before relaxing the lattice vectors, we performed convergence calculations to obtain the most accurate energy cutoff, k-points and vacuum value for each element. In −5 Hartree/Bohr. The optimized lattice constants are listed in We used oxygen, boron, nitrogen, germanium, tin and silicon to dope pure graphene. For our elements using interstitial doping, oxygen, boron and nitrogen, we have selected three typical positions for each dopant material, so in total, we have optimized nine atomic structures. In addition to the interstitial doped materials, we have optimized three structures using substitutional doping for germanium, tin and silicon elements. Using our previously converged values, we optimized the lattice constant and atomic positions for all of the doped graphene materials with the criterion requiring 1.0 × 10In order to perform band structure calculations, we have first performed total energy calculations for all the materials. Using the three converged values, the kinetic energy cutoff, k-point mesh and vacuum height as well as the optimized lattice constants and atomic positions, we performed total energy calculations, resulting in obtaining the converged charge density. Using the converged charge density, we performed non-selfconsistent band structure calculations for the nine materials. In the final step, utilizing all the values we had obtained thus far, we plotted the band structure and calculated the band gap of each material. For the doped materials, we chose the smallest of the band gaps out of the three sites  that still fit in the ideal range. The results are presented in In Figures 4Photothermal therapy needs a specific band light to excite a photosensitizer to a state where it is able to absorb vibrational energy in order to ablate the target tumor. Nanomaterials have been prime candidates in photothermal therapy as ablation agents to convert light to heat, due to their optimal optical absorption and electrical capabilities , 41. In In order to save experimental resources, theoretical calcations are required. Prior to an elevated concentration of attention and resources with respect to manufacturing materials for photothermal therapy, it was necessary to first optimize potential nanomaterials. Our research engineered twelve potential nanomaterials through doping, nine of which utilized interstitial doping and three of which utilized substitutional doping. Oxygen-, boron-, and nitrogen-doped graphene, each doped at the H-, B-, and T-site, constituted the nine interstitially doped materials, where a dopant atom was deposited on a graphene layer. Tin-, germanium-, and silicon-doped graphene constituted the three substitutionally doped materials, where a carbon atom was replaced with a dopant atom within the graphene structure. Boron doped graphene at the B- and T-site proved suitable as a nanomaterial to convert light to vibrational energy for tumor ablation, with band gaps of 0.69 eV and 0.68 eV respectively, fitting in the optimal range of 0.3–0.7 eV, in excellent agreement with previous calculations . The ideSince photothermal therapy operates through using near-infrared light lasers to ablate tumors on a patient, this method will most likely remain an option for malignancies near or on the surface of a cancer patient's body. However, if a more invasive tactic is needed due to tumors in the depths of a body cavity, photothermal therapy reaches its apex of effectiveness when used before or in conjunction with chemotherapy , 44 and Photothermal therapy is a relatively new and innovative treatment for many conditions, primarily cancer. The main obstacle hindering photothermal therapy from becoming a common and reliable treatment for cancer in the healthcare industry is the inefficient and inconsistent ability of materials used in the involved procedures. Using the knowledge of existing potential materials in the scientific sphere and theoretically engineering and testing compounded products, a choice nanomaterial to streamline the procedure of photothermal therapy will certainly be discovered. The breakthrough of photothermal therapy as an emerging treatment in the medical field will renew the simple and effective concept of utilizing heat to attack malignancies, bringing a non-invasive and less risky method into the realm of cancer treatment.5A wide range of materials have been introduced into the testing of photothermal therapy, depicting the high potential of this non-invasive and emerging cancer treatment. With the wonder material, graphene, as the base of our twelve nanomaterials, the potential for a successful ablation agent is large. Through our DFT calculations within the Abinit computational program suite, we found boron-doped graphene to be an unexpected but possible contender as an ablation agent in photothermal therapy, resulting in a band gap of 0.69 eV at B-site and 0.68 eV at the T-site. The band gap of boron-doped graphene matched the wavelength of near-infrared light, deeming it as an effective convertor of vibrational energy. As a possible ablation agent, boron-doped graphene holds many possibilities. Ablation agents in photothermal therapy require further evolvement to become multifunctional, as a drug carrier or contrast agent. In conclusion, our research serves to primarily theoretically optimize the chosen materials to be used in photothermal therapy, to save resources and money for the future of this treatment, prior to serious testing. Our research also serves the purpose opening a new avenue in the search of an ablation agent through the doping of graphene to create unique nanomaterials, which comprise a vast range of possibilities regarding the future of the medical field.The raw/processed data required to reproduce these findings can be available via special request to the author.Faith Cheung: Conceived and designed the experiments; Performed the experiments; Analyzed and interpreted the data; Contributed reagents, materials, analysis tools or data; Wrote the paper.This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.The authors declare no conflict of interest.No additional information is available for this paper.


It hinders native nucleation centers and breaks the propagation of defects through the layers, protecting from prolonged exposition to all common solvents found in biochemistry work, contrary to commonly used polymeric passivation. Since wet etch does not allow the required level of control over the lithographic process, a reactive ion etching process using a sacrificial metallic stopping layer is developed and used for patterning the passivation layer. The process achieves devices with high reproducibility at the wafer scale.This work is on developing clean-room processes for the fabrication of electrolyte-gate graphene field-effect transistors at the wafer scale for biosensing applications. Our fabrication process overcomes two main issues: removing surface residues after graphene patterning and the dielectric passivation of metallic contacts. A graphene residue-free transfer process is achieved by using a pre-transfer, sacrificial metallic mask that protects the entire wafer except the areas around the channel, source, and drain, onto which the graphene film is transferred and later patterned. After the dissolution of the mask, clean gate electrodes are obtained. The multilayer SiO Since first obtained by the exfoliation of graphite , graphen2O3 or SiO2 film [Graphene is a zero bandgap material that generates electrons and holes under an applied transverse electric field, which is a process known as electrostatic gating . TherefoiO2 film . In thisiO2 film ,11.EG-GFETs are commonly built without the reference gate electrode , which ix) and silicon oxide (SiO2) layers [2 is much more permeable to ions than SiNx. A higher permeability may allow ions from the test solution to reach the current lines and cause drift, cross-talking between electrodes, or corrosion of the metallic contacts [When designing EG-GFETs, it is crucial to consider their application, e.g., the device’s environment, to decide design and fabrication steps. Electrolyte gating implies using liquids on top of semiconductor materials that typically degrade upon contact with aqueous solutions. Moreover, both semiconductor and dielectric materials are prone to host ions that diffuse inside their lattice, degrading the materials or rendering electronic measurements unstable. Therefore, the passivation of all surfaces in contact with the electrolyte, except graphene, is recommended to prevent/minimize such effects . The pas) layers ,14. An a) layers , reduce ) layers , reduce ) layers . Thus, w) layers  to avoidcontacts .2 or SiNx layers allows exposing the devices to all solvents without compromising the passivation. However, it implies more complex lithographic and etching processes, thus increasing the fabrication cost. In conclusion, it is of paramount importance to keep in mind the application of the EG-GFET when designing the passivation of current lines.While using epoxy resins such as SU-8 negative photoresist provides a relatively inexpensive and straightforward process, it imposes a limit on the use of strong solvents in contact with the fabricated devices. For example, dimethylformamide (DMF) as a graphene cleaning agent after wafer fabrication and as a solvent in the graphene’s non-covalent functionalization  would noAn important consideration is to decide at which point of the fabrication process the passivation layer should be added. Overall, lithographic processes involving aggressive patterning steps  should be avoided once graphene is transferred onto the wafer since they increase the amount of residues left on graphene . Therefox/SiO2, the process implies more aggressive steps, e.g., plasma-based etching or sputtering depositions that can affect graphene integrity [Passivation based on photoresists is done in a relatively straightforward process, using one lithographic step only followed by development in solution (a mild process) and sometimes a final bake to harden the layer. However, for passivation based on SiNntegrity . Some auntegrity . HoweverDependence on wet etch processes always limits reproducibility and process upscaling . There aAnother critical step in EG-GFET fabrication is the graphene transfer. For applications requiring electronic grade material, there are few choices available beyond mechanically exfoliated graphene from highly oriented pyrolytic graphite (HOPG), Chemical Vapor Deposition (CVD) being one of them . Still, Although wet transfer methods of CVD-grown graphene give the most promising results for the large-area fabrication of GFETs, there are still challenges related to surface contaminants ,26 oftenMaterials used for microfabrication of EG-GFETs are listed in Confocal Raman spectroscopy  is used to confirm single-layer graphene presence in transferred samples and detect variations in graphene quality after microfabrication processes. Raman data analysis is done using WITec Project FOUR+ software, Ulm, Germany. All samples are analyzed using a 532 nm Nd:YAG laser for excitation. The laser beam with power in the range 2 to 3 mW is focused on the sample by a ×50 lens , and the spectra are collected with a 600 groove/mm grating using 5 acquisitions each with 2 s acquisition time. Within each experiment, the laser power is fixed to allow comparison of the acquired data.Scanning Electron Microscopy (SEM), FEI NovaNanoSEM 650, Hillsboro, OR, USA, is used to study surface features and energy-dispersive X-ray spectroscopy (EDX) analysis. SEM images are collected in the secondary electron imaging mode at a 5 mm working distance and an operating voltage of 5.0 or 10.0 kV, depending on the materials to be analyzed and the probing depth desired. EDX acquisition using Oxford Instruments INCA software, Oxfordshire, UK, is performed on selected regions from SEM images to confirm surface chemical composition and detect surface contaminants after completing the fabrication process.2 plasma-based etching steps.KLA—Tencor P-16 Surface Profiler, Scotia, NY, USA, is used to measure photoresist films’ step height after O2 and SiNx films’ thickness, using a deuterium–tungsten halogen light source. The thickness is determined by fitting to a model using reflected light between 40 and 800 nm.OPM Nanocalc—Optical Profilometer/Interferometer, Ettlingen, Germany, is used to estimate SiONikon Ni-E optical microscopes, Tokio, Japan, are used to visually assess the sample surface after each of the fabrication steps.SD), and the source–drain current (ISD) is measured. The high-impedance gate circuit is formed between gate and source contacts. It is biased by applying a voltage (VGS) by a Keithley 2400 source meter, Cleveland, OH, USA, which is programmed to apply voltage ramps from 0.2 to 1.2 V in steps of 0.01 V. All the measurements were performed using 10 mM phosphate buffer as gate electrolyte to close the circuit.For acquisition on the transfer curves of the fabricated EG-GFET samples, the source and drain contacts of each transistor are connected to a Keithley 4687 Picoammeter, Cleveland, OH, USA, which applied a constant (1 mV) source–drain voltage  and measuring the channel’s current, using a Keithley 2400 source meter. No liquid electrolyte is added to the devices, and no gate voltage is applied (the gate contact is left floating). Channel resistance values by the device are obtained by processing the current measurements using MATLAB scripts.In this study, graphene is grown by CVD in a hot-wall reactor  on high-purity Cu catalysts and transferred see . The pro3 solution that stay attached to the graphene film’s bottom side that stick to the surfaces to which graphene is transferred, as shown in 3 solutions and sequential dissolutions can improve the removal of Cu clusters. Regardless, small Cu atomic clusters and ions are always observed in the surfaces after graphene transfer, as shown by PIXE studies [Graphene transfer and patterning are crucial steps in the fabrication of graphene devices. Except for automated, continuous transfer systems , which a studies . Those p studies ,31. This2 partial pressure since they influence the etching efficiency and the exposure time that the photoresist can sustain. However, the process is dependent on the size of the etched area. For example, etching small substrates with a few tens of square centimeters is very different in etching time and uniformity than etching a 200 mm-wafer due to changes in the plasma current at the surface of the sample [The most common way to pattern graphene is reactive ion etching, using an oxygen plasma that readily attacks and removes carbon . For dene sample ,33.2 plasma time indicate that the photoresist is etched much faster when using the ICP O2 reactive ion etching (RIE)  b than wha source a. ECR shConsidering the etching times allowed by both methods, samples with pre-patterned contacts and graphene are patterned. For the ECR plasma source, the sample is coated with AZP4110 at 2200 nm  to maximize the etch time. The sample is etched for a total time of 18 min divided into 6 min etching periods . For the ICP plasma source, the sample is coated with AZ1505 at 1035 nm  and etched for 10 s. According to the values in 2 plasma is also expected to remove graphene transfer-related residues  from the surface. However, the optimal time for graphene patterning without removing the photoresist is usually not enough to achieve good surface cleaning. The use of low ECR-power O2 plasma requires increased time of process. Still, it allows for improved control of the system temperature, improving photoresist stability, reducing at least 10 times in the photoresist etch rate. With longer times, organic residues’ removal from the surface is also improved, and graphene is efficiently etched from a full 200 mm wafer in less than 18 min. Therefore, in the following, ECR-O2 plasma is preferred whenever the dry etching of graphene is required.High power processes (above 1000 W ) are hig2 plasma etching is removing metallic particles or other non-organic transfer-borne residues. These residues that come adsorbed to the backside of graphene upon transfer are not removed by O2 plasma and hinder device performance, as detailed above. A more elaborate strategy is necessary, preventing direct contact between residues and chip surface. In the next section, a lift-off process is studied to limit the wafer surface’s contamination by debris resulting from the graphene transfer process.The limitation for ECR-OA lift-off inspired process could be an alternative to the standard dry etch patterning, allowing minimum contact of graphene with unnecessary/undesired regions of the surface and achieving a cleaner fabrication process. It is our experience that when transferring graphene over a surface with relatively steep steps (above 100 nm), the film likely breaks and tears apart (crack propagation) at the step region. Therefore, using a lift-off technique to transfer graphene only to the wafer regions where transistor channels form should be possible. For lift-off assisted wet transfer, a sample with gold contacts is spin-coated with photoresist (AZ1505 1035 nm or AZP4110 2200 nm) and patterned by optical lithography. The transfer region is left unprotected, as schematically shown in Graphene transfer is performed as described in the The optical images in The clear advantage achieved with the lift-off strategy is the final quality of the device surface. Based on the results of A test sample was prepared using 2200 nm AZ4110 photoresist for the lift-off assisted graphene transfer. After transfer and PMMA removal, inspection by optical microscopy accesses the quality of the patterning. Although the features were large and well separated, 2 plasma using a photoresist mask. Any contaminants not removed by the oxygen plasma are removed together with the hard sacrificial mask. The contaminants possibly deposited with graphene on the source and drain are not avoided. Still, they do not significantly affect the device performance, since they are not in contact with the biological solutions.The previous sections show that lift-off patterning graphene films produce inferior results compared to patterning standard materials by the same technique. Consequently, a novel methodology is developed, as schematically shown in 2O3 film was sputtered for physical separation of the Au surfaces from the sacrificial metal layers, avoiding inter-layer diffusion. Films with 10 and later 20 nm of Al2O3 were used to ensure this layer’s stability during aluminum etch (the etchant is the same for both Au and Al2O3). The next layer in the stack is AlSiCu, the protective layer that avoids residues to deposit on the devices’ surface. The capping layer is TiW(N) to allow all lithographic processes (the photoresist developer quickly dissolves AlSiCu and is too reflective for precise laser exposure). Al2O3 may replace TiW(N) as a capping layer to avoid repeated use of H2O2 to etch TiW(N), which increases the risk of damaging graphene , leaving the graphene intact. With that in mind, it was designed as follows: first, a buffer Alhene see .2O2 removes TiW(N), or AZ400k 1:4 developer removes Al2O3, depending on which material was used as the capping layer. AZ400k can etch both Al2O3 and AlSiCu, so it is used to etch the adjacent AlSiCu layer. The etch rate of AlSiCu is 10 times higher than that of Al2O3, so the etch time is adjusted to preserve the Al2O3 buffer layer. However, optical images after the process . This forces stopping the fabrication process, since gold is no longer protected.At the point of the fabrication sequence where the sacrificial layer is added, only the contacts have been patterned, and so a standard lift-off can be used with no risk of damaging underlying layers. Thus, after a lithographic step that leaves the photoresist protecting the source, drain, and channel, the sacrificial layer stack is deposited by sputtering followed by lift-off using acetone and ultrasonic bath. Next, graphene is transferred by wet transfer a, and PM2O3 thickness could improve this result. However, it is difficult to envision because Al2O3 needs to be later selectively removed  was deposited between the buffer layer of Al2O3 and AlSiCu. In this way, the wet etch of AlSiCu is accomplished with no attack on the Al2O3.A further increase in AlFollowing the above process, a new sample is prepared and observed with the optical microscope revealing spotless surfaces with well-patterned graphene transistors, as seen in 2O3 as a capping layer: partial removal of the sacrificial layer occurs upon graphene transfer  should be chosen, because the HCl residues do not degrade it. Then, it should be as thin as possible to reduce the photoresist/graphene exposure time to H2O2 during TiW(N) etch.A final comment on the use of TiW(N) or Altransfer  due to H2O2 30% 150 s, then AZ400K 1:4 240 s, H2O2 30% 50 s. This stack proved useful in avoiding residues in the gold gate electrode since, after this process, the Al2O3 film on top of gold is particle-free.For these reasons, the sacrificial layer stack was defined as TiW(N) 5 nm/AlSiCu 100 nm/TiW(N) 15 nm. The wet etch process to remove it was H2 and SiNx films with a total thickness of 250 nm is designed, starting with a layer of SiO2 to take advantage of the good adhesion of SiO2 to graphene and the substrate, and terminating with SiNx to take advantage of the superior impermeability of SiNx. The multilayer, deposited by plasma-enhanced CVD (PECVD), hinders native nucleation centers and breaks the propagation of defects through the layers, creating tortuous diffusion paths for water and other small molecules [Before designing the passivation layer, several points need consideration. First, consider the final use of the devices. In our case, a clean biosensing interface is obtained by the use of strong solvents   that attolecules ,36. All 2, each containing 36 chips of 20 EG-GFETs, were fabricated as described in For testing, samples of 4 × 4 cmSome reports refer to dry etching methods  to open First, dry etching is used to open the top layer of the passivation stack d. Many a2/SiNx stack delamination, as shown in 2 film under the SiNx during the KOH wet etch process, promoting the top layer’s stress release by peeling  . However2O3, AlSiCu, TiW(N), Al, Cu, and Ni), ranging from metals to insulators, are sputtered (RF or DC with low and high power) on top of several graphene samples. After sputtering, a wet etch of those materials is performed at room temperature and with mild agitation for all samples. Different etching agents are used to match the material to etch: AZ 400k 1:4 for Al2O3, AlSiCu and Al, H2O2 30% for TiW(N), and FeCl3 0.5 M for Cu and Ni. The etching process is stopped when the samples seem clean. The graphene quality of these samples is analyzed by Raman Spectroscopy before and after sputtering and wet etch. The comparison of Raman spectra for all combinations shown in We propose a specific solution, consisting of the insertion of a stopping layer between graphene and the dielectric to be etched see . When a 2O3, seems to induce the oxidation of graphene. The deposition of AlSiCu also induced many defects that could be originated by the high power plasma of the sputtering system with an additional contribution from mechanical damage during the dissolution of aluminum, where bubbling was observed. A similar situation occurs with TiW(N), where the etchant H2O2 30% leads to the complete oxidation of graphene. Then, a low power (100 W) sputtering system with a sizeable target-sample distance of 30 cm (larger than in the system previously used) was tested. While the RF sputtering of pure aluminum lead to the damage of graphene after its removal, the DC sputtering of Cu and Ni did not induce a significant increase in the Raman defects peak  at 2 kW and 1 kW, respectively, and RF sputtering of aluminum oxide at 2.5 kW were found to damage or altered the material extensively. The deposition of oxide films, such as AlInterestingly, these metals are also well-known catalysts for graphene growth, and their deposition on graphene was reported as healing graphene . Once grThe next challenge for the preparation of the stopping layer is patterning. Patterning by wet etch should be avoided if we are to precisely control the features’ size, and patterning by standard lift-off is limited, since ultra-sonication is forbidden due to the graphene underlayer. Therefore, the lift-off process was changed as follows. Soaking the photoresist with a TMAH-based developer  before exposure creates a top hardened layer that behaves differently upon exposure and development. Development occurs faster in the remaining photoresist than in the hardened layer, producing “mushroom hat”-like features, or a negative profile, which creates a shadow during metal deposition and, therefore, facilitates lift-off. Since this feature forms at the top photoresist surface, immersion in a solvent peels-off this layer, where the sputtered materials are adhered. Testing this methodology on samples with pre-patterned contacts and graphene was highly effective and reproducible even at a wafer scale.2 and three 50 nm films of SiNx with 250 nm of final thickness. The passivation stack is patterned using 1035 nm of AZ1505 photoresist and optical lithography, followed by RIE using previously optimized parameters. After removing the remaining photoresist, the channels and the gate electrode are released by wet etch of the stopping layer (AZ 400K 1:4 for AlSiCu and FeCl3 0.5 M for Cu or Ni). The removal of the stopping layer was followed by EDX, allowing the final devices to be process contaminants free. The EDX spectrum in Based on the presented results, samples with pre-patterned gold contacts were prepared to test the passivation patterning process by dry etching using the best protective stopping layers. Samples with gold contacts and graphene are prepared as follows: the samples are coated with 600 nm of AZ1505 photoresist and soaked in the developer (AZ400k 1:4) previously to optical lithography. After lithography and development, each sample is sputter-coated with copper  or nickel , which is followed by aluminum alloy  and titanium-tungsten (TiW(N), 5 nm). Then, the samples are immersed in acetone for 1 h at room temperature and then rinsed with an acetone wash bottle to promote the loose material’s release. The soaking method avoids sonication, preventing the damage/delamination of graphene. Next, the passivation layer is deposited as a stack of two 50 nm films of SiO2/SiNx passivation stack and the capping layer of TiW(N) and stops at the AlSiCu layer. The removal of AlSiCu by an alkaline solution (AZ400k) is confirmed in the spectrum of 2O3 that is beneath the Cu of the stopping layer. The spectrum confirms the removal of the Cu by FeCl3 0.5 M in 2O3 from the gold surfaces and showing no evidence of significant contaminants at the surface of the device.The RIE etching step etches away the SiOCNP) indicating intrinsic p-doping of the devices. We obtain a field-effect mobility for electrons and holes of μe ≈1700 cm2 V−1 s−1 and μh ≈1300 cm2 V−1 s−1, respectively, by fitting the transfer curves to a model describing the DC conductivity of single-layer graphene (SLG), σ, as a function of gate voltage. The model is based on carrier resonant scattering due to the strong short-range potentials originating from impurities adsorbed at the graphene surface [Confirming the results shown in  surface ,41.This study’s main goal is to develop a process for the wafer-scale fabrication of high electronic quality devices for biosensing applications. The final devices produced at the 200 mm wafer scale following the process proposed in this paper are resistant to all the solvents used for graphene functionalization  and have2O3 protective layer following the results of The first step is to open the back-gate access using optical lithography and reactive ion etching . Then, aThe sacrificial layer for graphene transfer is prepared by lift-off following The processed PMMA/graphene films are transferred onto the wafer’s desired regions until full coverage is achieved see  below. A2O3 is selectively removed to improve adhesion of the passivation to the chips’ surface. Al2O3 is kept only at the gate and pads to prevent contact with the stopping layer by patterning 2200 nm thick AZP4110 photoresist and wet etching with alkaline solution (AZ400k 1:4). A hard coating for passivation is chosen . The defect-related D mode ratio to the G mode changes from 0.12 (as-transferred) to 0.24 , but 2D/G ≈ 2.3, indicating graphene quality, is not significantly affected by the fabrication process.Optical images acquired after each fabrication stage  are usedR, below ≈1000 Ω is expected in successful devices, while values up to ≈2500 Ω are still acceptable. Transistors with R > 2500 Ω were rejected and discarded. Two wafers were processed and studied. Wafer A is a shared design wafer containing 9 × 18 chips . In R < 2500 Ω. The color code refers to four classes of data values according to quartiles, iq . The spatial distribution of the resistance values looks random, and no correlation with the graphene patches individually transferred (R6 (R5) to 617.96 Ω (816.83 Ω) for R9 (R10).For the devices’ electrical characterization, an automated probe station is used to measure either the current or the voltage drop in the channel between source and drain contacts at a fixed voltage of 1 mV or a fixed current of 1 μA, respectively. Then, the measured values are converted to resistances to provide information on the homogeneity of the devices’ process and quality . For the18 chips , each chnsferred  is visibnsferred  showing R > 5 kΩ were rejected (4704 − 4107 = 597). The x- and y-coordinates of each data point corresponding to one pair of resistors. The color code reflects four classes of data values according to quartiles, iq . A second wafer (wafer B) was processed and measured at constant source–drain current. A process for the fabrication of chips containing graphene electrolyte-gated FETs is developed step by step in this study, having in mind their application as biosensors. Many technical solutions for different process issues were suggested, developed, tested, and critically discussed. Some of them were rejected, given the study’s goal, since they do not provide chips with enough chemical or electrical stability. However, for less demanding applications, these solutions could be useful.Dielectric passivation as the final step of the fabrication process allows an improvement of signal stability. It decreases electronic noise, since only the graphene channel and the gate electrode become exposed to the electrolyte during measurements. One of the most relevant results to obtain a useful chemical-resistant chip is the possibility of metal sputtering on top of graphene films without inducing relevant damage. This result can be extended to devices where metallic layers are required on top of graphene without significantly increasing the fabrication time.A novel approach to improve the surface cleanliness of the chip surface after graphene transfer is demonstrated. An effective sacrificial layer is developed, allowing the patterning of graphene while protecting the pristine gold surfaces. This optimization is of high importance for using the devices as biosensors. It promotes better inter-device homogeneity and less random molecular adsorption responsible for the sensor signal’s random response and noise. The process is general and suitable for other applications or devices with similar requirements.This study casts light on the critical field of microfabrication of graphene devices for chemical sensors with electric transduction and their chemical stability as a function of the process chosen in a manner that allows researchers in the field to pick, among the results presented, those that better suit their application.


The synthesis of TiO2-NTs is performed using a hydrothermal process. Sample characterization is carried out using X-ray diffraction and scanning electron microscopy. The results show that the sensors can measure moisture values in the range of 5% to 95% with very high precision and very low hysteresis. The humidity variation between 5% and 95% shows a change in the sensor resonance frequency of ~3180 Hz, which is a significant change compared to many magnetoelastic humidity sensors developed so far.In this study, TiO Magnetoelastic materials change their shape when exposed to a magnetic field and, conversely, undergo magnetization changes when a mechanical stress is applied. This bidirectional coupling provides the transduction capability when working as sensing devices ,2,3,4. Igiven by ,6,7:(1)ΔE. coli [Salmonella enterica typhimurium [Magnetoelastic sensor platforms have been used for chemical and physical detection, including liquid density and viscosity ,12,13,14E. coli  and Salmhimurium ,34.2 nanotubes (TiO2-NTs) was coated on the MES surface in order to increase the surface area of MES and the humidity sensing properties of the prepared MES are reported. Although there have been some studies regarding the humidity sensing properties of TiO2-coated MES, in this study, we use TiO2 in its nanotube form for the first time and we present detailed results compared to previous studies.Jain  develope2-NTs was performed using a hydrothermal process. For this purpose, a TiO2 nanopowder was synthesized by a reflux method. Titanium isopropoxide Ti(OPri)4  as a precursor was dissolved in 2-propanol  for 2-PrOH/Ti(OPri)4:10 (n/n) and stirred for 15 min at 800 rpm at ambient temperature to form solution A. It contains mol/mol ratios of H2O/Ti(OPri)4 n/n = 10 and H2SO4/Ti(OPri)4 n/n = 0.01 were mixed homogenously by magnetic stirring and allowed to stand on a magnetic stirrer at 800 rpm for 30 min to form solution B. Solution A was added to solution B dropwise with continuous stirring at 800 rpm at ambient temperature for 30 min to ensure the formation of a homogeneous solution. The mixture was transferred to reflux at 110 °C for 6 h to complete the synthesized TiO2-NPs. Centrifugation was carried out to remove the solvents from the medium and dried at 80 °C in a vacuum oven for 8 h to achieve the anatase phase of titania. TiO2-NPs (2 g) were dispersed in 40 mL of 10 M NaOH ultrasonically, followed by hydrothermal treatment at 180 °C for 48 h in a Teflon-lined autoclave. The solid phase was then washed with 0.1 M HCl and distilled water at pH 6 to 7 and the subsequently filtered TiO2-NTs were dried at 80 °C for 8 h. The synthesis of TiOThe block diagram of the humidity measurement system is shown in A temperature sensor was placed into this unit and the temperature was monitored during the humidity measurements and no major temperature variation was observed during the testing. The humidity of the measuring unit was controlled using two flow meters, one flow meter controlling the dry air flow and the other humidified air, so that two humid and moisture-free gases were supplied to the measuring system at the desired rate and different humidity values were generated in the measuring system, the total flow rate usually kept constant to be around 400 sccm. The resonant frequency, frequency shift, and the mass change on the MES were measured using the homemade system. The measurement system can measure resonance frequency with 1 Hz sensitivity. All parameters during the measurements were controlled by a computer. 2-NTs was analyzed by X-ray diffraction (XRD) using a Rigaku RadB-DMAX II diffractometer with Cu Kα radiation (λ = 1.5418 A) in the region 2θ = 25.3°. For a description of the surface morphology, a Leo Evo 40 model scanning electron microscope (SEM) was used.The crystal phase of the TiO40Ni38Mo4B18) amorphous ferromagnetic ribbons was used as MES. The ribbons were cut with 30 mm long and 4 mm wide using a dice saw. All samples were cleaned in an ultrasonic bath with acetone and deionized ultrapure water. Afterwards, the ribbons were quickly dried. Then, a Cr film of 100 nm thickness and Au film of 100 nm thickness were coated on both sides of the ribbon using a thermal evaporator Vaksis-midas PVD/4T thin film system. Coated ribbons were then heated at 200 °C for 3 h to ensure good adhesion of gold. A thin layer of TiO2-NTs on the surface of the Cr-Au plated ribbons was formed using a drop-casting method. About 20 µL of TiO2-NTs in ethanol were dripped onto the surface of the plated ribbon using a micropipette. Ethanol was then evaporated and later, it was observed that TiO2-NTs were clustered on the surface of the plated ribbon, thus MES is prepared as a humidity sensor.2826MB 2, NaCl, KCl, and K2SO4 solutions have RH levels of 11%, 33%, 43%, 52%, 75%, 85%, and 97%, respectively. The different humidity levels using these salts were applied to BQ225 and DHT11, the humidity sensor and calibrations of these sensors were checked. Then, we have used BQ225 and DHT11 sensors to monitor the humidity level in the test chamber, so the variation of resonant frequency of TiO2-NT deposited MES as a function of humidity level was obtained (The TiOobtained .2-NT coated MES-1 was recorded as follows: First 5% RH then 95% RH was applied for some time and the cycle was thus continued. In addition, with the same sensor, 50% and 75% RH were cycled (All measurements were performed at ~26 °C. The humidification and dehumidification response time measured with the TiOe cycled . The sen2-NT coated MES-1 measured at different 77.5% and 95% RH levels. The sensor was continuously tested for ~15,000 s at 4 s intervals. It was observed that the free frequency response of the TiO2-NT coated MES was almost unchanged.The static humidity detection response of the MES-1 is shown in 2-NT-coated MES-1, MES-2, MES-3 and MES-4 for 5–95% RH cycles. Such a cycle for the MES-4 sample is shown in 2-NTs.2O3 was coated onto a 2826MB amorphous ribbon, and they tested the sensor at two different humidity levels, 2% and 98%. They found that the sensor shows a 500 Hz change in the resonance frequency for these humidity changes, and it takes approximately 2 h to obtain a steady-state response. Craig et al. [2 onto 2826MB amorphous alloys, and they found that stabilizing the sensor output for 60% and 2% RH level cycling takes about 30 min. In this study, the stabilization of MES-1 sensor output for 95% and 5% RH level cycling takes about 40 s, as it can be seen that the sensor response time in this work is much faster than that of previously reported magnetoelastic humidity sensors. However, it was also observed that the sensor response time increases with the increasing coated mass of TiO2. It should be noted that there are differences between previous studies [Magnetoelastic humidity sensors have been studied by Jain et al. . A thin g et al. ,18 also  studies ,18 and t2 film coated QCM sensor exhibited excellent humidity sensing performance in terms of higher sensitivity and shorter response/recovery time compared with the nanosphere and nanoflower TiO2 nanostructure [It has been reported that a hollow ball-like TiOtructure  since, atructure . Moreovetructure . We assuA number of methods have been developed for humidity detection, including capacitance ,40,41,422-NT film on Fe40Ni38Mo4B18 amorphous ferromagnetic ribbons was successfully fabricated using a drop-casting method. The effect of coated layer mass was reported for the first time for magnetoelastic sensor and different amounts of TiO2-NTs were coated on the amorphous ribbon and it was found that the resonant frequency change for 5–95% RH cycles increases with increasing mass of the coated TiO2-NTs. Furthermore, it has been found that these increases in the low coated layer mass are sharp and then this sharpness decreases. For the sample coated 2.64 µg of TiO2-NTs, a ~3180 Hz change in the resonant frequency was observed for variation humidity levels of 5–95% RH. The humidity sensing properties of the TiO2-NT film on MES is very sensitive to humidity changes and reversible adsorption/desorption performance, which is indicative of a good humidity sensor. In conclusion, a TiO


However, the easy restacking and volume expansion properties of SnS2 during the charge/discharge process lead to the destruction of the electrode structure and a decrease in capacity. We successfully synthesized a SnS2 nanocrystalline-anchored three-dimensional porous graphene composite (SnS2/3DG) by combining hydrothermal and high-temperature reduction methods. The SnS2 nanocrystalline was uniformly dispersed within the connected reduced graphene oxide matrix. The SnS2/3DG battery showed a high reversible capacity of 430 mAh/g after 50 cycles at 100 mA/g. The SnS2/3DG composite showed an excellent rate capability with the current density increasing from 100 mA/g to 2 A/g. The excellent performance of the novel SnS2/3DG composite is attributed to the porous structure, which not only promoted the infiltration of electrolytes and hindered volume expansion for the porous structure, but also improved the conductivity of the whole electrode, demonstrating that the SnS2/3DG composite is a prospective anode for the next generation of sodium-ion batteries.Tin disulfide (SnS The volume expansion effect (~420%) can cause damage as it leads to the serious pulverization of the crystal structure [2 materials could be mitigated by nanosizing to improve the electrochemical properties of SnS2 materials, such as SnS2 nanorods [2 nanosheets [2 nanoflowers [The demand for high-performance electrochemical energy storage and energy conversion devices is ever-growing ,2,3. Altndliness . The octs forces ,11. The tructure ,13. Resenanorods ,15, SnS2nosheets ,17, SnS2oflowers ,19, etc.2 [2 nanosheets as the van der Waals force between adjacent layers of SnS2 is destroyed by graphene, which is favorable for the electron transfer rate [2 as the SIB anode, various structures of SnS2/graphene hybrids have been designed [2/graphene, the in-situ hydrothermal process is the most common. This method can simultaneously control the structure of composite materials and the morphology and particle size of SnS2 [2/graphene composites with a high capacity of 521 mAh/g (at 0.05 A/g) by stripping the commercial SnS2 particles with graphene oxide via the hydrothermal reaction. However, the capacity was only 165 mAh/g at 2 A/g [Compositing with carbon materials is also an effective method to improve the electrochemical performance of SnS2 . Among t2 . The intfer rate ,22,23. Tdesigned . In addi of SnS2 . Howeverat 2 A/g .2 nanocrystalline anchored 3D porous graphene composite. The presence of graphene can effectively inhibit the volume expansion effect of SnS2 and improve the conductivity of the SnS2/3DG composite. The two-step reduction method significantly improves the reduction degree of graphene, resulting in an enhancement in the rate performance of the SnS2/3DG composite.In this study, to simultaneously achieve a high capacity and a high rate, we used an effective method that combines the hydrothermal and high-temperature processes to prepare a SnS4·5H2O)  and 10 mmol of anhydrous citric acid (C6H8O7)  to 80 mL of deionized water and stirred for 1 h. Another 10 mmol of thioacetamide (CH3CSNH2)  was added to the mixture after SnCl4·5H2O and C6H8O7 were completely dissolved. The mixture was stirred for an additional 30 min. Next, the well-dissolved mixture was transferred into a 100 mL hydrothermal reaction kettle and reacted at 130 °C for 12 h. After the reactor cooled to room temperature, the obtained SnS2 precipitate was centrifuged with deionized water and ethanol.We added 10 mmol of tin(IV) chloride pentahydrate  was dispersed in deionized water (the preparation concentration was 4 mg/mL) and the graphene oxide suspension was obtained after ultrasonic stripping for 1 h. Next, 20 mL of the GO suspension was added into the reaction bottle and 1 mL of SnS2 dispersion was added with a pipette gun under ultrasonic conditions. After continuous ultrasonic dispersing for 30 min, 320 mg of vitamin C (VC)  was added to the reaction bottle. The mixed solution in the reaction bottle was placed in the 80 °C water bath after the VC was dissolved evenly. The mixture hydrothermally reacted for 8 h to obtain a hydrogel with a monolith structure. The hydrogel was then freeze-dried to obtain the three-dimensional porous graphene-loaded SnS2 composite (SnS2/3DG). Finally, the SnS2/3DG was placed in a tubular furnace and thermally treated at 400 °C for 2 h in an argon atmosphere. The prepared SnSThe microstructure of the material was characterized by a Philips FEI Quanta  200F high-resolution scanning electron microscope (SEM) and transmission electron microscope (TEM). The phase analysis was carried out by a Rigaku smart-lab III X-ray diffraction (XRD), using a Cu-Kα radiation source. The proportion of each component in the composite was analyzed by a thermogravimetric (TG) analyzer . The Raman spectra of the materials were analyzed by a Horiba LabRAM HR spectrometer .2/3DG composite powder, conductive carbon black, and adhesive polyvinylidene fluoride (PVDF) were mixed with a mass ratio of 8:1:1, and a certain amount of N-methylpyrrolidone (NMP) was used as solvent to grind and prepare uniform slurry. The slurry was coated on the pretreated clean copper foil collector and dried in a vacuum oven at 100 °C for 12 h. The CR2032 button cell was assembled in the glove box, as the sodium plate was used as the counter electrode and a glass fiber  porous membrane was used as the separator. A 1 M ethylene carbonate (EC) and dimethyl monocarbonate (DMC) solvent with a volume ratio of 1:1, which was dissolved with sodium perchlorate (NaClO4), was used as the electrolyte. The cyclic voltammetry (CV) of the cell was characterized by a VMP3 . The electrochemical impedance spectroscopy (EIS) was measured on a VMP3 workstation with an amplitude of 5 mV and a frequency range of 0.01–100,000 Hz.For the electrochemical characterization, the SnS2/3DG composite was fabricated on the basis of the hydrothermal method followed by a controllable, low-temperature water bath process. As illustrated in 2 particles were obtained by mixing CH3CSNH2 and SnCl4·5H2O. The adsorbed Sn4+ ions reacted with the gradually released H2S from the decomposition of CH3CSNH2 during the hydrothermal process [2 uniformly nucleated to form nanoparticles. Next, the prepared SnS2 nanoparticles were immersed into the well-dispersed GO suspension, and a mild solvothermal method with the adding of reducing agent was introduced to not only efficiently disperse the SnS2 nanoparticles but also to reduce GO. Finally, the porous SnS2/3DG composite was successfully fabricated by the freeze-drying and thermal reduction step. This unique 3D porous structure facilitates the migration of Na+ and electrons and benefits the high sodium storage performances.The SnS process , while S2 nanocrystalline was successfully synthesized by the hydrothermal process and SnS2/3D composite was obtained by the low-temperature water bath method. 2 nanocrystalline and the SnS2/3D composite. All diffraction peaks of pure SnS2 nanocrystalline corresponds well with the standard spectrum of hexagonal SnS2 (JCPDS 23-0677) [2/3DG composite, corresponding to the typical (002) plane of graphene [2 nanocrystalline and the SnS2/3DG composite are shown in 2 nanocrystalline near 315 cm−1 reveals the vibration modes of A1g of SnS2 [−1, which belong to the D and G peaks of graphene, respectively. The prominent D peak refers to the vibration caused by the defects of graphene, while the G peak refers to the in-plane vibration of the sp2 hybridized carbon atoms of graphene [D/IG) can show the disorder degree of the carbon material. The calculated ID/IG value of the SnS2/3DG composite decreased to 1.29, which proves the high reduction degree of graphene after the thermal reduction process [SnS23-0677)  without graphene ,29. The  of SnS2 . In addigraphene . The int process .2 nanocrystalline and the SnS2/3DG composite are shown in 2 nanocrystalline with an average diameter of 20 nm was seriously agglomerated, which is not conducive to maintaining good electrochemical stability. 2/3DG composite at different magnifications where the SnS2/3DG composite displays obvious 3D porous morphology with the graphene sheets connecting to form a continuous conductive network. The complete monolith structure of the SnS2/3DG is shown in the inset of 2/3DG composite, where SnS2 nanocrystalline particles are uniformly dispersed on the graphene sheets with no obvious agglomeration because the van der Waals force between the adjacent SnS2 is destroyed by well-dispersed graphene sheets [2 nanocrystals and graphene provide a good possibility for the electrochemical performance of the SnS2/3DG composites.The morphologies of the SnSe sheets . The uni2/3DG composite, which may guarantee the cycling stability. 2 and the SnS2/3DG composite. For the pristine SnS2 sample, the mass loss in the range from room temperature to 300 °C occurred due to the evaporation of water molecules, while the mass loss over 300 to 800 °C represents the transformation from SnS2 into SnO2 [2/3DG composite also displayed a mass loss in the temperature range of 25 to 300 °C, which was due not only to the evaporation of water molecules, but also to the decomposition of residual oxygen-containing functional groups in graphene. SnS2 gradually transferred to SnO2 from 300 to 450 °C, and the excess SnS2 was further oxidized and the graphene decomposed completely at the temperature range of 450 to 800 °C. The calculated content of SnS2 was 76 wt%.In addition, the EDS mapping in nto SnO2 . The SnS2/3DG anode, 2 and the SnS2/3DG composite in the voltage range of 0.01–3.0 V. For the pure SnS2 material, the reduction peak near 1.7 V corresponds to the insertion of sodium ions into SnS2 nanocrystalline in the first discharge process of the pure SnS2 electrode (SnS2 + 4Na+ + 4e− → Sn + 2Na2S2) [2 since the second cycle, indicating the low capacity of pure SnS2. The reduction peak near 1.7 V was also found in the SnS2/3DG composite. Sn produced in the reduction provided the tin source for the Sn/Na alloying reaction at 1.2 and 0.7 V (Sn + xNa+ + xe− → NaxSn) [2/3DG composite. 2 and the SnS2/3DG composite at the current density of 100 mA/g. The SnS2/3DG composite delivered a specific initial discharge capacity and a charge specific capacity of 1276 and 557 mAh/g for the first cycle, respectively, which are much higher than those of the pure SnS2 nanocrystal electrode.To understand the sodium storage process of a SnS 2Na2S2) , while t→ NaxSn) , and the2 and the SnS2/3DG composite at the current density of 100 mA/g are shown in 2/3DG composite after 50 cycles improved to 430 mAh/g, while that of pure SnS2 was only 22 mAh/g. 2 and SnS2/3DG composites at various current densities. The SnS2/3DG composite delivered a reversible discharge specific capacity of 462 mAh/g at the current density of 100 mA/g, and the specific capacity decreased to around 407, 345, and 292 mAh/g as the current density gradually reached 200 mA/g, 500 mA/g, and 1 A/g, respectively. Even when the current density reached 2 A/g, the SnS2/3DG composite still displayed a steady discharge capacity of around 247 mAh/g, indicating an excellent rate. In addition, the reversible specific capacity of the SnS2/3DG composite returned to about 414 mAh/g when the current density was reset to 100 mA/g. However, the specific capacity of pure SnS2 was as low as 90 mAh/g at the current density of 100 mA/g, and the specific capacity of pure SnS2 almost dropped to 0 mA/g when the current density increased to 2 A/g. The specific capacity was only about 50 mAh/g when the current density returned to 100 mA/g.The cycling performance of the pure SnS2 nanocrystalline and graphene that result in the composite having a strong electrochemical rate performance and a high capacity. The reasons why SnS2/3DG has high specific capacity and excellent rate performance are as follows: (1) The high-degree reduction of 3D graphene creates the continuous conductive matrix, which is beneficial for the rate performance; (2) the porous structure of SnS2/3DG is conducive to the diffusion of electrolyte and the diffusion rate of Na+ increases; (3) the volume expansion of the SnS2 nanocrystalline is restrained by the flexible graphene sheets, and the cycling stability is improved for the solid structure of the SnS2/3DG composite. A comparison of the performance of the SnS2/3DG composite with the literature is provided in 2S2, Na14Sn5, and Sn, which is consistent with the above charge–discharge process.It is the unique three-dimensional porous structure and the interaction between the SnS2 and the SnS2/3DG composite are shown in 2 and the SnS2/3DG composite showed semicircles in the high frequency region and a diagonal line in the low frequency region, which are related to the Warburg impedance. The equivalent circuit is shown in Re represents the electrolyte impedance contributed by current collectors, electrodes, separators, and the interface between electrodes and electrolytes. Rsf and CPEsf represent the resistance and capacity of the combination of migration and the interface impedance of SEI films, respectively. Rct and CPEct represent the charge transfer impedance and charge transfer capacitance, respectively. WZ is the Warburg impedance, which is usually revealed by the straight line in the low frequency region. The SnS2/3DG composite delivered a much lower total resistance of 230.2 Ω than the pristine SnS2 (316.8 Ω), which is also lower than the hydrothermal-treated flower-like SnS2/graphene battery [w) was calculated by the EIS results, as the σw is the slope of the function of real resistance (Z’) and ω−1/2 :R is the gas constant, T is the temperature, F is the Faraday constant, n is the electron transfer number, A is the apparent electrode surface area, and C is the maximum sodium ion concentration. The obtained sodium diffusion coefficient of SnS2/3DG (1.04 × 10−14 cm2/s) is much higher than that of the SnS2 electrode (1.01 × 10−15 cm2/s). The good conductivity and fast ion diffusion coefficient improve the electrochemical performance of the SnS2/3DG composite.The Nyquist spectra of the pure SnS battery , confirmnd ω−1/2 c. The Sn2 composite was successfully prepared by combining hydrothermal and high-temperature reduction methods. The reversible capacity of the SnS2/3DG composite can reach 430 mAh/g at a current density of 100 mA/g after 50 cycles. The resistance of the SnS2/3DG composite can be effectively reduced by introducing the conductive graphene network with a high reduction degree, which is beneficial to improving its rate performance. The SnS2/3DG composite delivers an outstanding rate capability with the current density increasing from 100 mA/g to 2 A/g. This three-dimensional porous SnS2/3DG anode shows significant potential for the next-generation of SIBs.In summary, a highly conductive graphene aerogel anchored with SnS


Twisted and coiled actuators (TCAs), fabricated by twisting cheap nylon sewing threads, have attracted a great deal of attention for their use as artificial muscles or soft actuators. Since the dynamic behavior of a thermally-operated TCA is governed by its thermal properties, graphene and silver nanoflowers (AgNFs) were spray-coated onto the surface of an actuator to achieve enhanced heat transfer. Addition of AgNFs improves interfacial thermal contacts between graphene flakes, while pristine graphene flakes have extremely high in-plane thermal conductivity. Thus, the synergistic effect of graphene and AgNFs reduced the total cycle time of the TCA by up to 38%. Furthermore, when a pulsed current with a 40% duty cycle was applied to the TCA, the graphene/AgNF-coated TCA exhibited a threefold larger peak-to-peak amplitude of the displacement oscillation of the actuator, as compared to that of the non-coated TCA, which demonstrates that the combination of graphene and AgNFs effectively reduced a cooling time of the TCA. This work shows great potential for a simple coating of graphene and AgNFs to produce high-performance thermally-operated soft actuators. Therefore, a great deal of effort has been invested in developing muscle-like actuators with high mechanical compliance and high specific power, including shape memory alloys (SMAs)5, pneumatic elastomeric actuators6, electro-active polymers (EAPs)8, twisted and coiled actuators (TCAs)10, and others. Among these soft actuators, TCAs fabricated by twisting and coiling sewing threads made of inexpensive polymers demonstrated an extremely high specific power of 5.3 kW/kg along with additional advantages including a large operating strain of over 20%, small hysteresis, high flexibility, low weight, and low fabrication cost9, which makes them a promising candidate for practical artificial muscles.Muscle-like actuators or soft actuators are a key component of advanced applications such as robotics, wearables, and medical devices because conventional actuators are bulky, heavy, rigid, and noisy9. However, this requires additional bulky components for temperature control of the TCA. Thus, conductive silver-coated polymer fibers were used to fabricate TCAs that enable temperature control by application of an electric current through the actuator for Joule heating11. This is a simple and efficient method for operating the TCAs with controlled actuation.When making TCAs, extreme twisting of polymer fibers forms spring-like coils and the gaps between coils are controlled by temperature change of the actuator; when the actuator is heated, the gaps between coils are closed and the actuator contracts. Repeated heating and cooling are typically achieved by applying hot air or flowing hot water through a tube surrounding the TCA12. However, twist-spun CNT yarns require a complicated fabrication process involving spinnable CNT forests, resulting in high fabrication cost and technical difficulties. To take advantage of TCAs made from cheap polymer fibers, a simple coating of graphene-based materials was recently introduced to enhance dynamic performance13. High-quality monolayer graphene with minimal defects has shown an extremely high thermal conductivity of over 2000 W/mK16. Thus, TCAs fabricated from nylon fibers were coated with various forms of graphene, such as monolayer large-area graphene, three-dimensional (3D) graphene foam, and graphene flakes, which enabled a reduction in the cycle time of the TCA; in particular, coating of graphene flakes demonstrated a dramatic decrease in the cycle time by 30.9%13. However, it has long been known that the out-of-plane thermal conductivity of graphitic materials is two orders of magnitude lower than the in-plane thermal conductivity due to the weak van der Waals interactions between individual graphene layers17 and the weak interaction between graphene flakes increases the interfacial thermal resistance. This limits the enhancement of the thermal properties of the graphene-based coating layer. In this respect, there is still a demand for coating layers comprised of graphene flakes with improved thermal properties that would allow for creation of high-performance TCAs. Metallic nanoparticles have been used to improve the thermal conductivity by bridging two-dimensional (2D) materials18. Recently, flower-shaped silver nanoparticles  have been developed for conductive electrodes and composites20. AgNFs have single-crystal petals that are around 20 nm thick. Due to their hierarchical structure with ultrathin petals, they provide better dispersion without agglomeration and allow for coalescence of petals at low temperatures of 80–120 °C19. Therefore, they have great potential for enhancing the interfacial thermal conductance between 2D materials by melting the silver petals and generating improved physical contacts to 2D materials.The dynamic behaviors of a TCA are dependent on its thermal properties. Since polymer fibers have relatively low thermal conductivity, other materials, such as carbon nanotubes (CNTs), have been utilized to fabricate super-coiled actuators. A coiled yarn made from sheets of CNTs demonstrated fast tensile actuation with large forces and strokes because of the high thermal and electrical properties of CNTsIn this study, AgNFs were embedded into graphene flakes to enhance thermal contacts between graphene flakes and thus improve the dynamic performance of TCAs. Since low-temperature curing can induce the active coalescence of silver petals, the interfaces between graphene flakes can be bridged by the AgNFs, ensuring better thermal contacts. AgNFs mixed with graphene flakes were spray-coated on the surface of the TCAs. The enhanced dynamic performance of the TCA coated with the graphene/AgNF hybrids was investigated by cyclic operations under repeated heating and cooling.21, a 2–4/TCA was used to maximize the stroke under an applied load . TCA performance is dependent on fabrication method. Following previous works22. A dispersion of graphene flakes (5 mg/mL) was prepared in a water/ethanol mixture with a volume ratio of 1:913. After AgNFs were synthesized using a previously published method19, AgNF powder was poured into the graphene dispersion. The fabricated TCAs were spray-coated with the mixture of graphene and AgNFs using a spray gun and dried in air  by sonicationScanning electron microscopy  was used to observe graphene flakes, AgNFs, and the surface of the fabricated TCAs. The surface morphology and the cross-sectional view of graphene flakes were observed by transmission electron microscopy . Raman spectroscopy  with a 532 nm wavelength laser was employed to characterize the graphene flakes.21. Briefly, the temperature of the TCAs was monitored with a micro thermistor placed on the end of the TCAs, which enabled closed-loop temperature control. A linear magnetic encoder was used to measure the displacement of the TCAs under a temperature range between 35 °C and 100 °C, while a 500 g payload was attached to the end of the vertically-positioned TCAs.As the TCAs were fabricated with electrically conductive silver-coated nylon fibers, the dynamic performance of the fabricated actuators was evaluated using Joule heating. A DC current was applied to the two ends of the TCAs to control the temperature for actuation. A detailed experimental set-up was described in previous papers−1 and the 2D band at 2700 cm−1  of the normalized displacement. When the current is shut off, the TCA starts to naturally cool from exposure to air and extends to its maximum length  at the lowest operating temperature. Figure TCAs coated with graphene/AgNF hybrids were tested with repeated heating and cooling. Displacements of each TCA were normalized to the maximum displacement in order to compare the cycle performance of different TCAs27:0 is the ambient temperature, P is the input electric power, and Cth and λ are the thermal mass and thermal conductivity of the thermally-operated actuator, respectively. The dynamic performance of the TCA can be determined by the time constant, τ = Cth/λ. Therefore, increasing the thermal conductivity of the TCA is one way to improve its cycle performance. As the thermal conductivity of pristine graphene is extremely high, a simple coating of graphene flakes on the surface of the TCA enhances the thermal response of the actuator13. However, the out-of-plane thermal conductivity of multi-layer graphene flakes is two orders of magnitude lower than the in-plane thermal conductivity17 and the weak interaction between graphene flakes induces thermal resistances at interfaces.A first-order linear model can be used to understand the thermal behavior of a TCA with the following equation28 and CNTs29 due to their high-aspect-ratio geometries and outstanding physical properties. However, our study (not shown here) revealed that the use of AgNWs could not grant the TCAs better dynamic behavior. This may be because long AgNWs reinforced the coating layer, interfering with TCA actuation. In addition, silver nanoparticles (AgNPs) have been utilized synergistically with other nanomaterials30. However, AgNPs tend to easily agglomerate31, which can increase stiffness of the TCAs. Due to their better dispersibility, high thermal and electrical conductivities, and ability to coalesce at very low temperatures, AgNFs offer thermally robust and mechanically flexible bridges between graphene flakes in the TCA coating.To obtain better thermal interfaces between graphene flakes, AgNFs were embedded into the graphene flakes. Silver nanomaterials with different morphologies have been used to bridge other electrically and thermally conductive nanomaterials. For instance, silver nanowires (AgNWs) provided robust electrical and thermal connections for graphene13. In contrast, the addition of AgNFs significantly improved the cycle time by 38% at a mass ratio of AgNFs to graphene of 1 (Fig. The synergistic effect of graphene/AgNF hybrids was investigated by evaluating the cycle performance of the coated TCAs. Heating, cooling, and total cycle times were evaluated from the dynamic responses shown in Fig. f 1 Fig. b; the im13.The effect of AgNF concentration on the performance of the TCAs was investigated by varying the mass ratio of AgNFs to graphene from 1 to 10. As shown in Fig. In addition, the dynamic behaviors of the TCAs were characterized by monitoring the displacement responses as a function of the frequency of the heating and cooling cycles Fig. . A pulseIn summary, the dynamic behaviors of a TCA, a promising artificial muscle material, were improved by treating the surface of the actuator with a graphene/AgNF hybrid coating. A simple spray-coating method was used to obtain thin, uniform layers on the fabricated TCAs. As the nylon fibers were coated with silver, the electrically conductive TCA was actuated by Joule heating and natural cooling in air. AgNFs had ultrathin petals with tens of nanometers in thickness, which enabled coalescence of the AgNFs by heat treatment at a low temperature. Therefore, the graphene/AgNF hybrid coating dramatically reduced the total actuation time in repeated heating and cooling cycles; the maximum reduction in cycle time was 38% at a mass ratio of AgNFs to graphene of 1. This is attributable to improved interfacial thermal contacts between graphene flakes caused by coalescence of AgNFs as well as high-quality graphene flakes with extremely high in-plane thermal conductivity. Furthermore, when a pulsed current with frequencies ranging from 0.1 to 0.4 Hz was applied to the TCAs, the graphene/AgNF-coated TCA showed a threefold greater peak-to-peak amplitude in the displacement response as compared to the neat TCA without any coating. This work demonstrates the great potential of the graphene/AgNF hybrid coating for development of high-performance thermally-operated soft actuators.


Cellular microenvironments are known as key factors controlling various cell functions, including adhesion, growth, migration, differentiation, and apoptosis. Many materials, including proteins, polymers, and metal hybrid composites, are reportedly effective in regulating cellular microenvironments, mostly via reshaping and manipulating cell morphologies, which ultimately affect cytoskeletal dynamics and related genetic behaviors. Recently, graphene and its derivatives have emerged as promising materials in biomedical research owing to their biocompatible properties as well as unique physicochemical characteristics. In this review, we will highlight and discuss recent studies reporting the regulation of the cellular microenvironment, with particular focus on the use of graphene derivatives or graphene hybrid materials to effectively control stem cell differentiation and cancer cell functions and behaviors. We hope that this review will accelerate research on the use of graphene derivatives to regulate various cellular microenvironments, which will ultimately be useful for both cancer therapy and stem cell-based regenerative medicine. Cells experience growth within the cell microenvironment ,2. SpeciECMs, which are part of the cellular microenvironment, are primarily composed of proteoglycan and fibrous proteins. In particular, fibrous protein contributes to cell adhesion mechanisms and tissue development and plays a pivotal role in the aforementioned control of the cellular microenvironment ,21,22,23Graphene is one of the most popular nanomaterials used in various studies mostly due to its unique physicochemical properties . GeneralFor these reasons, graphene and GO are considered to have sufficient properties to control cellular microenvironments. In fact, graphene and GO can be used in more diverse forms compared to fibrous proteins because they can form various artificial structures with other materials or by themselves relatively easily ,46,47,48To fully understand the use of graphene-based materials for controlling cellular behaviors, the control of cellular microenvironments using conventional protein-based materials should be overviewed. Standard protein-based materials are fibrous proteins, such as collagen and fibronectin, which possess excellent cell adhesion properties. They are used in many types of cell culture and assist in the proliferation of cells or induce differentiation ,51,52,53In the study, Teixeira et al. induced the osteogenic differentiation of MSCs by treating them with collagen on the PLA scaffold structure; several similar studies have been reported ,60,61,62Research on stem cell differentiation using graphene hybrid composites has been very prolific since 2010. Considering that graphene is less cytotoxic and allows stem cells to attach and proliferate ,68, grapLiu et al. developed conductive hydrogel containing carbon nanotubes and graphene oxide for nerve cell differentiation e–g 73,7,75,76,77Recently, Kim et al. induced differentiation of C2C12 mouse myoblast cells using graphene. Kim et al. produced a “crumpled grapheme” structure for cell differentiation  84]. Cr. Cr84]. Graphene patterns create a more deliberate physical impact beyond the control of microenvironments that can be expected from random arrangements or the electrical properties of graphene itself. An advantage is that graphene can be patterned into a specific shape or a specific arrangement to construct the cell culture type desired by researchers.Kang et al. reported a new form of GO patterning technology  91,92].,92.91,92If a graphene hybrid pattern is applied to stem cell culture, it can serve as a platform to induce their differentiation. Lee et al. produced nanoscale graphene–Au hybrid nanoarrays to induce differentiation of human mesenchymal stem cells (hMSCs)  97,98].,98.97,98This study is one NSC differentiation platform using LIL, and there are many cases where LIL is applied to NSC differentiation ,106,107.Controlling the cellular environment using graphene is not limited to stem cells. This control can also be applied to tumor cells, as demonstrated in recent studies . As prevCancer cell microenvironmental control using graphene has also been applied to a 3D cell culture method. Kim et al. produced a graphene oxide-based platform and reported HepG2 cell spheroid formation through cell proliferation  109]. T. T109]. Hu et al. devised a slightly different approach to control 3D cellular microenvironments  115]. T. T115]. Recently, Wan et al. also reported that GO exerts a positive effect on the growth of cancer cells when incorporated with the scaffold structure . In thisThrough the studies discussed above, we divided cellular microenvironmental control using graphene into two main categories. One is ‘cellular microenvironments of stem cells’, and the other is ‘cancer cell microenvironments’. These cellular microenvironments were controlled using various types of graphene-based platforms. In the case of stem cells, differentiation was induced or promoted. In the case of cancer cells, proliferation was adjusted to enable the formation of 3D spheroids of cancer cells and long-term cell culture. Graphene derivatives regulate the microenvironments of target cells in various ways. Specifically, the induction of differentiation of hNSCs has been demonstrated using graphene–polymer scaffolds, and the control of HeLa cell attachment and growth using graphene platforms such as crumpled graphene, and graphene patterning are notable. In addition, the GO vertical patterning method in which graphene is three-dimensionally patterned on the side wall of micro-well arrays, has provided a new platform for an effective method for 3D culture of cancer cells. All of these “controlling cellular microenvironments” approaches are enabled due to distinct physical and electrical properties of graphene including excellent cell adhesion, flexibility in physical transformations, and stability against physical/chemical stimuli. Such characteristics of graphene and GO are known to affect various biological phenomena including (i) the absorption or repulsion of growth/differentiation factors on the surface, (ii) ECM protein alignment, and (iii) anchoring of integrin receptors on the cell membrane to the artificial surface. These physicochemical properties of GO allow a limitation or enhancement of cell adhesion and spreading, which ultimately lead to the changes in various cell functions  via alterations in the upstream cytoskeletal dynamics and downstream gene expression. Broadening our horizons, we were able to determine the positive changes that graphene-based materials and platforms will have on regenerative and clinical medicine in the future. In particular, graphene-modified hydrogels and graphene patterns can be used to achieve cells of interest from various stem cell sources with high conversion efficiency, which will ultimately accelerate the use of stem cells for regenerative therapies. In the case of cancer research, graphene hybrid materials, including graphene-coated micro-wells, can be used to restrict cell adhesion and growth through generation of 3D tumor spheroid arrays and further rapid anticancer drug screening. Taken together, we can conclude that controlling cellular microenvironments using graphene-based materials is highly promising for both stem cell-based regenerative medicine and cancer research.


We have previously identified a delay in general practitioner (GP) referrals for patients with degenerative cervical myelopathy (DCM). The aim of this study was to evaluate whether an education gap existed for DCM along the GP training pathway by quantitatively assessing training in, and knowledge of, this condition.Gap analysis: comparison of DCM to other conditions. Comparators selected on the basis of similar presentation/epidemiology (multiple sclerosis), an important spinal emergency (cauda equina syndrome) and a common disease (diabetes mellitus).Medical students, foundation doctors and GP trainees.(1) Assessment of training: quantitative comparison of references to DCM in curricula (undergraduate/postgraduate) and commonly used textbooks (Oxford Handbook Series), to other conditions using modal ranks. (2) Assessment of knowledge: using standardised questions placed in an online question-bank (Passmedicine). Results were presented relative to the question-bank mean (+/−).DCM had the lowest modal rank of references to the condition in curricula analysis and second lowest modal rank in textbook analysis. In knowledge analysis questions were attempted 127 457 times. Performance for DCM questions in themes of presentation (+6.1%), workup (+0.1%) and management (+1.8%) were all greater than the question-bank mean and within one SD. For students and junior trainees, there was a serial decrease in performance from presentation and workup (−0.7% to +10.4% relative to question-bank mean) and management (−0.6% to −3.9% relative to question-bank mean).Although infrequently cited in curricula and learning resources, knowledge relating to DCM was above average. However, knowledge relating to its management was relatively poor. Search terms relating to degenerative cervical myelopathy (DCM) were queried from three UK specific medical school curricula and relevant postgraduate curricula.A large number of responses were obtained by placing questions in an online question-bank, relating to DCM.A limited number of learning resources were searched to assess references to DCM.Degenerative cervical myelopathy (DCM) is a common and insidious condition that can lead to severe disability.The diagnostic pathway for DCM almost exclusively starts with assessment and triage by a community physician, termed in the UK a general practitioner (GP).This period of the diagnostic pathway is difficult to examine in detail, and while delayed patient presentation is likely to contribute, delayed detection measured by multiple consultations and patient perspective, is certainly a relevant component.Our objective therefore was to evaluate whether an education gap exists for DCM among GPs, by quantitatively assessing their training in, and knowledge of, DCM.DCM patients were surveyed online and this confirmed that the diagnosis of DCM is frequently delayed.A gap analysis is a process to identify gaps in existing systems such as education curricula. It involves an assessment of existing knowledge or standards against predetermined standards that define core competency requirements.The study objective was therefore approached in two separate gap analyses .Assessment oftraining: quantification of DCM in curricula and commonly used learning resources, including assessment of relative importance through comparison to other conditions.Assessment ofknowledge: formal assessment of trainees’ knowledge using questions placed in an online question-bank.UK medical graduates complete the UK Foundation Programme to enter higher specialty training as formal GP trainees. There are several assessments along this route including: medical school final examinations to gain registration to practice in the UK, or the equivalent Professional and Linguistic Assessments Board (PLAB) test for international medical graduates; the Specialty Recruitment Assessment (SRA)—a written assessment taken towards the start of the second foundation year prior to higher specialty applications; and the Membership of The Royal College of General Practitioners (MRCGP), an exit examination for GP trainees. While alternative entry routes to general practice exist, this pathway represents the most common training route for GPs today.DCM was chosen as an inclusive term for a variety of diseases resulting in compressive myelopathy.Direct comparator to myelopathy: a disease that is a differential diagnosis for DCM with equivalent or greater incidence.Degenerative spine comparator: an alternative degenerative spine disease that is widely taught.Generic non-neuroscience comparator: a common disease that all clinicians would have some knowledge about and interaction with.The a priori hypothesis was, if an education gap existed within DCM, we would expect metrics of training and knowledge of DCM to rank inferior to controls. Controls were identified through a consensus author meeting and finalised after confirmation of epidemiological profiles through literature review.Oxford Handbook of Clinical Medicine, the Oxford Handbook for the Foundation Programme and the Oxford Handbook of General Practice.We selected learning resources that were in common usage by trainees, available in electronic format (to be amenable for searching) and stratifiable by training stage. Specifically, training curricula, the Oxford Handbook seriesSearch terms for analysing learning resources were created for DCM and each comparator using relevant terms from the search syntax of Cochrane Reviews, or if absent, recent systematic reviews. Curricula were searched for the number of references per disease, text books for the number of words per disease section and question-banks for the number of questions.The author panel includes GPs with an interest in education (JW), university appointed educationalists (JG) and neurosurgeons . The authors devised a set of questions to be included in an online question-bank, composed both multiple choice questions (MCQs) and extended matching questions (EMQs), designed to cover the different components of medical assessment; presentation, investigation and management. The final set consisted of 19 questions (13 MCQs and six EMQs). The questions together with answers are included in 10.1136/bmjopen-2018-028455.supp1Supplementary dataOnline question-banks including subsections devoted to each stage of the GP training pathway were contacted with details of the study. Only one question-bank—Passmedicine,Statistical analysis was performed using SPSS V.22. For assessment of training, frequencies of search terms were described and the mode and modal ranks determined. For assessment of knowledge, histograms were constructed with either a condition or question-bank along the x-axis and user performance relative to question-bank mean along the y-axis. The user performance relative to question-bank mean corresponded to the raw difference between the mean value for each theme and the mean value for a particular question-bank.Multiple sclerosis (MS), cauda equina syndrome (CES) and diabetes mellitus were selected as the three disease comparators and list of search terms compiled accordingly .16–19 MSDCM and CES had the lowest modal rank in curricula search analysis . This waOverall, DCM had the second lowest modal rank but above that of CES . The relPassmedicine was approached, on the basis it did not have any DCM questions previously which could influence analysis. Questions were introduced between the period June 2017 and October 2017. Section editors for each question-bank ultimately selected which of the 19 questions were relevant, such that finals/PLAB contained 14, SRA—19 and MRCGP—19.Overall, questions were attempted 127 457 times; finals/PLAB—36 706; SRA—47 530; MRCGP—43 221 . Data on10.1136/bmjopen-2018-028455.supp2Supplementary dataThere were differences in user performance in the three DCM question themes—presentation, workup and management, though average scores were all within one SD of the mean . PerformUser performance by disease showed large variation between question-banks . The meaIn this study, we found that DCM is relatively infrequently cited in curricula and commonly used textbooks, even compared with diseases such as MS, with similar epidemiology. Despite this however, user performance in some of the DCM questions remained consistently above question-bank averages. There was a sequential decrease in user performance across the themes of DCM presentation, workup and management for early years’ trainees, whereas for senior trainees, performance did not vary by theme of question. For other neuroscience themes such as MS and CES, the user performance was below average. This was in contrast to user performance in questions relating to diabetes mellitus, which was consistently above question-bank mean.We observed a below average performance in questions grouped under the neurology theme, which included all questions relating to the central and peripheral nervous system. Reduced knowledge pertaining to neurosciences has previously been linked to a term called neurophobia, though this is by no means a universally accepted concept.Second, our study supports the observation of poorer performance in management themes by clinicians at an earlier training stage. Prior studies on medical students that have evaluated knowledge formally have shown similar results in specialties such as ophthalmology.Our original hypothesis attempting to correlate delays in diagnosis for DCM with a deficiency in training and knowledge, was not conclusively demonstrated in the present study. Earlier stage trainee doctors demonstrated comparably higher levels of knowledge with regards to the presentation and work up of DCM and a potential gap with regards to management-related questions. These differences disappeared in individuals studying for the GP exit examinations. Nevertheless, the clinical argument for an education gap is strong—our previous analysis of the referral pathway for DCM identified a time to initial referral by the GP as representing 51% of the overall diagnostic delay.This study demonstrated DCM received relatively less training than other conditions. In the west, the prevalence of DCM is underestimated but at least 60 per 100 000, compared with around 100 per 100 000 for MS.One potential way of reconciling the absence of a gap in formal knowledge with the deficiencies in the diagnosis and management of DCM, is that factual knowledge may not translate into recognition of the disease in the clinical context. Causal association between training and clinical practice have not been clearly demonstrated, although prior studies have found good correlation between examination performance and clinical performance in a variety of medical and surgical specialties.There are several limitations to be considered in the context of these findings. First, only select learning resources were used in this study and questions were inserted into a single online question-bank. Second, question-bank data were not extractable per user, nor per first time answer. While this was not a comprehensive strategy, this is unlikely to have limited our results for at least two reasons: questions were attempted more than 100 000 times and analysis was relative within learning resources, and therefore limitations were applicable to each comparator. The native question-bank data extraction technique also did not provide data on the number of attempts on question themes other than DCM.The methodology employed in the present study may not have been sufficiently sensitive to detect a knowledge gap for DCM, for several reasons. First, our questions may not have been challenging enough given that they tested core principles all clinicians would be expected to achieve. Although we did not employ pilot testing of the questions in our target population, questions were designed by an experienced author panel including educationalists. Furthermore, our questions were subject to additional scrutiny by the question-bank editors, such that only those questions deemed appropriate were included in a particular question-bank. Second, there was no first-time answer data available for analysis. This means that ‘random effect answering’, users selecting an answer to read the explanation, was not accounted for, though this was the case for both DCM and controls. Third, our controls may not have been appropriate and certainly, educational comparisons between specialties is not always the best method of assessing knowledge adequacy.In this study, we set out to evaluate whether there is a deficiency in training and knowledge regarding DCM in the GP training pathway. Although DCM was infrequently referenced in learning resources, trainees performed above average for DCM questions in an assessment of knowledge using an online question-bank. The clinical suggestion of an education gap is strong, and these contrasting findings do not conclusively allay this concern. Future studies are required to better understand these observations.