Graphene, a two-dimensional carbon sheet with single-atom thickness, shows immense promise in several nanoscientific and nanotechnological applications, including in sensors, catalysis, and biomedicine. Although several studies have shown the cytotoxicity of graphene oxide in different cell types, there are no comprehensive studies on human embryonic kidney (HEK293) cells that include transcriptomic analysis and an in vitro investigation into the mechanisms of cytotoxicity following exposure to graphene oxide. Therefore, we exposed HEK293 cells to different concentrations of graphene oxide for 24 h and performed several cellular assays. Cell viability and proliferation assays revealed a significant dose-dependent cytotoxic effect on HEK293 cells. Cytotoxicity assays showed increased lactate dehydrogenase (LDH) leakage and reactive oxygen species (ROS) generation, and decreased levels of reduced glutathione (GSH) and increased level of oxidized glutathione indicative of oxidative stress. This detailed mechanistic approach showed that graphene oxide exposure elicits significant decreases in mitochondrial membrane potential and ATP synthesis, as well as in DNA damage and caspase 3 activity. Furthermore, our RNA-Seq analysis revealed that HEK293 cells exposed to graphene oxide significantly altered the expression of genes involved in multiple apoptosis-related biological pathways. Moreover, graphene oxide exposure perturbed the expression of key transcription factors, promoting these apoptosis-related pathways by regulating their downstream genes. Our analysis provides mechanistic insights into how exposure to graphene oxide induces changes in cellular responses and massive cell death in HEK293 cells. To our knowledge, this is the first study describing a combination of cellular responses and transcriptome in HEK293 cells exposed to graphene oxide nanoparticles, providing a foundation for understanding the molecular mechanisms of graphene oxide-induced cytotoxicity and for the development of new therapeutic strategies.  Graphene oxide is a two-dimensional monolayer composed primarily of carbon atoms. It is the oxidized form of graphene and contains various oxygen-containing functionalities, such as epoxide, carbonyl, carboxyl, and hydroxyl groups. Graphene oxide has a large surface area and is cheaper and easier to manufacture than graphene ,2. Due tIn vitro assays are effective strategies as a first approach for determining the cytotoxicity of nanomaterials. Several studies have been conducted to estimate the level of toxicity in different cell types, including pheochromocytoma-derived PC12 [Due to the extensive range of applications for graphene oxide, cytotoxicity studies are essential for the safe and sustainable development of graphene oxide-based nanotechnologies . In vitrved PC12 , HeLa, Mved PC12 ,12,13,14ved PC12 . Oxidatived PC12 .COX2 via epigenetic mechanisms in HEK293T cells.Graphene oxide biocompatibility with several cell lines is dependent on the size of the particles. Graphene oxide was found to elicit toxicity only at high concentrations in human fibroblast cells (HDF); moreover, Gurunathan et al.  reportedCell survival and death are two major toxicity endpoints that can potentially be affected by any nanoparticle treatment. Carbon nanoparticles, in particular, evoke severe toxicity by inducing apoptosis and mitochondrial dysfunction. Due to the extensive use of graphene oxide, it is necessary to minimize its cytotoxicity and determine the associated regulatory molecular mechanisms. Recent findings suggest that the graphene oxide treatment can impair the general cellular priming state, including eliciting disorders of the plasma membrane and cytoskeleton construction . GraphenIn this study, we selected HEK293 cells as a model system to investigate the effects of graphene oxide. These cells are widely used in cell biology and biotechnology to study signal transduction and protein interactions. Non- or low tumorigenic HEK293 cells are frequently used to test the oncogenic properties of cancer-associated genes. Furthermore, these cells most closely resemble adrenal cells, which possess numerous neuronal properties. Given the broad use of HEK293 cells for biomedical research, we used HEK293 cells to investigate the comprehensive cellular effects and molecular mechanisms associated with graphene oxide toxicity.4, NaNO3 anhydrous ethanol, H2SO4, 36% HCl, and 30% H2O2 aqueous solution were purchased from Sigma-Aldrich . The penicillin-streptomycin solution, trypsin-ethylenediaminetetraacetic acid solution, Dulbecco’s modified Eagle’s medium (DMEM), and 1% antibiotic-antimycotic solution were obtained from Gibco . Fetal bovine serum (FBS) and the in vitro toxicology assay kit were purchased from Sigma-Aldrich. The kits for measuring MDA and antioxidants levels were also purchased from Sigma-Aldrich, as were all other chemicals unless otherwise stated. HEK293 cell lines were purchased from the American Type Culture Collection . Graphite powder, NaOH, KMnO2SO4 at 0 °C; then, 8 g of KMnO4 and 1 g of NaNO3 were added gradually while stirring. The mixture was transferred to a 40 °C water bath and stirred for 60 min. Deionized water (250 mL) was slowly added, and the temperature was increased to 98 °C. The mixture was maintained at 98 °C for 30 min and the reaction was then terminated by adding 500 mL of deionized water and 40 mL of a 30% H2O2 solution. The color of the mixture changed to a brilliant yellow, indicating oxidation of pristine graphite to graphite oxide. The mixture was filtered and washed with dilute HCl to remove metal ions. The product was washed repeatedly with distilled water until a pH of 7.0 was achieved and then further sonicated for 15 min. To prepare smaller sized graphene oxide particles, the prepared, brownish mixture of graphene oxide was centrifuged and washed several times with deionized water. The unexfoliated graphene oxide was removed by centrifugation at 12,000 rpm for 5 min, and the as-prepared graphene oxide was dried at 40 °C. To obtain a uniform distribution of smaller sized graphene oxide sheets, a low-speed centrifugation was performed at 5000 rpm for 15 min to remove thick multilayer flakes until all the visible particles had been removed. The supernatant was then further subjected to ultrasonication for 1 h. The resulting graphene oxide samples were used for subsequent analyses.Graphene oxide was synthesized as described previously, with suitable modifications ,27. For 2 at 37 °C. Cells were routinely grown in 100-mm plastic tissue culture dishes  and harvested at the logarithmic phase of growth using a trypsin-EDTA solution. Experiments were performed in 96-, 24-, and 12-well plates and 100-mm cell culture dishes, as indicated. Cells were treated with various concentrations of graphene oxide or the required dose of graphene oxide. Silver nanoparticles (25 μg/mL) were used as a positive control and media without cells used as a negative control. In order to verify the performance of graphene oxide, all the cellular assays experiments, we used media without cells as a negative control (NC) and silver nanoparticles (AgNPs) as a positive control. HEK293 cell lines were maintained in Dulbecco’s modified Eagle’s medium (DMEM) supplemented with 10% FBS, 100 U/mL penicillin, and 100 μg/mL streptomycin in a humidified incubator in 5% CO2 in a humidified incubator, 10 μL of a CCK-8 solution was added to each well and the plate was incubated for an additional 2 h at 37 °C. The absorbance was measured at 450 nm using a microplate reader . Cell proliferation was determined according to the manufacturer’s instructions (Roche).Cell viability and cell proliferation were measured using a Cell Counting Kit-8 (CCK-8) and a BrdU assay kit. Briefly, HEK293 cells were plated in 96-well flat-bottom culture plates containing various concentrations of graphene oxide. After 24 h of culture at 37 °C and 5% COHEK293 cell membrane integrity was evaluated using an LDH Cytotoxicity Detection Kit according to the manufacturer’s instructions. Briefly, cells were exposed to various concentrations of graphene oxide for 24 h, following which dead-cell protease activity was assessed using a previously described method . The cytHEK293 cells were treated with various concentrations of graphene oxide for 24 h. ROS levels were measured according to a previous method based on the intracellular peroxide-dependent oxidation of 2′,7′-dichlorodihydrofluorescein diacetate  to form the fluorescent compound, 2′,7′-dichlorofluorescein (DCF) [Antioxidant enzyme activities and MDA content were measured using a previously described method . HEK293 HEK293 cells were treated with various concentrations of graphene oxide for 24 h. Changes in MMP were determined using the cationic fluorescent dye, JC-1 . Fluorescence of JC-1 aggregates and JC-1 monomers was measured at an excitation wavelength of 488 nm and emission wavelengths of 583 and 525 nm, respectively, using a Gemini EM fluorescence microplate reader .ATP levels were measured in HEK293 cells according to the manufacturer’s instructions . The cells were exposed to various concentrations of graphene oxide for 24 h and the ATP level was then measured.8-oxo-dG and its analogs were used as biomarkers of oxidative DNA damage and oxidative stress. To evaluate graphene oxide-induced oxidative stress in HEK293 cells, an 8-oxo-dG ELISA assay was utilized as previously described  and follCaspase 3 activity was measured according to previously described methods . Cells wTotal RNA was isolated from both untreated and AdNP-treated HEK293 cells using an RNeasy kit (Qiagen). Before the RNA extraction, the cells were thoroughly washed with ice-cold PBS to remove dead cells. The RNA concentration and quality were measured on a bioanalyzer using Bioanalyzer RNA chips . Total RNAs with ˃7 RNA integrity number (RIN) were used for library preparation. An RNA-Seq library was prepared using an Illumina TruSeq Stranded total RNA sample preparation kit following the manufacturer’s instructions. Approximately 1 µg of total RNA was reverse transcribed. The synthesized cDNA was then subjected to fragmentation, adaptor ligation, PCR amplification, and gel size selection. Sequencing was performed using a NextSeq500 sequencer . After sequencing, the reads were assessed for quality and mapped to the National Center for Biotechnology Information (NCBI) Human Genome Assembly (hg19) using FastQC and the STAR pipeline, respectively. Using the Cufflink tool, differentially expressed genes (DEGs) were determined using a cutoff value (FPKM) >3 and a fold change (FC) >3. The DEGs were then subjected to gene ontology (GO) term analysis using DAVID, and the results were plotted using GOplot . Scatter plot and GOplot images were generated in R (v3.3.2).p-value was calculated by right-sided hypergeometric tests and Benjamin–Hochberg adjustment was used for multiple test correction. KEGG pathways with a p-value < 0.05 were considered significant. Coexpression and physical interactions (protein–protein) of the DEGs were determined using GeneMANIA plug-in  for Cytoscape. A query-dependent weighting method for the selected genes was used in the analysis.GSEA  was used to determine the biological enrichment in the DEGs of the treatment group. For this, gene expression data in GCT format, molecular signature database (MsigDB) in GMT format, and phenotype labels in CLS file format were used. KEGG pathway enrichment analysis for the DEGs from the graphene oxide-treated HEK293 cells was performed using the ClueGO plug-in  for Cytoscape . ClueGO generates functionally clustered KEGG annotation networks with the DEGs. The t-test to determine the one sample to control and significant differences denoted by an asterisk. The results are presented as mean ± standard deviation of three experiments. *p < 0.05 was considered significant, **p < 0.01 was considered highly significant, and ***p < 0.001 was considered very highly significant.Independent experiments were repeated at least three times with three replicates for each concentration. Data were analyzed by a Student’s . Graphene oxide displayed two different characteristic features: A shoulder at approximately 300 nm, corresponding to an n-π* plasmon peak, and a separate shoulder at 230 nm, corresponding to a π-π* plasmon peak [Graphene oxide materials were synthesized as described in our recent study , and themon peak .−1 was assigned to O–H group stretching vibrations. The absorption peaks at 1736 and 1625 cm−1 were assigned to C=O stretching of carboxylic and/or carbonyl functional groups [−1 were assigned to C–O stretching vibrations (The FTIR spectra showed characteristic oxygen-containing groups in which the main absorption band at 3356 cmbrations B. The FTX-ray diffraction (XRD) was performed to determine the magnitude and location of peaks in the XRD curves. In general, natural graphite shows a sharp and highly intense reflection peak at 2θ = 26°. After oxidation, the sharp and intensive graphene oxide peak reflected at 2θ = 10.2° was due to the introduction of functional groups such as hydroxyl and carboxyl during oxidation and ultrasonic treatment C. This iDynamic light scattering is a simple technique that can be used to determine the size distribution of particles in solution. Although the prepared sample had a wide particle size distribution (between 10 and 300 nm), most of the particles were dispersed within 50 nm D in wateThe surface morphology of graphene oxide was confirmed by SEM. The SEM images indicate the formation of graphene oxide sheets with a closely packed lamellar structure, composed of waves that look like fine, alternating layers E. GrapheNext, we examined the surface morphology of graphene oxide by TEM. The TEM images of graphene oxide exhibited a closely packed, lamellar, swollen structure, with a clean and transparent surface. The TEM images also showed a typical flaky structure, which had the wrinkly/wavy characteristic of transparent pure graphene oxide F. Our re−1, which can be attributed to sp3-dependent defects on the breathing modes of the sp2 rings. These defects indicate flaws in the graphene structure and the G band at approximately 1600 cm−1, owing to the vibration of the sp2-bonded carbon atoms were observed in graphene oxide with the ID/IG value of 1.0. The D and G bands were attributed to disorders in the C–C bonds and in-plane vibrations of the C–C bonds, respectively, which is in agreement with previous reports [Raman spectroscopy is used to observe the atomic vibrational, rotational, and other low-frequency dynamic modes in carbon materials. It is a very well designed technique to identify the molecular or atomic composition of samples quickly and reliably. As depicted in  reports ,36,37,38The effects of graphene oxide on the viability and proliferation of HEK293 cells were determined after 24 h of exposure to different concentrations of graphene oxide (0−50 μg/mL) using the CCK-8 and BrdU assays, respectively. The results revealed that graphene oxide has a significant and dose-dependent toxic effect, even at 10 μg/mL A,B. p < 0.05) viability and proliferation with increasing concentrations of graphene oxide. We have previously shown the dose-dependent toxic effects of graphene oxide in a variety of cells, including human breast cancer, ovarian cancer, neuroblastoma, and human lung cancer cells [HEK293 cells show reduced  leakage and dead-cell protease activity appear to be sensitive and reliable. Moreover, both assays have been used previously to measure plasma membrane integrity. Therefore, we measured LDH leakage and dead-cell protease activity to determine the cytotoxicity of graphene oxide. Dead-cell protease activity is represented as the percentage of viable cells. When the cell membrane is damaged, LDH is released into the medium, while dead-cell protease activity is quantified as the level of proteases released from membrane-compromised cells. HEK293 cells were treated with graphene oxide for 24 h and LDH and the dead-cell protease were dose-dependently released into the media A,B.Graphene oxide induces cytotoxicity by increasing LDH leakage in a variety of cancer cells, including ovarian cancer, neuroblastoma, and human lung cancer cells ,28,31. COxidative stress is one of the major mechanisms involved in graphene oxide-induced oxidative stress in a variety of cell types, including bacterial and human cells ,32,43. OGraphene oxide-treated HEK293 cells showed a high rate of ROS formation with increasing doses of graphene oxide (10–50 μg/mL). ROS combine with hydrogen atoms, generating water and a fatty acid radical that can cause oxidative degradation of lipids and, subsequently, cell membrane damage ,44. We eSince thiol metabolism seems to play an important role in defense against exposure to toxicants such as nanoparticles, the concentration of reduced glutathione (GSH) was determined in HEK293 cells after incubation with graphene oxide. The level of GSH was significantly and dose-dependently decreased in graphene oxide-treated cells A. Glutathione is considered one of the most important ROS scavengers and is an important and ubiquitous component of the cellular defense mechanism against oxidative stress . A rapidIncreased levels of oxidative stress disrupts homeostasis, and the enzymes responsible for reducing ROS levels, such as glutathione peroxidase (GPx), cannot compensate for the damage to macromolecules like proteins, DNA, and lipids, which greatly influences cell metabolism and signaling . To bett2+ homeostasis [Mitochondrial function is essential for cellular energy balance, metabolism, modulation of calcium signaling, and cell death. Since mitochondria are the main source of ROS in the cell, we hypothesized that a relationship exists between the mitochondrial membrane potential (MMP) and the rate of ROS production. Therefore, we investigated the effects of graphene oxide on the MMP by measuring the JC-1 aggregate to monomer ratio, and found that it was significantly and dose-dependently lower in graphene oxide-treated HEK293 cells than in the control condition A. The fieostasis . Loss ofeostasis ,48.Since mitochondria are a major source of intracellular ATP generation, and the MMP is vital for ATP production, we measured the ATP levels in graphene oxide-treated HEK293 cells. As shown in Overproduction of ROS can induce oxidative stress, which can subject cells to DNA damage, unregulated signaling, changes in motility, cytotoxicity, apoptosis, and cancer initiation . DNA damC. elegans germ cells and mammalian cells [PUMA and NOXA. Graphene nanoparticles induce cytotoxicity in rat pheochromocytoma cells (PC12 cells) through mitochondrial injury-dependent release of LDH, increased activation of caspase 3, and ROS generation [Overall, caspases play significant roles in cell survival and cell death, since most apoptotic pathways are activated by caspase-dependent cleavage of numerous cytoplasmic and nuclear proteins. Apoptotic signaling by executioner caspases, including caspases 3, 6, and 7, is activated by initiator caspases  ,60. To ian cells . The p53neration  demonstrneration  observedLRP1 and CD24) and upregulated genes (HSPA1A) are illustrated using the IGV genome browser . In the DEG analysis, 119 and 148 genes were down- and upregulated, respectively, in response to graphene oxide treatment A. We nex browser .DDR2, a gene found in the GO term of “cell adhesion” , KEGG, and GeneMANIA was performed to know the mechanism by which graphene oxide promotes apoptosis. In the GSEA, 33 out of 50 and 17 out of 50 gene sets were respectively up- and downregulated in the graphene oxide-treated group, with an enrichment score of 0.4. Among them, the analysis revealed that groups of DEGs were enriched in the apoptosis and G2M checkpoint pathways A. KEGG aFOSB, JUNB, FOS, and FOSL1. Irradiating mammalian cells with ultraviolet (UV) light is known to rapidly induce c-Jun, JUNB, and c-Fos expression [HES5 and RARB  were queried among the DEGs. As shown in pression . In contand RARB B. Importand RARB C. CollecUnderstanding the molecular mechanism of graphene oxide-induced cytotoxicity and cellular responses in HEK293 cells is necessary. We therefore proposed an integrative analytical approach, using various cellular assays and transcriptome analysis, to identify the associated molecular and cellular pathways. We prepared smaller graphene nanoparticles with an average size of 50 nm and then characterized them using various analytical techniques. Furthermore, we also performed a series of assays that measured cell viability, proliferation, cytotoxicity, oxidative stress, antioxidant levels, mitochondrial dysfunction, DNA damage, caspase 3 activity, and the transcriptional profiles of genes involved in various cellular pathways. The CCK-8 and BrdU assays revealed a significant, dose-dependent decrease in cell viability and proliferation in response to graphene oxide. Our findings also demonstrated increased LDH leakage, ROS generation, and decreased levels of glutathione and glutathione peroxidase. This detailed, mechanistic approach shows that graphene oxide exposure results in decreased mitochondrial membrane potential and ATP synthesis, as well as increased DNA damage and caspase 3 activity. Our analysis revealed that graphene oxide directly alters the expression of genes involved in various apoptosis-related biological pathways. The RNA-Seq analysis of graphene oxide-treated HEK293 cells not only establishes mechanistic insights into how graphene oxide evokes extensive cell death in HEK293 cells, but also provides a basis for the development of therapeutic strategies to alleviate harmful effects during use. This study further provides a transcriptomic insight into the role of surface-mediated cellular signaling triggered by graphene oxide and will enable the development of nanomaterial-based therapeutics for regenerative medicine. This approach in understanding nanomaterial–cell interactions illustrates how changes in the transcriptomic profile can predict downstream effects following nanomaterial treatment.


The electrochemical decoration of CVD monolayer graphene with MoO2 is shown to originate from the edge plane like- sites/defects. Edge plane decoration of MoO2 nanowires upon monolayer graphene is observed via electrochemical deposition over short time periods only (ca. −0.6 V for 1 second (vs. Ag/AgCl)). At more electrochemically negative potentials (ca. −1.0 V) or longer deposition times, a large MoO2 film is created/deposited on the graphene sheet, originating and expanding from the original nucleation points at edge plane like- sites/defects/wrinkles. Nanowire fabrication along the edge plane like- sites/defects of graphene is confirmed with Cyclic Voltammetry, Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and Raman Spectroscopy. Monitoring the electrochemical response towards [Ru(NH3)6]3+/2+ and comparing the heterogeneous electron transfer (HET) kinetics at CVD grown monolayer graphene prior and post nanowire fabrication reveals key understandings into the fundamental electrochemical properties of carbon materials. The HET kinetics  grown monolayer graphene using a polymer-free transfer methodology is explored through the selective electrodeposition of Molybdenum (di)oxide (MoO Typically, graphene is fabricated via one of two routes; a bottom-up (BU) or a top-down (TD) approach. TD methods, such as chemical/thermal reduction of graphene oxide or using physical/chemical exfoliation, can give rise to a large quantity of graphene sheets; however, the fabricated graphene is generally highly defective and abundant with residual C/O groups or other contamination such as surfactants or metals24. Bottom-up (BU) fabrication routes typically lead to higher quality graphene, but in smaller quantities25. Chemical Vapour Deposition (CVD) growth of graphene onto a copper catalyst is a BU route that facilitates the study of high quality monolayer graphene sheets/films28, which can then either be transferred (commonly using Poly(methyl methacrylate), PMMA) onto a suitable substrate31. PMMA has previously been reported to affect the physical and electrical properties of CVD grown graphene samples transferred via this route38, therefore, in this work we address the fundamental properties and conduct performance studies on CVD grown monolayer graphene transferred via a polymer-free transfer method39.Graphene is extensively studied due to its reported unique electronic, mechanical and optical propertiesvia a BU approach), the reactivity of such electrodes is commonly assigned to the graphene edge planes, which are reported to exhibit ca. 4 orders of magnitude greater specific capacitance, faster electron transfer rates and higher electrocatalytic activity when compared to the graphene basal planes40. Recent work involving the electrochemical behaviour of CVD grown pristine graphene has shown a correlation in the structure of graphene, in terms of a dependence upon its number of layers and the macroscopic electrochemical response/performance42. Moreover, an identical relationship in terms of graphene’s geometric structure  has recently been reported with respect to the lateral flake size, in which smaller graphitic flake sizes  exhibited improved electrochemical properties when compared to the inverse43. Indeed, there have been numerous other studies reporting that, in comparison to the edge plane like- sites/defects45, the basal planes of graphitic and carbon-based materials are effectively inert47. However, regardless of the vast number of recent reports concerning graphene-based electrodes, researchers still debate the real contributions of edge and basal plane like- sites/defects at the macroscopic scale, in future experiments researchers should clarify the experimental configuration of their studies, ie. macro- vs microscopic voltammetry48 with respect to their observed heterogeneous electron transfer (HET) kinetics52; further work is required to explore this edge vs basal argument for carbon surfaces48. It is these aforementioned research considerations that we investigate herein, through the utilisation of a MoO2 deposition technique to decorate CVD grown monolayer graphene (transferred using a polymer-free method) so that one can determine the true electrochemical contributions arising from its structure.In terms of understanding the electrochemical response of CVD grown monolayer graphene  are responsible for the voltammetric signal, and Rowley-Neale et al.59 extended these insights with screen-printed graphitic electrodes (SPEs) with similar results. In these approaches, the selective deposition of metals and metal oxides onto graphite is called ‘step edge decoration’56, and has been utilised to demonstrate that electrochemical reactions at edge plane graphite are “anomalously fast” in comparison to the basal plane, which is effectively inert in comparison60. Through the selective coating and blockage method of the edge plane like- sites/defects with MoO2 nanowires , a reduction in the electrochemical response towards [Ru(NH3)6]3+/2+ 47 was reported; clearly demonstrating that the electrochemical reactivity of the HOPG is due to edge plane like- sites/defects. To the best of our knowledge, the above elegant approach has not previously been applied towards CVD grown monolayer graphene sheets (in addition to the polymer-free transfer method utilised herein) contributing to the understanding of graphene and all akin carbon-based electrode materials.Molybdenum oxide(s) and other metal oxides have been shown to electrochemically nucleate specifically onto the edge plane like- sites/defects of highly oriented pyrolytic graphite (HOPG)2 onto HOPG and SPEs59, where MoO2 selectively deposits upon the available edge plane like- site/defects, allowing their electrochemical contributions to be deduced. In consideration of these approaches, herein we adapt this method towards CVD grown monolayer graphene sheets. Presented within the Experimental Section and ESI (1.1–1.4) are details of the fabrication process, optimisation and physicochemical characterisation of the CVD grown monolayer graphene sheets and their MoO2 decorated counterparts. Briefly, Figure 2 decorated monolayer graphene, displaying the typical monolayer graphene D (1350 cm−1), G (1580 cm−1), 2D (2700 cm−1) and 2D’ (3250 cm−1) peaks, the presence of MoO2 (308 cm−1)61 and the presence of the underlying Si (514 and 985 cm−1) wafer . Additionally, AFM images were collected in order to characterise the MoO2 nucleation upon the edge plane like- sites/defects as depicted in Figure selective nucleation characterised by Rowley-Neale et al.59.Previously reported methodologies have utilised the electrochemical decoration of MoO3)6]3+/2+, which exhibits a peak-to-peak separation (ΔEp) of 160 mV (at 50 mV s−1vs. Ag/AgCl) and a HET . Note that this value is similar but slightly faster than other CVD monolayer graphene sheets previously reported by our research group41, which is due to a higher exposure of the edge plane like- sites/defects upon the graphene sheet. Furthermore, it is worth noting at this stage that each individual graphene sheet is unique in terms of its level of edge plane like- site/defects, so there is natural variation in the reported HET rates throughout the literature; thus, it is important to characterise each monolayer graphene sample62 prior to modification with MoO2. Figure 2 electrochemically decorated monolayer graphene sheet following applying chronoamperometry at a set voltage (−0.6 V vs. Ag/AgCl) for 1 second, where it is readily observed that the MoO2 nucleates upon the edge plane like- sites/defects/wrinkles of the monolayer graphene surface. Figure 3)6]3+/2+, which exhibits a ΔEp of 200 mV (at 50 mV s−1vs. Ag/AgCl) and a −4 cm s−1. Such decreased voltammetric behaviour implies that the insulating MoO2 nanowires have coated some of the available edge plane like- sites/defects, with some edge sites remaining unmodified. Figure θedge) values) the changes observed as one electrodeposits MoO2 onto the graphene electrode’s surface. Such voltammetric profiles show that the decorated electrode (dashed line) still exhibits relatively fast HET kinetics when compared to the unmodified electrode (solid line), but presents a lower current intensity due to the limited availability of edge plane like- sites/defects on the electrode surface. This is corroborated with the SEM presented within Fig. Figure vs. Ag/AgCl). Presented within Fig. 2 electrochemically decorated monolayer graphene sheet that has been applied at −0.6 V (vs. Ag/AgCl) for 10 seconds via chronoamperometry, where it is clear that electrodeposition is no longer isolated upon the edge plane like- sites/defects. Instead, the MoO2 has coated/blocked the entire electroactive surface. Upon electrodeposition at more electrochemically negative potentials (ca. −1.0 V) or longer deposition times, a large MoO2 film is created/deposited on the graphene sheet, originating and expanding from the original edge plane like- sites/defects (non-selective deposition), as shown in Figures 3)6]3+/2+, exhibits a ΔEp of 820 mV and a −6 cm s−1. As expected, the monolayer graphene sheets coated with insulating MoO2 (upon the edge plane like- sites/defects), give rise to an electrochemical response with a larger ΔEp (slower electron transfer) than the unmodified monolayer graphene. The aforementioned MoO2 coverage dependant electrochemical behaviour has been illustrated within the schematic presented within Fig. Next we investigate the effect of increased deposition times at −0.6 V (2 wires that nucleate onto the graphene’s edge plane (and or defect/wrinkle) sites when a electrodeposition for 1 second at −0.6 V is performed, resulting in a decrease in the reversibility of the [Ru(NH3)6]3+/2+ redox probe. Longer deposition times will increase the nucleation of the MoO2 onto remaining edge sites and towards the basal plane of the graphene sheet (deposition of 5 seconds at −0.6 V). Eventually, a complete coverage of the surface of the graphene is confirmed by the absence of cyclic voltammetric redox peaks of [Ru(NH3)6]3+/2+, for example, when a electrodeposition of 10 total seconds at −0.6 V is performed.Figure 2 wires are indeed being electrodeposited selectively onto the graphene edge plane like- sites/defects, at a set potential of −0.6 V (vs. Ag/AgCl) for 1 second and this results in a decrease in the 2 selectively electrodeposits upon the edge plane like- sites/defects, which is confirmed by physicochemical characterisation, indicating that these are the active sites for electron transfer. If no changes in the voltammetry were observed, this would indicate that basal planes sites are the origin of electron transfer, as this is not the case, our work provides convincing evidence that it is the edge plane like- sites/defects of the CVD grown monolayer graphene that are the origin. When utilising an electrodeposition of 10 seconds, an insulating film is created, which largely decreases the amount of available edge plane like- sites/defects by up to 99.9%. Note that in the case of sample B, however, due to the initial low θedge and hence 2 has fewer edge plane like- sites/defects to deposit upon. This demonstrates again that each individually grown CVD graphene sheet is unique in terms of edge plane like- sites/defects and i.e. too long deposition times and high deposition potentials, physicochemical characterisation would indicate a large film is created, which would give the false impression that the basal plane of monolayer graphene is as equally electrochemically active as the edge plane sites, which is not the case. However, there has been a great deal of elegant work published on the micro scale response of electron transfer at carbon materials using novel nanoscale techniques64, therefore it is intended that the data reported herein be considered in-conjunction with such other studies for the electrochemical community to better understand this phenomena as a whole.The experiments performed above confirm that the MoO2 nanowire arrays have been electrodeposited onto the edge plane like- sites/defects of CVD grown monolayer graphene using a polymer-free transfer method, which have been confirmed via physicochemical characterisation. The electrochemical activity pre and post MoO2 electrochemical deposition has been assessed using a near-ideal redox probe and in the latter case indicates that the HET kinetics (MoO3)6]3+/2+ (in 0.1 M KCl), 0.5 M H2SO4 and 1 mM Na2MoO4 (in 1 M NaCl).All chemicals used were of analytical grade and were used as received from the supplier  without any further purification. All solutions were prepared with deionised water of resistivity no less than 18.2 MΩ cm and were vigorously degassed prior to electrochemical measurements with high purity, oxygen free nitrogen. Test solutions were: 1 mM 3+/2+ (in 0.1 M KCl) using the well-known66 and utilised Nicholson method67, for quasi-reversible electrochemical reactions via the following formula59:φ is a kinetic parameter, D is the diffusion coefficient for [Ru(NH3)6]3+/2+ (D = 9.1 × 10−6 cm2 s−1)66, n is the number of electrons that are taking part in the process, F is the faraday constant, vis the scan rate, R is the gas constant and T is the temperature in Kelvin. In order to calculate the HET rate constant, we use the peak to peak separation (ΔEp) to deduce φ, where ΔEp is obtained at various voltammetric scan rates52. The standard heterogeneous constant 6]3+/2+, has been widely determined with a commercial simulation package providing a value of 0.4 cm s−1 for HOPG electrodes58.allowing the coverage of edge plane like- sites/defects upon the graphite electrode to be deduce; we use this and adapt this to the voltammetry observed at the CVD grown monolayer graphene sheets. %θ−1 . Scans were carried out at 40 µm/s with a force set point of 6 nN. Samples were attached to glass microscope slides using double sided tape.Raman Spectroscopy was performed using a DXR Raman Microscope  fitted with a 532 nm excitation laser at a low power of 3 mW to avoid any heating effects. Spectra were recorded using a 3 second exposure time for 3 accumulations at each point. Scanning electron microscope (SEM) images were obtained using a JSM-5600LV  model SEM equipped with an energy-dispersive X-ray microanalysis (EDS) package. Atomic force microscopy (AFM) images were obtained using a DualScope C26 , carried out using AC mode using DS 95 AC probes with a spring constant of 42 N mNote that the area studied is in the macroscale range which is not considered too large because indeed it averages the actual phenomena occurring locally . Such that this makes this study applicable for real applications. We are reporting on the average response of the macro electrode with varying contributions of the two micro features , which is relevant because the likely end use/application of such systems will be on that of the macro scale.Supplementary information


Azadirachta indica) is a tree from the Meliaceae family native to India, where it is considered as one of the most important plants worldwide. The anticancer effects of neem oil on breast cancer cells have been recently reported; however, its in vivo effects have not been studied. This prompted us to investigate the protective effects of neem oil on 7,12-dimethylbenz(a)anthracene (DMBA)-induced breast cancer in high-fat/sucrose-fed Wistar rats. Juvenile female Wistar rats were treated either with neem oil at a dose of 3 mL/kg body weight at 3 different frequencies, 2 times/week (Neem 1), 4 times/week (Neem 2), and every day (Neem 3), or with tamoxifen (3.3 mg/kg body weight), starting 1 week prior to DMBA treatment and lasting 12 weeks. Incidence, burden, volume, and histological analysis of mammary tumors were measured. Further toxicological parameters have been assessed. No tumors were detected in rats from the normal group, while all the rats from the negative control group (100%) developed mammary tumors. The regular consumption of neem oil at a dose of 3 mL/kg (2 or 4 times/week) significantly (p < 0.01) and in a dose-dependent manner reduced tumor incidence (80%), burden [35.78% (2 times/week) and 36.09% (4 times/week)], and weight. Neem consumption protected rats against DMBA-induced breast hyperplasia, with an optimal effect when taken 4 times weekly. Interestingly, all the animals that received a daily dose of 3 mL/kg died at the third week of the experiment. Further, animals that took the neem oil 4 times per week developed hepatotoxicity, evidenced by an increase of liver wet weight, transaminase (ALT and AST) activity, and histological abnormalities in liver. This study brings insight into the use of neem oil, which is greatly appreciated in traditional medicine. In summary, we demonstrated for the first time that the regular consumption of neem oil prevents breast cancer, but its excessive consumption is toxic.Neem ( Cancer is a growing health problem affecting millions of people worldwide. In 2012, it was estimated that 32.6 million people were suffering from cancer, and it is predicted that 18.5% of the world's population will likely develop cancer before the age of seventy-five . VariousBreast cancer continues to be an enigmatic challenge for researchers and is one of the most threats and a major cause of mortality in women worldwide . TreatmeAzadirachta indica) is a tropical or subtropical fast-growing evergreen with oblique leaves and stout trunk of timber values with insect-repellant properties [50 of 10 μl/ml and 20 μl/ml, respectively. According to the same authors, the neem oil induced apoptosis and cell cycle arrest at G0/G1 phase in both cell types. However, the in vivo effects of neem oil have not been studied, although it is being used increasingly in Cameroonian traditional system. We therefore analyze the in vivo anti-mammary cancer effects of neem oil.Neem anthracene (DMBA) (purity ≥ 95%) was purchased from Sigma-Aldrich . Tamoxifen citrate (Mylan®) was purchased from MYLAN SAS .Azadirachta indica L.) were harvested in Maroua  in June 2017 around 11:30 a.m. The plant was localized at the geographical coordinates of N10° 35.487' East and E0 14° 18.910' altitude with a “ESTREX” global positioning system. The city of Maroua is in the Sudano-Sahelian agroecological zone, characterized by two seasons: wet (June to September) and dry (October to May). Annual rainfall ranges between 800 and 1000 mm. Annual mean temperature is 298 C, with a maximum of 39 8C in March and minimum of 17 8C in January. This botanical sample was identified and authenticated by M. Victor Nana, a taxonomist at the National Herbarium of Cameroon (HNC-IRA), by comparison to the specimens deposited under the voucher number 4447 SRFK.The seeds of neem  was collected in a clean plastic flask after filtering with a Whatman N°2 filter paper constituting our neem oil.Fifty prepubertal female Wistar rats, aged 35-40 days at the beginning of experiment and weighing around 45-65 g, were supplied by the breeding facility of the Laboratory of Animal Physiology, University of Yaounde I . These rats were housed in plastic cages in groups of five at room temperature. The animals had free access to a standard (SD) or high-fat high-sucrose (HFHS) chow  and wateHousing of animals and all experiments were approved by the Cameroon Institutional National Ethic Committee, which adopted all procedures recommended by the European Union on the protection of animals used for scientific purposes . i.p.). On the one hand, blood samples were collected in anticoagulant (EDTA) tubes for hematological analysis; on the other hand, they were collected in dried tubes and centrifuged at 600 × g for 15 min at 4°C for biochemical analysis. Furthermore, the skin was dissected out to expose mammary tumors and all tumors were removed, counted, and weighed. A 1 mm precision sliding caliper (IGAGING®) was used to measure the size of tumors. Afterward, the formula from Faustino-Rocha et al. [π/6) was used to calculate the tumor volume. Estrogen target organs were also removed and weighed. Finally, all these organs were fixed in 10% neutral formalin solution for histomorphology.Thirty-five (35) female rats were acclimatized for 10 days and randomly assigned at age of 50-55 days into 7 groups of 5 animals each. At the beginning of the experiment, animals were divided into two groups: rats fed with standard (n = 5) and high-fat/sucrose (n = 30) diet. Animals received the following treatment schedule: the rats fed with standard diet (SD) served as normal control 1 (NOR-1) and received the vehicle (cotton oil) throughout the experiment. Regarding animals fed with HFHS, group 1 served as normal control 2 (NOR-2) and received the vehicle (cotton oil); group 2 served as negative control (DMBA) and also received the vehicle; group 3 (positive control) received tamoxifen (Mylan®) at the dose of 3.3 mg/kg dissolved in cotton oil. The remaining groups were treated with neem oil at a dose 3 mL/kg  at 3 different frequencies: 2 times/week (Neem 1), 4 times/week (Neem 2), and every day (Neem 3). All treatments were administered via intragastric gavage one week before DMBA administration, once a day around 2:00 p.m., and lasted for 3 months. Breast tumors were induced in group 2 to group 6 of animals that received HFHS by a single subcutaneous dose of DMBA (50 mg/kg) dissolved in 1 ml of cotton oil, while normal group (NOR-1 and NOR-2) received cotton oil only. Experimental rats were weighed weekly and palpated twice a week to check the development of mammary tumors from the first day of acclimatization until the end of the experiment. Tumorous latency (time of tumor appearance) was recorded. On days 1 and 84 of treatment, fasting glycaemia was measured using whole capillary blood obtained from the tip of the tail. The sacrifice and autopsy of either animals that died during the experiment or those that became moribund were carried out. At the end of the 3-month treatment, all survivors were sacrificed after a 12 h overnight nonhydric fasting under valium and ketamine anesthesia  and alanine transaminase (ALT) activities were measured as previously reported , 15 usinDifferent hematological parameters were evaluated using a Mindray BC-2800 Auto Hematology Analyzer from Shenzhen Mindray Bio-Medical Electronics Co., Ltd. These are white blood cell (WBC) count, lymphocytes, monocytes, granulocytes, red blood cell (RBC) count, hematocrit, hemoglobin, mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), and platelets.Results are presented as means ± standard deviation (SEM) for each experimental group. Statistical analysis of data with GraphPad Prism software version 6.00 (GPW6-242831-RBMZ-03274) was performed using the one-way analysis of variance (ANOVA) followed by Dunnett's post hoc test for multiple comparisons. Statistical significance of differences was considered at a p value < 0.05.The body weight change of animals during the 12 weeks of experiment is represented in rd week of the experiment.It is important to notice that all the animals treated with a daily dose of 3 mL/kg of neem oil died before the 3th day of treatment.3, those of Neem 1 (with a mean volume about 700 cm3) and Neem 2 (with a mean volume about 300 cm3) decreased. Interestingly, the animals that received tamoxifen showed a significant (p < 0.001) lower tumor volume from day 49 until the end of the experiment with an average tumor volume of 150 cm3 as compared to DMBA group.In this study, tamoxifen significantly (p < 0.001) decreased average tumor weight as compared to DMBA control group . The neeThe tamoxifen significantly (p < 0.01) decreased the endometrium height but did not induce significant change in the vaginal epithelial height. The regular consumption of neem oil induced a significant decrease in endometrium height (p < 0.001) as well as the vaginal epithelial height (p<0.05 with Neem 1 and p<0.001 with Neem 2).No statistical significance was observed between normal and DMBA groups in all measured parameters except for a significant (p < 0.001) increase in red blood count (RBC) and platelets level in the DMBA as compared to normal group . TamoxifThe mammary gland microarchitectures of rats from normal group showed normal acini surrounded by a small amount of fibrous conjunctive tissue . Rats thOn the other hand, histological abnormalities such as sinusoid dilatation, vascular congestion, and inflammation were observed in the liver of animals that took neem oil 4 times/week, as compared to the liver of normal animals. No significant alteration was observed in the microarchitecture of kidneys.Azadirachta indica) have been shown to inhibit the growth of cancer cells through several mechanisms [ in vivo antitumor effects of neem oil, based on its reported anticancer effects on breast cancer cells [ in vivo anticancer effects of neem oil observed in this study. Preclinical studies have shown compelling evidence suggesting that the anticancer effects of neem are mediated through modulation of multiple cellular processes. Numerous bioactive compounds have been isolated from neem oil and could explain the chemopreventive and anticancer therapeutic efficacy of A. indica. There are essentially triterpenoids and steroids: nimbin, nimbinin, nimbidic acid, salannin, meliantriol, azadirone, epoxyazadiradione, azadiradione, gedunin, 7-deacetyl-gedunin, meldenin, salannin-lactone, nimbin-lactone, vepinin, nimbidinin, nimbinene, nimbandiol, 3-deacetylsalannin, salannol, 6-o-acetyl-nimbandiol, 1,3-diacetyl-vilasinin, and 6-deacetyl nimbinene [Despite the improvement in the diagnosis and treatment of breast cancer, it remains a major health issue for women . Existinchanisms . The preer cells . It was er cells , which der cells . Nimbolier cells . These cimbinene . In factimbinene . It is pGiven that neem-based preparations have been consumed for several millennia, the normal consumption of neem products can be regarded as absolutely safe . It is a in vitro anticancer effects reported, we demonstrated for the first time that the regular consumption of neem oil prevents breast cancer in rats, but its excessive consumption is toxic.In summary, the regular consumption of neem oil at a dose of 3 mL/kg (2 or 4 times/week) significantly reduced tumor incidence (80%), burden, and mass in a dose-dependent manner. Neem consumption protected rats against DMBA-induced breast hyperplasia. However all the animals that received a daily dose of 3 mL/kg died at the third week of the experiment. Further, animals which took neem oil 4 times a week presented a hepatotoxicity. This study brings new insight into the use of neem oil, which is greatly appreciated in traditional medicine. In line with the previous


A suspended monolayer graphene has only about 2.3% absorption rate in visible and infrared band, which limits its optoelectronic applications. To significantly increase graphene’s absorption efficiency, a tunable dual-band and polarization-insensitive coherent perfect absorber (CPA) is proposed in the mid-infrared regime, which contains the silicon array coupled in double-layers graphene waveguide. Based on the FDTD methods, dual-band perfect absorption peaks are achieved in 9611 nm and 9924 nm, respectively. Moreover, due to its center symmetric feature, the proposed absorber also demonstrates polarization-insensitive. Meanwhile, the coherent absorption peaks can be all-optically modulated by altering the relative phase between two reverse incident lights. Furthermore, by manipulating the Fermi energies of two graphene layers, two coherent absorption peaks can move over a wide spectrum range, and our designed CPA can also be changed from dual-band CPA to narrowband CPA. Thus, our results can find some potential applications in the field of developing nanophotonic devices with excellent performance working at the mid-infrared regime. As a crucial issue for nanophotonics and optoelectronics, efficient light-matter interaction has widely caused concerns in recent years , 2, partMore specifically, among these devices based on graphene, optical absorber takes an important role in the field of developing advanced optoelectronic devices, such as solar energy-trapping devices and emitters. Recently, due to the unique attributes of graphene, some absorbers based on graphene have been reported. Moreover, as mentioned above, most of these absorbers are focused on the terahertz and infrared regimes, because graphene with special processes can excite SPPs, leading to the strong light-graphene interactions in these wavelengths . For insImportantly, coherent perfect absorber (CPA), which is another way to control and strengthen the optical absorption of graphene, has attracted great attention due to the all-optical modulation features , 28. DepIn this paper, we design and study a tunable dual-band and polarization-insensitive CPA in the mid-infrared band, which contains a silicon array coupled in double-layers graphene waveguide. The physical mechanism of the designed CPA is analyzed by the scattering matrix. Meanwhile, the features of proposed CPA are demonstrated by the finite-difference time-domain (FDTD) simulations. When the incident light is illuminated into the silicon array, since the plasmonic resonances on the double continuous graphene films can be emerged due to the mechanism of guided-mode resonance, then the coupling effect between them results in the perfect dual-band absorption peaks, which are achieved in 9611 nm and 9924 nm, respectively. Moreover, due to its center symmetric feature, the proposed absorber also demonstrates polarization-insensitive. Furthermore, most of the reported graphene-based absorbers are manipulated by only changing the properties of graphene through an electrostatic field, magnetic field, or chemical doping, which are the causes of additional losses and also make the devices more complicated. For our proposed CPA, the coherent absorptions can be all-optically modulated by altering the relative phase between two reverse incident lights, which improves the absorber’s adjustability and does not increase the complexity of the structure. Meanwhile, by manipulating the Fermi energies of two graphene layers, two coherent absorption peaks can move over a wide spectrum range, and our designed CPA can also be changed from dual-band CPA to narrowband CPA. Therefore, our work provides a very promising way with convenience and sensitivity for potential applications include switches, all-optical logical devices, and coherent photodetectors.x-direction) and width (y-direction) of every silicon square in the array are both set as w = 80 nm, as shown in Fig. x-direction and y-direction are p = 160 nm, and the thickness (z direction) of silicon square is h = 100 nm. Moreover, the thicknesses of the silica spacer and substrate are d1 = 75 nm and d2 = 150 nm, respectively. I1 and I2, as two coherent incident lights, are simultaneously irradiated on the proposed CPA from two contrary directions, as shown in Fig. I1 and I2 is I2 = αI1 exp(iφ + ikz), where α, φ, and z are the relative amplitude, phase difference, and phase reference point between I1 and I2, respectively. O1 and O2 are the emergent lights scattering from the bottom and top of proposed CPA. Furthermore, the thicknesses of two graphene films are both set as 0.34 nm in our simulations, and the conductivities of two graphene films are both computed within the local random phase approximation as follows [T = 300K is the room temperature and Ef is the Fermi energy. Meanwhile, the intrinsic relaxation time is described as υf is the Fermi velocity and μ = 10000cm2V−1s−1 is the carrier mobility. For our proposed structure, the Fermi energies of the upper and lower graphene films are assumed as Ef1 = 0.66eV and Ef2 = 0.31eV, respectively.As illustrated in Fig.  follows :1\documx- and y-directions, and perfectly matched layer is applied along the z-direction including both the top and bottom of the proposed device. Moreover, we utilize the non-uniform mesh to compute the simulation results, where the minimum mesh size inside the graphene layer equals 0.1 nm and gradually increases outside the graphene film to cut down on the storage space and computing time.In the simulation, we utilize the 3D FDTD method for the numerical calculation. Meanwhile, periodic boundary conditions are applied along the I1 in the z-direction. Since the graphene-based CPA is in the symmetry environment, the combined reflection and transmission coefficients can be expressed as r = η and t = 1 + η, respectively, where η is the self-consistent amplitude related to the graphene hybrid waveguide. Thus, the absorption is derived as A = 1 − |r|2 − |t|2 =  − 2η2 − 2η. The condition of maximum absorption is ∂A/∂η = 0  and we get Amax = 0.5. In our simulation, when only one incident beam I1 vertically illuminates on the proposed absorber, due to the plasmonic resonances on the double graphene films, which are emerged by incident light through the silicon array for the mechanism of guided-mode resonance, then the coupling effect between the double graphene films leads to the dual-band absorption peaks, as demonstrated in Fig. Firstly, in order to clearly explain the physical mechanism, we investigate the absorption of proposed CPA under normal illumination of only one incident beam I1 and I2 vertically incident on the proposed structure from opposite sides, the schematic diagram is shown in Fig. O1 and O2 can also be assumed as the intensities of emergent lights from the bottom and top of the proposed CPA. The relationship between the incident lights and emergent lights is demonstrated by the scattering matrix:Then, when r11 = r22 =  − 0.5 and t12 = t21 = 0.5), by considering the relationship I2 = αI1 exp(iφ + ikz) with z = 0, the coherent absorption Aco of the proposed graphene-based CPA is express as [When the incoherent absorption limit is satisfied π to 2Nπ.Thus, according to Eq. , Aco canφ = 0 and α = 1 are coherent illuminated on the proposed structure, dual-band perfect absorption peaks can be achieved in λ1 = 9611 nm and λ2 = 9924 nm, respectively. Moreover, compared with the absorption under the illumination of only one incident beam, the absorption of the proposed graphene-based CPA has been significantly enhanced. It is worth noting that due to its center symmetric feature, the proposed CPA also demonstrates polarization-insensitive. As shown in Fig. p or s polarization, the absorption spectrum remains the same.As illustrated in Fig. To clearly demonstrate the features of proposed CPA, we illustrate the magnetic fields around the double-layers graphene waveguide at the wavelengths of absorption peaks. As described in Fig. φ, as illustrated in Fig. α of coherent incident lights is set as 1, and the other structural parameters are kept as the same as that in Fig. φ from 0 to π, two absorption peaks at 9611 nm and 9924 nm decrease continuously from 0.982 and 0.993 to almost 0, respectively. Thus, the modulation contrast can be as high as 34.8 dB and 35.2 dB at the two coherent absorption peaks with different φ, which shows a significant all-optical modulation property.Next, for the sake of displaying all-optical modulation characteristics, we demonstrate the coherent absorption of proposed absorber with different phase differences εi and ki  are the permittivities and wave vectors of the silicon array-graphene waveguide (i = 1), silica layer (i = 2), graphene film (i = 3), and silica substrate (i = 4), respectively. dg is the thickness of graphene. Thus, by properly manipulating the Fermi energies of two graphene films, the features of plasmonic modes sustained by two graphene films could be significantly and independently controlled. As seen in Fig. Ef1 of upper-layer graphene remains unchanged and the Fermi energy Ef2 of lower-layer graphene decreases from 0.31 to 0.27 eV, the absorption peak at λ1 red-shifts and keeps the value almost unchanged, while the absorption peak at λ2 reduces rapidly and even disappears under Ef2 = 0.27 eV, as shown in Fig. Ef2 increases from 0.31 to 0.37 eV, the absorption peak at λ1 reduces rapidly and almost disappears under Ef2 = 0.37 eV, while the absorption peak at λ2 blue-shifts and keeps the value almost unchanged. Thus, the dual-band proposed perfect absorber can be changed to narrow-band perfect absorber by separately altering the Ef2. On the other hand, when Ef2 remains unchanged and Ef1 increases from 0.62 to 0.72 eV, both two absorption peaks blue-shifts and keeps their values almost unchanged over a wide wavelength range, which demonstrates a significantly tunable characteristic. Compared with the other absorbers based on the discrete graphene patterns, it is worth noting that two graphene films of the proposed CPA are in the continuous form, which is more convenient to get excellent tunability.In the following, for our four layers (silicon array-graphene waveguide/silica layer/graphene film/silica substrate) system, combined with continuous boundary conditions and the Maxwell equations, the dispersion relation can be expressed as :4\documw is increased, dual-band absorption peaks are both red-shifted due to the increment of effective resonance wavelength of localized plasmon mode. Moreover, the filling factor will increase with w, which further reinforces the intensity of field enhancement and concentration between neighboring silicon square and inside graphene. Thus, the absorption efficiency will firstly increase with w. However, with the continuous increment of filling factor, too many areas of graphene will be covered by silicon squares. As a result, the absorption efficiency will subsequently decrease with the increment of w. Then, as shown in Fig. p, because the resonant wavelength of localized plasmon mode becomes larger. Furthermore, it is noted that the resonant frequency of the plasmonic mode supported by the lower-layer graphene strongly depends on the separation distance d1. As shown in Fig. d1 is increased, the nearfield coupling strength between the upper- and lower-layer resonance modes will become more and more weak, which lead the dual-band absorption peaks eventually to degenerate into one peak. Meanwhile, we also investigate the absorption of proposed CPA with different dielectric array. As shown in Fig. 2 array (nT = 2.9) or the GaSb array (nG = 3.8) is not better than the one with silicon array. Moreover, it is worth noting that the wavelengths of absorption peaks are red-shifted with the increment of the refractive index of the dielectric array.In addition, we investigate the influences of different structure parameters on the optical absorption of proposed CPA, as shown in Fig. As mentioned before, most reported graphene-based perfect absorbers are polarization-sensitive and focused on the narrowband or broadband perfect absorbers, dual-band graphene-based perfect absorbers are seldom investigated in the mid-infrared regime. In this paper, we have designed a tunable dual-band and polarization-insensitive CPA in the mid-infrared regime, and the corresponding absorption features are discussed by using the scattering matrix and FDTD simulation, which illustrate that dual-band perfect absorption peaks are achieved in 9611 nm and 9924 nm, respectively. Moreover, due to its center symmetric feature, the proposed CPA also exhibits polarization-insensitive. Meanwhile, the coherent absorption peaks can be all-optically modulated by altering the relative phase between two reverse incident lights. Furthermore, by manipulating the Fermi energies of two graphene layers, two coherent absorption peaks can move over a wide spectrum range, and our designed CPA can also be changed from dual-band CPA to narrowband CPA. On the other hand, for the proposed CPA, subwavelength metamaterials based on silicon squares can be integrated for the current CMOS technology, and chemical vapor deposition (CVD) grown graphene can be transferred over the silica layer using standard transfer techniques . Moreove


Carbon allotropes with their dispersive electron states at the Fermi level and a small spin-orbit coupling are not an obvious candidate for ferromagnetism. Here we show that the origin of ferromagnetism in hydrogenated epitaxial graphene with a relatively high Curie temperature (>300 K) lies in the formation of curved specific carbon site regions in the graphene layer, induced by the underlying Si-dangling bonds and by the hydrogen bonding. Hydrogen adsorption is therefore more favourable at only one sublattice site, resulting in a localized state at the Fermi energy that can be attributed to a pseudo-Landau level splitting. This  This indicates that the observed peaks in the DOS can be assigned to pseudo-Landau levels (PLLs). It is worth to note that the H-induced PLLs are not only caused by ”mechanical” strain  and, hence, a pseudo-magnetic field. Using a Fermi velocity of 1.0 × 106 ms−1, the resulting pseudo-magnetic field extracted from the fit is ∼250 T and its value increases for higher hydrogen coverage and vice versa. This is in agreement with previous theoretical results [The adsorbed H atom breaks a π bond and slightly pulls out the carbon atom below due to a covalent bond interaction. This carbon atom changes its hybridization state from speference . The corous work  as arisious work , the consymmetry ,39. As isymmetry ,41, strun = 0) will split into two states; filled state (spin up) and empty state (spin down) denoted by red and blue lines in From the value of the pseudo-magnetic field, it is noteworthy that the magnetic length  SiC superstructure. Our calculation results for the isosurface of the spin density distribution of four hydrogen adsorbed atoms, occupying an A sublattice at the corners of the quasi – (6×6) SiC superstructure, are shown in The attached hydrogen atoms (remarked by arrows in the figure) are separated from each other by ∼1.7 nm, and, as clearly seen, the localized electron states extend over a few graphene unit cells around the H atoms. The long-range magnetic coupling is therefore attributed to these connected regions of spin-polarized quasi-localized states.n = 0 gives rise to two exchange split states lying in a band gap which is defined by the energy difference between the PLLs n = 1 and n = −1. The bandwidth of the filled (spin up) band is ~0.1 eV and the empty (spin down) band is almost flat. This is in agreement with Ref. [n = 0 which is ~200 meV. This value is well above kBT (kB is the Boltzmann constant) at room temperature.Very unexpectedly, experimental results of hydrogenated epitaxial graphene show room- temperature ferromagnetism ,43. Howeith Ref. , therefo2 to sp3 hybridization. In order to avoid this, we compress the (√3×√3)R30◦ SiC by 7% instead of stretching it. This leads to a very high coverage of hydrogen (∼12%) atoms in the unit cell and therefore it was replaced by a (4×4) graphene cell, commensurate with a (2√3×2√3)R30◦ SiC substrate, while keeping the 7% compression of the substrate to get the commensurability between the two lattices. This was also used for epitaxial two-layer graphene on the Si-face of SiC by Gao and Tosatti [In the previous sections, the origin of the room-temperature ferromagnetic property of hydrogenated graphene on SiC was, for simplicity, discussed excluding the effect of the SiC substrate and buffer layer in the electronic structure calculations, just to indicate the connection between the role of local strain and the existence of pseudo-Landau levels. So far, a ferromagnetic behaviour is reported only for hydrogenated graphene, which is grown on a SiC substrate ,43. So i Tosatti . Adding From the side view of the structure in The spin unrestricted calculated band structure of epitaxial graphene and hydrogenated epitaxial graphene on SiC are shown in n = 0. In the geometry we utilized, the hydrogen coverage is ∼3%; this leads to the observation of a filled (majority spin) pseudo-Level n = 0 at about 0.3 eV below the Fermi energy at the K point. This value may decrease if the hydrogen coverage is less and vice versa [n = −1 decreases when the hydrogen coverage is reduced since it is related to the pseudo-magnetic field.However, it is very likely to be attributed to Coulomb interactions between the localized electrons of the Si-dangling bonds. Looking more closely, while no spin polarization was obtained for the graphene π-electrons, each localized state attributed to the Si-dangling bonds ,46 splitn = 0 could play a role leading to an increase in the exchange splitting of this latter and hence gives rise to a larger magnetic moment.In addition, the calculated total magnetic moment without the SiC nor the buffer layer contribution but with the simulated effective electron doping as discussed in 3.2, is 0.5 μB per H adatom. This value is smaller than the one obtained when the Si-dangling bonds of the buffer layer are present in 3.3, which is 0.7 μB per H adatom. This indicates that Coulomb interactions between localized Si-dangling bond states and the quasi-localized PLL n = 0 give rise to long-range ferromagnetic coupling. The relative high Curie temperature is obtained due the narrow bandwidth of these states formed in a bulk energy gap leading to a high magnon stiffness. Furthermore, Coulomb interactions between the pseudo-Landau level and the Si-dangling bond states can lead to an increase of the total magnetic moment. The presence of localized electron states close to the Fermi level is evidenced by photoemission spectroscopy measurements, which also indicates the p-doping of epitaxial graphene due to hydrogenation.In conclusion, our electronic structure calculations in combination with published experimental results provides a coherent picture to understand the observed room-temperature ferromagnetism in hydrogenated epitaxial graphene on SiC. We have theoretically shown that specific carbon sites, due to the presence of Si-dangling bonds in the underlying buffer layer, result in a quasi (6×6)SiC superstructure of epitaxial graphene, favouring one sublattice site hydrogen occupation. The chemical modification of the graphene layer by H adatoms and strain-like effects generate a pseudo-magnetic field and consequently localized pseudo-Landau levels in the electron density of states. Extended spin-polarized electron states from the pseudo-Landau level


Standard photocurrent measurements on a graphene/WTe2 phototransistor reveal a pronounced photocurrent enhancement (a photoresponsivity ~8.7 A/W under 650 nm laser illumination). Transport and photocurrent mapping suggest that both photovoltaic and photothermoelectric effects contribute to the enhanced photoresponse of the hybrid system. Our results help to enrich the understanding of new and emerging device concepts based on 2D layered materials.Heterostructures based on two-dimensional (2D) materials have sparked wide interests in both fundamental physics and applied devices. Recently, Dirac/Weyl semimetals are emerging as capable functional materials for optoelectronic devices. However, thus far the interfacial coupling of an all-semimetal 2D heterostructure has not been investigated, and its effects on optoelectronic properties remain less well understood. Here, a heterostructure comprising of all semi-metallic constituents, namely graphene and WTe The absence of dangling bonds on the surfaces of vdWs materials enables the creation of high-quality hetero-interfaces without the constraints of lattice matching and processing compatibility6. Indeed, vdWs heterostructures have been realized using different combinations of 2D materials, including metallic graphene7, insulating boron nitride (BN)8 and semiconducting transition metal dichalcogenides (TMDCs)10. While interesting electronic and optical properties of these 2D materials are being investigated, peculiar physics at the hetero-interfaces are attracting ever growing attentions14. Elucidating the interfacial effects and coupling mechanisms for different types of heterostructures and constituents compounds will provide important guidelines for developing functional 2D materials heterostructures.Heterostructures based on van der Waals (vdWs)-bonded layered materials have opened new avenues for fundamental scientific studies and applied devices21. Graphene is, strictly speaking, an exemplary 2D Dirac semimetal. Owing to its unique physical properties, e.g. mono-atomic thickness, universal optical absorption and gate tunable Fermi level, a variety of remarkable optoelectronic devices have been demonstrated by forming different types of graphene heterostructures. For instance, stacking graphene with semiconductors can form a versatile Schottky-type metal-semiconductor junction that is widely used in photodetection, solar energy collection and Schottky diode, etc26. Graphene-hexagonal boron nitride (hBN) heterostructure, as a paradigm of semimetal-insulator junction, offers a huge potential application in the fabrication of atomically thin field-effect transistors, resonant tunneling transistors and diodes29. In addition, due to the work function difference, graphene is usually doped by 3D metal contact, which can effectively improve the performance of graphene-based photodetectors34. Although considerable amount of work has focused on graphene heterostructures, graphene-semimetal heterostructures  have remained less well studied37.In addition to conventional semiconductor and metal materials, Dirac/Weyl semimetals are emerging as capable functional quantum materials for optoelectronic and photonic applications2 is investigated. WTe2 is chosen to form an all-semimetal 2D heterostructure as it belongs to an emerging class of Weyl semimetal with significant relevance to optics and photonics42. In addition to providing potentially better metallic contact than commonly used 3D metals43, study of the fundamental properties of such heterostructures may yield new insights into the design and optimization of 2D materials based nanodevices. Here, we study the interfacial transport and photoresponse of all-semimetal graphene and WTe2 heterostructure. Multi-fold of photocurrent enhancement, with a photoresponsivity ~8.7 A/W under 650 nm laser illumination, is observed in the graphene/WTe2 hybrid device. Transport and photocurrent mapping suggest that both photovoltaic and photothermoelectric effects contribute to the enhancement of photocurrent. Our experimental results, provide new insights in the design of photonic functional vdWs heterostructures.In this work, the optoelectronic properties of a hetero-interface formed by semimetal graphene and WTe2 heterostructure. Few-layer WTe2 flakes were mechanically exfoliated onto the SiO2/Si substrate. Chemical vapor deposition (CVD) grown monolayer graphene was then transferred onto the WTe2 flakes using the polymethyl methacrylate (PMMA) supported procedures (see Methods for details). Optical contrast measurements were first used to identify the thickness of WTe2 and graphene samples, and further characterizations were conducted by Raman spectroscopy, as shown in Supplementary Figure 2 sample well coincide with its Td structure, confirming its semimetallic nature44. Figure 2 stack. From the height profile of the WTe2 flake on the substrate, the thickness of it is estimate to be ∼8 nm, corresponding to ~10 layers of WTe2. The heterostructure devices are prepared by a standard photolithography procedure (see Methods for details). Since thin WTe2 flakes tend to degrade in ambient environment45, a fatigue test of the graphene/WTe2 film was conducted through optical contrast and Raman spectroscopy, in which the hybrid film showed no discernible change after 11 days of exposure in ambient conditions . Figure 2 device. The graphene channel is about 30 × 35 μm. The quality of the heterostructure device is confirmed by Raman spectroscopy again. As shown in Fig. 2 agree well with the previous results46, confirming no significant perturbation to either material during the fabrication processes.Figure 2 heterostructure and to provide insights into the hybridization of the all-semimetal interface, we conducted standard photocurrent measurements with a focused 650 nm continuous wave laser in vacuum (<10−5 Torr) at room temperature. Figure 2 heterostructure and a pure graphene control sample with the same design  and external quantum efficiency (EQE) are the key figure-of-merit that are used to evaluate the performance of a photodetector. R is defined as the photocurrent at unit incident optical power and is given by:Iph is the photocurrent and Popt is the incident light power on the effective area of the photodetectors. Apparently, high photoresponsivity indicates a large photocurrent can be achieved under relatively low incident illumination power. On the other hand, EQE characterizes the effectiveness of conversion of photons to electrons and is defined as:h is Planck’s constant, c the velocity of light, e is the electronic charge and λ is the wavelength of the incident power. To compare with other devices, we measured the power-dependent photocurrent of the graphene/WTe2 hybrid device at 650 nm . Such a shift in transfer curve is compatible with the previously discussed Fermi level pinning effect, when considering the work function for graphene and WTe2 are 4.5 eV and 4.39 eV, respectively39. It should be noted that the rather small work function mismatch (~0.1 eV) would lead to a built-in field that is weak and easily screened by impurity at the interface. The inset of Fig. 2 interface as stipulated by the difference in work function.To shed lights on the photocurrent enhancement at the semimetal interface, it should be noted that due to the requirement of continuity of Fermi level, the difference in work function between metallic materials  and graphene can drive a charge transfer process, resulting in an inhomogeneous doping profiles (built-in field) along graphene, which is capable of separating light-induced electron-hole (e-h) pairs. To confirm such a ‘photovoltaic’ picture, transfer characteristics of the graphene/WTe2 heterostructure, we fabricated a staggered graphene/WTe2 heterostructure device as shown in Fig. I-V) characteristic of the staggered graphene/WTe2 device . As shown in Fig. 2 junction, which further confirm the important role of the interfacial effects in the heterostructure system. Clearly, the photocurrent enhanced area in Fig. 33. Therefore, photothermoelectric effect is considered to be another contributing factor to the photocurrent, which results from local heating of the graphene and WTe2 junction due to the incident laser58. On one hand, inhomogeneous doping profiles of the graphene and WTe2 junction as mentioned above, give different Seebeck coefficients at the junction. On the other hand, considering graphene’s excellent (up to 5000 Wm−1 K−1) and WTe2’s rather poor (~3 Wm−1 K−1) thermal conductivities60, we assume that heat is accumulated in the graphene and WTe2 junction when illuminated by light, which leads to a temperature gradient across the device. Then, a thermoelectric photocurrent was induced due to the different Seebeck coefficients and temperature gradient. Considering the small electron capacity and large light-induced changes in electron temperature in graphene, the photothermoelectric effect may play as important a role as in the photovoltaic effect. Investigation of photocurrent generation as a function of layer thickness therefore would yield more insights into the interfacial charge transfer dynamics but is beyond the scope of the current study.To further elaborate the photocurrent generation mechanism of the graphene/WTe2 flakes with monolayer graphene. The photocurrent investigation suggests that, despite the all-semimetal nature of the heterostructure (by graphene and few-layer WTe2), the interfacial effects can effectively separate the photo-induced electron-hole pairs and lead to pronounced photocurrent enhancement, both due to photovoltaic and photothermoelectric effects. A photoresponsivity ~8.7 A/W is obtained for the heterostructure device under 650 nm laser illumination. These results advance the understanding of fundamental properties of all-semimetal heterostructures and provide guidelines for designing novel photonic devices.In conclusion, we demonstrated an all-semimetal vdWs heterostructure device through the integration of few-layer WTe2 flakes and transferred them onto a highly doped Si wafer capped by a 285-nm-thick SiO2 layer. Thickness of the exfoliated WTe2 flakes was measured by means of optical contrast and Raman spectra.A standard mechanical exfoliation method was employed to isolate few-layer WTe2 flakes. The PMMA was immediately removed using hot acetone (60 °C).A 0.5 cm × 0.5 cm CVD grown monolayer graphene coated with PMMA on copper was immersed in ammonium persulfate for 3 h and deionized water for 30 min, respectively. Subsequently, the graphene film supported by PMMA was transferred onto the WTe2 stacks through a shadow mask by electron beam evaporation. The graphene/WTe2 channel was patterned using photolithography procedure and oxygen plasma etching.The source and drain electrodes  were deposited on top of the graphene/WTeThe Raman spectroscopy measurements were carried out using a Horiba Jobin Yvon LabRAM HR-800 Raman spectrometer with a 514 nm argon ion laser. Surface morphology of the films was studied using atomic force microscopy (AFM) .−5 Torr) at room-temperature. The photocurrent mapping was performed in a custom data collecting system with a 532 nm continuous wave laser generator, a mechanical chopper, a source meter (Keithley 2612B), and a lock-in amplifier . The transport characterization of the staggered device was measured under vacuum at 24 K for suppressing the outside interference.For photoresponse characterization, the 650 nm laser beam is guided through an optical fiber with a FC/PC ferrule and is subsequently incident onto the channel of the devices without focusing. The beam at the device was measured to be Gaussian-shaped with a diameter of about 300 μm. The electrical measurements were conducted using a semiconductor parameter analyzer (Keithley 4200) in a closed cycle cryogenic probe station under vacuum (<10Supplementary Information


The influence of hydrogen overflow was decreased and the current response was enhanced because the modified graphene extended the potential range of the electrode. The Gr/l-cysteine/gold electrode showed high electrochemical conductivity, producing a marked increase in anodic peak currents (vs. the glass carbon electrode (GCE) and boron-doped diamond (BDD) electrode). The calculated detection limits are 1.15, 0.30, and 1.42 µg/L, and the sensitivities go up to 0.18, 21.69, and 152.0 nA·mm−2·µg−1·L for, respectively, the BDD electrode, the GCE, and the Gr/l-cysteine/gold electrode. It was shown that the Gr/l-cysteine/gold-modified electrode is an effective means for obtaining highly selective and sensitive electrodes to detect trace levels of cadmium.Cadmium(II) is a common water pollutant with high toxicity. It is of significant importance for detecting aqueous contaminants accurately, as these contaminants are harmful to human health and environment. This paper describes the fabrication, characterization, and application of an environment-friendly graphene (Gr)/ Cadmium (Cd) has long been recognized as one of the most notable toxic heavy metals to ecosystems and human health ,2. It waConventional spectrometric measurements for metals include atomic absorption spectrophotometry (AAS) ,7,8, indTo address this issue, several nanoparticles have been modified on the surface of electrode based on nanotechnology, which has demonstrated exciting prospects in both chemical and optical determination of Cd(II) over the past decades. A variety of electrode surface modifications have been explored to increase sensitivity for metal detection. Sensitive, environment-friendly, and efficient determinations of heavy metal have been developed by grafting various kinds of nanomaterials onto the surface of electrodes. Platinum and gold electrodes in different forms and sizes have been widely used as backing material in electrochemical analysis due to their excellent electron transfer kinetics. However, they have been limited to detection in a positive potential range for most heavy metals due to the low hydrogen overvoltage that reduces the cathodic potential window, while the stripping peak of cadmium is comparatively negative. Platinum and gold electrodes can be combined with various nanoparticles and have a wide potential range.2-bonded carbon atoms [Carbon-based electrodes, such as the glass carbon electrode (GCE), the boron-doped diamond (BDD) electrode, and the graphene-modified electrode, have a wide working potential range to make extensive analyses, low background currents to obtain high sensitivity, and stable structures to overcome harsh chemical environments. Graphene, a new type of environmental film, has also shown high hydrogen overpotential, which can suppress the hydrogen overflow on a gold electrode. Graphene is a 2D nanomaterial of spon atoms ,17. Moreon atoms ,19. Sincon atoms  and exceon atoms ,23,24,25l-cysteine was selected as the linker between graphene and gold microelectrode as it provides fast electron transfer for electrochemical detection and amino group that can potentially join with graphene by dehydration-condensation reaction. The boron-doped diamond (BDD) electrode and the glass carbon electrode (GCE) were also examined for Cd measurements, and the results were compared with that of the Gr/l-cys/Au electrode.In this paper, graphene was modified on a gold electrode via a self-assembled method based on thiols and related molecules, which provided a way to perform Cd detection in a negative potential range . We trie2+ in 3% nitric acid) was purchased from the China National Research Centre for Certified Reference Material. Cadmium samples were carefully diluted from the stock solution with double-distilled water. Carboxyl graphene (2 mg/L) was from Nanjing XFNANO Materials Tech Co., Ltd. . Dichloroethane (EDC) and N-Hydroxysuccinimide (NHS) were purchased from Sigma-Aldrich . Sodium acetate and glacial acetic acid were obtained from Xilong Tech Co., Ltd. . Ferricyanide solution (0.5 mM) was added into 0.1 M KCl solution.The purities of all reagents were in analytical grade except those stated separately. Double distilled water (18 MΩ·cm) was used to prepare for samples. Cadmium standard stock solution  using a three-electrode system based on a microelectrode chip. For comparison, traditional electrochemical bulk electrodes were used, while the glassy carbon electrode and the boron-doped diamond electrode (3 mm in diameter) served as the working electrode, the platinum disk electrode (3 mm in diameter) served as a counter electrode, and Ag/AgCl (saturated KCl) served as the reference electrode.Field-emission scanning electron microscope  produced by Hitachi  was used to check the morphologies of the graphene.2SO4 until a stable curve was obtained. The gold microelectrode was dipped in 20 µL of 10 mM l-cysteine (C2H7NS) solution for 6 h at 4 °C. The l-cysteine-modified gold electrode was obtained after 6 h of immersion. The modified gold microelectrode was washed with deionized water and dried in air for 24 h. Then, a mixed solution of NHS and EDC was applied into the carboxyl graphene (GN–COOH) solution for 15 min at 4 °C. Three microliters of the graphene-mixed solution was dispensed on the surface of the l-cysteine-modified gold microelectrode for 12 h at 25 °C. The hydroxyl group of the GN–COOH bond with the amino group of l-cysteine on the Au microelectrode with those steps. Finally, the carboxyl graphene (GN–COOH)-modified gold microelectrode was modified with l-cysteine as shown in The ring-disk microelectrode chip contains a gold working microelectrode, a platinium counter electrode. The microelectrode was prepared by the MEMS technique. The gold-working electrode was fabricated by standard optical lithography and a lift-off process with a diameter of 3 mm. Before modification, the gold microelectrode was cleaned in 0.01 M HDifferential pulse stripping voltammetry (DPSV) was applied to detect trace levels of cadmium under an optimized condition. All solutions were stored in a 20-mL Teflon bottle. DPSV parameters were optimized such that cadmium was deposited for 360 s at −1.1 V in 0.1 M acetate buffer (pH 4.50). The DPSV of electrodeposit metal was performed in the potential range of −1.1 to 0.5 V. The samples were homogeneous medium via stirring during the deposition steps, and the magnetic stirrer turned off for 120 s to equipoise prior to the DPSV scan.l-cysteine/Au electrode are shown in l-cysteine composite is rougher and sheets of graphene are clear in the edge of electrode. There are some thin folds on the surface in the center of the electrode. The electrochemical properties of different gold electrodes were characterized by CV. l-cys/Au, Gr/l-cys/Au, and Gr/l-cys/Au electrodes in solution containing 0.5 mM Fe(CN)33− and 0.1 M KCl. Compared with the CV curve of the bare gold electrode (curve a), an obviously increased redox current was obtained by the l-cysteine-modified gold electrode (curve b). After the chemical bond between GN–COOH and l-cysteine layer, the redox current of Gr/l-cysteine/Au electrode (curve c) decreases compared with the l-cysteine/Au electrode. It can be seen from the reduced redox current that electron transfer was inhibited by the graphene layer. Reduction of GN–COOH to rGN–COOH (curve d) increases the conductivity of the catalyst. The existence of rGN–COOH results in a stronger combination of cadmium with the modified electrode. The subsequent stripping of cadmium was therefore kinetically harder, and the stripping potential became more negative. However, this potential shift brings about fierce hydrogen evolution, which may damage the deposition layer. Consequently, the rG/l-cys/Au electrode cannot be applied to Cd detection.The typical SEM images of Gr/l-cys/Au on the surface is shown in 2 to H2O2 at the gold surface depending on the pH of the medium, which easily occurred in acidic media [l-cys/Au electrode. Such behavior was due to the fabrication of graphene on the gold electrode and the graphene-modified gold electrode can be used in cadmium determination.The influence of oxygen on the voltammetric behaviors of the bare gold electrode and the Gr/ic media . It can l-cys/Au electrode. As the pre-concentration time increased from 120 to 840 s, the peak currents for Cd2+ at pH 4.50 linearly increased, owing to the increased amount of cadmium ion on the Gr/l-cys/Au electrode. However, the stripping currents tended to slightly deviate from the linear region after 360 s, as shown in In order to investigate the influence of the deposition time and pH value of the detection solution, experiments were designed with 10 µg/L Cd(II) by DPSV to identify the current response on the Gr/l-cys/Au (B) electrodes drawn by AFM. The height profile of one layer’s is about 120 nm along the line across the membrane surface. It is believed that 2D graphene sheets combined to create an interconnected framework. The overlap of graphene can greatly enhance the specific surface area of the Gr/l-cys/Au electrode and can give the unfolded graphene a significant character to capture metal ions during deposition time in aqueous phase [The thickness of the one layer was measured by atomic force microscope (AFM). us phase .l-cysteine composite-modified electrodes generated improved the electrochemical character in a solution containing 0.5 mM ferri/ferrocyanide and 0.1 M KCl. The redox current decreased when the amount of GN–COOH loading increased from 3 to 9 µL, indicating that adding more GN–COOH to the electrode surface could diminish the electrochemical sensitivity of modified gold electrode. Graphene incorporation into l-cysteine is crucial for improving the electrochemical properties of the composite. One graphene layer displayed the best sensitivity, stability, and firm combination.l-cysteine was used to connect the electrode surface with the graphene by a self-assembly process. Calibration samples of deionized water (DW) were used to test the analytical performance of our method. Samples were spiked with 0, 5, 10, 15, and 20 µg/L cadmium(II) from standard stock solutions. The resulting calibration plots are linear over a range from 5 to 20 µg/L, with correlation coefficients exceeding 0.95 (To detect trace levels of Cd(II), DPSV is used because of its high sensitivity and linearity . To incring 0.95 . The anal-cysteine nanocomposite-modified gold electrode was compared to the GCE and the BDD electrode in similar systems for measuring trace levels of Cd(II). l-cys/Au electrode, the glass carbon electrode, and the boron-doped diamond electrode. The sensitivities go up to 0.18, 21.69, and 152.0 nA·mm−2·μg−1·L for, respectively, the BDD electrode, the GCE, and the Gr/l-cys/Au electrode. The sensitivity of the Gr/l-cys/Au electrode was higher than the other carbon-based electrodes, and the detection limit of the proposed method was comparable to other electrochemical detection methods. It was thus shown that the Gr/l-cys/Au-modified electrode is an effective method for obtaining highly selective and sensitive electrodes for detecting trace levels of cadmium.Furthermore, carbon-based electrodes have obtained significant attention in previous reports because of its environmental-friendly effect and high sensitivity, especially the GCE, the BDD electrode, and the graphene ,32. A val-cysteine film was successfully modified on gold microelectrode, and the structure of the microelectrode chip demonstrated the fabrication of this composite electrode. The Gr/l-cysteine/gold electrode showed microelectrode behavior and yielded a high, steady current. The electrochemical characteristics of the microelectrode during modifications were investigated by cyclic voltammetry in [l-cysteine gold microelectrode, the GCE, and BDD electrode for Cd(II) determination are linear with a range from 5 to 20 µg/L, with correlation coefficients exceeding 0.95. The Gr/l-cysteine gold microelectrode showed the highest sensitivity compared with the bare glassy carbon and boron-doped diamond due to the use of graphene and microelectrodes. In addition to the present work, this modified microelectrode can also be used for the detection of other trace metals that have lower deposition potentials than cadmium.In this work, the gold disk microelectrodes with the sensing diameter of 3 mm were fabricated by the MEMS technique on a glass wafer. The novel Gr/metry in . The rep