Graphene is the material elected to study molecules and monolayers at the molecular scale due to its chemical stability and electrical properties. The invention of scanning tunneling microscopy has deepened our knowledge on molecular systems through imaging at an atomic resolution, and new possibilities have been investigated at this scale. Interest on studies on biomolecules has been demonstrated due to the possibility of mimicking biological systems, providing several applications in nanomedicine: drug delivery systems, biosensors, nanostructured scaffolds, and biodevices. A breakthrough came with the synthesis of molecular systems by stepwise methods with control at the atomic/molecular level. This article presents a review on self-assembled monolayers of biomolecules on top of graphite with applications in biodevices. Special attention is given to porphyrin systems adsorbed on top of graphite that are able to anchor other biomolecules.  Graphene is considered one of the most important materials of the century, having numerous applications in areas including electronics, medicine, agriculture, structural engineering, and many others that are under investigation. Graphene is attractive due to its flexibility, elasticity, hardness, resistance, and biocompatibility, being inert on one hand but easily functionalized, if required, and having high thermal and electrical conductivity properties on the other. In addition, it is transparent and nonreactive in the presence of ionizing radiation. Recently, graphene has been explored has a potential material for biomedical applications in areas such as biosensing, cancer therapies, drug delivery systems (DDS), and tissue engineering, allowing the development of new research fields associated with the interactions of biomolecular systems and graphene. The interactions between biomolecules and the flat surface of graphene have mainly been studied at the molecular level, mostly of them by using scanning tunneling microscopy (STM) to evaluate the molecular conformation and organization as well as the conductivity of single molecules, the molecular mechanical properties, and the stability of specific molecular systems . Two types of molecular interactions with graphene systems have been addressed: physically adsorbed systems on graphene and molecules covalently linked to graphene oxide (GO). The oxide form of graphene, known as GO, is usually used to attach molecules on its oxygen functional groups, allowing the study of covalently linked molecular systems. GO is an interesting material due to its biocompatibility and ease of use in surface functionalization. For these reasons, GO is the material elected to study biomolecules that can be attached directly to the epoxy or hydroxyl groups existing on its surface or attached to other molecules working as anchor points to the GO surface . Physically adsorbed systems, such as self-assembled monolayers, are a promising method to build two-dimensional organized surfaces with important applications in organic electronics. STM is the technique of choice to study systems with atomic and molecular resolution. At the liquid interface it is possible to “observe” the molecular organization on top of graphene in real time and to induce molecular organization through the solvent, tip voltage, and temperature. Usually, physisorbed systems on graphene are governed by π-π interactions and are established by aromatic rings that contain π orbitals. These interactions are very promising for several applications, because they are spontaneous, contribute for the self-organization of molecular systems, and are nondestructive and reversible. The development of materials for bioapplications has been greatly advanced due to these types of interactions, mainly for biosensor applications, nucleic acid sequencing, crystal packing, protein folding, and DDS, among other multilayered film systems containing graphene . This article reviews the most recent studies on biomolecules on top of graphene surfaces and the potential applications of these biomolecules with a focus on self-assembly systems. The main applications of graphene biosensors are summarized and include electrochemical, field-effect transistor, mid-infrared plasmonic, optical, and fluorescent biosensors. Finally, a future perspective of the potential of these materials is given. 2 domains allows for interaction/anchoring with a wide range of biomolecules, such as DNA, peptides, proteins, including enzymes, viruses and others, via covalent and noncovalent interactions, as seen in Graphene and its derivatives have attracted increasing research interest due to their ordered honeycomb lattice pore structure, high surface area with a great number of active sites, mechanical strength, high thermal conductivity, and great electrical and optical properties. GO, with its two-dimensional network and heterogeneous chemical and electronic structure, has gained particular interest ,3,4. HowMany properties of graphene nanomaterials are due to the oxygen functional groups, hydroxyl, and epoxy spread over the surface of GO; therefore, these constitute the most important part of the functionalization of graphene and its interactions with other molecules.The anchoring of biomolecules allows the active sites to be accessible to target molecules as well as preserve their conformational stability and bioactivity. For good immobilization, it is important to look at the properties of the biomolecule, like its functional groups, size, and polarity . Graphene/biomolecule systems have numerous applications in relevant fields, like biology and materials science. They can be used in DDS with a vehicle function to load and transport drugs into target cells and release these drugs through a specific process, and also as a biosensor that can be either an electrochemical, field-effect transistor (FET), mid-infrared plasmonic, optical, or fluorescent biosensor . DNA is a crucial molecule that stores and transfers genetic information by acting as a template for RNA synthesis. Due to its biocompatibility, renewability, and helix structure, DNA is an important biomolecule for the functionalization of graphene materials. The graphene–DNA link can be achieved through noncovalent interactions . As demonstrated by Zhang and co-workers, DNA can be immobilized on the graphene surface by electrostatic interactions between the functionalized positively charged graphene and the negatively charged nucleotides ,7. NoncoProteins are large-sized, complex molecules composed of one or more amino-acid chains. They are present in all living organisms and have various functions, such as catalyzing metabolic reactions, structural functions, regulating tissues and organs, replicating DNA, responding to stimuli, and transporting molecules between locations. Similar to DNA, proteins can be attached to graphene by covalent and noncovalent interactions. To anchor proteins on graphene covalently, the GO nanosheets have to be functionalized first. However, Hui et al. stated that proteins can easily be adsorbed on GO nanosheets using different interactions with hydrophilic adsorption favored by the hydrophobic aromatic groups on the GO surface ,11. Due Peptides are short strings of amino acids called the “building blocks” of proteins. They are smaller than proteins, and the main differences between them are their sizes and structures, with peptides having less-defined structures. Natural peptide monomers can be directly attached to graphene through covalent interactions. For example, Kanchanapally et al. constructed 3D GO-based membranes with an antimicrobial peptide ,13. The 2O2 biosensor based on silver nanowires (AgNW) to form the nanocomposite rGO-PNF-AgNW. The development was made in four steps, namely through the synthesis of rGO-PDDA, the creation of PNFs, the deposition of AgNPs on the PNF surface, and the binding of PNF-AgNW (silver nanowires) nanohybrids onto the rGO surface [Wang and Lin proposed a nonenzymatic, electrochemical hydrogen peroxide sensor, using a glassy carbon electrode modified by GO-peptide-Silver Nanoparticles (AgNPs) ,15. Rece surface ,16.Viruses are composed of nucleic acids (DNA or RNA) covered in a thin coat of protein; thus, the graphene–virus interaction essentially occurs through noncovalent interactions, such as hydrogen bonding, electrostatic interactions, or redox reactions . GraphenEnzymes are biomolecules  that act as highly selective catalysts of the chemical reactions of a biological system, accelerating the rate and specificity of metabolic reactions ranging from the digestion of food to muscle and nerve function and DNA synthesis. They are composed of long chains of amino acids, organized in a 3D structure. Because of the enrichment of oxygen groups, GO is the perfect substrate to immobilize enzymes on its surface, as it does not require any modifications or functionalization. Interactions between GO and enzymes can be achieved through covalent forces, noncovalent π-π stacking, and electrostatic interactions. Covalent bonding is the most commonly used method for the immobilization of enzymes on the GO surface. Unnikrishnan et al. described an easy way to immobilize glucose oxidase (GOx) on rGO, in which free amino groups of GOx link covalently with edge-plane functionalized groups of GO . Noncova2O2) [Due to the large surface of graphene and its excellent properties for immobilizing enzymes, many studies on the use of GO–enzyme complexes have been conducted, for example, in the medical field as biosensors or in the environmental field with applications on water treatments. One example of a GO–enzyme complex in biosensors was given by Liu et al., who presented a glucose biosensor based on an oxidoreductase enzyme (GOx) which can catalyze the oxidation of glucose to hydrogen peroxide (H2O2) . In the 2O2) ,21. An e2O2) ,22.Porphyrins are highly colored organic compounds composed of four pyrrole-type subunits connected by methinic bridges in a cyclic model with great applications in the medical field, especially in cancer therapy, due to their unique physical, chemical, and spectroscopic properties. Because of their noninvasive nature, porphyrins have generated great interest as an efficient alternative to chemotherapy .2H groups of GO and the –NH2 groups of porphyrins, like the condensation reaction of 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (TAPP) with the GO-activated group –CO2H. Another approach was made by Santos et al., in which GO was linked directly to porphyrins previously functionalized with different glycol branches. In the first step, the authors performed carboxylation of GO with chloroacetic acid under basic conditions to maximize the –CO2 groups, and these were subsequently linked (by ester bonds) to the functionalized porphyrin groups through covalent interactions [Porphyrins are being used to functionalize GO to obtain nanohybrid platforms with special photoactive properties. Porphyrins can interact with the GO surface through electrostatic interactions; however, covalent interactions may occur between the –COractions . This GOAs mentioned before, cationic porphyrins and GO suspensions can bond through electrostatic interactions; however, these interactions are pH-dependent. For example, Larowska et al. demonstrated that GO sheets have weaker linkages to 5,10,15,20-tetrakis(4-trimethylammoniumphenyl) porphyrin (TMAP) at an acid pH when compared with interactions at a pH of around 7 . In anotPorphyrins are also able to organize themselves into different supramolecular structures when conjugated with GO . An examA summary of self-assembled biomolecular systems on graphene is given in Therefore, to design a better system, it is crucial to know the structure and properties of each biomolecule to select the most appropriate anchoring approach . Self-assembled structures on graphite, such as monolayers or supramolecular structures, are of particular interest due to their auto-organization ability, allowing highly reproducible fabrication. Despite their self-organization, the formation of a self-assembled system on graphite is dependent on several factors, such as the functionalization of the substrate, the solvents used, the temperature, the number of components that adsorbed on the surface, and the existence of an external stimulus that can interfere with the adsorption. The functionalization of graphite to anchor biomolecules is a challenge considering that no reactive groups are present. Recently, with the increasing interest in the use of graphene in DDS or in biosensors to identify drugs, the anchorage of nanocarriers on the top of graphite has been exploited. Cyclodextrins (CDs) are an example of biomolecules that have attracted particular attention from researchers. CDs are a family of cyclic oligomers with a hydrophobic cavity and a hydrophilic shell. The nomenclature and cavity size of CDs depend on the number of glucose units in the structure. All three forms, namely α-CD (6 units), β-CD (7 units), and γ-CD (8 units), have similar structures. They are homogeneous, crystalline, and nonhygroscopic in nature and have a hydrophobic inner cavity and a hydrophilic exterior. However, β-CD has a higher number of hydroxyl groups and a lower solubility due to the internal hydrogen bond network that is created between the secondary hydroxyl groups. β-CD enhances the water solubility and bioavailability of several substances, allowing for the incorporation of drugs into aqueous vehicles and therefore being of great pharmacological interest.The geometric shape and hydrophobic cavity of CDs make them ideal to accommodate various hydrophobic guest molecules in aqueous environments, giving them applications in molecular recognition, drug delivery, explosive detection, water purification, and chiral separation. CDs can also be applied in sensors, allowing for the formation of complexes with electroactive guests; however, this requires special conditions to immobilize the host molecule.2 carbon on the surface. The complex β-CD-HOPG was characterized by STM, atomic force microscopy (AFM), and Raman spectroscopy. The electrochemical behavior of the developed modified surface was tested by cyclic voltammetry towards ferrocene, hexycyanoferrate, and the neurotransmitter dopamine (DA), and it was used as a sensor for the detection of these substances. The sensor exhibited excellent sensitivity for DA detection at the nanomolar level, higher than the results reported at the time for a 3D nitrogen-doped graphene/β-CD electrode and comparable to the highest sensitivity reported for any electrochemical dopamine sensor [De Feyter et al. demonstrated a simple and fast one-step covalent immobilization of β-CD on a highly oriented pyrolitic graphite (HOPG) surface. On their study, the authors used diazonium salt from aniline-modified β-CD that was electrochemically grafted on HOPG by the formation of C–C bonds between aryl radicals and spe sensor .The STM is one of the techniques elected to analyze biomolecules on top of graphite, since it allows for not only the observation of molecules adsorbing onto a surface but also the promotion or manipulation of the adsorption. This ability enables the design of complex and customized structures starting from single atoms or molecules . For thiSTM also enables the achievement of supramolecular systems through bottom-up approaches at the solid/liquid interface based on atom-by-atom or molecule-by-molecule assembly working inside of a drop. The molecules present in a solvent drop are adsorbed to form one or more monolayers, whose growth is monitored by STM high-resolution imaging. Different types of molecules can be adsorbed using well-defined specific conditions, such as the nature of the substrate and solvent, the operating temperature, the concentration, and the characteristics of the tip . This me12) on monolayers of n-pentacontane (n-C50H102) on the HOPG surface. The STM images showed the formation of three distinct phases during HBC-C12 packing at the molecular level. Self-assembled monolayers of n-C50H102 were deposited onto the HOPG surface from a solution of n-tetradecane. To the HOPG- n-C50H102 modified surface, HBC-C12 was added as a saturated solution of n-tetradecane. STM images were recorded for eight hours, revealing three successive distinct phases: the α-phase (oblique structure), β-phase (dimer structure), and γ-phase (row structure). The α-phase formed in the first hour, and the transition to a more stable β-phase occurred during the second hour after the deposition of the HBC-C12 molecules and was completed in two/three hours. After five/six hours of HBC-C12 deposition, the final transition from β to γ-phase occurred and was completed in two more hours. With this experiment allied with STM images, it was possible to analyze and characterize the monolayer’s phases during the formation steps. It was demonstrated to be a possible way to control the structure of a molecular 2D lattice [STM at the solid/liquid interface allows for the visualization of the dynamics of the self-assembled system formation by controlling the formation of a monolayer to achieve a highly stable molecular organization. To study the different formation stages of monolayers on a substrate, Fichou et al. used STM in real time and evaluated the structural evolution of Hexakis(n-dodecyl)-peri-hexabenzocoronene -octaethylporphyrin (ZnOEP) monolayer formation on the HOPG surface in real time. Self-assembled monolayers were formed by the addition of a porphyrin-saturated solution of n-tetradecane to a n-tetradecane droplet (on HOPG surface) . The reaAt a liquid/solid interface, STM allows for the manipulation of reactions using the tip voltage as an initiator. De Feyter et al. studied this principle by applying a voltage pulse on the STM tip to a manganese chloride-porphyrin (Mn(III)-PP) monolayer on a HOPG substrate. The authors observed the formation of bright spots during the application of voltage pulses to the STM tip at different places. With the topographical images, apparent heights, and the oxygen dependence observed, the authors concluded that these bright spots represent µ-oxo dimers, a characteristic oxidation product of the reaction of Mn-porphyrin with oxygen. Furthermore, it was proved that it is possible to induce a local reaction on a surface by applying a voltage pulse on the tip of the STM .22-Rh-1 and C30-Rh-2. STM measurements were performed at the 1-octanoic acid/HOPG interface with a constant current mode. The concentrations of the two porphyrins were optimized for a stronger affinity to the HOPG surface with a 20 times higher concentration for C22-Rh-1. After this optimization, the tip was immersed into the sample solution on the HOPG surface, and images were collected. With the obtained images, the apparent height of the two porphyrins was determined by section analysis and histograms that were fitted with a single Gaussian function. The results of seven scans showed a difference in the apparent height between the two porphyrins of around −1.10 ± 0.55 Å. Since the aim was to compare the single molecular conductance of molecular wires with different lengths, Equation (1), which expresses the conductance ratio (G1/G2) as an exponential function of the apparent heights (Δhstm) and molecular heights (Δx) was applied.Another demonstration of STM’s versatility is the possibility of analyzing the individual electrical properties of molecular systems using scanning tunneling spectroscopy (STS). Matsuda et al. measured molecular wires attached to 2D phase-separated templates for the evaluation of single molecular conductance. STM allowed the evaluation of the single molecular conductance of two molecular wires with distinctive alkyl side chain lengths on the HOPG surface . For thi22-Rh-1 and C30-Rh-2 was estimated to be 1.3 ± 0.7, a value that is in accordance with previously reported data obtained by the mechanically controllable break junction (MCBJ) method. With STM studies, the authors concluded that the apparent height ratio and conductance ratio showed a straightforward correlation for a single layer of molecules [Molecular heights (Δx) were obtained by considering both the s-cis and s-trans conformations of the two wires using the density function theory (DFT) calculation. The conductance ratio of Colecules .In the last decade, graphene and its derivatives have generated great interest in the development of biosensors for different applications, from the diagnosis and treatment of diseases to the detection of enviromental contaminants or applications in the food industry, as schematized in A graphene-based biosensor is composed of three main parts: the analyte, which is the target molecule to be detected; the bioreceptor, which is a biomolecular system that is able to receive/detect/identify the target molecule; and a transducer, which is responsible for converting the biorecognition occurrence to a signal that can be measured and which is proportional to the concentration of the analyte. Several sensor types can be adopted: Electrochemical, Mid-Infrared Plasmonic biosensors, Fluorescent graphene-based biosensors, and Optical and field effect transistors (FET) biosensors.Electrochemical biosensors are the most commonly used type based on GO due mainly to the hydrophilicity of GO, which enables different biomolecules and nanomaterials, such as quantum dots (QDs), semiconducting NPs, polymers, and metals to adsorb onto its surface. This enhances electron transfer between the bioreceptor and transducer, which is advantageous for electrochemical sensors with high sensitivity . GraphenThe challenge is to attach the bioreceptor to the graphene surface (transducer) to ensure the correct analysis of the target molecule. The most common bioreceptors used on graphene transducers are DNA, antibodies, and enzymes. The method used to immobilize these systems is known, and it was reported that DNA and antibodies are fixed on the top of graphene via 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC)/N-hydroxysuccinimide (NHS) chemistry and the enzymes are physisorbed. The following sections highlight the three main types of bioreceptores: enzymes, nuclei acids, and antibodies.2O2) [+ and NADH, which are present in several enzymatic reactions. NADH, one of the most important coenzymes in the cells, is involved in metabolic processes, and this is the reason why NAD is used as the standard. Cheraghi et al. demonstrated the efficacy of glutathione peroxidase in biological fluids. Glutathione peroxidase is an enzyme that is involved in glutathione metabolism, being the ideal marker for glutathione detection. In the work of Cheraghi et al., glutathione peroxidase was adsorbed to the GO surface covalently via EDC and NHS onto a glassy carbon electrode (GCE) functionalized with GO and nafion polymer. The resulting biosensor demonstrated great sensitivity to glutathione and was successfully used in real samples with acceptable data and results confirmed with statistical tests (F-test and t-test) [Enzymes are commonly fixed on top of graphene to detect glucose, phenols, cholesterol, glutathione, and hydrogen peroxide (H2O2) ,40. For  t-test) .2/Si) substrate without a transfer process, eliminating residue contamination by polymer transfer-support and heavy metal ions. After this process, GOx was sequentially immobilized, and the polymer nafion layer was deposited on the functionalized graphene surface (by oxygen-plasma treatment). Another example was reported by Liu et al. where GOx enzymes were immobilized on carboxyl acid (COOH)GO groups through covalent interactions and amide bonds in the presence of EDC and NHS. This biosensor showed good sensitivity and exhibited biocompatibility with human retinal pigment epithelium cells [Glucose biosensors are still under development to increase their sensitivity and effectiveness. The blood glucose level is the most important parameter for the diagnosis and management of diabetes, one of the most common diseases worldwide. Therefore, it is crucial to monitor this pathology to avoid severe comorbidities. For the detection of glucose levels, the enzyme glucose oxidase (GOx) is used, and significant effort is being made to enhance the electrical contact of redox enzymes with the surface electrodes of enzyme-based electrochemical glucose sensors. Qi et al. immobilized gold nanoparticles (AuNPS) on GO surfaces via a benzene (Ph) bridge with aryldiazonium salt. The hybrid system GO-Ph-AuNPS was then incorporated into a 4-aminophenyl modified GCE. After that, GCE/GO-Ph-AuNPS were functionalized with 4-carboxyphenyl (CP), and finally, GOx was attached through covalent interactions to obtain the glucose sensor GCE/GO-Ph-AuNPS-CP/GOx. The sensor demonstrated a good range of sensitivity for the detection of glucose levels as well as good selectivity results ,42. Glucum cells ,45.Cholesterol sensors are also based on the enzymatic detection approach. Cholesterol is a fat-like substance that is present in all cells and is an important building block of healthy cells. However, high levels of cholesterol can lead to the development of deposits in blood vessels, increasing the risk of heart disease. Therefore, the determination of cholesterol levels is important to help with the prevention of the development of cardiovascular diseases, such as atherosclerosis, hypertension, cardiopathy, and myocardial infarction.Cholesterol biosensors must be able to detect the precise level of cholesterol; therefore, many studies have been focused on achieving the desired sensitivity using the enzyme cholesterol oxidase (ChOx). For example, Dey et al. used an enzymatic detection approach in which they attached ferrocene redox units to the surface of GO through covalent interactions. The resulting cholesterol biosensor showed a good linear response, as well as good sensitivity ,46.In another experiment, Agnihotri et al. reported a nonenzymatic cholesterol sensor based on β-CD functionalized graphene. The authors proposed that β-CD could be linked to GO sheets covalently, forming the complex GO-β-CD, which has a good sensitivity range ,47.2O2, which is a subproduct of numerous enzymatic reactions as well as being an important product in the food industry that could have pharmaceutical and environmental applications, especially due to its oxidizing and reducing properties. For the detection of glucose, cholesterol, and H2O2 levels in blood, Li et al. developed tyramine (TYR)-functionalized Graphene Quantum Dots (TYR-GQDs), in which tyramine is adsorbed on the GQD surface by covalent interactions between the TYR amino groups (NH2) and the GQD carboxyl groups (COOH). The TYR-GQDs fluorescent sensor showed high sensitivity and selectivity [2O2 detection. The incorporation of MWCNT improved the performance of the sensor due to the enlarged electroactive surface area and decreased charge-transfer resistance at the laser-induced graphene-electrolyte interface. This enhanced sensor showed better sensitivity than those without MWCNT [Enzymatic biosensors have been applied to detect Hectivity ,48. Thesut MWCNT .Graphene biosensors using enzymes as bioreceptors are also available to detect pesticides. Pesticides are substances used to control pests in agriculture and include herbicides and insecticides. Their excessive and uncontrolled use can cause food and environment contamination and, therefore, illness in humans and animals.To prevent toxic effects, it is imperative to detect contaminants from pesticide residues in food and water. Hondred et al. presented an electrochemical sensor PtNP-IML-PGE/GA  for the detection of organophosphorus pesticides (Ops), which are insecticides used to protect crops. The authors electrodeposited PtNP on patterned graphene electrodes (IML-PGE) to improve the electrical conductivity, electrocatalytic activity and surface area. After this step, the phosphotriesterase enzyme was conjugated with the functional cross-linking molecule glutaraldehyde (GA). The final biosensor showed a quick response to the insecticide paraoxon (a type of organophosphate) with high sensitivity and a low detection limit ,50.Graphene quantum dots (GQDs) have been widely used in the development of biosensors for the detection of pesticides applying the Förster resonance energy transfer (FRET) mechanism due to their unique fluorescence quenching properties. Gao et al. presented a N-(aminobutyl)-N-(ethylisoluminol) (ABEI) functionalized GQDs biosensor with great selectivity for the detection of multiple pesticides. This biosensor can detect different pesticides, such as flubendiamide, thiamethoxam, dimothoate, and chlorpyrifos .A recent approach was made by Wang et al. to develop a highly sensitive and selective OP biosensor improved by the immobilization of acetylcholinesterase (AChE) on the gold gate electrode with chitosan (Chi), as schematized in The unique properties of graphene-base nanomaterials make them ideal for the development of biosensors. In Dopamine (DA) is a neurotransmitter present in the brain that acts as a chemical messenger between neurons. It is involved in motivation, memory, attention, and even in the regulation of body movements. Ascorbic acid (AA) is a natural water-soluble vitamin that is a potent reducing and antioxidant agent. It has many functions, such as detoxifying reactions, fighting bacterial infections, and forming collagen in fibrous tissue, teeth, bones, skin, and capillaries.Uric acid (UA) is a natural waste product from the digestion of purine foods. A high uric acid level normally occurs when kidneys are not capable of eliminating it efficiently.The three substances DA, AA, and UA have electrooxidation peaks almost at the same potential values; therefore, several efforts have been made to separate their signal potentials with greater sensitivity and selectivity. To overcome issues with amplifying the detection signal, graphene and GO can be doped with nitrogen, polymers, different inorganic metals, and metal oxide particles. An example of this approach was demonstrated by Srivastava et al., who proposed a functionalized multilayer graphene system to use on an amperometric urea sensor with high sensitivity ,53.To achieve a biosensor that is capable of detecting the vesicular secretion of catecholamine molecules , He et al. developed a rGO FET with living neuroendocrine PC-12 cells. These cells are widely used in brain disease research.+) was also used to depolarize the cell membrane and promote the influx of calcium ions (Ca2+) through the voltage-gated Ca2+ channels, as can been seen in rGO FET devices were functionalized in the first step with poly-L-Lysine, and then PC-12 cells were directly cultured on the top of rGO FET sensor. A solution with a high concentration of potassium ions label-free near-infrared fluorescent biosensor with direct readout of the near-IR fluorescence of GO for the selective and sensitive detection of DA. This sensor was presented by Chen et al. and was used for DA detection in biological fluids with quantitative recovery (98–115%) ,55.The neurotransmitter DA is also associated with Parkinson’s disease (PD), a neurodegenerative disease involving the progressive loss of nigrostriatal neurons. For this reason, the control of DA levels might be a biomarker for diagnosing the pathology in the early stages and also to optimize DA replacement therapy. To improve the sensor sensitivity, Butler et al. tuned the graphene surface chemistry with a simple one-step thermal annealing process with no need for subsequent chemical or biomolecular functionalization, as demonstrated in DNA and RNA are nucleic acids that have distinct functions in living beings: DNA is responsible for storing and transferring genetic information, while RNA acts as a messenger between DNA and ribosomes to make proteins. Nucleic acid biosensors have attracted the attention of researchers due to their importance in gene engineering and in the diagnosis of genetic diseases. Many approaches, including fluorescence, electrochemistry, colorimetry, chemiluminescence, electrochemiluminescence, and SPR have been used to develop several biosensor types.DNA and RNA have characteristic structures that are favorable to the establishment of π-π bonds between nucleobases, their conjugated systems, and graphene. However, the π-π interactions between nucleic acids and graphene are weak, and to improve them, Loan et al. deposited gold (Au) films on graphene layers, which modified them to enable stronger covalent interactions .Huang et al. also used this Au advantage and presented a DNA biosensor (graphene/Au nanorods/polythionine) for the electrochemical detection of human papillomavirus (HPV) with a strong detection performance. The principle is based on the attachment of target DNA to the DNA structure of the capture probe on the electrode surface ,57.Recently, Bagherzadeh et al. studied the charge transfer and electrostatic potential of an armchair graphene nanoribbon (AGNR) to improve DNA hybridization detection. 1-Pyrenebutanoic acid succinimidyl ester (PBASE) binds to graphene surfaces through noncovalent forces via stacking of its pyrene group. Single-strand DNA (ssDNA) was immobilized on the AGNR surface by covalent interactions with PBASE. The bonding of probe DNA to PBASE was achieved with the formation of an amide bond, which resulted from the nucleophilic substitution of N-hydroxysuccinimide by an amine group of probe DNA. It was concluded that the functionalization of AGNR with PBASE increased the conductance of the sensor. The developed sensor showed a sensitivity of 10% at a zero bias voltage and a higher sensitivity with the application of a suitable gate voltage .GO-based fluorescent biosensors have been widely used in research for the detection of biomolecules, such as DNA, RNA, and proteins. In many of these biosensors, DNA is used as a base matrix of the biosensor for target molecule recognition and reporting. An example of this usage was presented by Xing et al. through a fluorescent aptasensor based on a double-stranded DNA (dsDNA)/GO complex as the signal probe to study exonuclease I activities. dsDNA is adsorbed on the GO surface, allowing fluorescence quenching, and when the target molecule is introduced, the aptamer (short DNA folded molecule) preferentially binds with its target, which results in a nuclease reaction with a minor change in fluorescence when GO is introduced due to the weak affinity between generated mononucleotides and GO ,59.The detection of changes in living cells, namely transformation in cancer cells, has been a challenge; therefore, significant research effort has occurred, especially in the field of optical sensors. Wang et al. developed a graphene-based optical biosensor for the detection of drug responses in live cells with sensitivity for detecting cancer cell responses to anticancer drugs, as represented in E. coli O157:H7 strain was immobilized on the GO functionalized surface through covalent interactions. The authors demonstrated that the incorporation of GO improved the electrochemical properties of the complex and the DNA detection of E. coli, resulting in a highly selective and sensitive biosensor [Nucleic acid biosensors are used also to detect pathogens. Tiwari et al. developed an electrochemical biosensor iron oxide-Chi functionalized GO layers. The iosensor ,61.E. coli O157:H7. Jaiswal et al. used aminopropyltrimethoxysilane (APTMS)-functionalized zinc oxide nanorods (ZnONRs) and carboxylated graphene nanoflakes (c-GNF) that were electrophoretically deposited on an indium tin oxide (ITO) coated glass substrate and used as electrodes for the covalent immobilization of an E. coli O157:H7-specific DNA probe. The ZnONRs were functionalized with APTMS to incorporate amino groups on its surface, and then the electrostatic interactions with the carboxylic acid groups on c-GNF promoted the formation of an APTMS-functionalized ZnONR/c-GNF composite (APTMS-ZnONR/c-GNF). This composite was electrophoretically deposited on ITO substrate, and the final platform was immobilized with probe DNA sequences for the selective determination of E. coli O157:H7DNA using the impedimetric technique. The sensor retained its activity for five repetitive uses and with a low concentration detection [Efforts have been made towards improving the sensitivity of biosensors to detect etection .2+), chromium (Cr3+), lead (Pb2+), copper (Cu2+), and mercury (Hg2+), which are relatively dense metals or metalloids that are characterized by their potential toxicity. Heavy metal ions can enter and accumulate in the human body through food chains. Graphene and its derivatives have shown great efficiency in removing toxic heavy metals in aqueous solutions. Muralikrishna et al. had the objective of developing a sensor for the simultaneous detection of Cd2+, Cu2+, Pb2+, and Hg2+, and focused on the development of a L-cysteine/rGO based sensor. The GO surface was functionalized with L-cysteine through amidation between the GO carboxyl groups and L-cysteine amine groups and nucleophilic substitution in one step. The complex L-cysteine/rGO worked as a cathode with the ability to simultaneously detect all four heavy metal ions. This sensor showed detection limits for metal ions lower than the World Health Organization standards [+, Pb2+, Hg2+, Cu2+, and F3+ (Fluor). Wen et al. developed a fluorescent nanoprobe based on GO and an Ag-specific nucleotide for the detection of Ag+ ions, and this showed good sensitivity [Acid nucleic biosensors have also been used to detect toxic heavy metals, such as cadmium  to GO’s doped surface to prepare a biosensor for the detection of cancer biomarkers (carcino-embryonic antigen and nuclear matrix protein 22). The authors developed a tri-antibody dual-channel biosensing platform to increase the detection sensitivity of the two antigen types, as illustrated in Recently, Zahra et al. presented a herceptin (HER2)-conjugated graphene biosensor that uses the special antibody of HER2, which turns this biosensor into an immunosensor for single-cell breast cancer detection. A graphene-based immunosensor was prepared on the surface of a GCE to quantify SK-BR-3 (human breast cancer cell line that overexpresses HER2 antibody) cancer cells. Selective tests showed excellent results in real samples and a linear range of 1–80 cells. The reproducibility of the biosensor was estimated to be about 66%. The stability and functionality range was about 40 days [Graphene biosensors using antibodies have demonstrated successful results in food toxin analysis. Food toxins are natural substances generated by the metabolism of fungi, algae, plants, or bacteria that have negative effects on humans and animals. Examples of natural toxins in plant-based foods include those from the fungi Aspergillus flavus and Penicillium verrucosum. To prevent food contamination and subsequent illness, some studies have focused on the development of biosensors. Srivastava et al. developed an electrochemical biosensor for the detection of the food toxin AFB1. The authors used rGO sheets, and through covalent interactions, attached monoclonal antibodies to the toxin AFB1(anti-AFB1) to form the rGO/anti-AFB1 based sensor, which showed high sensitivity and stability for a period of 45 days. These improvements were due to the good electrochemical properties, large surface area, and fast electron transfer kinetics of rGO ,67. Apta2 at 400 °C to functionalize the graphene surface with carboxyl and carbonyl groups, improving the interaction between the antibody and the graphene interdigitated electrode. The developed biosensor showed a wide histamine sensing range and a low detection limit [For food safety monitoring, Parate et al. wanted to develop a biosensor to detect histamine levels. Histamine (2-(1H-imidazol-4-yl)ethanamine) is a biogenetic amine present in seafood that is related to fish product spoilage and seafood allergies. To create the biosensor, the authors used the aerosol jet printing (AJP) technique, which is based on three main steps: graphene ink formulation, aerosol jet printing, and post-print baking. Graphene ink was aerosol jet printed into interdigitated electrode patterns and then baked at 350 °C in air circulation to improve graphene’s mechanical properties and to increase the electrical conductivity. In the final step, the devices were annealed in COon limit .Many studies have been carried to develop biosensors for the biomedical, clinical, and even environmental fields. To ensure enduring success, continuous improvement is needed, and therefore, new methods for graphene usage are still being studied. As pointed out throughout this manuscript, significant developments have been made in the development of graphene-based nanomaterials by exploring their excellent properties that make them ideal for use in applications in a large variety of fields, from medicine to the environment. The good thermal and electrical conductivity of graphene along with its large surface area and numerous active groups makes it the ideal material for the immobilization of biomolecules for their application in biosensors.This review has described the most recent advances in graphene-based nanomaterials as a platform for biomolecules. We presented the different interactions between graphene materials and biomolecules such as DNA, proteins, peptides, viruses, enzymes, and porphyrins as well as examples of their applications. A large number of graphene-based biosensors reported in the literature have shown good sensitivity in the targeting of biomolecules as well as good stability. To improve the sensitivity of biosensors, authors have functionalized the graphene surface with biomolecules or even nanoparticles, such as gold, obtaining excellent results. However, new functionalization methods for Graphene surfaces are needed to improve the immobilization of biomolecules. It is also important to improve the selectivity to detect and even predict severe pathologies in the initial stages. The early detection of some diseases is crucial to the success of treatments.The detection of biomarkers is becoming the most important parameter to allow actions to be taken in a timely manner to avoid severe comorbidities and excessive spending costs on health and to provide relief for hospital resources and increase the quality of life of patients. One example was presented by De Feyter et al. with the development of a simple and fast single-step process for the immobilization of β-CD on the HOPG surface for the detection of DA, a neurotransmitter associated with Parkinson’s disease. Zahra et al. made another great advance by developing a biosensor for breast cancer cells that achieved good results. These two diseases are directly related to patients’ quality of life, and every step forward in their early diagnosis makes a difference.Graphene and its derivatives also have great potential in applications involving drug delivery, and increasing interest in their applications in the biomedical field has emerged due to their exceptional physiochemical properties and unique planar structure. GO has a high drug-loading capacity, because of its hydrophilic oxygenated functional groups that allow the biomolecules to bind through both covalent and noncovalent interactions.A DDS is able to deliver therapeutic drugs inside the affected cells in a controllable way, reducing the side effects on healthy tissues. GO, as a DDS, provides better biodistribution of drugs, reduced adverse effects on healthy cells, specific selectivity, and higher local therapeutic absorption. Due to these capacities, GO has been studied as a carrier for several drugs. For example, Wei et al. functionalized GO as a DDS for platinum anticancer drugs. The authors functionalized GO with high-molecular-weight polymers  and folic acid for the accommodation of platinum anticancer drugs . Because of the limitations of platinum anticancer drugs, such as the high protein binding rate, cross resistance, significant toxic side effects, and lack of specificity, the authors wanted to develop a drug carrier with good biocompatibility and high efficiency for drug delivery to the target site, reducing the side effects of platinum drugs. Wei et al. also analyzed the toxicity of drug delivery systems with GO in cell culture through the MTT assay. The results showed a viability rate of more than 80%, proving the low cytotoxicity of GO nanocarriers .Another application of GO DDS in cancer therapy was presented by Abdelhamid and Hussein, who used Graphene Oxide as a DDS of methotrexate. The authors synthesized GO using Hummer’s method, and then methotrexate was loaded onto the GO surface via noncovalent interactions, including electrostatic and π-π interactions. They tested the drug delivery efficiency in hepatocellular carcinoma cells (HepG2 cells), human embryonic kidney cells (HEK293A cells), and porcine skin fibroblasts by incubating the cells with MTX-GO, MTX, or GO at 37 °C for 24 h. They evaluated the cell viability through the MTT assay and concluded that GO does not promote any side effects on the three cell types; however, the GO-MTX system induced significant cytotoxicity in the tumor cell line (HepG2 cells) compared to the normal cells (HEK293A and PEF cells), proving the efficiency of GO as a carrier .There are many ways to control the release of the drug present in DDS—via pH, enzymatic interactions, Near-infrared (NIR) light, and electrical fields. Graphene functionalization can also play a role in controlling drug release.2COONa and was further neutralized and dialyzed [There is evidence that the effects of photosensitizers on tumor cells are improved when they are conjugated with GO (as a carrier). This improvement is due to the large surface area and the availability of reactive functional groups on GO, which confers great efficiency to the delivery of photoactive drugs into tumor cells. Tumor sites have a characteristic acidic pH, and this promotes the release of anticancer drugs, since almost all GO-based delivery systems have pH-dependent behavior. To test this, Huang et al. developed a hybrid system with folic acid (FA) and GO-COOH. GO-COOH was produced by the reaction between GO, NaOH, and ClCHdialyzed . With thdialyzed .The focus of this review was on graphene as a base material for biomolecule immobilization and its application in biosensors, a promising field that covers different areas. Significant efforts are being made to improve the sensitivity and efficiency of biosensors that are crucial for medical analyses, as well as those that can be used for the detection of pathogens in food and environmental contaminants. The potential of graphene-based biosensors to detect infectious diseases is enormous, and the translation of this concept into clinical use would be revolutionary. However, with limitations, such as the ability of graphene to adsorb nontarget molecules, may cause false-positive detections, especially if noncovalent functionalization methods are applied. Additionally, the incorporation of biomolecules onto the graphene layer may be affected by external environmental factors like the temperature, pH, salt concentration, as well as the intrinsic properties of graphene itself. Future efforts should be directed toward improving the fabrication of biosensors with more cost-effective and easier techniques to achieve the desired biodevice. Future perspectives on sensor development should be directed toward the development of more portable, reproducible, miniaturized, and high-throughput detection devices.


This was accompanied by the appearance of an electronic gap of 0.022 eV, as evidenced by the Arrhenius analysis. The observed increase in the conductance of the samples with temperature can be explained by thermally activated carrier transport, dominating the scattering processes.Despite the impressive performance and incredible promise for a variety of applications, the wide-scale commercialization of graphene is still behind its full potential. One of the main challenges is related to preserving graphene’s unique properties upon transfer onto practically desirable substrates. In this work, few-layer graphene sheets deposited via liquid-phase transfer from copper onto a quartz substrate have been studied using a suite of experimental techniques, including scanning electron microscopy (SEM), Raman spectroscopy, admittance spectroscopy, and four-point probe electrical measurements. SEM measurements suggest that the transfer of graphene from copper foil to quartz using the aqueous solution of ammonium persulfate was accompanied by unintentional etching of the entire surface of the quartz substrate and, as a result, the formation of microscopic facet structures covering the etched surface of the substrate. As revealed by Raman spectroscopy and the electrical measurements, the transfer process involving the etching of the copper foil in a 0.1 M solution of (NH Due to its high electrical and thermal conductivity, combined with thermal stability, mechanical strength, and chemical inertness, graphene has been considered for use in a variety of applications such as transistors ,2, powerGraphene usually comes in single-layer (SLG) or few-layer (FLG) modifications. This paper studies FLG transferred onto a quartz slide following etching of the original copper foil substrate. Typical routes for the transfer of graphene to a desired technological substrate include non-electrochemical reaction-based bubble-mediated transfer, the dry transfer route, electro-chemical delamination, the scalable roller-assisted delamination transfer method, and the support-free transfer route ,16,17,18For many applications, it is necessary to have graphene on dielectric substrates ,35,36,37The focus of this study is placed on a combination of electrical and optical measurements using admittance spectroscopy, optothermal Raman spectroscopy, and four-point Hall measurements to investigate the transfer-induced evolution of the FLG properties. This will eventually enable us to assess the performance of the material in real-life applications and help to develop strategies for preserving its remarkable characteristics observed in free-standing films.Sample preparation: Few-layer chemical-vapor deposited (CVD) graphene grown on the backside of an 18-μm-thick Cu foil was purchased from Graphenea Inc., . The graphene film was transferred onto a quartz slide according to the following special procedure to avoid damage to the film. The quartz substrate was placed in advance in a Petri dish, which was then filled with a 50 mL aqueous solution of 0.1 M ammonium persulfate (NH4)2S2O8 [4)2S2O8 solution was subjected to a 10× partial substitution (10 mL) with distilled water via a syringe, whilst keeping the graphene sheet floating on the surface. This step was intended to carefully remove the remains of the copper from the solution. Particular attention here should be placed on avoiding surface waves during the solvent exchange, which can affect the quality of the resulting film. The deposition of graphene onto quartz was performed by carefully removing water via a syringe from the Petri dish. During this step, the substrate (quartz) was placed directly under the graphene layer to obtain a quartz-graphene system. Finally, the film was dried in an oven at 70 °C for 1 h.H4)2S2O8 . The graMeasurements: The microscopy images of the FLG layers were obtained using a Crossbeam 4500 scanning electron microscope (SEM). Raman laser-induced heating was applied using a continuous-wavelength (CW) Laser Quantum Torus diode-pumped solid-state 532 nm single longitudinal mode laser beam focused onto the sample down to a spot with a 0.9 μm diameter by means of an OptoSigma 40× numerical aperture (NA = 0.75) . Simultaneous micro-Raman spectral measurements from laser-heated samples were performed in real-time using a Sol Instruments Nanofinder 30 confocal Raman microscope coupled to an Andor iStar iCCD camera . The spectral resolution for an 1800/mm grating was 1.4 cm−1. The pixel size on the iCCD camera and the entrance slit to the spectrometer were 13 μm and 150 μm, respectively. All reported Raman intensities, positions, and linewidths are the results of the Lorentzian fitting.For electrical measurements, the samples were coated with Indium-Gallium contacts at the point of contact with the electrical probes. Four-point probe electrical measurements were performed at room temperature using a Hall effect measurement system HEM-2000 . The optical transmission spectra in the wavelength range of 300–1100 nm were taken using a QEX10 PV Measurement setup. Temperature-dependent electrical characterization of the graphene-on-quartz samples was performed using admittance spectroscopy in an evacuated low-temperature chamber between 170 and 350 K . The meaCVD-grown graphene on Cu  often coAn SEM image of FLG following its transfer onto quartz a shows m−1), G (~1582 cm−1) and 2D bands (~2675 cm−1). The D-band appears due to lattice disorder [−1, which corresponds to four-layer graphene. In addition, the positions of the G and 2D peaks indicate the p-type doping of the graphene. This is consistent with previous findings on the nature and quality of FLG and confirms the validity of the selected transfer approach γ=1w0graphene , the biagraphene  and biaxgraphene  strainedgraphene , the shi13 cm−2 and the carrier mobility of 190 cm2·V−1·s−1. Similar p-type doping in few-layer graphene was observed earlier in Ref. [2·V−1·s−1. Nevertheless, the sample preserves high optical transparency upon transition onto quartz, as demonstrated by the UV-vis transmission measurements, highlighting the material’s potential for use as a transparent conductive layer 2S2O8 demonstrates the appearance of a bandgap, as indicated by the activation energy of 22 meV for conductivity. The microscopic facet structure on the sample surface after transfer from copper foil to a quartz substrate, observed using SEM and AFM, is apparently related to the anisotropic mechanism of substrate etching. The Raman spectral analysis makes it possible to determine the number of graphene layers, as well as the type of doping. Four-point probe Hall effect measurements of the few-layer graphene sample showed an apparent p-type sheet doping density of 5 × 1013 cm−2 and carrier mobility of 190 cm2 V−1 s−1. It should be noted that the sample preserves high optical transparency upon its transfer to quartz, which was demonstrated by the UV-vis transmission measurements. The sample conductivity shows an increase with temperature, as for a typical semiconductor. This is accompanied by the observation of defects, as evidenced by Raman spectroscopy, which may be introduced into FLG during the transfer process. It is obvious that the presence of impurities may change the density of charge carriers, thereby also influencing the electronic properties of FLG. It is hoped that the results of this study will find use in the development of graphene-based composite materials for electronics.In conclusion, an FLG-on-quartz sample obtained by the etching of copper foil in 0.1 M (NH


Graphene oxide (GO) was synthesised by an improved Hummers' method and was further used for the in situ synthesis of graphene via GO reduction and the formation of a CdMoO4 nanowire/graphene composite. The structural phase formation of tetragonal CdMoO4 was confirmed from X-ray diffraction measurements. The small nanoparticle assembled nanowires, prismatic microsphere morphology and crystalline nature of the synthesized material were investigated using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Due to its unique morphology and stability, the CdMoO4/graphene composite was used as a photocatalyst for H2O splitting. In comparison to pristine CdMoO4, the CdMoO4/graphene composite showed the best hydrogen evolution rate, i.e. 3624 μmole h−1 g−1, with an apparent quantum yield of 30.5%. The CdMoO4/graphene composite has a higher photocatalytic activity due to the inhibition of charge carrier recombination. H2 production measurements showed that the ternary semiconductor/graphene composite has enhanced photocatalytic activity for H2 generation.Herein, a facile  in situ solvothermal technique for the synthesis of a CdMoO4/graphene composite photocatalyst for hydrogen generation under natural solar light.Herein, a facile  Hydrogen has been identified as a potential eco-friendly energy carrier in many low greenhouse gas energy scenarios.4 However, Arbuj et al. have previously discussed that only limited success has been achieved in the generation and storage of hydrogen.4 The different efficient ways to produce hydrogen, using, for example, photocatalytic, electrochemical and photoelectrochemical methods, have attracted much attention.1,5,6 Currently, coal gasification and the steam reformation of methane are the well-known and promising methods for high purity hydrogen production, but these are energy intensive processes and are undesirable in terms of the effect that they have on the environment.7,8 However, the technology to produce hydrogen in a cost-effective and eco-friendly way has not yet been developed. Considering the overall scenario and the abundant water supply on the Earth, hydrogen generation via photocatalytic water spitting is the most promising technique for renewable hydrogen production.9Hydrogen has been considered as one of the best clean energy fuels owing to its green and renewable properties, compared with those of other fuels  was added to a mixture of graphite flakes  containing NaNO3 , and the reaction mixture was cooled to 0 °C. Further to this, the addition of KMnO4  was carried out by keeping the reaction temperature below 20 °C. The reaction mixture was warmed to 35 °C and allowed to stir for 30 min, followed by the slow addition of water (138 ml), producing a large exothermic increase in the reaction temperature to 98 °C. After that, external heating was introduced to maintain the reaction temperature at 98 °C for 15 min, then the heating was stopped, and the reaction was cooled in a water bath for 10 min. Additional water (420 ml) and 30% H2O2 (3 ml) were added, which produced another exothermic reaction, and the solution was then allowed to cool naturally. After natural cooling, the mixture was centrifuged (6000 rpm for 1 h), and the supernatant was decanted away. The obtained solid was dried overnight at room temperature, resulting in 1.2 g of solid product.All of the chemicals used for the synthesis of graphene oxide (GO) and CdMoO4 nanowire composites. The detailed method for the synthesis of CdMoO4 nanowires and CdMoO4 prisms can be found in the ESIThe synthesized GO was used for the further synthesis of graphene/CdMoO2.2The crystalline phases were investigated using powder X-ray diffraction . The morphologies of the synthesized samples were investigated by field emission scanning electron microscopy . The optical properties of the powder samples were studied using a UV-visible-near infrared spectrometer . For HRTEM  studies, samples were prepared by dispersing the powder in ethanol, followed by ultrasonication in an ultrasonic bath for 5 min. The resulting dispersion was then drop-casted onto a carbon coated copper grid and was subsequently dried under vacuum. Room temperature Raman spectroscopy measurements were performed using a Renishaw InVia microscope Raman system with a laser wavelength of 532 nm in back scattering geometry laser power mode on a 5 mW sample with a laser spot size of 1 μm. The purity of the collected gas was analyzed by gas chromatography .2.32) generation via water splitting using CdMoO4 and its graphene composites as photocatalysts, in an aqueous solution containing methanol as a hole scavenger, was performed in an air tight quartz reactor . The assembly was arranged on a terrace and the quartz reactor containing the reaction mixture was irradiated with solar light. The quartz reactor was equipped with a water circulator in order to absorb the IR radiation, which minimizes the effects of overheating. The intensity of the solar light was measured using a digital Lux meter. The observed average intensity of sunlight reaching the surface of the Earth is 125 000 lux. Here, a known quantity (15 mg) of powder photocatalyst was suspended in a solution containing 20% (v/v) aqueous methanol. The total volume of the reaction mixture was 25 ml and there was 45 ml of free space in the reactor. The reactor was made air tight with a rubber septum and was sonicated for 5 min and then stirred for 30 min to homogenize the suspension. Finally, it was bubbled with ultra-high purity (UHP) nitrogen (N2) gas to remove all dissolved gases and purging was continued for 30 min to ensure and inert atmosphere in the reactor. After purging the gas, the flow of N2 was stopped and the reactor was made air tight. As soon as the reactor was irradiated with solar light, the photocatalytic splitting of water was initiated and the generated H2 gas was collected in the empty head space of the reactor. The amount and purity of the gas evolved was analyzed by gas chromatography . The apparent quantum efficiency (AQE) of the hydrogen generated was calculated using the following equation:Photocatalytic hydrogen , and in a 1 : 1 ratio, denoted as MEG (1 : 1), and the 0.5%, 1%, 2% and 4% graphene composites synthesized using CdMoO4 in MEG (3 : 1) were characterized using PXRD, as shown in 4 synthesized in MEG (3 : 1) and MEG (1 : 1) shown in 4 synthesized in both solvent systems could be well indexed and show body centred tetragonal phase formation, in good agreement with the reported JCPDS card no. 007-0209. The PXRD peak intensity of the CdMoO4 synthesized in MEG (3 : 1) was observed to be slightly higher than that of CdMoO4 synthesized in MEG (1 : 1). The peak intensity can be attributed to the crystalline nature and small particle size of the material. Along with the PXRD pattern of the CdMoO4 synthesized in MEG (3 : 1), the PXRD patterns of its 0.5%, 1%, 2% and 4% graphene composites are shown in θ = 14.1 slightly increases upon an increase in the percentage of graphene. In 4 composite patterns, there are no extra peaks present, revealing the phase purity of the synthesized samples.The synthesized CdMoO4 in the MEG (3 : 1) solvent system were performed using FESEM and the results are shown in 4 such as this has not been previously synthesized using a solvothermal process. The average size of the CdMoO4 nanowire bundles is observed to be 5 μm  system were carried out using FESEM and the results are shown in via the assembly of tiny close-packed nano prisms. It is also worth noting that such unique microspheres of CdMoO4 synthesized via a solvothermal process has not been previously observed. More significantly, the nanoparticles at the surface of the structure are prismatic in shape and the overall average size of the nano prisms is 50–100 nm  and the powder pattern is shown in −1 and a broad G band at 1590 cm−1, assigned to the first-order scattering of the E2g mode. The prominent D band peak is due to structural defects created by hydroxyl and epoxide functional groups on the carbon basal plane. The surface morphology of the GO layered sheets was investigated using FESEM and the results are shown in 4 nanowire/graphene composite materials. It shows the presence of sheets of graphene decorated with CdMoO4 nanowire bundles (5–7 μm size). It can be clearly observed that the nanowire CdMoO4 bundles are well dispersed over the multi-layer graphene sheets and remain firmly adhered to them, as is shown in 4 nanowire bundles to the graphene sheets during the photoexcitation process, which minimises the recombination of electrons (e−) and holes (h+). The presence of the CdMoO4 nanowire bundles anchored on the surface of the graphene sheets results in a larger surface area for moving electrons and holes and makes the material available for photocatalytic activity for a longer time period. This results in more active adsorption sites and photocatalytic reaction centres becoming available, therefore resulting in an enhanced photocatalytic activity.Raman spectroscopy is a very precise technique that is used to investigate the number of layers present in materials, so it was used to characterize the as-synthesized GO sample and the results are shown in 4 nanowires and their 0.5, 1, 2 and 4 weight% graphene composites were further analyzed using Raman spectroscopy and the results are shown in 4 and its graphene composites show a peak at 866.1 cm−1, assigned as the ν1(Ag) symmetric stretching vibration mode of the [MoO4] cluster in the CdMoO4 structure. The Raman peaks at 820 and 760.5 cm−1 can be assigned to the significant anti-symmetric stretching ν3(Bg) and ν3(Eg) vibration modes of the CdMoO4 structure, respectively. Furthermore, the peaks at 397 and 306 cm−1 were assigned to the weaker ν4(Bg) and stronger ν2(Ag) modes of the [MoO4] tetrahedrons. A significant D band peak of graphene at 1358 cm−1 and a G band peak at 1593 cm−1 indicates the presence of layered structured graphene in the composite material. With an increase in the concentration of graphene in the CdMoO4 nanowire composites, the Raman peak intensity of the CdMoO4 peaks slightly decreases, whereas the magnified D and G band spectra, as shown in Fig. S3 in the ESI,4 composite materials.The solvothermally synthesized CdMoO4 microspheres, CdMoO4 nanowires and CdMoO4 nanowire/graphene composites were further investigated using UV-Vis spectroscopy and the results are shown in 4 microspheres and nanowires show an absorption edge cut off at ∼375 nm (3.31 eV), as shown in 4 nanowires show a slightly higher absorption than that of the CdMoO4 microspheres, which can be attributed to the crystalline nature of the CdMoO4 nanowires. In the case of the CdMoO4 nanowire composites with graphene, a slight red-shift in the UV-Visible absorption spectra is observed. The absorption edge cut off of the composite materials is observed to be ∼380 nm (3.2 eV) for the 0.5 and 1% graphene composite materials. With an increase in the graphene concentration (in the 2–4% samples), a shift in the absorption spectra towards a longer wavelength at 401 nm (3.1 eV) is observed. The corresponding band gap energy of the composite materials was calculated from the Tauc plot, as shown in Fig. S1 in the ESI.†The optical properties of the synthesized CdMoO4 nanowires allows generated electrons and holes to move easily to the surface of the catalyst, making it available for photocatalytic activity, whereas in the case of the CdMoO4 microspheres, the generated electrons and holes cannot move easily to the surface of the catalyst due to the closely packed structure. It is proposed that in the graphene composites, the generated electrons and holes track into the layered graphene and move in the layered structure for a longer time, which reduces the electron and hole pair recombination and makes the material available for photocatalytic activity for a longer time period.The smaller size and crystalline nature of the CdMoO3.14 microspheres, nanowires and the graphene composite materials were evaluated by measuring the amount of H2 generated via photocatalytic water splitting. The photocatalytic H2 generation activity of the synthesized materials was carried out in the presence of solar light. In the present study, methanol was used as a sacrificial reagent. F. Guzman et al. earlier discussed the use of methanol as a sacrificial reagent and its detailed mechanism.47 It seems that the presence of methanol decreases the e− and h+ pair recombination time. Methanol suppresses the evolution of oxygen through the formation of free radicals. As the reactor containing the photocatalyst is irradiated with solar light, the electrons in the conduction band (CB) and holes in the valence band (VB) are generated. The photogenerated holes (h+) in the VB oxidize the water molecules into H+ ions, while the electrons (e−) in the CB reduce the two H+ ions into one molecule of H2. The photocatalytic water splitting mechanism can be described as follows:The photocatalytic activity of the CdMoO2 generated in μmole with respect to time for the CdMoO4 prismatic microspheres, nanowires and the graphene composites are shown in −1 g−1 of H2 were generated for the CdMoO4 nanowires and prismatic microspheres, respectively. The linear plots of H2 generated in μmole vs. the time in minutes are shown in 2 generation from the water splitting over time. It was concluded that the higher photocatalytic activity observed for the CdMoO4 nanowires is due to the small size of the CdMoO4 particles, resulting in a greater surface area and increase in the number of active sites for photocatalytic activity. Slightly less hydrogen was generated by the CdMoO4 prismatic microspheres than that by the nanowires. The reason for the lower photocatalytic activity is that the nanoparticles in the CdMoO4 prismatic structure are agglomerated and closely packed, reducing the surface area and number of active sites, which restricts the easy movement of generated electrons and holes to the surface. It is well acknowledged that the surface morphology and size of the material plays a crucial and significant role in the context of photocatalytic H2 generation.3 The highest H2 generation of 3624 μmole h−1 g−1 was achieved for the 1% graphene–CdMoO4 nanowire composite. It was observed that the H2 generation activity increased for the 0.5 and 1% graphene CdMoO4 composites. Furthermore, the H2 generation activity was observed to decrease for the 2% and 4% graphene composites.The results of the amount of H4 nanowire composite shows almost double the hydrogen generation than that of the pristine CdMoO4 nanowires. It can be concluded that the highest photocatalytic H2 generation performance of the 1% graphene composite is due to the nanoparticles of the CdMoO4 nanowires and edge sites of the graphene and the vacancy defects in the structure. Graphene, in its composite form with semiconductor materials, has exhibited comparatively good photocatalytic activity compared with individual semiconductors due to its highly outstanding properties, such as high electron mobility, large surface area, excellent conductivity, stability and mechanical strength. The 2D layered conjugated structure of graphene in the composite helps to reduce the electron and hole pair recombination time, which is beneficial for the photocatalytic activity. During the photocatalysis experiments, the carbon-related material acted as both an electron-acceptor and electron-transport material; facilitating the migration of photoinduced electrons and obstructing the charge recombination, resulting in an enhanced photocatalytic performance. A schematic representation of the photocatalytic hydrogen generation catalyzed by the CdMoO4–graphene composite photocatalysts in natural sunlight is illustrated in Interestingly, the 1% graphene/CdMoO4 particles facilitate the easy transport of the generated electrons and holes to the surface of the catalyst and track them into the graphene, which reduces the recombination time. Furthermore, there are more defects in the 1% graphene–CdMoO4 nanowire/graphene composite, which significantly suppress the recombination of photogenerated charge carriers. Considering the optical properties of the CdMoO4 and its graphene composite materials, the higher photocatalytic activity observed for the CdMoO4 nanowire/1% graphene composite is quite understandable. As the graphene% increases in the CdMoO4 nanowires, an increase in the absorption of visible light is observed. This enhanced absorbance leads to the formation of a large number of e− and h+ pairs, resulting in higher photocatalytic activity. In the present study, few layered graphene nanosheets with CdMoO4 nanowires were used, which have good stability along with a short carrier diffusion time and hence show good photocatalytic activity. A further increase in the graphene content (in the 2% and 4% graphene composites) led to a decrease in the observed H2 generation activity. It is quite reasonable that the introduction of a greater percentage of graphene led to a shielding of the active sites on the catalyst surface. This shielding effect, brought about by the presence of an excess amount of carbon based material in metal oxide catalyst materials has been discussed in detail by Yu et al.48 Optimized graphene content plays a significant role in attaining the highest photocatalytic activity in the graphene/CdMoO4 nanowire composites. In the present study, the highest photocatalytic activity obtained for the 1% graphene CdMoO4 nanowire composite is higher than that previously reported for a metal oxide/graphene composite material.40,49–51 Overall, the results show that the 1% graphene/CdMoO4 nanowire composite is an excellent stable photocatalyst for H2 generation in solar light.The small CdMoO2 production via H2O splitting under solar light catalyzed by a graphene/CdMoO4 nanowire composite. The stability of the catalyst was confirmed by performing repeatability studies, which showed that the catalyst retains its activity after being recycled five times, which shows the reproducibility of the results. The PXRD pattern of the reused catalyst sample did not show any change in the phase of the CdMoO4 nanowire/graphene composite catalyst, which clearly shows the stability of the catalyst. No H2 production was observed in the absence of a catalyst or under dark conditions (in the absence of light). Overall, it is concluded that the CdMoO4 nanowire/graphene composite catalyst is quite a stable and active photocatalyst for photocatalytic H2O splitting in solar light.This is the only report which reveals photocatalytic H4.in situ one step solvothermal approach has been demonstrated for the synthesis of CdMoO4 and its graphene composites. The syntheses of CdMoO4 nanowires and prismatic microspheres were demonstrated. CdMoO4 nanowire bundles were observed to uniformly decorate few layered graphene sheets. Photocatalytic H2 generation via water splitting in solar light was investigated for CdMoO4 and its graphene composites. The highest H2 generation of 3624 μmole h−1 g−1 achieved for the 1% graphene CdMoO4 nanowire composite, which has not previously been reported. The small particles, edge sites and defects of the graphene in the catalyst structures play an important key role in the enhancement of H2 generation. The generated electrons and holes easily transfer to the surface and quite easily track into the graphene due to the thinness of the graphene nanosheets, which inhibits charge recombination.In conclusion, an Author has no conflicts of interest.RA-008-C8RA01557K-s001


It has been proposed that processing sentential negation recruits the neural network of inhibitory control . In addi Imagine you are a Spanish-English bilingual, you read a news item from a Spanish newspaper and then you share the news item with two friends, one a Spanish monolingual and the other an English monolingual. After telling them the news, they began to ask you many details in Spanish or English, such as “Who had the accident? Mary?” and you replied “No,” or “>Quién conducía el coche? >Peter?” [Who was driving the car? Peter?] and you answer “Sí” [Yes]. This is an example of how learning and retrieving linguistic information can rely on the same language (L1 – L1), or on a different language (L1 – L2) to produce an affirmative or negative answer in the appropriate language. In this situation, you retrieve information in the original language, but, to answer some questions, you eventually need to switch to another language. To do that, one remarkable ability of bilinguals is cognitive control or monitoring to discern between their two languages and select one of them while suppressing the other to minimize the interference. Numerous studies have investigated how language control plays a crucial role in bilinguals , giving The role of cognitive control in bilinguals has been studied with the so-called language-switching paradigm. This paradigm requires the naming of pictures or digits in either of two languages, depending on explicit cues , a pre-oMost of the research in this field has focused on bilinguals’ production of isolated words. However, some research also reported language switching effects on comprehension  and longNegation processing has often been associated with the suppression of negated information see , and theThe above studies mainly focus on the processing of sentential negation, that is, how sentences with a negative marker are understood. Yet, people produce negations as much as understand them. Thus, developmental studies have shown that children begin to use negative responses (no/not) very early, during the second year of life, to reject an object, or to stop or prevent an imminent action, establishing thus a strong association between the verbal markers of negation and the rejection and prevention of an action. Moreover, in this early stage of linguistic development, the child often use negation for self-prohibition, when she is about to engage in a forbidden action e.g., . In fact1. For example, One important pragmatic function of negations is denial . Denial Most research on the inhibitory effects of negation has been conducted with monolingual participants, while the processing of negation by bilinguals received little attention. Previous research on negation in bilinguals is generally driven by the idea that negation is universal and the processing of negation is more complicated than processing affirmation, regardless of the language e.g., . Yet, siThis study aims to explore the impact of language-switching on the processing of negation in an encoding-retrieval memory task. To this end, an online behavioral experiment was conducted with two groups of unbalanced Spanish-English bilinguals. One group of participants initially read stories in Spanish (L1), and the other group read the same stories in English (L2). Immediately after reading each story, the participants received a set of verification questions about the story contents, requiring a “yes” or “no” response. Some of the questions for verification were presented in the original language of the story (non-switch condition) and others in the alternative language (switch condition). In other words, the two critical manipulations of response polarity (affirmative vs. negative) and language sequence (switch vs. non-switch) occur in the verification tasks, given an opportunity to explore their combined effects on performance. Based on the literature reviewed above, we can expect both a switch cost and a negation cost in terms of longer response times and reduced accuracy. Most importantly, an interaction between the two factors is possible; for instance, the cost of negation could be reduced (primed) or increased (interfered) in the context of language switch, compared to the language non-switch. If so, this would suggest that the two processes share resources from the same inhibitory control mechanism.M = 20.4 years, SD = 5.12).A total of 121 psychology students from the University of La Laguna voluntarily participated in the current study. All the participants were neurologically healthy and right-handed with normal or corrected-to-normal eyesight. They were given informed consent and received course credit for their participation. Spanish is their native language (L1) and they use English as the second language (L2). Three participants were excluded for choosing “I find it difficult to understand most of the sentences.” In a post-survey. The final sample consisted of 118 participants . The average age of L2 acquisition (AoA) was 5.05-year-old.To assess the participants’ language proficiency, we inquired about the age of L2 acquisition (AoA), and administered a self-rated language skills questionnaire, in which participants rated on a five-point scale their own-perceived L1 (Spanish) and L2 (English) knowledge, with 5 indicating excellent and 1, poor. All participants reported having an L2 level higher than the B1 in the CEFR test or an equivalent level in other English tests. As illustrated in M = 45.25), among which, 36 were about the protagonists. These experimental items consisted of 18 semantically related pairs, with each member of a pair assigned to one of the protagonists . The remaining items were fillers (M = 9.25) to make the story natural and coherent . There were two versions of the stories written in Spanish (L1) and English (L2), respectively, although with identical content.The experimental task was composed of a study phase and a verification phase. The study phase required participants to read four stories involving two protagonists (Montse and Jordi), describing their main personal traits and their activities in four different scenarios: daily life in the university, vacations, going to the beach, and a birthday party. Each story included 44–46 items each , and were followed by the name of one of the characters in a separate frame . The participants had to judge whether the name was a correct answer to the question, pressing the “yes” or the “no” response button. The remaining 8 questions referred to the filler items . Of the experimental questions, 12 were non-switching questions asked in the same language as the initial story, and 6 were switching questions asked in the other language. The filler questions were always formulated in the same language as the story. All the questions were presented in pseudo-random order. For each story block, the first two questions were always fillers. The switching questions were always followed by 2–4 non-switching questions. Within each context language group, we created 8 counterbalanced lists resulting from 1) the facts attributed to the protagonists in the stories; 2) the facts asked in the verification questions 3) the response polarity.L1, in L1 context, or L2 → L2 in an L2 context), while the switch questions were in a different language from the context and were preceded by at least 2 questions in the context language .The experimental design was composed of Language Sequence (switch vs non-switch), and Response Polarity (affirmative vs negative), as within-subject factors, and Context Language (L1 vs L2) as a between-subject factor. Non-switch questions were in the same language as the context story and were preceded by a question in that language (L1 → U tests: age of L2 acquisition , L2 proficiency  and L1 proficiency .Due to the COVID-19 situation, the experiment was programmed and conducted online, using the Psytoolkit toolkit , 2017. TParticipants received an email with the experiment link and were instructed to complete the experiment online on a computer and a keyboard in a quiet room, previously turning off the mobile phone to avoid distractions. In the study phase, participants were first instructed to read the story carefully, keeping in mind that there would be related questions later. Then, the story was freely read by the participants in 4 self-paced paragraphs with 8–15 sentences in each paragraph see . In the car: Anova (χ2 variant) to test significance and compute p values for the fixed-effects, avoiding issues of estimating denominator degrees of freedom in unbalanced designs, both mathematical and computational , Language Sequence , and Context Language . These effects reflected longer RTs for: 1) negation than affirmation responses, 2) switch than non-switch questions, and L1 than L2 contexts. The two-way interactions between Response Polarity and Language Sequence did not reach significance . However, Context Language interacted significantly with Response Polarity  and with Language Sequence . Post hoc analyses revealed larger costs for language switch  when L1 was the main language (L1 context)  than when it was L2 . Similarly, negation cost was larger in L1 context  than L2 context . More importantly, the three-way interaction between Response Polarity, Language Sequence and Context Language reached also significance (χ2(1) = 5.29, p = 0.021) . Regarding the switch sequence, the two Context Languages differed significantly both when producing a “yes” and a “no” response , with a longer response time in L1 Context compared to L2 Context.The average RTs for correct trimmed response time and the percentage accuracy rates across conditions are shown in 021) See . Given tt = −9.010, p < 0.0001), indicating longer RTs for “no” than “yes” responses. However, for this group, neither Language Sequence  nor the interaction reached significance . In contrast, for the L1 context group, there were main effects of Response Polarity , and Language Sequence , which reflected longer RTs for negation than affirmation, and for switch than non-switch questions. Most importantly, the interaction between these two factors was significant for the L1 context group , indicating relatively diminished switch cost for “no” responses in comparison to “yes” responses. All these findings indicated that the RT did not differ at the “baseline” condition (responding “yes” to non-switch questions), but the response time was highly and differentially modulated by Response Polarity and Language Sequence in both L1 and L2 groups.To better understand the three-way interaction, further analyses with the same LMEMs strategy as above was performed for each Context Language group separately. Fixed effects were reported for each Context Language group. For the L2 context group, there was a main effect of Response Polarity  = 12.79, nses see . The absThe present study investigated for the first time whether bilinguals’ language switch modulates negation processing. To this end, we tested bilingual Spanish-English speakers using a two-step encoding and verification memory-based task. The encoding phase involved reading stories that were shown in the participants’ native language (Spanish), or in their second language (English). The language switch was induced during the verification phase, by presenting the questions in the same language (non-switch) or in the alternative language (switch) as the main story. On the other hand, responses to both types of verification questions were affirmative (yes) or negative (no), so the polarity was not a feature of the sentences themselves, but rather arose during the response production. An unexpected result was that the verification times for the L1 Context were longer than for the L2 Context, which seems to be at odds with the well-known fact that unbalanced bilinguals are usually more efficient at processing their native language rather than a second language. However, this result is misleading if we neglect the interactive effects of Language Context with Response polarity and Language Sequence. Thus, if we focus on the baseline condition (non-switch and affirmative) the response time and accuracy did not differ for both language contexts. However, beyond the baseline, the RTs were modulated differently in the L1 Context (both by switching and negative polarity) and in the L2 Context (only by negative polarity). The main results of the modulation were as follows. First, an asymmetric language switch effect was found. That is, in the context of L1 (Spanish), switching to L2 in the verification involved more cognitive cost (slower and less accurate responses) than keeping the same language (L1-L1). However, in the context of L2 (English) switching to L1 did not imply an additional cognitive cost compared to keeping the same language (L2-L2). Secondly, a classical negation effect was observed, with a longer reaction time to produce negative (“no”) than affirmative responses (“yes”). Finally, although the negation effect was patent for the L1 and L2 context groups, negation only interacted with language switching in the former. That is, in the context of L1, the cost of switching from L1 to L2 was reduced for “no” responses in comparison to “yes” responses, implying a sort of priming, which is, producing negative responses benefits from a language switching sequence. These results will be discussed in detail below.The finding of switching costs from L1 to L2 is consistent with the research on language-dependent differences in memory retrieval processes . Such reThe switch cost asymmetry might be attributed to the usual direction of translation. As suggested by The asymmetry of switching cost obtained here (poorer performance when switching from L1 to L2 than from L2 to L1) contrasts with the commonly reported pattern in language switching studies using naming tasks . In thesConsistent with the previous work . In factLanguage switch has been described as a conflict monitoring process, since the bilinguals must be able to actively inhibit one language while using the other, to minimize interference. Neuroimaging studies have provided evidence that inhibitory control networks, including the anterior cingulate, the SMA or the prefrontal gyrus are recruited during language switch . MoreoveThis is the first study, to our knowledge, that examined how two apparently unrelated linguistic processes (language switching and producing negative answers) modulate each other in different language contexts. The choice of the two processes was motivated by the hypothesis that they recruit inhibitory control resources, and therefore they could interact when combined in the same task. The results found asymmetric switch cost (L1 to L2 > L2 to L1), negation cost (negation > affirmation), and interactive effects between them, which are suggestive of shared processes. This could have implications for theoretical and applied research fields, for instance, implement methods to learn a second language, better understand decision making processes, study inhibitory control disorders, long-term memory processes, etc. However, the current study has some limitations. First, despite the fact that the two groups of participants submitted to the L1 and L2 contexts, respectively, did not differ significantly in language proficiency and despite adopting the same material contents in Spanish and English for the study phase and verification phase, the between-group design of language context could induce biased results. Future studies are needed to adopt a within-participant design to better control for these possible biases. Second, future studies are needed to clarify whether the observed interactions between response polarity and language switch involves specific inhibitory control networks in the brain , using neuroimaging, EEG and non-invasive brain stimulation. Also, it might be useful to test these interactive effects with different task demands and materials, including sentential negation, naming paradigms, etc.The original contributions presented in this study are included in the article/ceiba@ull.es. The patients/participants provided their written informed consent to participate in this study.The studies involving human participants were reviewed and approved by Comité de Ética de la Investigación y Bienestar Animal Vicerrectorado de Investigación y Transferencia de Conocimiento Universidad de La Laguna, La Laguna. Email: AZ, MV, and DB contributed to the conception and design of the study. AZ and YF performed the statistical analysis. AZ wrote the first draft of the manuscript. MV and DB wrote sections of the manuscript. AZ, MV, YF, HW, and DB contributed to the manuscript revision, read, and approved the submitted version. All authors contributed to the article and approved the submitted version.