Graphene-based electrochemical sensors

Differential potential ratiometric sensing platform for enantiorecognition of chiral drugs

A versatile, robust and efficient differential potential ratiometric sensing platform was developed for enantioselective recognition of dual chiral targets based on a composite membrane of molecularly imprinted polymers (MIPs) and reduced graphene oxide (rGO) modified glassy carbon electrode (GCE). The functional chitosan-based MIPs and rGO were compatibly immobilized on the GCE with high selectivity and efficient signal amplification. Moreover, via the systematic optimization of series conditions, a distinct potential difference (PD), reaching 135 mV, was obtained between the R-/S-prop based on the MIPs/rGO/GCE. In a controllable concentration range from 50 μM to 1000 μM, different ratios of R-/S-prop were linearly related to the peak potentials (Eps) in the racemic mixture. Using this low-cost reversible electrochemical platform, both Prop enantiomers were simultaneously identified with high repeatability and time-based stability. This novel semi-quantitative electrochemical sensing platform was established to rapidly quantify the ratio of S-/R-prop by Ep for the chiral drug recognition with great potential for practical applications in fields of pharmacological detection and clinical analysis.

Graphene-derived nanomaterials as recognition elements for electrochemical determination of heavy metal ions: a review

This review (with 155 refs.) summarizes the progress made in the past few years in the field of electrochemical sensors based on graphene-derived materials for the determination of heavy metal ions. Following an introduction of this field and a discussion of the various kinds of modified graphenes including graphene oxide and reduced graphene oxide, the review covers graphene based electrodes modified (or doped) with (a) heteroatoms, (b) metal nanoparticles, (c) metal oxides, (d) small organic molecules, (e) polymers, and (f) ternary nanocomposites. Tables are provided that afford an overview of representative methods and materials for fabricating electrochemical sensors. Furthermore, sensing mechanisms are discussed. A concluding section presents new perspectives, opportunities and current challenges. Graphical Abstract Schematic illustration of electrochemical sensor for heavy metal ion sensing based on heteroatom-doped graphene, metal-modified graphene, metal-oxide-modified graphene, organically modified graphene, polymer-modified graphene, and ternary graphene based nanocomposites.

Hybrids of Fullerenes and 2D Nanomaterials

Fullerene has a definite 0D closed-cage molecular structure composed of merely sp2-hybridized carbon atoms, enabling it to serve as an important building block that is useful for constructing supramolecular assemblies and micro/nanofunctional materials. Conversely, graphene has a 2D layered structure, possessing an exceptionally large specific surface area and high carrier mobility. Likewise, other emerging graphene-analogous 2D nanomaterials, such as graphitic carbon nitride (g-C3N4), transition-metal dichalcogenides (TMDs), hexagonal boron nitride (h-BN), and black phosphorus (BP), show unique electronic, physical, and chemical properties, which, however, exist only in the form of a monolayer and are typically anisotropic, limiting their applications. Upon hybridization with fullerenes, noncovalently or covalently, the physical/chemical properties of 2D nanomaterials can be tailored and, in most cases, improved, significantly extending their functionalities and applications. Here, an exhaustive review of all types of hybrids of fullerenes and 2D nanomaterials, such as graphene, g-C3N4, TMDs, h-BN, and BP, including their preparations, structures, properties, and applications, is presented. Finally, the prospects of fullerene-2D nanomaterial hybrids, especially the opportunity of creating unknown functional materials by means of hybridization, are envisioned.

Electrically-Transduced Chemical Sensors Based on Two-Dimensional Nanomaterials

Electrically-transduced sensors, with their simplicity and compatibility with standard electronic technologies, produce signals that can be efficiently acquired, processed, stored, and analyzed. Two dimensional (2D) nanomaterials, including graphene, phosphorene (BP), transition metal dichalcogenides (TMDCs), and others, have proven to be attractive for the fabrication of high-performance electrically-transduced chemical sensors due to their remarkable electronic and physical properties originating from their 2D structure. This review highlights the advances in electrically-transduced chemical sensing that rely on 2D materials. The structural components of such sensors are described, and the underlying operating principles for different types of architectures are discussed. The structural features, electronic properties, and surface chemistry of 2D nanostructures that dictate their sensing performance are reviewed. Key advances in the application of 2D materials, from both a historical and analytical perspective, are summarized for four different groups of analytes: gases, volatile compounds, ions, and biomolecules. The sensing performance is discussed in the context of the molecular design, structure-property relationships, and device fabrication technology. The outlook of challenges and opportunities for 2D nanomaterials for the future development of electrically-transduced sensors is also presented.

Co/Co9S8 nanoparticles coupled with N,S-doped graphene-based mixed-dimensional heterostructures as bifunctional electrocatalysts for the overall oxygen electrode

A Co/Co₉S₈/rGO/MWCNT composite catalyst was designed and fabricated via a combined hydrothermal reaction with a calcination method for the ORR/OER.

Organophilic graphene nanosheets as a promising nanofiller for bio-based polyurethane nanocomposites: investigation of the thermal, barrier and mechanical properties

The present study focuses on the design of new nanocomposite films using bio-based thermoplastic polyurethane (TPU) as a polymer matrix and long chain amine functionalized reduced graphene oxide (G-ODA) as a nanofiller.

Laser-Cut Polymer Tape Templates for Scalable Filtration Fabrication of User-Designed and Carbon-Nanomaterial-Based Electrochemical Sensors

We report here a simple filtration method for the scalable fabrication of user-designed and carbon-nanomaterial-based electrode arrays using laser-cut poly(vinyl chloride) (PVC) tape templates. This method can produce electrode arrays with high uniformity and low resistance from the dilute dispersions of single-walled carbon nanotubes (SWNTs) and graphene nanoplatelets (GNPs). For these two carbon arrays, the SWNT array is demonstrated to possess several interesting properties, e.g., good mechanical properties, excellent flexibility, and favorable electrochemical behavior. Moreover, its porous structure enables the construction of a paperlike solid-state electrochemical sensor using Nafion electrolytes, which is suitable for the on-site monitoring of trace phenol pollutants in electrolyte-free water. Besides, an electrochemically addressable 36-zone sensor was constructed by this method. With the aid of an inexpensive 3D printer, the addressable sensor can achieve the semiautomatic and high-throughput evaluation of antioxidant capacity on a series of vegetables and fruits using a single-channel electrochemical analyzer.

Mimicking of five human senses using nanostructured ZnO single material

We demonstrated a single-material multifunctional sensor using ZnO nanorods, which is capable of mimicking the five human senses. A simple method for the growth of ZnO nanorods and their application as a multifunctional sensor was studied. High-density ZnO nanorods were synthesized by the carbothermal transport method on a graphene catalyst. To optimize the sensing mechanisms, we investigated ZnO nanostructure growth under two oxygen flow rates. ZnO nanorods as sensors for smell, light, sound, touch, and taste, the five human senses, showed stable electrical signals under standard ambient conditions.

A bioinspired structured graphene surface with tunable wetting and high wearable properties for efficient fog collection

Inspired by the fog harvesting ability of the spider net and the interphase wetting surface of Namib desert beetles, we designed a kind of special bioinspired hybrid wetting surface on a Cu mesh by combining polydimethylsiloxane (PDMS) and graphene (G). A surface containing hydrophobic and superhydrophobic areas is prepared by a combination of laser etching and ultrasonic vibration. Thus, this as-prepared hybrid wetting surface can quickly drive tiny water droplets toward more wettable regions, which makes a great contribution to the improvement of collection efficiency. Moreover, the PDMS/G surface not only is tolerant to many stresses such as excellent anti-corrosion ability, anti-UV exposure and oil contamination, but also shows self-healing simply by burning the worn areas, which thus endows the surface with tunable-wettability change between flame treatment and abrasive wear. This study offers a novel insight into the design of burned healed materials with interphase wettability that may enhance the fog collection efficiency in engineering liquid harvesting equipment and realizes renewable materials in situ cheaply and rapidly by processes that can be easily scaled and automated.

Progress on nanostructured electrochemical sensors and their recognition elements for detection of mycotoxins: A review

Nanomaterial-embedded sensors have been developed and applied to monitor various targets. Mycotoxins are fungal secondary metabolites that can exert carcinogenic, mutagenic, teratogenic, immunotoxic, and estrogenic effects on humans and animals. Consequently, the need for the proper regulation on foodstuff and feed materials has been recognized from times long past. This review provides an overview of recent developments in electrochemical sensors and biosensors employed for the detection of mycotoxins. Basic aspects of the toxicity of mycotoxins and the implications of their detection are comprehensively discussed. Furthermore, the development of different molecular recognition elements and nanomaterials required for the detection of mycotoxins (such as portable biosensing systems for point-of-care analysis) is described. The current capabilities, limitations, and future challenges in mycotoxin detection and analysis are also addressed.

Electrochemical and Electronic Properties of Transparent Coating from Highly Solution Processable Graphene Using Block Copolymer Supramolecular Assembly: Application toward Metal Ion Sensing and Resistive Switching Memory

Here, we have discussed the preparation of a highly solution processable graphene from a novel supramolecular assembly consisting of block copolymer polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) and pyrenebutyric acid (PBA)-modified reduced graphene oxide (RGO). The PBA molecules anchored on the graphene surface form supramolecules with PS-b-P4VP through H-bonding between the carboxylic acid group of 1-pyrenebutyric acid and the pyridine ring of P4VP. The formation of a supramolecular assembly results in a highly stable solution of reduced graphene oxide in common organic solvents, such as 1,4-dioxane and chloroform. Highly transparent and mechanically stable thin films can be deposited from these supramolecular assemblies on a relatively smooth surface of different substrates such as silicon wafer, glass, indium tin oxide, and flexible polymer substrates like poly(ethylene terephthalate). The graphene surface modifier (PBA) can be selectively removed from the thin film of the hybrid material by simple dissolution, resulting in a porous structure. Hybrid thin films of around 50 nm thickness exhibit interesting electrochemical properties with an areal capacitance value of 17.73 μF/cm2 at a current density of 2.66 μA/cm2 and good electrochemical stability. The pendent P4VP chains present in the composite thin film were further exploited for electrochemical detection of metal ions. The electrical measurement of the thin film sandwich structure of the composite shows a bipolar resistive switching memory with hysteresis-like current-voltage characteristics and electrical bistability. The OFF state shows ohmic conduction at a lower voltage and trap-free space-charge-limited current (SCLC) conduction at high voltage, whereas the ON state conduction is controlled by ohmic at low bias voltage, trap-free SCLC at moderate voltage, and tarp-assisted SCLC at high voltage.

Layer-by-Layer-Assembled AuNPs-Decorated First-Generation Poly(amidoamine) Dendrimer with Reduced Graphene Oxide Core as Highly Sensitive Biosensing Platform with Controllable 3D Nanoarchitecture for Rapid Voltammetric Analysis of Ultratrace DNA Hybridization

The structure and electrochemical properties of layer-by-layer-assembled gold nanoparticles (AuNPs)-decorated first-generation (G1) poly(amidoamine) dendrimer (PD) with reduced graphene oxide (rGO) core as a highly sensitive and label-free biosensing platform with a controllable three-dimensional (3D) nanoarchitecture for the rapid voltammetric analysis of DNA hybridization at ultratrace levels were characterized. Mercaptopropinoic acid (MPA) was self-assembled onto Au substrate, then GG1PD formed by the covalent functionalization between the amino terminals of G1PD and carboxyl terminals of rGO was covalently linked onto MPA, and finally AuNPs were decorated onto GG1PD by strong physicochemical interaction between AuNPs and -OH of rGO in GG1PD, which was characterized through different techniques and confirmed by computational calculation. This 3D controllable thin-film electrode was optimized and evaluated using [Fe(CN)₆]^3-/4- as the redox probe and employed to covalently immobilize thiol-functionalized single-stranded DNA as biorecognition element to form the DNA nanobiosensor, which achieved fast, ultrasensitive, and high-selective differential pulse voltammetric analysis of DNA hybridization in a linear range from 1 × 10^-6 to 1 × 10^-13 g m^-1 with a low detection limit of 9.07 × 10^-14 g m^-1. This work will open a new pathway for the controllable 3D nanoarchitecture of the layer-by-layer-assembled metal nanoparticles-functionalized lower-generation PD with two-dimensional layered nanomaterials as cores that can be employed as ultrasensitive and label-free nanobiodevices for the fast diagnosis of specific genome diseases in the field of biomedicine.

Functionalization of Graphene Aerogels and their Applications in Energy Storage and Conversion

Functionalized graphene aerogels (GAs) not only own the advantages of the original ones like large specific surface area, three-dimensional porous structures, high specific capacitance and excellent cyclic stability, but also realize the function expansion due to the collective properties endowed via different methods. These characteristics make them advantageous in some promising applications. In this minireview, we focus on the various functionalization methods of GAs and especially their use in the applications of energy storage and conversion like batteries, supercapacitors and fuel cells, etc.

Sensitive detection of hydroquinone using exfoliated graphene-Au/glassy carbon modified electrode

Graphene nanosheets (EGr) were electrochemically prepared through one-step exfoliation of a graphite rod in a mixture of H₂SO₄:HNO₃ (3:1) at low bias (4 V). Subsequently, gold nanoparticles were attached to the graphene surface (EGr-Au) by the reduction of the metal precursor (HAuCl₄) in aqueous solution containing dispersed graphene sheets. According to the XRD investigation, the synthesized material consists of a mixture of few-layer (86%) and multi-layer (14%) graphene. The interlayer distance was found to be in the range of 0.466-0.342 nm, which is larger than the interlayer distance in graphite (0.335 nm). The average size of gold nanoparticles in the EGr-Au sample was 24 nm, in excellent agreement with the TEM results. The synthesized material was then employed to modify a glassy carbon (GC) substrate, in order to obtain a modified electrode (GC/EGr-Au). Next, the electrochemical behavior of hydroquinone (HQ) in the presence and absence of interfering species, catechol (CAT) and bisphenol A (BPA) was studied and the corresponding calibration curves were plotted. Thus, in solutions without interfering species, the GC/EGr-Au electrode has a wide linear range (3 × 10^-7-10^-4 M), high sensitivity (0.089 A M^-1) and low detection limit (LOD = 10^-7 M; S/N = 3). The presence of either catechol or bisphenol A leads to the increase of LOD to 2 × 10^-7 M, and in addition changes the electrode sensitivity, up to 0.146 A M^-1.

Temperature-tunable wettability on a bioinspired structured graphene surface for fog collection and unidirectional transport

We designed a type of smart bioinspired wettable surface with tip-shaped patterns by combining polydimethylsiloxane (PDMS) and graphene (PDMS/G). The laser etched porous graphene surface can produce an obvious wettability change between 200 °C and 0 °C due to a change in aperture size and chemical components. We demonstrate that the cooperation of the geometrical structure and the controllable wettability play an important role in water gathering, and surfaces with tip-shaped wettability patterns can quickly drive tiny water droplets toward more wettable regions, so making a great contribution to the improvement of water collection efficiency. In addition, due to the effective cooperation between super hydrophobic and hydrophilic regions of the special tip-shaped pattern, unidirectional water transport on the 200 °C heated PDMS/G surface can be realized. This study offers a novel insight into the design of temperature-tunable materials with interphase wettability that may enhance fog collection efficiency in engineering liquid harvesting equipment, and realize unidirectional liquid transport, which could potentially be applied to the realms of microfluidics, medical devices and condenser design.

Electrodeposition of reduced graphene oxide with chitosan based on the coordination deposition method

The electrodeposition of graphene has drawn considerable attention due to its appealing applications for sensors, supercapacitors and lithium-ion batteries. However, there are still some limitations in the current electrodeposition methods for graphene. Here, we present a novel electrodeposition method for the direct deposition of reduced graphene oxide (rGO) with chitosan. In this method, a 2-hydroxypropyltrimethylammonium chloride-based chitosan-modified rGO material was prepared. This material disperses homogenously in the chitosan solution, forming a deposition solution with good dispersion stability. Subsequently, the modified rGO material was deposited on an electrode through codeposition with chitosan, based on the coordination deposition method. After electrodeposition, the homogeneous, deposited rGO/chitosan films can be generated on copper or silver electrodes or substrates. The electrodeposition method allows for the convenient and controlled creation of rGO/chitosan nanocomposite coatings and films of different shapes and thickness. It also introduces a new method of creating films, as they can be peeled completely from the electrodes. Moreover, this method allows for a rGO/chitosan film to be deposited directly onto an electrode, which can then be used for electrochemical detection.

Towards the electrochemical diagnostic of influenza virus: development of a graphene–Au hybrid nanocomposite modified influenza virus biosensor based on neuraminidase activity

An effective electrochemical influenza A biosensor based on a graphene–gold (Au) hybrid nanocomposite modified Au-screen printed electrode has been developed.

Chemical sensing with 2D materials

During the last decade, two-dimensional materials (2DMs) have attracted great attention due to their unique chemical and physical properties, which make them appealing platforms for diverse applications in sensing of gas, metal ions as well as relevant chemical entities.

Defect-enhanced performance of a 3D graphene anode in a lithium-ion battery

Morphological defects were generated in an undoped 3D graphene structure via the involvement of a ZnO and Mg(OH)₂ intermediate nanostructure layer placed between two layers of vapor-deposited graphene. Once the intermediate layer was etched, the 3D graphene lost support and shrank; during this process many morphological defects were formed. The electrochemical performance of the derived defective graphene utilized as the anode of a lithium (Li)-ion battery was significantly improved from ∼382 mAh g^-1 to ∼2204 mAh g^-1 at 0.5 A g^-1 compared to normal 3D graphene. The derived defective graphene exhibited an initial capacity of 1009 mAh g^-1 and retention of 83% at 4 A g^-1 for 500 cycles, and ∼330 mAh g^-1 at a high rate of 20 A g^-1. Complicated defects such as wrinkles, pores, and particles formed during the etching of the intermediate layer, were considered to contribute to the improvement of the electrochemical performance.

DNA@Mn3(PO4)2 Nanoparticles Supported with Graphene Oxide as Photoelectrodes for Photoeletrocatalysis

A novel deoxyribose nucleic acid (DNA)-based photoelectrode consisting of DNA@Mn3(PO4)2 nanoparticles on graphene oxide (GO) sheets was successfully fabricated for photoelectrocatalysis. DNA served as a soft template to guide the nucleation and growth of Mn3(PO4)2 nanoparticles in the synthesis of Mn3(PO4)2 nanoparticles. More importantly, the DNA also serves as semiconductor materials to adjust charge transport. Under UV light irradiation (180-420 nm, 15 mW/cm2), the photocurrent density of DNA@ Mn3(PO4)2/GO electrodes reached 9 μA/cm2 at 0.7 V bias (vs. SCE). An applied bias photon-to-current efficiency (ABPE) of ~0.18% can be achieved, which was much higher than that of other control electrodes (<0.04%). In this DNA-based photoelectrode, well-matched energy levels can efficiently improve charge transfer and reduce the recombination of photogenerated electron-hole pairs.

An Electrochemical Enzyme Biosensor for 3-Hydroxybutyrate Detection Using Screen-Printed Electrodes Modified by Reduced Graphene Oxide and Thionine

A biosensor for 3-hydroxybutyrate (3-HB) involving immobilization of the enzyme 3-hydroxybutyrate dehydrogenase onto a screen-printed carbon electrode modified with reduced graphene oxide (GO) and thionine (THI) is reported here. After addition of 3-hydroxybutyrate or the sample in the presence of NAD⁺ cofactor, the generated NADH could be detected amperometrically at 0.0 V vs. Ag pseudo reference electrode. Under the optimized experimental conditions, a calibration plot for 3-HB was constructed showing a wide linear range between 0.010 and 0.400 mM 3-HB which covers the clinically relevant levels for diluted serum samples. In addition, a limit of detection of 1.0 µM, much lower than that reported using other biosensors, was achieved. The analytical usefulness of the developed biosensor was demonstrated via application to spiked serum samples.

One Dimensional Silver-based Nanomaterials: Preparations and Electrochemical Applications

One dimensional (1D) silver-based nanomaterials have a great potential in various fields because of their high specific surface area, high electric conductivity, optoelectronic properties, mechanical flexibility and high electro-catalytic efficiency. In this Review, the preparations of 1D silver-based nanomaterials is classified by structure composed of simple silver nanowires/rods/belts/tubes, core-shells, and hybrids. The latest applications based on 1D silver nanomaterials and their composite materials are summarized systematically including electrochemical capacitors, lithium-ion/lithium-oxygen batteries, electrochemical sensors and electrochemical catalysis. The preparation process, tailored material properties and electrochemical applications are discussed.

Double Biocatalysis Signal Amplification Glucose Biosensor Based on Porous Graphene

Controllable preparation of nanopores to promote the performance of electrochemical biosensing interfaces has become one of the researching frontiers in biosensing. A double biocatalysis signal amplification of glucose biosensor for the study of electrochemical behaviors of glucose oxidase (GOx) was proposed by using horseradish peroxidase biosynthesized porous graphene (PGR) as the platform for the biocatalytic deposition of gold nanoparticles (AuNPs). The biosensor showed a linear range from 0.25 to 27.5 μM with a detection limit of 0.05 μM (S/N = 3) towards glucose. Furthermore, the proposed AuNPs/GOx–PGR modified glassy carbon electrode (AuNPs/GOx–PGR/GCE) achieved direct electron transfer of GOx.

Controlled modification of electrochemical microsystems with polyethylenimine/reduced graphene oxide using electrophoretic deposition: Sensing of dopamine levels in meat samples

Microsystems play an important role in many biological and environmental applications. The integration of electrical interfaces into such miniaturized systems provides new opportunities for electrochemical sensing where high sensitivity and selectivity towards the analyte are requested. This can be only achieved upon controlled functionalization of the working electrode, a challenge for compact microsystems. In this work, we demonstrate the benefit of electrophoretic deposition (EPD) of reduced graphene oxide/polyethylenimine (rGO/PEI) for the selective modification of a gold (Au) microelectrode in a microsystem comprising a Pt counter and a Ag/AgCl reference electrode. The functionalized microsystem was successfully applied for the sensing of dopamine with a detection limit of 50nM. Additionally, the microsystem exhibited good performance for the detection of dopamine levels in meat samples.

Bioinspired Fabrication of one dimensional graphene fiber with collection of droplets application

We designed a kind of smart bioinspired fiber with multi-gradient and multi-scale spindle knots by combining polydimethylsiloxane (PDMS) and graphene oxide (GO). Multilayered graphene structures can produce obvious wettability change after laser etching due to increased roughness. We demonstrate that the cooperation between curvature and the controllable wettability play an important role in water gathering, which regulate effectively the motion of tiny water droplets. In addition, due to the effective cooperation of multi-gradient and multi-scale hydrophilic spindle knots, the length of the three-phase contact line (TCL) can be longer, which makes a great contribution to the improvement of collecting efficiency and water-hanging ability. This study offers a novel insight into the design of smart materials that may control the transport of tiny drops reversibly in directions, which could potentially be extended to the realms of in microfluidics, fog harvesting filtration and condensers designs, and further increase water collection efficiency and hanging ability.

Laser-Induced Functionalization of Organo/Carbon Interfaces for Selective Adsorption of Au Nanoparticles in Microsized Domains

Laser microprocessing of highly oriented pyrolytic graphite (HOPG) in conjunction with chemical functionalization routines is used to fabricate functional microsized domains. Infrared and Auger electron spectroscopy, contact angle measurements, and electron microscopy are used for characterization of laser-fabricated structures. HOPG samples are coated with alkylsiloxane monolayers. Laser-induced bromination of coated HOPG samples in gaseous bromine is carried out using a microfocused laser beam at a wavelength of 514 nm and 1/e² laser spot diameter of about 2 μm. Subsequent azidation and amination results in functional domains with sizes in the range of 1.2 to 40 μm and more. At low laser powers and irradiation times fully functionalized circular-shaped structures are formed. At high laser powers and irradiation times laser processing results in decomposition of the organic monolayer and substrate in the center of the structures yielding donut-shaped structures. After laser processing and chemical transformation Au nanoparticles are selectively adsorbed onto the functional domains. This provides an opportunity to build up functional nanoparticle microarrays on carbon-based materials, e.g., for applications in sensing and electrocatalysis.