Yuehe Lin

Nitrogen-Doped Graphene and Its Application in Electrochemical Biosensing

Chemical doping with foreign atoms is an effective method to intrinsically modify the properties of host materials. Among them, nitrogen doping plays a critical role in regulating the electronic properties of carbon materials. Recently, graphene, as a true two-dimensional carbon material, has shown fascinating applications in bioelectronics and biosensors. In this paper, we report a facile strategy to prepare N-doped graphene by using nitrogen plasma treatment of graphene synthesized via a chemical method. Meanwhile, a possible schematic diagram has been proposed to detail the structure of N-doped graphene. By controlling the exposure time, the N percentage in host graphene can be regulated, ranging from 0.11 to 1.35%. Moreover, the as-prepared N-doped graphene has displayed high electrocatalytic activity for reduction of hydrogen peroxide and fast direct electron transfer kinetics for glucose oxidase. The N-doped graphene has further been used for glucose biosensing with concentrations as low as 0.01 mM in the presence of interferences.

Low-Potential Stable NADH Detection at Carbon-Nanotube-Modified Glassy Carbon Electrodes

Abstract Carbon-nanotube (CNT)-modified glassy carbon electrodes exhibiting strong and stable electrocatalytic response toward NADH are described. A substantial (490 mV) decrease in the overvoltage of the NADH oxidation reaction (compared to ordinary carbon electrodes) is observed using single-wall and multi-wall carbon-nanotube coatings, with oxidation starting at ca. −0.05 V (vs. Ag/AgCl; pH 7.4). Furthermore, the NADH amperometric response of the coated electrodes is extremely stable, with 96% and 90% of the initial activity remaining after 60 min stirring of 2×10−4 and 5×10 −3 M NADH solutions, respectively (compared to 20% and 14% at the bare surface). The CNT-coated electrodes thus allow highly sensitive, low-potential, stable amperometric sensing. Such ability of carbon nanotubes to promote the NADH electron-transfer reaction suggests great promise for dehydrogenase-based amperometric biosensors.

Glucose Oxidase-graphene-chitosan modified electrode for direct electrochemistry and glucose sensing

Direct electrochemistry of a glucose oxidase (GOD)-graphene-chitosan nanocomposite was studied. The immobilized enzyme retains its bioactivity, exhibits a surface confined, reversible two-proton and two-electron transfer reaction, and has good stability, activity and a fast heterogeneous electron transfer rate with the rate constant (k(s)) of 2.83 s(-1). A much higher enzyme loading (1.12 x 10(-9)mol/cm(2)) is obtained as compared to the bare glass carbon surface. This GOD-graphene-chitosan nanocomposite film can be used for sensitive detection of glucose. The biosensor exhibits a wider linearity range from 0.08mM to 12mM glucose with a detection limit of 0.02mM and much higher sensitivity (37.93microAmM(-1)cm(-2)) as compared with other nanostructured supports. The excellent performance of the biosensor is attributed to large surface-to-volume ratio and high conductivity of graphene, and good biocompatibility of chitosan, which enhances the enzyme absorption and promotes direct electron transfer between redox enzymes and the surface of electrodes.

Graphene and graphene oxide: biofunctionalization and applications in biotechnology

Graphene is the basic building block of 0D fullerene, 1D carbon nanotubes, and 3D graphite. Graphene has a unique planar structure, as well as novel electronic properties, which have attracted great interests from scientists. This review selectively analyzes current advances in the field of graphene bioapplications. In particular, the biofunctionalization of graphene for biological applications, fluorescence-resonance-energy-transfer-based biosensor development by using graphene or graphene-based nanomaterials, and the investigation of graphene or graphene-based nanomaterials for living cell studies are summarized in more detail. Future perspectives and possible challenges in this rapidly developing area are also discussed.

Aptamer/Graphene Oxide Nanocomplex for In Situ Molecular Probing in Living Cells

Graphene has shown fascinating applications in bionanotechnology, including DNA sensing, protein assays, and drug delivery. However, exploration of graphene with intracellular monitoring and in situ molecular probing is still at an early stage. In this regard, we have designed an aptamer-carboxyfluorescein (FAM)/graphene oxide nanosheet (GO-nS) nanocomplex to investigate its ability for molecular probing in living cells. Results demonstrate that uptake of aptamer-FAM/GO-nS nanocomplex and cellular target monitoring were realized successfully. The dramatic delivery, protection, and sensing capabilities of GO-nS in living cells indicate that graphene oxide could be a robust candidate for many biological fields, such as DNA and protein analysis, gene and drug delivering, and intracellular tracking.

Facile and controllable electrochemical reduction of graphene oxide and its applications

Graphene oxide is electrochemically reduced which is called electrochemically reduced graphene oxide (ER-G). ER-G is characterized with scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The oxygen content is significantly decreased and the sp2 carbon is restored after electrochemical reduction. ER-G exhibits much higher electrochemical capacitance and cycling durability than carbon nanotubes (CNTs) and chemically reduced graphene; the specific capacitance measured with cyclic voltammetry (20 mV s−1) is ∼165, ∼86, and ∼100 F g−1 for ER-G, CNTs, and chemically reduced graphene, respectively. The electrochemical reduction of oxygen and hydrogen peroxide are greatly enhanced on ER-G electrodes as compared with CNTs. ER-G has shown promising features for applications in energy storage, biosensors, and electrocatalysis.

Novel catalyst support materials for PEM fuel cells: current status and future prospects

Catalyst support materials exhibit great influence on the cost, performance, and durability of polymer electrolyte membrane (PEM) fuel cells. This feature article summarizes several important kinds of novel support materials for PEM fuel cells (including direct methanol fuel cells): nanostructured carbon materials (carbon nanotubes, carbon nanofibers, mesoporous carbon), conductive doped diamonds and nanodiamonds, conductive oxides (tin oxide/indium tin oxide, titanium oxide, tungsten oxide), and carbides (tungsten carbides). The advantages and disadvantages, the acting mechanism to promote electrocatalytic performance, and the strategies to improve present catalyst support materials and search for new ones are discussed. This is expected to shed light on future development of catalyst supports for PEM fuel cells.

Electrochemical sensors and biosensors based on nanomaterials and nanostructures

Taking advantage of exceptional attributes, such as being easy-to-operate, economical, sensitive, portable, and simple-to-construct, in recent decades, considerable attention has been devoted to the integration of recognition elements with electronic elements to develop electrochemical sensors and biosensors.Various electrochemical devices, such as amperometric sensors, electrochemical impedance sensors, and electrochemical luminescence sensors as well as photoelectrochemical sensors, provide wide applications in the detection of chemical and biological targets in terms of electrochemical change of electrode interfaces. With remarkable achievements in nanotechnology and nanoscience, nanomaterial-based electrochemical signal amplifications have great potential of improving both sensitivity and selectivity for electrochemical sensors and biosensors. First of all, it is well-known that the electrode materials play a critical role in the construction of high-performance electrochemical sensing platforms for detecting target molecules through various analytical principles. Furthermore, in addition to electrode materials, functional nanomaterials can not only produce a synergic effect among catalytic activity, conductivity, and biocompatibility to accelerate the signal transduction but also amplify biorecognition events with specifically designed signal tags, leading to highly sensitive biosensing. Significantly, extensive research on the construction of functional electrode materials, coupled with numerous electrochemical methods, is advancing the wide application of electrochemical devices. For example, Walcarius et al. highlighted the recent advances of nano-objects and nanoengineered and/or nanostructured materials for the rational design of biofunctionalized electrodes and related (bio)sensing systems.1 The attractiveness of such nanomaterials relies on their ability to act as effective immobilization matrices and their intrinsic and unique features as described above. These features combined with the functioning of biomolecules contribute to the improvement of bioelectrode performance in terms of sensitivity and specificity. Our group recently presented a general overview of nanomaterial-enhanced paper-based biosensors including lateral-flow test-strip and paper microfluidic devices.2 With different kinds of nanoparticles (NPs), paper-based biosensor devices have shown a great potential in the enhancement of sensitivity and specificity of disease diagnosis in developing countries. This Review focuses on recent advances in electrochemical sensors and biosensors based on nanomaterials and nanostructures during 2013 to 2014. The aim of this effort is to provide the reader with a clear and concise view of new advances in areas ranging from electrode engineering, strategies for electrochemical signal amplification, and novel electroanalytical techniques used in the miniaturization and integration of the sensors. Moreover, the authors have attempted to highlight areas of the latest and significant development of enhanced electrochemical nanosensors and nanobiosensors that inspire broader interests across various disciplines. Electrochemical sensors for small molecules, enzyme-based biosensors, genosensors, immunosensors, and cytosensors are reviewed herein (Figure ​(Figure1).1). Such novel advances are important for the development of electrochemical sensors that open up new avenues and methods for future research. We recommend readers interested in the general principles of electrochemical sensors and electrochemical methods to refer to other excellent literature for a broad scope in this area.3,4 However, due to the explosion of publications in this active field, we do not claim that this Review includes all of the published works in the past two years and we apologize to the authors of excellent work, which is unintentionally left out. Figure 1 Schematic illustration of electrochemical sensors and biosensors based on nanomaterials and nanostructures, in which electrochemical sensors for small molecular, enzyme-based biosensors, genosensors, immunosensors, and cytosensors are demonstrated.

Direct Assembly of Large Arrays of Oriented Conducting Polymer Nanowires

Although oriented carbon nanotubes, oriented nanowires of metals, semiconductors and oxides have attracted wide attention, there have been few reports on oriented polymer nanostructures such as nanowires. In this paper we report the assembly of large arrays of oriented nanowires through controlled nucleation and growth during a stepwise electrochemical deposition process in which a large number of nuclei were first deposited on the substrate using a large current density. After the initial nucleation, the current density was reduced step by step to grow the oriented nanowires from the nucleation sites created in the first step. A very different morphology was also demonstrated by first depositing a monolayer of close-packed colloidal spheres using a similar step-wise deposition process. As a result, the polymer nanofibers grew from the spheres in a radial fashion and formed the continuous three-dimensional network of nanofibers in the film. The principles of control nucleation and growth in electrochemical deposition investigated in this paper should be applicable to other electrical conducting and electrochemical active materials, including metals and conducting oxides. We also hope the oriented electroactive polymer nanostructure will open the door for new applications, such as miniaturized biosensors.

Stabilization of Electrocatalytic Metal Nanoparticles at Metal−Metal Oxide−Graphene Triple Junction Points

Carbon-supported precious metal catalysts are widely used in heterogeneous catalysis and electrocatalysis, and enhancement of catalyst dispersion and stability by controlling the interfacial structure is highly desired. Here we report a new method to deposit metal oxides and metal nanoparticles on graphene and form stable metal-metal oxide-graphene triple junctions for electrocatalysis applications. We first synthesize indium tin oxide (ITO) nanocrystals directly on functionalized graphene sheets, forming an ITO-graphene hybrid. Platinum nanoparticles are then deposited, forming a unique triple-junction structure (Pt-ITO-graphene). Our experimental work and periodic density functional theory (DFT) calculations show that the supported Pt nanoparticles are more stable at the Pt-ITO-graphene triple junctions. Furthermore, DFT calculations suggest that the defects and functional groups on graphene also play an important role in stabilizing the catalysts. These new catalyst materials were tested for oxygen reduction for potential applications in polymer electrolyte membrane fuel cells, and they exhibited greatly enhanced stability and activity.