Every few years, a new material with unique properties emerges and fascinates the scientific community, typical recent examples being high-temperature superconductors and carbon nanotubes. Graphene is the latest sensation with unusual properties, such as half-integer quantum Hall effect and ballistic electron transport. This two-dimensional material which is the parent of all graphitic carbon forms is strictly expected to comprise a single layer, but there is considerable interest in investigating two-layer and few-layer graphenes as well. Synthesis and characterization of graphenes pose challenges, but there has been considerable progress in the last year or so. Herein, we present the status of graphene research which includes aspects related to synthesis, characterization, structure, and properties.

Graphene: The New Two-Dimensional Nanomaterial

Graphene, emerging as a true 2-dimensional material, has received increasing attention due to its unique physicochemical properties (high surface area, excellent conductivity, high mechanical strength, and ease of functionalization and mass production). This article selectively reviews recent advances in graphene-based electrochemical sensors and biosensors. In particular, graphene for direct electrochemistry of enzyme, its electrocatalytic activity toward small biomolecules (hydrogen peroxide, NADH, dopamine, etc.), and graphenebased enzyme biosensors have been summarized in more detail; Graphene-based DNA sensing and environmental analysis have been discussed. Future perspectives in this rapidly developing field are also discussed.

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Graphene Based Electrochemical Sensors and Biosensors: A Review

Graphene, a two-dimensional, single-layer sheet of sp(2) hybridized carbon atoms, has attracted tremendous attention and research interest, owing to its exceptional physical properties, such as high electronic conductivity, good thermal stability, and excellent mechanical strength. Other forms of graphene-related materials, including graphene oxide, reduced graphene oxide, and exfoliated graphite, have been reliably produced in large scale. The promising properties together with the ease of processibility and functionalization make graphene-based materials ideal candidates for incorporation into a variety of functional materials. Importantly, graphene and its derivatives have been explored in a wide range of applications, such as electronic and photonic devices, clean energy, and sensors. In this review, after a general introduction to graphene and its derivatives, the synthesis, characterization, properties, and applications of graphene-based materials are discussed.

Graphene-Based Materials: Synthesis, Characterization, Properties, and Applications

Bacterial toxicity of graphene nanosheets in the form of graphene nanowalls deposited on stainless steel substrates was investigated for both Gram-positive and Gram-negative models of bacteria. The graphene oxide nanowalls were obtained by electrophoretic deposition of Mg2+-graphene oxide nanosheets synthesized by a chemical exfoliation method. On the basis of measuring the efflux of cytoplasmic materials of the bacteria, it was found that the cell membrane damage of the bacteria caused by direct contact of the bacteria with the extremely sharp edges of the nanowalls was the effective mechanism in the bacterial inactivation. In this regard, the Gram-negative Escherichia coli bacteria with an outer membrane were more resistant to the cell membrane damage caused by the nanowalls than the Gram-positive Staphylococcus aureus lacking the outer membrane. Moreover, the graphene oxide nanowalls reduced by hydrazine were more toxic to the bacteria than the unreduced graphene oxide nanowalls. The better antibacteri...

Toxicity of Graphene and Graphene Oxide Nanowalls Against Bacteria

In this paper, the characterization and application of a chemically reduced graphene oxide modified glassy carbon (CR-GO/GC) electrode, a novel electrode system, for the preparation of electrochemical sensing and biosensing platform are proposed. Different kinds of important inorganic and organic electroactive compounds (i.e., probe molecule (potassium ferricyanide), free bases of DNA (guanine (G), adenine (A), thymine (T), and cytosine (C)), oxidase/dehydrogenase-related molecules (hydrogen peroxide (H2O2)/β-nicotinamide adenine dinucleotide (NADH)), neurotransmitters (dopamine (DA)), and other biological molecules (ascorbic acid (AA), uric acid (UA), and acetaminophen (APAP)) were employed to study their electrochemical responses at the CR-GO/GC electrode, which shows more favorable electron transfer kinetics than graphite modified glassy carbon (graphite/GC) and glassy carbon (GC) electrodes. The greatly enhanced electrochemical reactivity of the four free bases of DNA at the CR-GO/GC electrode compare...

Electrochemical sensing and biosensing platform based on chemically reduced graphene oxide.

We report a novel microwave plasma enhanced chemical vapor deposition strategy for the efficient synthesis of multilayer graphene nanoflake films (MGNFs) on Si substrates The constituent graphene nanoflakes have a highly graphitized knife-edge structure with a 2-3 nm thick sharp edge and show a preferred vertical orientation with respect to the Si substrate as established by near-edge X-ray absorption fine structure spectroscopy The growth rate is approximately 16 mu m min(-1), which is 10 times faster than the previously reported best value The MGNFs are shown to demonstrate fast electron-transfer (ET) kinetics for the Fe(CN)(6)(3-/4-) redox system and excellent electrocatalytic activity for simultaneously determining dopamine (DA), ascorbic acid (AA) and uric acid (UA) Their biosensing DA performance in the presence of common interfering agents AA and UA is superior to other bare solid-state electrodes and is comparable only to that of edge plane pyrolytic graphite Our work here, establishes that the abundance of graphitic edge planes/defects are essentially responsible for the fast ET kinetics, active electrocatalytic and biosensing properties This novel edge-plane-based electrochemical platform with the high surface area and electrocatalytic activity offers great promise for creating a revolutionary new class of nanostructured electrodes for biosensing, biofuel cells and energy-conversion applications

Catalyst-Free Efficient Growth, Orientation and Biosensing Properties of Multilayer Graphene Nanoflake Films with Sharp Edge Planes**

Disposable graphite pencil electrodes (PGE) modified with multiwalled carbon nanotubes (MWCNTs)-streptavidin (STR) conjugates were used for electrochemical monitoring of label-free DNA hybridization. The surface morphology of PGE electrode before and after hybridization was characterized by scanning electron microscopy. Electrochemical impedance spectroscopy was used to monitor each step of the construction of the DNA biosensor. The biosensor was demonstrated to have excellent selectivity, being able to differentiate complementary sequences from a noncomplementary ones and in addition select the target sequence of DNA from a mixture of other DNA without loss in current sensitivity.

Streptavidin Modified Carbon Nanotube Based Graphite Electrode for Label-Free Sequence Specific DNA Detection

Aptamer conjugated Mo6S9−xIx nanowires for direct and highly sensitive electrochemical sensing of thrombin

We demonstrate a novel and highly sensitive electrochemical detection of estrone based on an immunosensor platform, composed of bioassembled nanocircuits of Mo6S9−xIx nanowires (MoSI NWs) covalently connected to anti-estrone antibodies. The one-step, label-free, and quantitative detection of estrone is realized by employing the [Ru(NH3)6]3+/2+ redox ions to sense anti-estrone antibody and estrone interactions. The MoSI NWs/anti-estrone antibody nanocircuit architectures provide an amplification and conductive pathway for the specific electrochemical sensing of estrone hapten. A detection limit of 1.4 pg·mL−1 was achieved in contrast to previous electrochemical techniques in which the sensitivity was limited to the nanomolar range.

Martin McMullan

Papers

Catalyst-Free Efficient Growth, Orientation and Biosensing Properties of Multilayer Graphene Nanoflake Films with Sharp Edge Planes**

Streptavidin Modified Carbon Nanotube Based Graphite Electrode for Label-Free Sequence Specific DNA Detection

Aptamer conjugated Mo6S9−xIx nanowires for direct and highly sensitive electrochemical sensing of thrombin

Bioassembled nanocircuits of Mo6S9-xIx nanowires for electrochemical immunodetection of estrone Hapten.

Amplified optical transduction of proteins derived fromMo6S9−xIx nanowires