Biosensors with high sensitivity, selectivity and a low limit of detection, reaching nano/picomolar concentrations of biomolecules, are important to the medical sciences and healthcare industry for evaluating physiological and metabolic parameters. Over the last decade, different nanomaterials have been exploited to design highly efficient biosensors for the detection of analyte biomolecules. The discovery of graphene has spectacularly accelerated research on fabricating low-cost electrode materials because of its unique physical properties, including high specific surface area, high carrier mobility, high electrical conductivity, flexibility, and optical transparency. Graphene and its oxygenated derivatives, including graphene oxide (GO) and reduced graphene oxide (rGO), are becoming an important class of nanomaterials in the field of biosensors. The presence of oxygenated functional groups makes GO nanosheets strongly hydrophilic, facilitating chemical functionalization. Graphene, GO and rGO nanosheets can be easily combined with various types of inorganic nanoparticles, including metals, metal oxides, semiconducting nanoparticles, quantum dots, organic polymers and biomolecules, to create a diverse range of graphene-based nanocomposites with enhanced sensitivity for biosensor applications. This review summarizes the advances in two-dimensional (2D) and three-dimensional (3D) graphene-based nanocomposites as emerging electrochemical and fluorescent biosensing platforms for the detection of a wide range of biomolecules with enhanced sensitivity, selectivity and a low limit of detection. The biofunctionalization and nanocomposite formation processes of graphene-based materials and their unique properties, surface functionalization, enzyme immobilization strategies, covalent immobilization, physical adsorption, biointeractions and direct electron transfer (DET) processes are discussed in connection with the design and fabrication of biosensors. The enzymatic and nonenzymatic reactions on graphene-based nanocomposite surfaces for glucose- and cholesterol-related electrochemical biosensors are analyzed. This review covers a very broad range of graphene-based electrochemical and fluorescent biosensors for the detection of glucose, cholesterol, hydrogen peroxide (H2O2), nucleic acids (DNA/RNA), genes, enzymes, cofactors nicotinamide adenine dinucleotide (NADH) and adenosine triphosphate (ATP), dopamine (DA), ascorbic acid (AA), uric acid (UA), cancer biomarkers, pathogenic microorganisms, food toxins, toxic heavy metal ions, mycotoxins, and pesticides. The sensitivity and selectivity of graphene-based electrochemical and fluorescent biosensors are also examined with respect to interfering analytes present in biological systems. Finally, the future outlook for the development of graphene based biosensing technology is outlined.

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A review on graphene-based nanocomposites for electrochemical and fluorescent biosensors

The study of electrochemical behavior of bioactive molecules has become one of the most rapidly developing scientific fields. Biotechnology and biomedical engineering fields have a vested interest in constructing more precise and accurate voltammetric/amperometric biosensors. One rapidly growing area of biosensor design involves incorporation of carbon-based nanomaterials in working electrodes, such as one-dimensional carbon nanotubes, two-dimensional graphene, and graphene oxide. In this review article, we give a brief overview describing the voltammetric techniques and how these techniques are applied in biosensing, as well as the details surrounding important biosensing concepts of sensitivity and limits of detection. Building on these important concepts, we show how the sensitivity and limit of detection can be tuned by including carbon-based nanomaterials in the fabrication of biosensors. The sensing of biomolecules including glucose, dopamine, proteins, enzymes, uric acid, DNA, RNA, and H2O2 traditionally employs enzymes in detection; however, these enzymes denature easily, and as such, enzymeless methods are highly desired. Here we draw an important distinction between enzymeless and enzyme-containing carbon-nanomaterial-based biosensors. The review ends with an outlook of future concepts that can be employed in biosensor fabrication, as well as limitations of already proposed materials and how such sensing can be enhanced. As such, this review can act as a roadmap to guide researchers toward concepts that can be employed in the design of next generation biosensors, while also highlighting the current advancements in the field.

http://pubs.acs.org/doi/pdf/10.1021/acsnano.5b05690

Engineered Carbon-Nanomaterial-Based Electrochemical Sensors for Biomolecules

Dopamine (DA) is an important neurotransmitter and its abnormal concentrations are associated with different diseases. Electrochemical detection of DA in real samples is challenging because of the presence of high concentrations of electroactive interferents such as uric acid (UA) and ascorbic acid (AA). Chemically modified electrodes have been widely used to counter the problems of poor sensitivity and selectivity faced at bare electrodes. We have briefly reviewed the materials that have been extensively used to fabricate modified electrode surfaces for detection of DA. The characteristics of the materials that improve the electrocatalytic activity of the modified surfaces are discussed. The boundary of search was limited to the electrochemical methods dealing with the simultaneous detection of DA, UA, and AA levels or detection of only DA in the presence of UA and AA. Challenges associated with the quantitative determination of dopamine in real samples are critically reviewed and the possible solutions are described.

Chemically modified electrodes for electrochemical detection of dopamine in the presence of uric acid and ascorbic acid: A review

Dopamine (DA) is an important catecholamine neurotransmitter in the mammalian central nervous system that influences several physiological functions. The impact of DA levels within the human body significantly affects the body functions. Maintaining DA level is essential and the electrochemical detection methods are often used to detect the DA level to regulate the body function. In this review, graphene (functionalized graphene and N-doped graphene) and its composites (metal, metal oxide, polymer, carbonaceous materials, clay, zeolite, and metal–organic framework based graphene composites) modified electrodes with their improved sensing performance towards DA along with several interfering species are described. Further, recent developments on the fabrication of various graphene based composite modified electrodes are also presented. Some important strategies to improve the selectivity and sensitivity towards DA with graphene based composite modified electrodes are also described.

/pdf/graphene-and-its-nanocomposite-material-based-4uplsnd3g3.pdf

Graphene and its nanocomposite material based electrochemical sensor platform for dopamine

Herein, we report a multitasking Cu-MOF/rGO hybrid, fabricated by simple ultra-sonication of slow diffusion driven Cu-MOF crystals with chemically synthesized reduced graphene oxide (rGO). The molecular structure of the Cu-MOF was authenticated by single crystal X-ray studies. The prepared materials have been probed by various physicochemical characterization techniques. Due to the positive synergistic effects between Cu-MOF crystals and rGO nanosheets, the newly synthesized Cu-MOF/rGO hybrid delivers high charge storage efficiency (685.33 F g−1 at 1.6 A g−1), high energy (137.066 W h kg−1) and power density (4800.04 W kg−1) and excellent rate ability (retains 71.01% of its initial capacitance at 8 A g−1). Furthermore, the long cycle life (91.91% after 1000 cycles) of this hybrid indicates its high stability on the electrode surface. Additionally, the electrode modified with the Cu-MOF/rGO hybrid performs exceptionally towards the electrochemical detection of nitrite in a wide dynamic linear range of 3–40 000 μM (R2 = 0.99911), with a notable detection limit of 33 nm and a high sensitivity of 43.736 μA μM−1 cm−2. The versatility of the Cu-MOF/rGO modified electrode can be observed by distinguished selectivity in the presence of some common interfering species and also ability to detect nitrite in real samples.

A fascinating multitasking Cu-MOF/rGO hybrid for high performance supercapacitors and highly sensitive and selective electrochemical nitrite sensors

CTAB functionalized graphene oxide/multiwalled carbon nanotube composite modified electrode for the simultaneous determination of ascorbic acid, dopamine, uric acid and nitrite

Yu Jun Yang

Papers

CTAB functionalized graphene oxide/multiwalled carbon nanotube composite modified electrode for the simultaneous determination of ascorbic acid, dopamine, uric acid and nitrite