Ramendra Sundar Dey

A rapid room temperature chemical route for the synthesis of graphene: metal-mediated reduction of graphene oxide

A rapid and facile route for the synthesis of reduced graphene oxide sheets (rGOs) at room temperature by the chemical reduction of graphene oxide using Zn/acid in aqueous solution is demonstrated.

Nanomaterial-based functional scaffolds for amperometric sensing of bioanalytes

Functional nanomaterials have emerged as promising candidates in the development of an amperometric sensing platform for the detection and quantification of bioanalytes. The remarkable characteristics of nanomaterials based on metal and metal oxide nanoparticles, carbon nanotubes, and graphene ensure enhanced performance of the sensors in terms of sensitivity, selectivity, detection limit, response time, and multiplexing capability. The electrocatalytic properties of these functional materials can be combined with the biocatalytic activity of redox enzymes to develop integrated biosensing platforms. Highly sensitive and stable miniaturized amperometric sensors have been developed by integrating the nanomaterials and biocatalyst with the transducers. This review provides an update on recent progress in the development of amperometric sensors/biosensors using functional nanomaterials for the sensing of clinically important metabolites such as glucose, cholesterol, lactate, and glutamate, immunosensing of cancer biomarkers, and genosensing.

Redox-functionalized graphene oxide architecture for the development of amperometric biosensing platform.

We describe the redox functionalization of graphene oxide (GO) and the development of versatile amperometric biosensing platforms for clinically important analytes such as cholesterol ester, uric acid and glucose. Ferrocene (Fc) redox units were covalently tethered onto the GO backbone using diamine sigma spacers of different chain lengths (C3-, C6-, and C9-diamines). The functionalized GO (Fc-GO) displays a pair of redox peak corresponding to Fc/Fc(+) redox couple at ~0.225 V. The surface coverage and heterogeneous electron transfer rate constant of Fc-GO depends on the length of sigma spacer. Amperometric biosensors for cholesterol (total), uric acid and glucose have been developed by integrating Fc-GO and the respective redox enzymes with screen printed electrode. Fc-GO efficiently mediates the bioelectrocatalytic oxidation of the substrates in the presence of the redox enzymes. The spacer length of Fc-GO controls the bioelectrocatalytic response of the biosensing platforms. The sensitivity of the biosensors based on C9 sigma spacer is significantly higher than the others. The detection limit (S/N = 3) of the biosensors for cholesterol and uric acid was 0.1 μM and for glucose it was 1 μM. Excellent stability, reproducibility, selectivity and fast response time were achieved. Biosensing of cholesterol, uric acid and glucose in human serum sample is successfully demonstrated with the biosensors, and the results are validated with the clinical laboratory measurement.

Approaching the theoretical capacitance of graphene through copper foam integrated three-dimensional graphene networks

We report a facile and low-cost approach for the preparation of all-in-one supercapacitor electrodes using copper foam (CuF) integrated three-dimensional (3D) reduced graphene oxide (rGO) networks. The binder-free 3DrGO@CuF electrodes are capable of delivering high specific capacitance approaching the theoretical capacitance of graphene and exhibiting high charge–discharge cycling stability.

A hybrid functional nanoscaffold based on reduced graphene oxide–ZnO for the development of an amperometric biosensing platform

A novel one-pot chemical route for the synthesis of functional reduced graphene oxide–ZnO hybrid material (rGO–ZnO) and the development of an amperometric biosensing platform are described. The synthesis of rGO–ZnO involves the reduction of graphene oxide (GO) by zinc metal and the subsequent facile growth of ZnO over the surface of rGO using the in situ generated Zn(II) ions in aqueous solution. The ZnO nanostructures on rGO have the trigonal/tetragonal pyramidal shape with an average size of 100 nm. The hybrid material was characterized by FTIR and Raman spectroscopic, electron microscopic, XRD and electrochemical measurements. The XRD profile reveals that the ZnO has hexagonal wurtzite phase. The potential application of rGO–ZnO hybrid material in the development of amperometric biosensing platform is demonstrated with the direct electrochemistry of glucose oxidase (GOx) as a model system. GOx was immobilized on the rGO–ZnO-based electrode and direct electron transfer for the immobilized GOx was realized with a heterogeneous electron transfer rate constant of 7.55 s−1. Amperometric biosensing of glucose was achieved in the absence of oxygen at the potential of −0.3 V (Ag/AgCl). The biosensor shows a linear response from 0.2 to 6.6 mM with sensitivity and response time of 13.7 ± 0.1 μA mM−1 cm−2 and 4 s, respectively. The biosensor can detect glucose as low as 0.2 μM (S/N = 3) without any interference from common coexisting electroactive species. The biosensor has excellent operational and storage stability and reproducibility. Biosensing of glucose in a small volume has been successfully demonstrated with screen printed electrodes using a human serum sample and the results are validated with clinical laboratory measurements.

Bioanalytical applications of au nanoparticles.

Nanoscale Au particles are received with significant interest in the recent years owing to their unique properties, which originate from the quantum scale dimension. Although colloidal Au has been known since ancient times for the decoration of glasses and for its curative powers, the technological importance has been understood only in the last two decades. The fascinating optical and electronic properties of the Au nanoparticles made them an excellent candidate in the development of nanoscale devices. Significant amount of research has been devoted to explore the technological application of these tiny particles. Various biosensing devices, catalytic interfaces and bioanalytical methodologies based on Au nanoparticles have been developed in the last two decades for different applications. Au nanoparticles are considered to be the key building blocks in the emerging nanoscale energy and sensing devices of 21(st) century. In this review, we highlight some of the recent patents and related literature on the bioanalytical applications of Au nanoparticles. A brief outline on the synthesis of Au nanoparticles of various size and shape and a detailed account of their potential utilization in the development of optical and electrochemical sensors/biosensors and analytical methods for drug delivery are discussed.

Enzyme-integrated cholesterol biosensing scaffold based on in situ synthesized reduced graphene oxide and dendritic Pd nanostructure.

A new approach for the one-pot synthesis of reduced graphene oxide-dendritic Pd nanoparticle (rGO-nPd) hybrid material and the development of biosensing scaffold for the amperometric sensing of H2O2 and total cholesterol in human serum are described. In situ reduction of both graphene oxide (GO) and PdCl4(2-) in acidic solution was achieved with Zn to obtain rGO-nPd hybrid material. The oxygen containing functionalities of GO were reduced by the liberated atomic hydrogen in 20 min. The formal potential of Zn/Zn(2+) and PdCl4(2-)/Pd couples favor the facile reduction of PdCl4(2-). The in situ produced Pd nanoparticles behave like hydrogen sponge and increase the local concentration of atomic hydrogen. Biosensing platforms for H2O2 and cholesterol in human serum and butter sample were developed using the hybrid material. Amperometric sensing of H2O2 at 0.2 nM level without any redox mediator or enzymes in neutral pH is demonstrated. The cholesterol biosensing platform was developed by integrating cholesterol oxidase and cholesterol esterase with the hybrid material. The biosensor is highly sensitive (5.12±0.05 μA/μM cm(2)) and stable with a fast response time of 4 s; it could detect cholesterol ester as low as 0.05 µM (S/N=3). The biosensor is successfully used for the analysis of total cholesterol in human serum and butter.

Polyelectrolyte-Functionalized Gold Nanoparticle Scaffold for the Sensing of Heparin and Protamine in Serum

We describe a shape-controlled synthesis of polyelectrolyte-functionalized flowerlike and polyhedral Au nanoparticles and the development of a nanoarchitectured platform for the selective and highly sensitive detection of protamine and heparin by voltammetric, impedimetric, and microgravimetric techniques. The functionalized Au nanoparticles were chemically synthesized in aqueous solution at room temperature in the presence of the polyelectrolyte (either protamine or heparin). The charge on the polyelectrolyte controlled the shape and surface morphology of the nanoparticles. The negatively charged heparin-functionalized Au nanoparticles have multiple branched flowerlike shapes with an average size of 50 nm, whereas the cationic protamine-functionalized nanoparticles are of polyhedral shape with an average size of 25 nm. Both flowerlike and polyhedral nanoparticles have (111), (200), (220), and (311) planes of a face-centered cubic lattice of Au. Voltammetric, impedimetric, and microgravimetric sensing platforms based on functionalized Au nanoparticles have been developed for the sensing of heparin and protamine. The sensing platforms are developed by self-assembling the functionalized nanoparticles on a thiol-functionalized three-dimensional silicate network. The microgravimetric sensing platform shows very high sensitivity and it can detect heparin and protamine at concentrations as low as 0.05 μg mL(-1). The selectivity of the sensing platform towards heparin was examined with potential interferents such as hyaluronic acid (HA) and chondroitin-4-sulfate (CS). Both HA and CS did not interfere with the measurement of heparin. The practical application of the sensing platform was demonstrated by measuring the concentration of heparin and protamine in human serum samples. The sensing platform could successfully quantify the concentration of heparin and protamine in the real serum samples with excellent recovery. The sensing platform was robust and could be used for repeated measurement without compromising the sensitivity.

Electrochemically Derived Redox Molecular Architecture: A Novel Electrochemical Interface for Voltammetric Sensing

Redox-active molecular architectures are electrochemically derived on the electrode surface by Michael addition reaction of o-quinone with surface adsorbed nucleophiles. Electrogenerated o-quinone undergoes facile Michael addition reaction with nucleophile mercaptotriazole (MTz) and mercaptoimidazole (MIm) preassembled on Au electrode. The Michael addition reaction yields redox molecular architectures of 4-(3-mercapto-[1,2,4]triazol-1-yl)-benzene-1,2-diol (MTBD) and 4-(2-mercapto-imidazol-1-yl)-benzene-1,2-diol (MIBD). Solution pH controls the Michael addition reaction; the reaction of o-quinone with MTz nucleophile is more favorable in neutral pH whereas it is favorable in pH >or=9 with MIm. Michael addition of electrogenerated o-quinone with the nucleophile is quantitatively followed in real time using electrochemical quartz crystal microbalance (EQCM). The redox molecular architecture on the electrode surface is characterized by attenuated total reflection (ATR) spectral and electrochemical measurements. ATR spectral measurement confirms the Michael addition with the nucleophile. The redox molecular architecture displays reversible voltammetric response at 0.2 V corresponding to the redox reaction surface confined catechol moiety. The surface coverage of MTBD and MIBD on the electrode surface at pH 7.2 is estimated to be (5.4 +/- 0.2) x 10(-10) and (2.0 +/- 0.2) x 10(-10) mol/cm(2), respectively. Both redox molecular assemblies efficiently mediate the oxidation of reduced nicotinamide adenine dinucleotide (NADH) at a favorable potential. A large decrease in the overpotential associated with an enhancement in the voltammetric peak current with respect to the unmodified electrode is observed. Flow injection amperometric sensing of NADH is performed at the potential of 230 mV. These modified electrodes could detect NADH at micromolar level. Mixed molecular architecture of cysteamine (CYST) and MTz/MIm are developed for the interference free voltammetric sensing of NADH.

Large area few-layer graphene with scalable preparation from waste biomass for high-performance supercapacitor

Carbonaceous materials with high surface area and a sheet-like structure promote fast ion-transport kinetics, making them an ideal choice to be used in supercapacitors. Few-layer graphene (FLG)-like nanosheets with abundance of micro as well as mesopores are achieved via mechanical exfoliation method from an agricultural waste biomass: peanut shell (PS). A well-known elementary method of probe-sonication, for the achievement of FLG sheets from renewable sources, is introduced in this study for the very first time. The Peanut shell-derived FLG (PS-FLG) possesses remarkably high specific surface area (2070 m2 g−1) with a sufficiently large pore volume of 1.33 cm3 g−1. For the fabrication of a binder-free supercapacitor, the PS-FLG-based electrodes exhibited a high specific capacity of 186 F g−1 without the use of any binder in 1 M H2SO4 as supporting electrolyte. The highest energy density of 58.125 W h Kg−1 and highest power density of 37.5 W Kg−1 was achieved by the material. Surprisingly, the working potential increased to 2.5 V in an organic electrolyte leading to an obvious increase in the energy density to 68 W h Kg−1. Solid-state-supercapacitor was fabricated with this material for the possible use of low-cost, high energy promising energy storage device.