Chellakannu Rajkumar

Determination of 4-nitrophenol in water by use of a screen-printed carbon electrode modified with chitosan-crafted ZnO nanoneedles

The toxicity and environmental pollution by nitro aromatic compounds in water samples is the most recognized problem in worldwide. Hence, we have developed a simple and highly sensitive electrochemical method for the determination of 4-nitrophenol (4-NP) in water samples based on a chitosan (CHT) crafted zinc oxide nanoneedles (ZnO NDs) modified screen printed carbon electrode. The CHT/ZnO NDs were characterized by Field emission scanning electron microscope, Fourier transform infrared spectroscopy and X-ray diffraction technique. The CHT/ZnO NDs modified electrode showed an enhanced electrocatalytic activity and lower potential detection towards 4-NP, compared with other modified electrodes. Under optimum conditions, the differential pulse voltammetry (DPV) response of CHT/ZnO NDs modified electrode displayed a wide linear response range from 0.5 to 400.6μM towards the detection of 4-NP with a detection limit (LOD) of 0.23μM. The CHT/ZnO NDs modified electrode was used for specific and sensitive detection of 4-NP in presence of possible interfering species and common metal ions with long-term stability. In addition, the excellent analytical performance of the proposed sensor was successfully applied for determination of 4-NP in water samples.

Highly stable biomolecule supported by gold nanoparticles/graphene nanocomposite as a sensing platform for H2O2 biosensor application

A highly active and stable composite of hemin (HN) supported by reduced graphene oxide/gold nanoparticles (HN-RGO/AuNPs) was prepared by one-pot hydrothermal method. The physicochemical properties of the as-prepared composites were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), UV-vis spectroscopy, Raman spectroscopy and X-ray diffraction technique (XRD). The HN-RGO/AuNP-modified electrode shows a stable and well-defined, surface-confined redox couple at an apparent formal potential of -0.317 V vs. Ag|AgCl with a surface coverage value of 2.239 × 10-10 mol cm-2. Compared with HN, HN-GO and HN-RGO, the HN-RGO/AuNP-modified electrode exhibits excellent electrocatalytic activity towards hydrogen peroxide (H2O2). Under optimum conditions, the HN-RGO/AuNP-modified electrode shows a wide linear response ranges from 0.05 μM to 518.15 μM towards H2O2 with a fast response time (3 s). The calculated sensitivity and limit of detection (LOD) of the biosensor were 3.99 μA μM-1 cm-2 and 16 nM, respectively. In addition, the Michaelis-Menten constant value of the biosensor is 0.13 mM, which indicates the high affinity of HN towards the reduction of H2O2. The proposed biosensor displays high sensitivity and selectivity towards H2O2 in the presence of common biologically co-existing species. The biosensor shows an acceptable practical ability in human serum, contact lens solution and milk samples with an appreciable recovery.

One-Pot Green Synthesis of Graphene Nanosheets Encapsulated Gold Nanoparticles for Sensitive and Selective Detection of Dopamine

We report a simple new approach for green preparation of gallic acid supported reduced graphene oxide encapsulated gold nanoparticles (GA-RGO/AuNPs) via one-pot hydrothermal method. The as-prepared composites were successfully characterized by using Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray powder diffraction techniques (XRD), scanning electron microscope (SEM), high resolution transmission electron microscopy (HRTEM) and elemental analysis. The GA-RGO/AuNPs modified electrode behaves as a hybrid electrode material for sensitive and selective detection of dopamine (DA) in presence of ascorbic acid (AA) and uric acid (UA). The GA-RGO/AuNPs modified electrode displays an excellent electrocatalytic activity towards the oxidation of DA and exhibits a wide linear response range over the DA concentrations from 0.01–100.3 μM with a detection limit (LOD) of 2.6 nM based on S/N = 3. In addition, the proposed sensor could be applied for the determination of DA in human serum and urine samples for practical analysis.

A simple preparation of graphite/gelatin composite for electrochemical detection of dopamine

In this study, we demonstrate a simple preparation of graphite (GR) sheets assisted with gelatin (GLN) polypeptide composite was developed for sensitive detection of dopamine (DA) sensor. The GR/GLN composite was prepared by GR powder in GLN solution (5mg/mL) via sonication process. The prepared GR/GLN composite displays well dispersion ability in biopolymer matrix and characterized via scanning electron microscope (SEM), Fourier transform infrared (FTIR) spectroscopy and electrochemical impedance spectroscopy (EIS) studies. The GR/GLN modified electrode showed an excellent electrocatalytic activity toward the oxidation of DA, suggesting that the successful formation of GR sheets crosslinked with the functional groups of GLN polypeptide. In addition, the GR/GLN modified electrode achieved a wide linear response ranging from 0.05 to 79.5μM with a detection limit of 0.0045μM. The calculated analytical sensitivity of the sensor was 1.36±0.02μAμM-1cm-2. Conversely, the modified electrode demonstrates a good storage stability, reproducibility and repeatability. In addition, the sensor manifests the determination of DA in human serum and urine samples for practical applications.

Novel electrochemical preparation of gold nanoparticles decorated on a reduced graphene oxide–fullerene composite for the highly sensitive electrochemical detection of nitrite

In this study, we report a novel amperometric nitrite sensor based on a glassy carbon electrode (GCE) modified with gold nanoparticles (AuNP) decorated reduced graphene oxide–fullerene (RGO–C60) composite. The RGO–C60/AuNPs composite modified electrode was prepared via the electrochemical reduction of a GO–C60 composite modified electrode in pH 3 solution containing 5 mM gold(III) chloride trihydrate at the constant potential of −1.4 V for 200 s. The as-prepared materials were characterized using scanning electron microscopy, and Raman and Fourier transform infrared spectroscopy. Cyclic voltammetry results confirm that the RGO–C60/AuNPs composite modified electrode has high catalytic activity for the detection of nitrite compared with other modified electrodes. The RGO–C60/AuNPs modified electrode exhibits a stable amperometric response for nitrite in the liner concentration range of 0.05–1175.32 μM and its detection limit was estimated to be 0.013 ± 0.003 μM. The modified electrode shows high selectivity towards the determination of nitrite in the presence of potentially active common metal ions. In addition, the fabricated sensor exhibits many advantages for the detection of nitrite such as fast amperometric response, excellent operational and storage stability and appropriate practicality.

Ruthenium Nanoparticles Decorated Tungsten Oxide as a Bifunctional Catalyst for Electrocatalytic and Catalytic Applications

The syntheses of highly stable ruthenium nanoparticles supported on tungsten oxides (Ru-WO3) bifunctional nanocomposites by means of a facial microwave-assisted route are reported. The physicochemical properties of these Ru-WO3 catalysts with varied Ru contents were characterized by a variety of analytical and spectroscopic methods such as XRD, SEM/TEM, EDX, XPS, N2 physisorption, TGA, UV-vis, and FT-IR. The Ru-WO3 nanocomposite catalysts so prepared were utilized for electrocatalytic of hydrazine (N2H4) and catalytic oxidation of diphenyl sulfide (DPS). The Ru-WO3-modified electrodes were found to show extraordinary electrochemical performances for sensitive and selective detection of N2H4 with a desirable wide linear range of 0.7-709.2 μM and a detection limit and sensitivity of 0.3625 μM and 4.357 μA μM-1 cm-2, respectively, surpassing other modified electrodes. The modified GCEs were also found to have desirable selectivity, stability, and reproducibility as N2H4 sensors, even for analyses of real samples. This is ascribed to the well-dispersed metallic Ru NPs on the WO3 support, as revealed by UV-vis and photoluminescence studies. Moreover, these Ru-WO3 bifunctional catalysts were also found to exhibit excellent catalytic activities for oxidation of DPS in the presence of H2O2 oxidant with desirable sulfoxide yields.