Koushik Barman

Electrochemical detection of adenine and guanine using a self-assembled copper(II)–thiophenyl-azo-imidazole complex monolayer modified gold electrode

Electrochemical detection of adenine (A) and guanine (G) using the self-assembled monolayer of copper(II)–thiophenyl-azo-imidazole modified gold electrode (Cu2+–IATP–Au) is reported. The self-assembled momolayer of 4-(2′-imidazolylazo)thiophenol (IATP) on a gold electrode surface was prepared by covalent immobilization of imidazole onto a 4-aminothiophenol monolayer modified gold electrode by a diazotization-coupling reaction. The catalyst was formed by immobilizing Cu(II) ion on the IATP modified gold electrode. The modified gold electrode was characterised by Field emission scanning electron microscopy, Energy dispersive X-ray analysis, Infrared spectroscopy, Cyclic voltammetry and Electrochemical Impedance spectroscopic techniques. The Cu2+–IATP–Au electrode exhibits excellent electrocatalytic activity towards the oxidation of A and G. Without separation or pre-treatment, the modified electrode can detect A and G simultaneously in a mixture and DNA samples. In the presence of excess common interferents such as ascorbic acid, citric acid, cysteine, glucose, Na+, K+, Cl−, SO42− had no effect on the peak current of A and G. In differential pulse voltammetry measurement, the oxidation current response of A and G was increased linearly in the concentration range 10–60 μM and the detection limit was found to be 0.06 μM and 0.01 μM (S/N = 3), respectively. The proposed method was applied to determine adenine and guanine in herring sperm DNA and the result was satisfactory.

Bifunctional gold–manganese oxide nanocomposites: benign electrocatalysts toward water oxidation and oxygen reduction

Gold–manganese oxide nanocomposites were synthesised by seed-mediated epitaxial growth at the water/n-heptane interface under mild reflux conditions. These nanocomposites exhibit efficient electrocatalytic activity toward the water oxidation reaction (WOR) and the simultaneous oxygen reduction reaction (ORR) at a low overpotential (η ≈ 370 mV) and under neutral pH conditions.

Non-enzymatic electrochemical sensing of glucose and hydrogen peroxide using a bis(acetylacetonato)oxovanadium(IV) complex modified gold electrode

A non-enzymatic electrochemical sensor, bis(acetylacetonato)oxovanadium(IV) complex, [VO(acac)2], fabricated on a self-assembled 4-(pyridine-4′-amido)thiophenol (PATP) monolayer modified gold electrode, was developed for the detection of glucose and hydrogen peroxide (H2O2) at neutral pH. The modified electrode was characterized by electrochemical and microscopic techniques. The non-enzymatic sensor exhibited a remarkable catalytic performance for glucose oxidation and H2O2 reduction. Chronoamperometry was used for the electrochemical determination of glucose and H2O2. The non-enzymatic sensing of glucose was realized with a linear response range from 0.001 to 0.5 mM with a detection limit of 0.1 μM (S/N = 3). The sensor also has a good performance for the electrocatalytic reduction of H2O2 with a linear response range from 0.02 to 0.9 mM with a detection limit of 0.03 μM (S/N = 3). In addition, [VO(acac)2]–PATP–Au showed a good selectivity for glucose and H2O2 detection in the presence of potential interfering agents such as ascorbic acid, uric acid, L-dopa, L-cysteine and different ions like Na+, K+, Cl− etc. The kinetic parameters such as the electron transfer coefficient and the catalytic reaction rate constant were also determined for glucose and H2O2. Finally, the modified electrode was used to achieve quantitative detection of glucose and H2O2 in blood and milk, respectively for practical applications.

Simultaneous electrochemical detection of dopamine and epinephrine in the presence of ascorbic acid and uric acid using a AgNPs–penicillamine–Au electrode

A highly selective and sensitive electrochemical sensor, AgNPs–penicillamine–Au, was developed for the simultaneous detection of dopamine (DA) and epinephrine (EP) in the presence of a high concentration of ascorbic acid (AA) and uric acid (UA). Microscopy and voltammetry techniques were used for the characterization of the modified electrode. Chronoamperometry was used for the determination of DA and EP in the linear range of 0.1 to 100.0 μM with detection limits of 0.2 nM and 0.5 nM, respectively. The simultaneous determination of DA, EP, AA and UA was achieved by using differential pulse voltammetry. The proposed sensor was successfully applied for the simultaneous determination of DA and EP in human blood sample with excellent recovery.

Electrocatalytic oxidation of water by a self-assembled oxovanadium(IV) complex modified gold electrode

Bis(acetylacetonato)oxovanadium(IV) was immobilized on a self-assembled 4-(pyridine-4′-amido)thiophenol modified gold electrode. The modified electrode showed excellent electrocatalytic activity towards water oxidation at neutral pH. The turnover frequency of the catalyst for water oxidation was 0.64 s−1 at an overpotential of ~284 mV (at J = 3.82 mA cm−2).

Cerium(III) Complex Modified Gold Electrode: An Efficient Electrocatalyst for the Oxygen Evolution Reaction

Exploring efficient and inexpensive electrocatalysts for the oxidation of water is of great importance for various electrochemical energy storage and conversion technologies. In the present study, a new water-soluble [Ce(III)(DMF) (HSO4)3] complex was synthesized and characterized by UV-vis, photoluminescence, and high-resolution X-ray photoelectron spectroscopy techniques. Owing to classic 5d → 4f transitions, an intense photoluminescence in the UV region was observed from the water-soluble [Ce(III)(DMF) (HSO4)3] complex. A stacking electrode was designed where self-assembled l-cysteine monolayer modified gold was immobilized with the synthesized cerium complex and was characterized by scanning electron microscopy, electrochemical impedance spectroscopy, and cyclic voltammetry. The resulting electrode, i.e., [Ce(III)(DMF) (HSO4)3]-l-cysteine-Au stacks shows high electrocatalytic water oxidation behavior at an overpotential of η ≈ 0.34 V under neutral pH conditions. We also demonstrated a way where the overpotential is possible to decrease upon irradiation of UV light.

MnO doped SnO2 nanocatalysts: Activation of wide band gap semiconducting nanomaterials towards visible light induced photoelectrocatalytic water oxidation

Semiconducting nanomaterials are very important by means of their stability and wide band gap tunability. Visible light induced photoelectrocatalytic water oxidation based on these material are challenging as they have large band gap energies. Herein, we report that MnO doping can activate wide band gap semiconductors like SnO2 towards visible light induced water oxidation. Rutile SnO2 nanoparticles (band gap 3.6eV), usually absorbing at UV region, was capable of harvesting visible light when doped with MnO thereby minimizing the energy requirement for photoelctrocatalytic water splitting. The system was characterized using UV-Vis, TEM and XPS. Photoelectrocatalytic activity was examined by LSV and CPE. The highly stable catalyst showed very good photoelectrocatalytic activity for the oxidation of water under alkaline condition with low overpotential of ∼370mV at 1.0mAcm-2.

Fluid interface-mediated nanoparticle membrane as an electrochemical sensor

A poly(ethyleneglycol) (PEG-13)-stabilised magnetic Fe3O4 nanoparticle decorated ultra-thin membrane has been devised at the water/chloroform interface by ligand cross-linking between pendant hydroxyl groups of PEG with terephthaloyl chloride. This robust nanoparticle-decorated membrane has been employed as an electrochemical sensor for the detection of L-Dopa up to nanomolar concentration.

Hybrid Mn3O4–NiO nanocomposites as efficient photoelectrocatalysts towards water splitting under neutral pH conditions

Mimicking photosynthesis, water splitting has been adopted as the key step for solar energy conversion. As this route is thermodynamically unfavourable (H = 572 KJ mol−1) and is interesting from a kinetic point of view, the development of cheap and efficient catalysts is a subject of fundamental importance to overcome the clean energy demands of the modern world. In this work, dual oxide nanocomposites consisting of manganese oxide (Mn3O4) and nickel oxide (NiO) have been synthesised for electrochemical water oxidation reaction in the presence of sunlight and ultraviolet light under neutral pH conditions. Kinetic parameters of the electrocatalytic oxygen evolution reaction have been extracted from Tafel plots and faradic efficiency calculations. Our results show that these nanocomposites could catalyse water oxidation in neutral phosphate buffer saline (pH ∼ 7.0) with a current density of 2.2 mA cm−2 and turnover frequency of 4.3 s−1 and in the presence of UV light with 4.5 mA cm−2 and 5.1 s−1 at an applied overpotential of just 280 mV. The significant aspects of this approach include the use of earth-abundant nickel and manganese precursors, facile preparation of the electrocatalysts, the low overpotential and the extremely high turnover frequency for O2 evolution in neutral aqueous media.