S. Ashok Kumar

Nanostructured Zinc Oxide Particles in Chemically Modified Electrodes for Biosensor Applications

Abstract Zinc oxide (ZnO) has received considerable attention because of its unique optical, semiconducting, piezoelectric, and magnetic properties. ZnO nanostructures exhibit interesting properties including high catalytic efficiency and strong adsorption ability. Recently, the interest has been focused toward the application of ZnO in biosensing because of its high isoelectric point (9.5), biocompatibility, and fast electron transfer kinetics. Such features advocate the use of this exciting material as a biomimic membrane to immobilize and modify biomolecules. This review highlights the potential use of ZnO in modified electrodes and biosensing.

Electroanalytical determination of acetaminophen using nano-TiO2/polymer coated electrode in the presence of dopamine

We report a new method for selective determination of acetaminophen (AP) in physiological condition. A new hybrid film modified electrode was fabricated using inorganic semiconducting nano-TiO(2) particles and redox active polymer. Redox polymer, poly(acid yellow 9) (PAY) was electrochemically deposited onto nano-TiO(2) coated glassy carbon (GC) electrode. Surface characterizations of modified electrode were investigated by using atomic force microscope and scanning electron microscope. The PAY/nano-TiO(2)/GC hybrid electrode shows stable redox response in the pH range 1-12 and exhibited excellent electrocatalytic activities towards AP in 0.1M phosphate buffer solution (pH 7.0). Consequently, a simple and sensitive electroanalytical method was developed for the determination of AP. The oxidation peak current was proportional to the concentration of acetaminophen from 1.2 x 10(-5) to 1.20 x 10(-4)M and the detection limit was found to be 2.0 x 10(-6)M (S/N=3). Possible interferences were tested and evaluated that it could be possible to selective detection of AP in the presences of dopamine, nicotinamide adenine dinucleotide (NADH), ascorbic acid and uric acid. The proposed method was used to detect acetaminophen in commercial drugs and the obtained results are satisfactory.

Zinc oxide/redox mediator composite films-based sensor for electrochemical detection of important biomolecules

Electrochemical oxidation of serotonin (SN) onto zinc oxide (ZnO)-coated glassy carbon electrode (GCE) results in the generation of redox mediators (RMs) that are strongly adsorbed on electrode surface. The electrochemical properties of zinc oxide-electrogenerated redox mediator (ZnO/RM) (inorganic/organic) hybrid film-coated electrode has been studied using cyclic voltammetry (CV). The scanning electron microscope (SEM), atomic force microscope (AFM), and electrochemical techniques proved the immobilization of ZnO/RM core/shell microparticles on the electrode surface. The GCE modified with ZnO/RM hybrid film showed two reversible redox peaks in acidic solution, and the redox peaks were found to be pH dependent with slopes of -62 and -60 mV/pH, which are very close to the Nernst behavior. The GCE/ZnO/RM-modified electrode exhibited excellent electrocatalytic activity toward the oxidations of ascorbic acid (AA), dopamine (DA), and uric acid (UA) in 0.1M phosphate buffer solution (PBS, pH 7.0). Indeed, ZnO/RM-coated GCE separated the anodic oxidation waves of DA, AA, and UA with well-defined peak separations in their mixture solution. Consequently, the GCE/ZnO/RMs were used for simultaneous detection of DA, AA, and UA in their mixture solution. Using CV, calibration curves for DA, AA, and UA were obtained over the range of 6.0 x 10(-6) to 9.6 x 10(-4)M, 1.5 x 10(-5) to 2.4 x 10(-4)M, and 5.0 x 10(-5) to 8 x 10(-4)M with correlation coefficients of 0.992, 0.991, and 0.989, respectively. Moreover, ZnO/RM-modified GCE had good stability and antifouling properties.

Amperometric determination of H2O2 at nano-TiO2/DNA/thionin nanocomposite modified electrode

We report electrochemical preparation and characterization of a new biosensor made of nanostructured titanium dioxide (nano-TiO2) particles and deoxyribonucleic acid (DNA). Thionin (TN) redox mediator was electrochemically deposited onto DNA/nano-TiO2 modified glassy carbon electrode (GCE). The X-ray diffraction analysis, atomic force microscope (AFM) and scanning electron microscope (SEM) were used for surface analysis of TN/DNA/nano-TiO2 film. In neutral buffer solution, TN/DNA/nano-TiO2/GCE biosensor exhibited excellent electrocatalytic activity towards the reduction of hydrogen peroxide (H2O2) and oxygen (O2). The biosensor shows excellent analytical performance for amperometric determination of H2O2, at reduced overpotential (-0.2V). The detection limit and liner calibration range were found to be 0.05 mM (S/N=3) and 0.05-22.3 mM, respectively. In addition, determination of H2O2 in real samples was carried out using the new biosensor with satisfactory results. The TN/DNA/nano-TiO2/GCE showed stable and reproducible analytical performance towards the reduction of H2O2. This biosensor can be used as an amperometric biosensor for the determination of H2O2 in real samples.

Electrochemical Analysis of H2O2 and Nitrite Using Copper Nanoparticles/Poly(o-phenylenediamine) Film Modified Glassy Carbon Electrode

Copper nanoparticles (Cu-NPs) have been electrochemically synthesized onto a poly(o-phenylenediamine) (PoPD-) coated glassy carbon electrode (GCE). Electrochemical properties and surface characterizations were studied using cyclic voltammetry, atomic force microscopy (AFM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) analysis. Cyclic voltammetry, AFM, SEM, and XRD confirmed the presence of Cu-NPs on the electrode surface. Cu-NPs are firmly stabilized by surface attachment of the PoPD functionality that can be attached to the electrode surface, thus becoming an integral part of the polymer backbone. The Cu-NPs-polymer film-coated GCE (Cu-NPs/PoPD/GCE) showed excellent electrocatalytic activity toward the reduction of hydrogen peroxide (H 2 O 2 ) and nitrite (NO ― 2 ). Amperometry was carried out to determine the concentration of H 2 O 2 and NO ― 2 at ―0.3 V. The dependence of the current response on the H 2 O 2 concentration was explored under neutral conditions, and an excellent linear concentration range from 1.0 × 10 ―6 to 1.0 × 10 ―3 M was found. The Cu-NPs/PoPD/GCE allows highly sensitive, low working potential, stable, and fast amperometric sensing of H 2 O 2 and NO ― 2 . This is promising for the future development of nonenzymatic sensors. The real-sample analysis of commercial H 2 O 2 samples was performed using the proposed method, and the obtained results are satisfactory.

Myoglobin/arylhydroxylamine film modified electrode: Direct electrochemistry and electrochemical catalysis

The adsorption processes and electrochemical behavior of 4-nitroaniline (4-NA) adsorbed onto glassy carbon electrodes (GCE) have been investigated in aqueous 0.1M nitric acid (HNO(3)) electrolyte solutions using cyclic voltammetry (CV). 4-NA adsorbs onto GCE surfaces, and upon potential cycling past -0.2V, is transformed into the arylhydroxylamine (ArHA) derivative which exhibits a well-behaved pH dependent redox couple centered at 0.32V at pH 1.5. It is noted as arylhydroxylamine modified glassy carbon electrodes (HAGCE). This modified electrode can be readily used as an immobilization matrix to entrap proteins and enzymes. In our studies, myoglobin (Mb) was used as a model protein for investigation. A pair of well-defined reversible redox peaks of Mb (Fe(III)-Fe(II)) was obtained at the Mb/arylhydroxylamine modified glassy carbon electrode (Mb/HAGC) by direct electron transfer between the protein and the GCE. The formal potential ( [Formula: see text] ), the apparent coverage (Gamma(*)) and the electron-transfer rate constant (k(s)) were calculated as -0.317V, 8.26x10(-12)mol/cm(2) and 51+/-5s(-1), respectively. Dramatically enhanced biocatalytic activity was exemplified at the Mb/HAGC electrode by the reduction of hydrogen peroxide (H(2)O(2)), trichloroacetic acid (TCA) and oxygen (O(2)). The Mb/arylhydroxylamine film was also characterized by UV-visible spectroscopy (UV-vis), scanning electron microscope (SEM) indicating excellent stability and good biocompatibility of the protein in the arylhydroxylamine modified electrode. This new Mb/HAGC electrode exhibited rapid electrochemical response (2s) for H(2)O(2) and had good stability in physiological condition, showing the potential applicability of the films in the preparation of third generation biosensors or bioreactors based on direct electrochemistry of the proteins.

Electrochemical properties of myoglobin deposited on multi-walled carbon nanotube/ciprofloxacin film.

We report the direct electrochemical and electrocatalytic properties of myoglobin (MB) on a multi-walled carbon nanotube/ciprofloxacin (MWCNT/CF) film-modified electrode. A highly homogeneous MWCNT thin-film was prepared on an electrode surface using ciprofloxacin (CF) as a dispersing agent. MB was then electrochemically deposited onto the MWCNT/CF-modified electrode. The MB/MWCNT/CF film was characterized by scanning electron microscopy and UV-visible spectroscopy (UV-vis). UV-vis spectra confirmed that MB retained its original state on the MWCNT/CF film. Direct electrochemical properties of MB on the MWCNT/CF film were investigated by cyclic voltammetry. The formal potential and electron transfer rate constant were evaluated in pH 7.2 buffer solution as -0.327V and 300s(-1), respectively. In addition, the MB/MWCNT/CF-modified electrode showed excellent electrocatalytic properties for the reduction of hydrogen peroxide (H(2)O(2)). The MB/MWCNT/CF-modified electrode was used for the detection of H(2)O(2) at concentrations from 1×10(-6)M to 7×10(-4)M in pH 7.2 buffer solution. Overall, the MB/MWCNT/CF-modified electrode was very stable and has potential for development as a H(2)O(2) sensor.

Electrochemical Sensing of H2O2 at Flavin Adenine Dinucleotide/Chitosan/CNT Nanocomposite Modified Electrode

In this study, multiwalled carbon nanotubes MWCNTs were dispersed in chitosan Chi solution, and the dispersion was used to modify glassy carbon electrode GCE and indium tin oxide coated glass electrode. Further, MWCNTs/Chi thin-film modified electrodes were used for the immobilization of flavin adenine dinucleotide FAD from an aqueous solution. FAD could be immobilized very strongly onto the MWCNTs/Chi film, and the modified electrode was very stable in a wide pH range of 1‐12. The FAD-attached MWCNTs/Chi modified GCE FAD/MWCNTs/Chi/GCE was used to test its electrochemical and electrocatalytic properties. Moreover, the FAD/MWCNTs/Chi/GCE was used for the electrocatalytic reduction of hydrogen peroxide H2O2 at low potential in neutral buffer solution.