jaya kumar | Loyola College ,Chennai (original) (raw)

Papers by jaya kumar

Biomedical Engineering, IEEE …, Jan 1, 1988

Analytical chemistry, Jan 1, 1991

Glucose microelectrodes have been formed with glucose oxidase immobilized in poly[(vinylpyridine)... more Glucose microelectrodes have been formed with glucose oxidase immobilized in poly[(vinylpyridine)Os(bipyridine)2Cl] derivative-based redox hydrogels on beveled carbon-fiber microdisk (7 microns diameter) electrodes. In the resulting microelectrode, the steady-state glucose electrooxidation current density is 0.3 mA cm-2 and the sensitivity is 20 mA cm-2 M-1. The current density and sensitivity are 10 times higher than in macroelectrodes made with the same hydrogel. Furthermore, the current is less affected by a change in the partial pressure of oxygen. The higher current density and lower oxygen sensitivity point to the efficient collection of electrons through their diffusion in the redox hydrogel to the electrode surface. These results contrast with those observed for enzyme electrodes based on diffusing mediators, where loss of the enzyme-reduced mediator by radial diffusion to the solution decreases the current densities of microelectrodes relative to similar macroelectrodes.

Analytical …, Jan 1, 1996

Many of the molecules involved in biological signaling processes are easily oxidized and have bee... more Many of the molecules involved in biological signaling processes are easily oxidized and have been monitored by electrochemical methods. Temporal response, spatial considerations, and sensitivity of the electrodes must be optimized for the specific biological application. To monitor exocytosis from single cells in culture, constant potential amperometry offers the best temporal resolution, and a low-noise picoammeter improves the detection limits. Smaller electrodes, with 1-micron diameters, provided spatial resolution sufficient to identify the locations of release sites on the surface of single cells. For the study of neurotransmitter release in vivo, larger cylindrical microelectrodes are advantageous because the secreted molecules come from multiple terminals near the electrode, and the greater amounts lead to a larger signal that emerges from the Johnson noise of the current amplifier. With this approach, dopamine release elicited by two electrical stimulus pulses at 10 Hz was detected with fastscan cyclic voltammetry in vivo. Nafion-coated elliptical electrodes have previously been shown to be incapable of detecting such concentration changes without extensive signal averaging. In addition, we demonstrate that high-pass filtering (200 Hz) of cyclic voltammograms recorded at 300 V/s decreases the background current and digitization noise at these microelectrodes, leading to an improved signal. Also, high-pass filtering discriminated against ascorbic acid, DOPAC, and acidic pH changes, three common interferences in vivo.

Electroanalysis, Jan 1, 2003

A novel hydrogen peroxide biosensor has been constructed based on the characteristics of the carb... more A novel hydrogen peroxide biosensor has been constructed based on the characteristics of the carbon nanotube. The multiwall carbon nanotube (MWNT) was used as a coimmobilization matrix to incorporate horseradish peroxidase (HRP) and electron transfer mediator methylene blue (MB) onto a glassy carbon electrode surface. Cyclic voltammetry and amperometric measurements were employed to demonstrate the feasibility of methylene blue as an electron carrier between the immobilized peroxidase and the surface of glassy carbon electrode. The amperometric response of this resulting biosensor to H 2 O 2 shows a linear relation in the range from 4 mM to 2 mM. The detection limit was 1 mM when the signal to noise ratio is 3. The presence of dopamine and ascorbic acid hardly affects the sensitive determination of H 2 O 2 . This biosensor also possesses very good stability and reproducibility.

… chemistry and interfacial …, Jan 1, 1986

Abstract Methods for the elimination of residual current in fast scan (> 300 V s− ... more Abstract Methods for the elimination of residual current in fast scan (> 300 V s− 1) voltammetry have been evaluated at microvoltammetric electrodes. Staircase voltammetry is found to give only a modest improvement in the ratio of the faradaic current to the residual ...

Ultramicroscopy, Jan 1, 2003

An electrochemical methodology for bio-molecule sensing using an array of well-defined nanostruct... more An electrochemical methodology for bio-molecule sensing using an array of well-defined nanostructures is presented. We describe the fabrication by e-beam lithography of nanoelectrodes consisting of a 100 mm  50 mm area containing interdigitated electrodes of 100 nm in width and interelectrode distance of 200 nm. Sensitivity and response time of the nanoelectrodes are compared to the responses of macro-and microelectrodes. The specificity of the sensor is studied by modifying the gold electrodes with DNA. The technique enables to characterize both single and double-stranded DNA of 15 nucleotides. A special electrochemical cell is adapted to control the temperature and measure the DNA concentration by UV analysis. The electrochemical method requires no label on the DNA, only redox mediators were used.

Analytical Chemistry, Jan 1, 1981

... instrumentation ,st M concentrations gave relatively poor values which had a low signal-to-no... more ... instrumentation ,st M concentrations gave relatively poor values which had a low signal-to-noiseratio. ... per potential step, we consider the data in Figure 1 to have a very good signal-... by electrogenerated products from compounds known to be present in the brain (see below). ...

Bio-assays for oxidative …, Jan 1, 2001

Low-molecular weight antioxidants (LMWAs) play a major role in protecting biological systems agai... more Low-molecular weight antioxidants (LMWAs) play a major role in protecting biological systems against reactive oxygen-derived species and reflect the antioxidant capacity of the system. Cyclic voltammetry (CV), shown to be convenient methodology, has been validated for quantitation of the LMWA capacity of blood plasma, tissue homogenates, and plant extracts. Analysis of the CV tracing yields the values of (i) the biological oxidation potential, E and E 1/2 , which relate to the nature of the specific molecule(s); (ii) the intensity (Ia) of the anodic current; and (iii) the area of the anodic wave (S). Both Ia and S relate to the concentration of the molecule(s). LMWA components of human plasma and animal tissues were identified and further validated by reconstruction of the CV tracing and by high-performance liquid chromatography-electrochemical detection. To reflect the oxidative stress status, the use of an additional parameter, R, has been proposed. R represents the level (%) of oxidized ascorbate (compared with total ascorbate) and is measured by high-performance liquid chromatography-electrochemical detection. All these parameters were monitored in healthy human subjects as well as in chronic (diabetes mellitus) and acute care patients (subjected to total body irradiation before bone marrow transplantation). The electroanalytical methodologies presented here could be widely employed for rapid evaluation of the status of subjects (in health and disease) for monitoring of their response to treatment and/or nutritional supplementation as well as for screening of specific populations.

Analytical letters, Jan 1, 2006

Page 1. PHARMACEUTICAL ANALYSIS Fast Monitoring of Nano-Molar Level of Gentamycin by Fast Fourier... more Page 1. PHARMACEUTICAL ANALYSIS Fast Monitoring of Nano-Molar Level of Gentamycin by Fast Fourier Transform Continuous Cyclic Voltammetry in Flowing Solution Parviz Norouzi, Mohammad Reza Ganjali, and Leila ...

Analytical chemistry, Jan 1, 1989

the coatings would depend on both the pH of the bathing solution and the potential of the electro... more the coatings would depend on both the pH of the bathing solution and the potential of the electrode (i.e., the net charge of the polyanionic coating).

Biomedical Engineering, IEEE …, Jan 1, 1988

Analytical chemistry, Jan 1, 1991

Glucose microelectrodes have been formed with glucose oxidase immobilized in poly[(vinylpyridine)... more Glucose microelectrodes have been formed with glucose oxidase immobilized in poly[(vinylpyridine)Os(bipyridine)2Cl] derivative-based redox hydrogels on beveled carbon-fiber microdisk (7 microns diameter) electrodes. In the resulting microelectrode, the steady-state glucose electrooxidation current density is 0.3 mA cm-2 and the sensitivity is 20 mA cm-2 M-1. The current density and sensitivity are 10 times higher than in macroelectrodes made with the same hydrogel. Furthermore, the current is less affected by a change in the partial pressure of oxygen. The higher current density and lower oxygen sensitivity point to the efficient collection of electrons through their diffusion in the redox hydrogel to the electrode surface. These results contrast with those observed for enzyme electrodes based on diffusing mediators, where loss of the enzyme-reduced mediator by radial diffusion to the solution decreases the current densities of microelectrodes relative to similar macroelectrodes.

Analytical …, Jan 1, 1996

Many of the molecules involved in biological signaling processes are easily oxidized and have bee... more Many of the molecules involved in biological signaling processes are easily oxidized and have been monitored by electrochemical methods. Temporal response, spatial considerations, and sensitivity of the electrodes must be optimized for the specific biological application. To monitor exocytosis from single cells in culture, constant potential amperometry offers the best temporal resolution, and a low-noise picoammeter improves the detection limits. Smaller electrodes, with 1-micron diameters, provided spatial resolution sufficient to identify the locations of release sites on the surface of single cells. For the study of neurotransmitter release in vivo, larger cylindrical microelectrodes are advantageous because the secreted molecules come from multiple terminals near the electrode, and the greater amounts lead to a larger signal that emerges from the Johnson noise of the current amplifier. With this approach, dopamine release elicited by two electrical stimulus pulses at 10 Hz was detected with fastscan cyclic voltammetry in vivo. Nafion-coated elliptical electrodes have previously been shown to be incapable of detecting such concentration changes without extensive signal averaging. In addition, we demonstrate that high-pass filtering (200 Hz) of cyclic voltammograms recorded at 300 V/s decreases the background current and digitization noise at these microelectrodes, leading to an improved signal. Also, high-pass filtering discriminated against ascorbic acid, DOPAC, and acidic pH changes, three common interferences in vivo.

Electroanalysis, Jan 1, 2003

A novel hydrogen peroxide biosensor has been constructed based on the characteristics of the carb... more A novel hydrogen peroxide biosensor has been constructed based on the characteristics of the carbon nanotube. The multiwall carbon nanotube (MWNT) was used as a coimmobilization matrix to incorporate horseradish peroxidase (HRP) and electron transfer mediator methylene blue (MB) onto a glassy carbon electrode surface. Cyclic voltammetry and amperometric measurements were employed to demonstrate the feasibility of methylene blue as an electron carrier between the immobilized peroxidase and the surface of glassy carbon electrode. The amperometric response of this resulting biosensor to H 2 O 2 shows a linear relation in the range from 4 mM to 2 mM. The detection limit was 1 mM when the signal to noise ratio is 3. The presence of dopamine and ascorbic acid hardly affects the sensitive determination of H 2 O 2 . This biosensor also possesses very good stability and reproducibility.

… chemistry and interfacial …, Jan 1, 1986

Abstract Methods for the elimination of residual current in fast scan (> 300 V s− ... more Abstract Methods for the elimination of residual current in fast scan (> 300 V s− 1) voltammetry have been evaluated at microvoltammetric electrodes. Staircase voltammetry is found to give only a modest improvement in the ratio of the faradaic current to the residual ...

Ultramicroscopy, Jan 1, 2003

An electrochemical methodology for bio-molecule sensing using an array of well-defined nanostruct... more An electrochemical methodology for bio-molecule sensing using an array of well-defined nanostructures is presented. We describe the fabrication by e-beam lithography of nanoelectrodes consisting of a 100 mm  50 mm area containing interdigitated electrodes of 100 nm in width and interelectrode distance of 200 nm. Sensitivity and response time of the nanoelectrodes are compared to the responses of macro-and microelectrodes. The specificity of the sensor is studied by modifying the gold electrodes with DNA. The technique enables to characterize both single and double-stranded DNA of 15 nucleotides. A special electrochemical cell is adapted to control the temperature and measure the DNA concentration by UV analysis. The electrochemical method requires no label on the DNA, only redox mediators were used.

Analytical Chemistry, Jan 1, 1981

... instrumentation ,st M concentrations gave relatively poor values which had a low signal-to-no... more ... instrumentation ,st M concentrations gave relatively poor values which had a low signal-to-noiseratio. ... per potential step, we consider the data in Figure 1 to have a very good signal-... by electrogenerated products from compounds known to be present in the brain (see below). ...

Bio-assays for oxidative …, Jan 1, 2001

Low-molecular weight antioxidants (LMWAs) play a major role in protecting biological systems agai... more Low-molecular weight antioxidants (LMWAs) play a major role in protecting biological systems against reactive oxygen-derived species and reflect the antioxidant capacity of the system. Cyclic voltammetry (CV), shown to be convenient methodology, has been validated for quantitation of the LMWA capacity of blood plasma, tissue homogenates, and plant extracts. Analysis of the CV tracing yields the values of (i) the biological oxidation potential, E and E 1/2 , which relate to the nature of the specific molecule(s); (ii) the intensity (Ia) of the anodic current; and (iii) the area of the anodic wave (S). Both Ia and S relate to the concentration of the molecule(s). LMWA components of human plasma and animal tissues were identified and further validated by reconstruction of the CV tracing and by high-performance liquid chromatography-electrochemical detection. To reflect the oxidative stress status, the use of an additional parameter, R, has been proposed. R represents the level (%) of oxidized ascorbate (compared with total ascorbate) and is measured by high-performance liquid chromatography-electrochemical detection. All these parameters were monitored in healthy human subjects as well as in chronic (diabetes mellitus) and acute care patients (subjected to total body irradiation before bone marrow transplantation). The electroanalytical methodologies presented here could be widely employed for rapid evaluation of the status of subjects (in health and disease) for monitoring of their response to treatment and/or nutritional supplementation as well as for screening of specific populations.

Analytical letters, Jan 1, 2006

Page 1. PHARMACEUTICAL ANALYSIS Fast Monitoring of Nano-Molar Level of Gentamycin by Fast Fourier... more Page 1. PHARMACEUTICAL ANALYSIS Fast Monitoring of Nano-Molar Level of Gentamycin by Fast Fourier Transform Continuous Cyclic Voltammetry in Flowing Solution Parviz Norouzi, Mohammad Reza Ganjali, and Leila ...

Analytical chemistry, Jan 1, 1989

the coatings would depend on both the pH of the bathing solution and the potential of the electro... more the coatings would depend on both the pH of the bathing solution and the potential of the electrode (i.e., the net charge of the polyanionic coating).