Dhammanand J. Shirale

Label-Free Chemiresistive Immunosensors for Viruses

We report development, characterization, and testing of chemiresistive immunosensors based on single polypyrrole (Ppy) nanowire for highly sensitive, specific, label free, and direct detection of viruses. Bacteriophages T7 and MS2 were used as safe models for viruses for demonstration. Ppy nanowires were electrochemically polymerized into alumina template, and single nanowire based devices were assembled on a pair of gold electrodes by ac dielectrophoretic alignment and anchored using maskless electrodeposition. Anti-T7 or anti-MS2 antibodies were immobilized on single Ppy nanowire using EDC-NHS chemistry to fabricate nanobiosensor for the detection of corresponding bacteriophage. The biosensors showed excellent sensitivity with a lower detection limit of 10(-3) plaque forming unit (PFU) in 10 mM phosphate buffer, wide dynamic range and excellent selectivity. The immunosensors were successfully applied for the detection of phages in spiked untreated urban runoff water samples. The results show the potential of these sensors in health care, environmental monitoring, food safety and homeland security for sensitive, specific, rapid, and affordable detection of bioagents/pathogens.

Synthesis and Characterization of Ppy-PVS, Ppy-pTS, and Ppy-DBS Composite Films

Composite films of polypyrrole-poly(vinyl sulphonic acid) (Ppy-PVS), polypyrrole-p-toluene sulphonic acid (Ppy-pTS) and polypyrrole-dodecylbenzene sulphonic acid (Ppy-DBS) were synthesized on ITO coated glass, using electrochemical polymerization. The synthesized films were characterized using electrochemical technique, electrical conductivity, UV-Vis spectroscopy, FTIR spectra, and scanning electron microscopy (SEM). This study reveals that Ppy-PVS composite films provide a polymer matrix with very good mechanical and environmental stability, uniform surface morphology, and higher conductivity, which are suitable for the immobilization of biocomponent.

Synthesis of H2SO4 doped polyaniline film by potentiometric method

H2SO4 doped polyaniline films were synthesized in aqueous acidic media. The polyaniline film deposited on platinum electrode exhibits highest conductivity. The conductivity of each H2SO4 doped polyaniline sample was determined by the four-probe technique. The current-voltage curve exhibits that polyaniline sample has an ohmic behaviour. Experiments were conducted to establish the conductivity of the sample from room temperature to 110°C. The current was set constant. It has been observed that at lower current as well as higher current conductivity of the polyaniline sample is due to the electrons transferred to the conduction band. It is observed that the concentration ratio of 0.2:1 of aniline and H2SO4 for synthesis of PANI film on platinum electrode shows good conductivity.

Glucose Oxidase Immobilized on Galvanostatically Synthesized Poly(N-Methylpyrrole)/Polyvinyl Sulfonate Film for Determination of Glucose

Abstract Glucose oxidase immobilized on electrochemically polymerized poly(N-methylpyrrole) (P(NMP)) film with polyvinyl sulfonate (PVS) dopant has been investigated. It was found that the galvanostatically synthesized P(NMP) matrix is suitable for the development of poly(N-methylpyrrole)/polyvinyl sulfonate/glucose oxidase (P(NMP)/PVS/GODx) electrode. Cross-linking via glutaraldehyde is adopted for the immobilization of GODx. Incorporation of the glucose in the presence of phosphate and acetate buffer was studied. The effect of phosphate buffer and acetate buffer for the development of biosensors has also been investigated. The kinetics parameters determined for the P(NMP)/PVS/GODx electrode developed in phosphate buffer and acetate buffer at pH 7.4 were 12.5 mM and 16.6 mM for k m and 20 µA and 24 µA for I max respectively. The sensitivity of P(NMP)/PVS/GODx electrode in phosphate and acetate buffer has been studied. It was found that the sensitivity for the phosphate buffer is higher than that for the acetate buffer. The stability of synthesized P(NMP)/PVS/GODx electrode in phosphate buffer was found to be more than that in acetate buffer. The characterization of electrochemically polymerized P(NMP) film was done by FTIR and scanning electron micrography (SEM).

Potentiometric study of polyaniline film synthesized with various dopants and composite-dopant: A comparative study

The potentiometric study of polyaniline (PANI) film synthesized with dopants viz. polyvinyl sulfonic acid (PVS),p-toluene sulfonic acid (pTS), dodecyl benzene sulfonic acid (DBS) and composite-dopants viz. PVS-pTS and PVS-DBS, has been carried out. The synthesized PANI films were characterized by electrochemical technique, UV-visible spectroscopy, Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and conductivity measurement. It was found that the PANI doped with PVS gives good electrochemical properties, conductivity as well as surface morphology as compared topTS and DBS, whereas in composite dopants the PANI doped with PVS-pTS gives good polymer matrix as compared to PVS-DBS.

Effect of Gamma-Irradiation on Admittance, Suceptance and Conductance of Polyacrylonitrile Gel

We have successfully demonstrated the effect of Gamma-irradiation on Polyacrylonitrile (PAN) gel in terms of admittance (Y), Susceptance (B) and Conductance (G). The trend of Y and B decreases by 297 microSec and 138 microSec respectively and conductance (G) increases by 100 μS. Electrical mechanism associated with microstructure of PAN gel under external DC bias potential is the novelty of this work. External field stimuli responded due to delocalization of charge carriers. These properties are important as novel electronic material.

Influence of Process Parameters on the Conductivity and Surface Morphology of Polypyrrole Films

Influence of electrochemical process parameters such as monomer and electrolyte concentrations, current density, pH of the electrolyte, and type of electrolyte have been studied during polymerization of polypyrrole (Ppy). The changes in the conductivity of synthesized Ppy film for different electrolytes were observed by chronopotentiograms recorded during the electrochemical polymerization and it was confirmed by measuring it using four probe techniques. It was found that the electrochemical process parameters have a considerable influence on the conductivity of the film. The Ppy film was synthesized on a platinum substrate by electrochemical polymerization with different electrolytes such as potassium nitrate, sodium nitrate, sulphuric acid, hydrochloric acid, potassium chloride, sodium chloride, oxalic acid, and sodium salicylate, under galvanostatic condition over a wide range of pH of the reaction medium and applied current density. The different concentration ratios of pyrrole and sodium nitrate were considered during synthesis of Ppy films. It has been observed that the polymerization potential increases with the pH and applied current density. One could synthesize Ppy film with very good surface morphology and conductivity with optimized process parameters. The characterization of synthesized Ppy film was done by electrochemical technique, electrical conductivity, Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM).

Designing of Optical Fiber Sensing Probe

Evanescent wave configuration has been extensively used in the development of fiber-optic sensor for different biomedical applications. In the present investigation we have theoretically proposed the designing of single-mode and multimode optical fiber sensing probes, which can be prepared by removing a few centimeters of cladding near the distal end of the step index optical fiber. In this theoretical study, we found that the removal of cladding causes V-number mismatching and this has led to the loss of signal acquisition from the sensing region. Therefore, to minimize these losses we have proposed to reduce the radius by step etch and tapering technique. It was found that step etching and tapering enhances the strength and penetration depth of the evanescent wave significantly.

Immobilization of GOD on Ppy–PVS Composite Film for Determination of Glucose: A Comparative Study of Phosphate and Acetate Buffers

The Polypyrrole-polyvinylsulphonate-glucose oxidase (Ppy–PVS–GOD) biosensor for determination of glucose has been described in the present investigation. The enzyme, glucose oxidase (GOD) was immobilized by crosslinking via glutaraldehyde on a polypyrrole–polyvinyl sulphonate (Ppy–PVS) composite film. The Ppy–PVS film was electrochemically synthesized on indium-tin-oxide (ITO)–coated glass plate. The synthesized composite films were characterized using galvanostatic electrochemical technique, electrical conductivity, UV-Visible spectroscopy, Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The crosslinking of enzyme and porous morphology of the polymer film leads to high enzyme loading and an increase in lifetime, stability, and fast response time of the enzyme electrode. Characterization of resulting amperometric biosensor for the estimation of glucose has been experimentally determined in terms of linear response range, optimum pH, applied potential, and shelf-life. These Ppy–PVS–GOD electrodes can be used for glucose estimation from 1 to 50 mM and have a shelf-life of about 5–6 weeks at 4°C. The sensitivity of Ppy–PVS–GOD electrode in phosphate and acetate buffer has been studied. It was found that the phosphate buffer gives fast response as compared to acetate buffer in amperometric measurements.

Anti-typhi immobilized MWCNT-PANI nano sensor for salmonella typhi detection

An electronic Nano bio-sensor is developed to detect the presence of typhoid in the earlier stage with high accuracy. The sensor is developed on a silicon substrate and Multi Walled Carbon Nano tube is aligned over it and coated with polyaniline. The antibody anti-typhi was immobilized on to the electrode to have a sensitive detection of the salmonella antigens from the samples. The resultant variation of resistance by the sensor indicates the detection of Salmonella Typhi in earlier stage and shows the accuracy of the sensor developed