Suman Singh

Cholesterol oxidase (ChOx) has been covalently immobilized onto poly(aniline-co-pyrrole), electrochemically deposited onto indium-tin-oxide (ITO) glass plates, using glutaraldehyde as a crosslinker. These poly (An-co-Py)/ChOx films have been characterized using UV–visible spectroscopy fourier transform infrared spectroscopy, scanning electron microscopy, and photometric and amperometric techniques, respectively. The poly(An-co-Py)/ChOx bioelectrodes have been utilized for cholesterol estimation in the range of 1–10 mM. The ChOx activity in poly(An-co-Py)/ChOx bioelectrode has been found to be the highest at pH 7.0 at 25°C. The sensitivity and stability of poly(An-co-Py)/ChOx bioelectrode have been experimentally determined as 93.35 μA/mM and 10 weeks at 4°C, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Cholesterol oxidase (ChOx) and cholesterol esterase (ChEt) have been covalently immobilized onto tetraethylorthosilicate (TEOS) sol–gel films. The tetraethylorthosilicate sol–gel/ChEt/ChOx enzyme films thus prepared have been characterized using scanning electron microscopic (SEM), UV–vis spectroscopic, Fourier-transform-infrared (FTIR) spectroscopic and amperometric techniques, respectively. The results of photometric measurements carried out on tetraethylorthosilicate sol–gel/ChEt/ChOx reveal thermal stability up to 55 °C, response time as 180 s, linearity up to 780 mg dL−1 (12 mM), shelf life of 1 month, detection limit of 12 mg dL−1 and sensitivity as 5.4 × 10−5 Abs. mg−1 dL−1.

Cholesterol esterase (ChEt) and cholesterol oxidase (ChOx) have been covalently immobilized on electrochemically prepared polyaniline (PANI) films. These PANI/ChEt/ChOx enzyme films have been characterized using UV–visible, Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). Electrochemical behavior of these films has been studied using cyclic voltammetry (CV) and amperometric techniques, respectively. The PANI/ChEt/ChOx enzyme films show broad oxidation peak from 0.2 to 0.5 V. These PANI/ChEt/ChOx biosensing electrodes have a response time of about 40 s, linearity from 50 to 500 mg/dl of cholesterol oleate concentration. These PANI/ChEt/ChOx films are thermally stable up to 46 °C. This polyaniline based cholesterol biosensor has optimum pH in the range of 6.5–7.5, sensitivity as 7.5 × 10−4 nA/mg dl and a lifetime of about 6 weeks.

Cholesterol esterase (ChEt) and cholesterol oxidase (ChOx) enzymes were entrapped within polypyrrole (PPy) films on a platinum disc electrode during electrochemical polymerization. The characteristics of the PPy/ChEt/ChOx enzyme electrode thus prepared were investigated as a function of the time, pH, temperature, and concentration of cholesteryl palmitate by a spectrophotometric method. PPy/ChEt/ChOx electrodes can be used for the estimation of cholesteryl palmitate concentrations from 1 to 8 mM, can be used least 10 times, and have a shelf life of about 1 month at 4–10°C. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3769–3773, 2004

Fabrication of an amperometric cholesterol biosensor by co-immobilization of cholesterol esterase (ChEt) and cholesterol oxidase (ChOx) onto conducting polypyrrole (PPY) films using electrochemical entrapment technique is described. Electrochemical polymerization was carried out using a two-electrode cell configuration at 0.8 V. Characterization of resulting amperometric biosensor for the estimation of cholesterol has been experimentally determined in terms of linear response range, optimum pH, applied potential, temperature, and shelf-life. These PPY/ChEt/ChOx electrodes can be used for cholesterol ester estimation from 1 to 8 mM and have shelf-life of about 4 weeks at 4 °C during which about 15 estimations of cholesterol ester could be made. The sensitivity of PPY/ChEt/ChOx electrode has been found to be 0.15 μA/mM and the apparent Km value for this electrode is 9.8 mM. Conductivity of the polymer films found to be about 3×10−3 S/cm.

Cholesterol oxidase, cholesterol esterase and peroxidase have been co-immobilized onto electrochemically prepared polyaniline films. These polyaniline–enzyme films characterized using spectroscopic techniques, have been used to fabricate a cholesterol biosensor. This polyaniline-based cholesterol biosensor has a response time of about 240 s, an apparent Km value as 75 mg dl−1 and can be used to estimate cholesterol concentration up to 500 mg dl−1. These polyaniline/cholesterol oxidase/cholesterol esterase films have a detection limit of 25 mg dl−1 with sensitivity of 0.042 μA mg dl−1. The enzyme films were found to be thermally stable up to 48 °C and have a shelf-life of about 6 weeks when stored at 4 °C. The values of the activation energy before and after the critical temperature were found to be 191 and 95.5 kJ mol−1, respectively.