Research Article
Jeyashanthi-Navamani, Ravik
Abstract
Measurements of serum cholesterol levels are important in the diagnosis and classification of hyper lipoproteinemias. Elevated cholesterol levels may occur with hypothyroidism, nephrotic syndrome, diabetes, and various liver diseases. The present investigation was carried out for the development of rapid, highly sensitive and economic cholesterol biosensor for the determination of blood cholesterol. The PVP encapsulated ZnS nanoparticals have been synthesized and characterized by Fourier Transform InfraRed (FTIR) spectroscopy, UV-visible spectroscopy, and Atomic force microscopy techniques in the present investigation. The size of the nanoparticles is found to be ranging between 21-22 nm. The surface morphology of the sensing area of functionalized MWCNT was examined using Scanning Electron Microscopy (SEM). The length of the MWCNTs is found to be approximately 2 microns. In the IR spectrum of functionalized MWCNTs, the presence of bands at 1636 cm-1 and 3434 cm-1 confirmed the presence of carbonyl and hydroxyl moieties of carboxylic acid group. Cholesterol Oxidase was immobilized on to the ZnS nanoparticles and Multiwall Carbon Nanotubes (MWCNTs) which they were placed on a glassy carbon electrode surface using Nafion by LBL assembly technique. Cyclic voltammetric study reveals that the fast electron transfer between electrodes was achieved through the incorporation of ChOx into the Nafion-ZnS-MWCNTs film. ZnS and MWCNTs played an important role in facilitating the electron transfer between the ChOx and the electrode surface. The cholesterol bioelectrode shows detection range of 10-450 mg/dl and good linearity is obtained in 50-450 mg/dl (1.3 -11.6 mM) range with linear regression coefficient 'R2' as 0.986. The Michaelis-Menten constant Km value obtained as 0.84 mM using Lineweaver-Burke plot by plotting 1/V vs 1/Conc. The low Km value 0.84 mM indicates high affinity of immobilized ChOx to cholesterol. It exhibits optimum pH 7.0 and optimum temperature 35°C. Therefore, the bioelectrode fabricated in this study is promising for cholesterol detection in human blood.