Hydrogel network entrapping cholesterol oxidase and octadecylsilica for optical biosensing in hydrophobic organic or aqueous micelle solvents

Two optical cholesterol biosensors have been fabricated by immobilizing cholesterol oxidase (ChOx) and octadecylsilica (ODS) particles in hydrogel network matrixes of copolymer of poly(vinyl alcohol) (PVA)/hydroxyethyl carboxymethyl cellulose (HECMC), and sol-gel, respectively. In conjunction with an optical oxygen transducer, the immobilized ChOx in the sol-gel/ODS matrix was assembled as an optical cholesterol biosensor to continuously detect free cholesterol in aqueous micelle solution, while the immobilized ChOx in the PVA/HECMC/ODS matrix was constructed as an organic-phase optical cholesterol biosensor for the continuous analysis of free cholesterol in hydrophobic organic solvent. The compositions and properties of the immobilization matrixes, the effects of solvents and the analytical features were studied in detail. Both biosensors showed stable and reliable responses toward free cholesterol. For the aqueous micelle cholesterol biosensor, the analytical working range was from 0.05 to 8.0 mM cholesterol, the response time was 7-12 min, the operation life was more than 35 assays, and the shelf life was similar to4 months. For the organic-phase cholesterol biosensor, the analytical working range was from 0.07 to 18.0 mM cholesterol, the response time was 4-8 min, the operation life was more than 120 assays, and the shelf life was longer than 5 months. The organic-phase cholesterol biosensor has been successfully applied to determine the free cholesterol content in commercial butter samples.