Optical isomer piezoelectric crystal sensor for l-amino acid esters based on immobilized C60–lipase enzyme

Immobilized fullerene C60–lipase enzyme was synthesized and applied in a piezoelectric crystal sensor for detecting the optical isomer of amino acid esters. The C60-coated piezoelectric quartz crystal sensor was employed to study the interaction between C60 and lipase. The partially irreversible response for lipase was observed by the desorption study, which implied that lipase could be adsorbed on C60 by chemisorption. Effects of pH, C60 coating load and concentration of lipase on the response of the C60-coated piezoelectric crystal sensor for lipase were also investigated. Optimum pH was found to be at 7 for adsorption of lipase by C60. The water insoluble C60–lipase was synthesized and identified with IR spectrometry. The C60–lipase-coated silica plate with pore size of about 5–10 μm was prepared. The activity of immobilized C60–lipase was investigated and was still activated. The immobilized C60–lipase could catalyze the hydrolysis of l-amino acid esters, but not d-amino acid esters. The C60–cryptand22-coated piezoelectric (PZ) crystal sensor with immobilized C60–lipase-coated silica plate was prepared to detect l-amino acid esters in aqueous solutions. The homemade optical isomer PZ sensor for esters was based on the adsorption of l-amino acid, the product of the hydrolysis of l-amino acid ester with C60–lipase, onto the C60–cryptand22-coated quartz crystal. The optical isomer PZ sensor for esters based on C60–lipase was successfully applied to distinguish between d-form and l-form amino acid esters. The optical isomer PZ sensor exhibited good sensitivity, selectivity and reproducibility for l-amino acid esters in aqueous solutions.