Biosensor for antioxidant determination in herbal tea, Orthosiphon stamineus benth

Abstract

An amperometric biosensor has been developed using xanthine oxidase (XO) enzyme as sensing materia] for the determination of antioxidant property of Orthosiphon stamineus benth (Cat whiskers) extracts. The enzyme was physically entrapped in modified chitosan membrane on carbon paste electrode. Experimental variables concerning the biosensor preparation such as the effect of enzyme amount, chitosan pH, pH of working buffer were optimized. The sensor showed linear response towards xanthine (poised at +600mV vs. Ag/AgCl) between 5.0 x 10ֿ7M to 43 x 10ֿ5M at pH 7.0 with detection limit of (S/N=3) of 1.5 x 10 ֿ7M. The biosensor reached 95% of it's steady-state current at about 6 seconds. The usefulness of the biosensor for the herbal extracts was demonstrated by determining percentage of inhibition of Orthosiphon stamineus extracts and compared with the method reported earlier by Tadataka Noro et al. using the uv-vis spectrophotometry.