A Novel Tyrosinase Base Biosensor for the Quantification of Antioxidant Capacity: Evaluation on Infusions of Medicinal Plants

Abstract

The working electrode of a screen-printed-type electrodes, SPE, was modified with Tyrosinase enzyme (Tyr) using different immobilization method namely: entrapment, using polyvynil alcohol, PVA, cross-linking using glutaraldehyde, GA, and cross-linking using GA and Human Serum Albumin, HSA, the resulting electrodes were named as SPE/Tyr/PVA, SPE/Tyr/GA and SPE/Tyr/HSA/GA respectively. All these biosensors were characterized from amperometry and EIS thechniques. From the amperimetric evaluation the apparent Michaelis-Menten constant, Km´, of each biosensor were evaluated and from the impedance measurements the respective charge transfer resistance, Rct , were assessed. It was found that the biosensor SPE/Tyr/GA has the lowest Km´(57±7)mM and Rct values, the lowest detection and quantification limits for catechol quantification notwithstanding, the highest sensitivity corresponds to others biosensor. Using the SPE/Tyr/GA biosensor, the Trolox Equivalent Antioxidant Capacity (TEAC) was determined for infusions prepared with Mirto (Salvia microphylla), Hierba dulce (Lippia dulcis) and Salve Real (Lippia alba); medicinal plants commonly used in Mexico.