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

The working electrode of screen-printed-type electrodes, SPE, was modified with Tyrosinase enzyme (Tyr) using different immobilization methods namely: entrapment, using water soluble polyvynil alcohol, PVA, cross-linking using glutaraldehyde, GA, and cross-linking using GA and Human Serum Albumin, HAS. The resulting electrodes were named: SPE/Tyr/PVA, SPE/Tyr/GA and SPE/Tyr/ HSA/GA, respectively. All these biosensors were characterized through amperometry, immersed in an aqueous solution containing different catechol concentrations, and EIS techniques. From the amperometric evaluation, the apparent Michaelis-Menten constant, K_m´, of each biosensor were evaluated and from the impedance measurements the respective charge transfer resistance, R_ct, were assessed. It was found that the biosensor SPE/Tyr/GA has the lowest K_m´ (57 ± 7) μM and R_ct values. Moreover, this electrode also displays both the lowest detection and quantification limits for catechol quantification, notwithstanding, the highest sensitivity corresponds to the SPE/Tyr/PVA 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.