RESUMEN
Metal-organic Frameworks (MOFs) have emerged as promising materials for different electrochemical applications. Their low conductivity, however, is a major challenge to overcome. Therefore, a deeper understanding on the charge transfer mechanism is needed to improve the conductivity of MOF-based electrodes. For this contribution, we focused on metalated MOF-525 and found that the nature of the metal center is one of the many factors contributing to the charge transfer kinetics, which is attributed to differences in redox behaviour, affecting the hopping distance and the electron transfer rate. These results highlight the importance of the nature of the redox active site to optimize charge transfer in MOF-based electrodes.
RESUMEN
The working area of a screen-printed electrode, SPE, was modified with the enzyme tyrosinase (Tyr) using different immobilization methods, namely entrapment with water-soluble polyvinyl alcohol (PVA), cross-linking using glutaraldehyde (GA), and cross-linking using GA and human serum albumin (HSA); the resulting electrodes were termed SPE/Tyr/PVA, SPE/Tyr/GA and SPE/Tyr/HSA/GA, respectively. These biosensors were characterized by means of amperometry and EIS techniques. From amperometric evaluations, the apparent Michaelis-Menten constant, Km', of each biosensor was evaluated while the respective charge transfer resistance, Rct, was assessed from impedance measurements. It was found that the SPE/Tyr/GA had the smallest Km' (57 ± 7) µM and Rct values. This electrode also displayed both the lowest detection and quantification limits for catechol quantification. Using the SPE/Tyr/GA, the Trolox Equivalent Antioxidant Capacity (TEAC) was determined from infusions prepared with "mirto" (Salvia microphylla), "hHierba dulce" (Lippia dulcis) and "salve real" (Lippia alba), medicinal plants commonly used in Mexico.