Electrochemistry of ABTS at Glassy Carbon Electrodes

Potentiometric and UV-Vis spectrophotometric titrations for evaluation of the antioxidant capacity of chicoric acid

Potentiometric/spectrophotometric titrations have revealed the antioxidation behavior and mechanisms of chicoric acid (ChA, versus trolox) against ABTS˙⁺ radical cations.

Stable ABTS Immobilized in the MIL-100(Fe) Metal-Organic Framework as an Efficient Mediator for Laccase-Catalyzed Decolorization

The successful encapsulation of 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS), a well-known laccase mediator, within a mesoporous metal-organic framework sample (i.e., MIL-100(Fe)) was achieved using a one-pot hydrothermal synthetic method. The as-prepared ABTS@MIL-100(Fe) was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, nitrogen sorption, and cyclic voltammetry (CV). Our ABTS@MIL-100(Fe)-based electrode exhibited an excellent electrochemical response, indicating that MIL-100(Fe) provides an appropriate microenvironment for the immobilization and electroactivity of ABTS molecules. ABTS@MIL-100(Fe) was then evaluated as an immobilized laccase mediator for dye removal using indigo carmine (IC) as a model dye. Through the application of laccase in combination with a free (ABTS) or immobilized (ABTS@MIL-100(Fe)) mediator, decolorization yields of 95% and 94%, respectively, were obtained for IC after 50 min. In addition, following seven reuse cycles of ABTS@MIL-100(Fe) for dye treatment, a decolorization yield of 74% was obtained. Dye decolorization occurred through the breakdown of the chromophoric group by the Laccase/ABTS@MIL-100(Fe) system, and a catalytic mechanism was proposed. We therefore expect that the stability, reusability, and validity of ABTS@MIL-100(Fe) as a laccase mediator potentially render it a promising tool for dye removal, in addition to reducing the high running costs and potential toxicity associated with synthetic mediators.

Design of Laccase-Metal Organic Framework-Based Bioelectrodes for Biocatalytic Oxygen Reduction Reaction

Laccase in combination with 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) as a mediator is a well-known bioelectrocatalyst for the 4-electron oxygen reduction reactions (ORR). The present work deals with the first exploitation of mesoporous iron(III) trimesate-based metal organic frameworks (MOF) MIL-100(Fe) (MIL stands for materials from Institut Lavoisier) as a new and efficient immobilization matrix of laccase for the building up of biocathodes for ORR. First, the immobilization of ABTS in the pores of the MOF was studied by combining micro-Raman spectroscopy, X-ray powder diffraction (XRPD), and N2 porosimetry. The ABTS-MIL-100(Fe)-based modified electrode presents excellent properties in terms of charge transfer kinetics and ionic conductivity as well as a very stable and reproducible electrochemical response, showing that MIL-100(Fe) provides a suitable and stabilizing microenvironment for electroactive ABTS molecules. In a second step, laccase was further immobilized on the MIL-100(Fe)-ABTS matrix. The Lac-ABTS-MIL-100(Fe)-CIE bioelectrode presents a high electrocatalytic current density of oxygen reduction and a reproducible electrochemical response characterized by a high stability over a long period of time (3 weeks). These results constitute a significant advance in the field of laccase-based bioelectrocatalysts for ORR. According to our work, it appears that the high catalytic efficiency of Lac-ABTS-MIL-100(Fe) for ORR may result from a synergy of chemical and catalytic properties of MIL-100(Fe) and laccase.

Hybrid microfluidic fuel cell based on Laccase/C and AuAg/C electrodes

A hybrid glucose microfluidic fuel cell composed of an enzymatic cathode (Laccase/ABTS/C) and an inorganic anode (AuAg/C) was developed and tested. The enzymatic cathode was prepared by adsorption of 2,2'-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and Laccase on Vulcan XC-72, which act as a redox mediator, enzymatic catalyst and support, respectively. The Laccase/ABTS/C composite was characterised by Fourier Transform Infrared (FTIR) Spectroscopy, streaming current measurements (Zeta potential) and cyclic voltammetry. The AuAg/C anode catalyst was characterised by Transmission electron microscopy (TEM) and cyclic voltammetry. The hybrid microfluidic fuel cell exhibited excellent performance with a maximum power density value (i.e., 0.45 mW cm(-2)) that is the highest reported to date. The cell also exhibited acceptable stability over the course of several days. In addition, a Mexican endemic Laccase was used as the biocathode electrode and evaluated in the hybrid microfluidic fuel cell generating 0.5 mW cm(-2) of maximum power density.