Electrochemically Activated Histidine-tagged Flavoenzyme-mediated Biopseudocapacitor

Abstract

Abstract Polypeptides or enzyme proteins have specific functions depending on their unique three-dimensional structures. Active-site histidine or histidine tags in an enzyme protein can be used to fix an electrochemically active species to the enzyme and can be further used as an electroactive material for the electrode substrate of a faradaic supercapacitor, which is an energy storage device with high power density. Here, we introduce an enzyme-linked electric double-layer capacitor and a pseudocapacitor prepared by cyclovoltametrically intercalating histidine moieties of the linked enzymes with ferricyanide ions. Indium tin oxide (ITO) was employed as the electrode substrate for immobilization of histidine-tagged methyl tryptophan oxidase (HMTO). After attaching HMTO via amino-glutaraldehyde cross-linking chemistry, the resulting HMTO-ITO electrodes were further activated with ferricyanide. The approximate amount of HMTO immobilized on an ITO substrate of area 1.13 cm2 was 3.3 ± 0.46 µC, equivalent to 11.4 pmole (0.49 µg) of HMTO. The specific capacity of the biopseudocapacitor determined using cyclic voltammetry was 6.19 C g− 1 at a scan rate of 10 mV s− 1.