Polypeptides or enzyme proteins have specifi c functions depending on their unique three-dimensional structures. Active-site

histidine or histidine tags in an enzyme protein can be used to fi x 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

cm 2 was 3.3 ± 0.46 μC, equivalent to 11.4 pmol (0.49 μg) of HMTO. The specifi c capacity of the biopseudocapacitor determined

using cyclic voltammetry was 6.19 C g −1 at a scan rate of 10 mV s −1 .