Improved Interfacial Electron Transfer in Modified Bilirubin Oxidase Biocathodes



The reducing inhibition of interfacial electron transfer and the resulting impact on the catalytic current of bilirubin oxidase (BOx) biocathodes is explored. Polymer-coated multi-wall carbon nanotubes (MWNTs) are modified with tethering and orientating agents to provide stable immobilization and efficient enzyme orientation. 1-pyrenebutanoic acid, succinimidyl ester (PBSE) is used as a cross-linker. A BOx natural substrate, bilirubin, and its artificial analogues are explored as orientating agents. It is established that bilirubin/PBSE-modified BOx cathodes show approximately 0.4- and 3.2-fold increases in the current density compared to cathodes modified separately with either PBSE or bilirubin, respectively. In subsequent experiments, the incorporation of PBSE and 2,5-dimethyl-1-phenyl-1H-pyrrole-3-carbaldehyde, a functional analogue of bilirubin, into the MWNT matrix results in a further 2–2.5-fold increase in the generated current density compared to the hybrid bilirubin/PBSE-modified cathode, which is, therefore, 20 times higher than the unmodified BOx cathode. This significant enhancement in the performance of the cathode is attributed to the concomitant covalent attachment and proper orientation of BOx, which leads to improved enzyme/electrode interactions.