Enzyme-capped relay-functionalized mesoporous carbon nanoparticles: Effective bioelectrocatalytic matrices for sensing and biofuel cell applications

The porous high surface area and conducting properties of mesoporous carbon nanoparticles, CNPs (<500 nm diameter of NPs, pore dimensions ∼6.3 nm), are implemented to design electrically contacted enzyme electrodes for biosensing and biofuel cell applications. The relay units ferrocene methanol, Fc-MeOH, methylene blue, MB⁺, and 2,2′-azinobis(3- ethylbenzothiazoline-6-sulfonic acid), ABTS^2-, are loaded in the pores of the mesoporous CNPs, and the pores are capped with glucose oxidase, GOx, horseradish peroxidase, HRP, or bilirubin oxidase, BOD, respectively. The resulting relay/enzyme-functionalized CNPs are immobilized on glassy carbon electrodes, and the relays encapsulated in the pores are sufficiently free to electrically contact the different enzymes with the bulk electrode supports. The Fc-MeOH/GOx CNP-functionalized electrode is implemented for the bioelectrocatalyzed sensing of glucose, and the MB⁺/HRP-modified CNPs are applied for the electrochemical sensing of H₂O₂. The ABTS^2-/BOD-modified CNPs provide an effective electrically contacted material for the bioelectrocatalyzed reduction of O₂ (k_cat = 94 electrons·s^-1). Integration of the Fc-MeOH/GOx CNP electrode and of the electrically wired ABTS^2-/BOD CNP electrode as anode and cathode, respectively, yields a biofuel cell revealing a power output of ∼95 μW·cm^-2.