Effects of Film Morphology and Surface Chemistry on the Direct Electrochemistry of Cytochrome c at Boron-Doped Diamond Electrodes

Abstract

The effects of film morphology and surface termination on the direct electron transfer of horse heart cytochrome c on boron-doped ultrananocrystalline (B-UNCD) and microcrystalline (B-MCD) diamond thin-film electrodes were investigated. Quasi-reversible, diffusion-controlled cyclic voltammetric responses were observed on oxygen-terminated (atomic O/C ~0.015), but not hydrogen-terminated (atomic O/C ~0.02) diamond thin films. The effect of the surface termination was the same for both the nanostructured B-UNCD film with sp2-bonded carbon atoms in the grain boundaries and the well faceted B-MCD film with micron-sized grains and largely devoid of sp2 carbon. Stable cyclic voltammetric i-E curves were recorded with cycling for both oxygen-terminated films indicating the absence of protein denaturation and electrode fouling. The peak currents increased linearly with the square root of the scan rate and the protein concentration; both indicative of a reaction rate limited by semi-infinite linear diffusion of the protein. Similar heterogeneous electron-transfer rate constants were observed for oxygen-terminated B-UNCD (3.48 (± 1.25) × 10−3 cm/s) and B-MCD films (2.38 (± 0.72) × 10−3 cm/s). The results clearly reveal that the oxygen-terminated surface is more active for electron-transfer with this soluble redox protein than is the hydrogen-terminated surface. The film morphology does not influence the diffusion-controlled response of the redox protein.

Direct Electron Transfer to Cytochrome c Induced by a Conducting Polymer

“…The k° value amounts to 0.049 cm s –1 , as obtained from the average value of peak separation between 0.04 and 0.7 μm (Δ E p = 62 mV, SD 2 mV). This number indicates that the electron transfer reaction is faster through the PEDOT–PSS-modified electrode than for other widely used electrodes, such as ITO, carbon materials, or chemically modified gold substrates, for which typical values on the order of 10 –3 –10 –4 cm s –1 are reported. ,− …”

“…Due to its adaptability and ease of preparation, conducting polymers have been also used as 4 promoters of DET to several redox proteins and, particularly, to cyt c. Polyaniline (PANI) is, probably, the most studied synthetic conducting material, but the lack of electrical conductivity observed at neutral pH hampers its use in biological systems. Self-doped polyanilines could be adopted for this application but due to their low activity for DET reactions, they were mainly used as protein entrappers in combination with carbon materials [40][41][42] . Similar application can be found for pyrrole and thiophene-based conducting polymers despite they seemed more adequate than PANI since both are electroactive at physiological pH.…”

Assessment of heterogeneous electron‐transfer rate constants for soluble redox analytes at tetrahedral amorphous carbon, boron‐doped diamond, and glassy carbon electrodes

“…BDD electrodes can be prepared as a single crystalline or a polycrystalline material as we recently documented . Polycrystalline diamond films can be one of three types: microcrystalline, nanocrystalline (NCD), or ultrananocrystalline (UNCD) .…”

An optimal surface concentration of pure cardiolipin deposited onto glassy carbon electrode promoting the direct electron transfer of cytochrome-c

“…[47] This value is in good agreement with those reported in literature for cytochrome-c in solution. [20,[48][49][50] The apparent kinetic rate constant has been estimated through numerical simulations of the cyclic voltammograms using the KISSA software. [51,52] The kinetic rate constant k s of cytochrome-c in solution at a cardiolipin-modified glassy carbon electrode was determined as 1.0 (± 0.5) × 10 -3 cm s -1 .…”