Efficient Direct Electron Transfer with Enzyme on a Nanostructured Carbon Film Fabricated with a Maskless Top-Down UV/Ozone Process

Abstract

We have developed a new carbon film electrode material with thornlike surface nanostructures to realize efficient direct electron transfer (DET) with enzymes, which is very important for various enzyme biosensors and for anodes or cathodes used in biofuel cells. The nanostructures were fabricated using UV/ozone treatment without a mask, and the obtained nanostructures were typically 2-3.5 nm high as confirmed by atomic force microscopy measurements. X-ray photoelectron spectroscopy and transmission electron microscopy revealed that these nanostructures could be formed by employing significantly different etching rates depending on nanometer-order differences in the local sp(3) content of the nanocarbon film, which we fabricated with the electron cyclotron resonance sputtering method. These structures could not be realized using other carbon films such as boron-doped diamond, glassy carbon, pyrolyzed polymers based on spin-coated polyimide or vacuum-deposited phthalocyanine films, or diamond-like carbon films because those carbon films have relatively homogeneous structures or micrometer-order crystalline structures. With physically adsorbed bilirubin oxidase on the nanostructured carbon surface, the DET catalytic current amplification was 30 times greater than that obtained with the original carbon film with a flat surface. This efficient DET of an enzyme could not be achieved by changing the hydrophilicity of the flat carbon surface, suggesting that DET was accelerated by the formation of nanostructures with a hydrophilic surface. Efficient DET was also observed using cytochrome c.

Molecular Functionalization of Graphite Surfaces: Basal Plane versus Step Edge Electrochemical Activity

“…[1][2][3][4] Glassy carbon (GC), boron doped diamond and graphite have long received attention for electroanalytical and electrocatalytic measurements, [5][6][7][8][9][10][11] and, more recently, carbon nanotubes and graphene have generated considerable interest. [12][13][14][15][16][17] However, despite well-defined bulk properties and structure, carbon materials can possess rather complex surface chemistry that may substantially impact the resulting electrochemistry.…”

Electrospun Carbon Nanofiber Webs with Controlled Density of States for Sensor Applications

“…[1c, 2] Common strategies to accomplish this control include modification of surface chemistry, [1c] variation of graphene orientation, [3] and manipulation of surface roughness. [4] These strategies, however, offer little control over the density of electronic states (DOS) near the Fermi level, which plays a crucial role in the electrochemical activity of electrode materials. [1c, 5] Lack of direct control of the intrinsic properties (i.e., DOS) of the electrodes results in an inability (1) to modulate kinetics for outer-sphere systems because their kinetic behavior is only affected by the DOS of the electrode, and (2) to alter universally the kinetics for different types of inner-sphere systems since one particular strategy usually can only influence the kinetics of a specific inner-sphere system, not all of them.…”

Remarkably High Heterogeneous Electron Transfer Activity of Carbon-Nanotube-Supported Reduced Graphene Oxide

“…Both electrodes exhibited well-defined voltammetric responses towards Cyt c with peak currents located around 0.04 to -0.06 V versus Ag/AgCl, consistent with the DET-type electrocatalysis of this enzyme. [30][31][32][33] We observed the electrocatalytic currents immediately upon adding Cyt c into the background electrolyte solution, and little deviation from the initial voltammetric response after multiple subsequent scans. The linear relation between the voltammetric peak current and (scan rate) 1/2 ( Figure 9b) suggested a diffusion-controlled charge transfer behavior of this enzyme on both rGO-ctrl and rGO/CNT.…”

“…[28][29] Furthermore, we find that, compared to rGO-ctrl, rGO/CNT exhibited significantly higher direct electron transfer (DET) efficiencies with two enzymes of great interest in biotechnology, cytochrome c and horse radish peroxidase. [30][31][32][33] Development of electrodes having high DET efficiencies with redox enzymes is of great interest in various potential applications such as biosensors, 33 bioelectronics, 34 enzyme catalysts 35 and biofuel cells. 36 Our study is the first investigation of the HET activities of rGO/CNT, a novel graphene system, and indicates its potential application in various electrochemical technologies.…”

“…DET Efficiencies with Enzymes. Cyt c is a DET-type enzyme studied extensively, [30][31][32][33] and it has been shown that conventional carbon electrodes, such as glassy carbon, graphitized carbon fiber, and carbon paste electrodes, show very low DET efficiencies with this enzyme. [15][16]33 Figure 9a shows representative backgroundsubtracted voltammograms of 100 µM Cyt c in 100 mM phosphate buffer solution (pH = 7.0) at different scan rates on rGO-ctrl and rGO/CNT with identical ESAs of 0.37 cm 2 each.…”