Topological and Electron-Transfer Properties of the 2-Thiobarbituric Acid Adlayer on Polycrystalline Gold Electrodes

Abstract

The voltammetric behavior of [Ru(NH(3))(6)](3+) on bare gold and that on 2-thiobarbituric acid (TBA)-modified gold surfaces are almost identical, with formal rate constants for the electron-transfer process of 0.25 and 0.21 cm s(-1), respectively. A detailed analysis of the modified surface allowed us to establish that this behavior is due to (i) a high surface coverage of 0.67, (ii) a low adsorption resistance that minimizes the potential drop across the TBA monolayer, (iii) the enhanced hydrophilic character of the modified surface compared with that of bare gold, and (iv) a low decay constant for the electronic coupling of the TBA adlayer that minimizes the tunneling barrier for the electron transfer. The electron-transfer process from Au and Au|TBA electrodes to the soluble [Ru(NH(3))(6)](3+/2+) redox couple can be explained according to the multistate model under the Landau-Zener formalism in the nonadiabatic regime that was recently proposed (Feldberg, S. W.; Sutin, N. Chem. Phys. 2006, 324, 216-225). The behavior of soluble [Ru(NH(3))(6)](3+) changes from semi-infinite linear diffusion on Au to finite-length bounded on Au|TBA, in agreement with a surface dimension of 2.17 for the TBA adlayer with a bidimensional underlying gold surface. This value for the surface dimension was determined by two essentially different electrochemical techniques with different sensing capabilities: cyclic voltammetry and electrochemical impedance spectroscopy. The estimated dielectric constant of the adlayer (around 37) and the low potential drop across the monolayer suggest the formation of a "mirror" pattern of water molecules in the diffusion layer, which explains this result.

Zwitterionic Phenyl Layers: Finally, Stable, Anti-Biofouling Coatings that Do Not Passivate Electrodes

“…To evaluate the passivating ability of the difference modification layers, we performed the electrochemistry of the redox probes, Fe(CN) 6 3– and Ru(NH 3 ) 6 3+ , using CVs (see the Supporting Information, Figures SI 6 and SI 7) and electrochemical impedance spectroscopy (EIS) in physiological buffer. As displayed in Table , the charge transfer resistance R ct and calculated rate constants k et of Fe(CN) 6 3– and Ru(NH 3 ) 6 3+ on the bare electrode surfaces compare favorably with the literature. − Apart from the two bare surfaces presenting the lowest R ct , the comparison of charge transfer resistance between coated surfaces has shown essentially the same trend for both Fe(CN) 6 3– and Ru(NH 3 ) 6 3+ solutions. The mix-GC surface exhibited the lowest R ct of all modified surfaces, followed by PPC-GC, and then OEG-Ph-GC.…”

Mesoporous Silica Containers and Programmed Catalytic Hairpin Assembly/Hybridization Chain Reaction Based Electrochemical Sensing Platform for MicroRNA Ultrasensitive Detection with Low Background

“…The EIS technology was introduced to observe the stepwise assembly on the gold electrode surface by a redox probe [Fe(CN) 6 ] 3−/4− , which was corresponding to the electrontransfer resistance (Ret). 45 As shown in Figure 3A, the cleaned bare gold electrode (AuE) just showed a narrow semicircle (curve a), which was attributed to a facilitated electron transfer. After incubation with SH−CP, the Ret was increased (curve b) owing to the resistance of negative DNA phosphoric skeleton.…”

“…The feasibility of electrochemical response was first verified by electrochemical impedance spectroscopy (EIS). The EIS technology was introduced to observe the stepwise assembly on the gold electrode surface by a redox probe [Fe­(CN) 6 ] 3–/4– , which was corresponding to the electron-transfer resistance (Ret) . As shown in Figure A, the cleaned bare gold electrode (AuE) just showed a narrow semicircle (curve a), which was attributed to a facilitated electron transfer.…”

The Protein Surface as a Thermodynamic Frontier: A Fractal Approach

“…In this regard, we assumed that the maximum interaction between two surfaces is achieved upon equality of their surface dimensions. For such purpose, we have designed a modified surface based on the adsorption of 2-thiobarbituric acid onto a gold surface, for which we obtained a surface dimension of 2.17, that is, of the same order to the protein surface (Méndez et al, 2008). Upon contacting both surfaces, we have obtained a high www.intechopen.com protein coverage and a high electron transfer, indicating that indeed the surface of the protein behaves as a true thermodynamic frontier.…”