In the light of the studies for the preparation of new devices for monitoring biochemical analytes the Chemically Modified Electrodes (CME) are a powerful tool for their versatile and reproducible behavior. In particular, the Self Assembled Monolayer (SAM) electrodes modified by thiols are very popular for the possibility of modulating the physico-chemical properties of thiol layer. Moreover, the metallic surface to which thiols can be attached plays a key role in the light of stability of the layer, accessibility of the electrode surface and possibility of fast electron transfer. In this work the electron transfer (ET) activity of cytochrome c (cyt c) adsorbed on thiol-based self assembled monolayer will be discussed in term of interactions between the protein and a redox couple probe, Fe(CN) 6 3− /Fe(CN) 6 4− , added to the electrolytic solution. The outcomes point to a reaction mechanism similar to Saveant enzyme mechanism, with a rate constant value of 35,000 M −1 · s −1 , for the ET between cyt c and Fe(CN) 6 3−/4− . The electrochemical characterization, by means of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), of mixed thiols layer in the presence of cyt c will be also discussed in term of thiol terminal functionalized groups and gold electrode substrate morphology.
Single and two component self assembled organic monolayers (SAM) formed of HS-C 10 H 20 -COOH and the HS-C 10 H 20 -COOH + HS-C 6 H 12 -OH mixture and applied on gold electrodes of different shapes and roughness are studied. The resulting monolayers are characterized in 1 M NaNO 3 solutions by the methods of electrochemical impedance spectroscopy in the frequency range from 1 Hz to 100 kHz and cyclic voltammetry in the potential range from 0 to -0.4 V (SCE). Using these method, the behavior of modified single crystal and polycrystalline gold electrodes in electrolyte solutions of different acidity is assessed and the standard rate constants for the Ru[(NH 3 ) 6 ] 3+/2+ redox reaction are determined. The SAM film formed from the ethanol solution of the HS-C 10 H 20 -COOH + HS-C 6 H 12 -OH mixture (0.025 M) on the Au(210) single crystal face lowers down the rate of the heterogeneous Ru[(NH 3 ) 6 ] 3+/2+ reaction from 1.5 to 4.02 × 10 -4 cm/s in the electrolyte solution with pH from 2. In solutions with higher pH, the rate constant is higher by almost an order of magnitude (2.74 × 10 -3 cm/s). The distribution of micropores in SAM films is studied within the framework of a model of micro array electrodes. The results of studies are compared with the literature data on the gold electrode in solutions of inactive electrolytes in the absence and in the presence of SAM films formed by alkylmercaptans with equal chain lengths.
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