Toluidine blue covalently immobilized onto gold electrode surfaces: An electrocatalytic system for nadh oxidation

Abstract

The electrochemical behavior of toluidine blue in solution has been studied and found to be strongly dependent on the electrode surface nature. Monolayers of cystamine (C) or 3-mercaptopropionic acid (MP) chemisorbed onto gold electrode surfaces have been used as support for covalent attachment of toluidine blue (TOB) through its aromatic amino group in position 3 and the amino or carboxylic groups covering the electrode surface. After covalent attachment of TOB onto an MP monolayer, three different species remained stably attached to the electrode surface. Physically adsorbed TOB, which showed the same midpoint potential as in the solubilized state, El,z = -24 j mV (Ag/AgCl); covalently attached TOB, whose midpoint potential was shifted toward 120 mV more positive potentials; and an unknown species, probably physically adsorbed TOB dimers, with a midpoinc potential, = +135 mV (Ag/AgCl). Toluidine blue modified electrodes started to oxidize catalytically NADH at -100 mV with an amperometric response dependent on the concentration of the substrate. An electrode fouling process was observed after successive additions of NADH leading to the loss of catalytic activity.

Phenoxazine Functionalized, Exfoliated Graphite Based Electrodes for NADH Oxidation and Ethanol Biosensing

“…Electro-polymerization and electrochemical functionalization are recent additions towards this direction [34 ± 40]. The disadvantage with this modification procedure is −surface fouling× that hinders the use of these electrodes for repetitive measurements [9,27,29]. Bulk modified electrodes with mediator covalently attached to the matrix are expected overcome the leaching problems.…”

Flow-Injection Analysis and Voltammetric Detection of NADH with a Poly-Toluidine Blue Modified Electrode

“…[11][12][13][14][15][16] Phenothiazine and phenoxazine dyes as mediators modified on the electrode surface were investigated recently. [17][18][19][20][21][22][23][24] These dyes exhibit great electrocatalytical activity toward NADH oxidation, and their catalytic reactions undergo a two-electron-proton mechanism. 25 Adsorption is a common immobilization of these dyes on a solid electrode surface.…”

Immobilized redox mediators for electrochemical NAD(P)+ regeneration

“…To this end, mediators have been electrochemically polymerized at the electrode surface, covalently attached, or physically entrapped in polymers that were enclosed in the electrode material. Another technique is the covalent linkage of the mediator, for example, to a monolayer deposited onto the electrode (Schlereth et al 1994). Table 1 shows examples of mediators immobilized by different techniques.…”

“…Polymerization Toluidine blue (Cai and Xue 1998;Zhou et al 1998), methylene green (Zhou et al 1996), bisphenothiazin-3-yl methane (Gligor et al 2009b Covalent linkage Toluidine blue (Ju et al 2002;Schlereth et al 1994),…”

“…The TBO terminated SAMs yielded a surface coverage of (2.5 ± 0.5)×10 −10 mol cm −2 and (6.8±0.1)×10 −11 mol cm −2 , respectively, and both monolayers showed good electrocatalytic activities. After covalent attachment of toluidine blue on a 3-mercaptopropionic acid monolayer, Schlereth et al (1994) have shown that NADH can be oxidized at −297 mV vs. NHE. In another study, the electrochemical oxidation of NADH and its model compound, N-benzyl-1,4-dihydronicotinamide, was investigated at a gold electrode modified with SAM of cystamine, mercaptopropionic acid, and mercaptoethanol.…”