Covalent Modification of a Glassy Carbon Surface by 4-Aminobenzoic Acid and Its Application in Fabrication of a Polyoxometalates-Consisting Monolayer and Multilayer Films

Abstract

4-Aminobenzoic acid (4-ABA) was covalently grafted on a glassy carbon electrode (GCE) by amine cation radical formation in the electrooxidation process of the amino-containing compound. X-ray photoelectron spectroscopy measurement proves the presence of 4-carboxylphenylamine monolayer on the GCE. The redox responses of various electroactive probes were investigated on the 4-ABA-modified GCE. Electron transfer to Fe(CN)6 3in solutions of various pHs was studied by both cyclic voltammetry and electrochemical impedance analysis on the modified electrode. Changes in the solution pH value result in the variation of the terminal group charge state, based on which surface pKa values are estimated. The 4-ABA-modified GCE was used as a suitable charged substrate to fabricate polyoxometalates-consisting (POM-consisting) monolayer and multilayer films through layer-by-layer assembly based on electrostatic attraction. Cyclic voltammetry shows the uniform growth of these three-dimensional multilayer films. Taking K10H3[Pr-(SiMo7W4O39)2]‚xH2O (abbreviated as Pr(SiMo7W4)2), for example, the preparation and electrochemical behavior of its monolayer and multilayer film had been investigated in detail. This modification strategy is proven to be a general one suitable for anchoring many kinds of POMs on the 4-ABA-modified GCE.

Grafting of phenylboronic acid on a glassy carbon electrode and its application as a reagentless glucose sensor

“…5B were obtained at pH 7. There are clear differences between EIS plots obtained at pH 3.5 (near the pK a of [5,5]PBA/GC) and at pH 7. First, the semi-infinite diffusion in the low frequency region is no more apparent, and this phenomenon can be explained by the low current involved in the Fe(CN) 3−/4− 6 redox reaction on a PBA/GC electrode in the potential range studied.…”

“…6B. Considering the results for the two types of grafting conditions, the most significant effect on |Z| response is obtained for [5,30]PBA/GC electrode.…”

“…Faradic impedance measurements for PBA/GC in the presence of probe molecule To elucidate the affinity of PBA/GC electrodes toward glucose, EIS measurements were carried out in the presence of 1 mM K 3 Fe(CN) 6 at different pH conditions. The EIS plots for [5,5]PBA/GC at pH 3.5 are shown in Fig. 5A and the plots give a typical shape, with a semicircle in the high-frequency domain characteristic of an interfacial charge-transfer mechanism and a straight line with near unity slope in the low-frequency domain characteristic of a semiinfinite diffusion phenomenon.…”

“…In general, these methods use an electrochemical generation of radicals, followed by formation of covalent bonds between the radicals and the carbon electrode surface. Radical species can be generated by an electrochemical oxidation of aromatic amines [5] or aliphatic amines [6], and reduction of aryl diazonium salts [7]. Among them, reduction of diazonium salts can be achieved by either in acetonitrile [8] or aqueous acid solutions [9] and is easily and rapidly carried out in one step, and the reduction method is applicable to a wide variety of aromatic amines many of which are commercially available [10].…”

Biosensors for Cancer Biomarkers

“…This is both non-specific bindings to blocked Zhuo et al, 2005, in press) and to use of TB as a mediator and H 2 O 2 as a result of reduction feature makes the system more sensitive (Yang et al, 1998;Zhang et al, 2005). Radical cation method was used SAA to bond on GCE electrode (Cheng et al, 2001, Liu et al, 2000Downard and Mohamed, 1999) to the PSAA / GCE modified electrode forming. Sulfonate groups of the modified electrode has been created with TB treatment.…”