Electrochemical behavior of the bis(2,2'-bipyridyl)copper(II) complex immobilized on a self-assembled monolayer modified electrode for L-ascorbic acid detection

Modification of a gold electrode has been achieved by immobilizing a bis(2,2'-bipyridyl)copper(II) complex in a self-assembled monolayer (SAM) of 3-mercaptopropionic acid. The electrostatic interaction of the negatively charged SAM with a di-positive copper complex allowed the attachment. The modified electrode exhibited excellent redox behavior. The dependence of the modified electrode response was investigated in terms of pH, supporting electrolyte and ionic strength. Moreover, it showed good electrocatalytic activity for ascorbic acid oxidation, allowing convenient quantification at levels down to 8.1 x 10(-8) mol l(-1). The Cu(bipy)2]/SAM modified electrode under optimized operational conditions (PIPES buffer 0.01 mol l(-1) at pH 6.8 and 200 mV vs. SCE) presented a linear response range between 1.0 micromol l(-1) and 100.0 micromol l(-1) for ascorbic acid. This modified electrode also presented an excellent repeatability, showing a relative standard deviation of 2.1% for a series of 12 successive measurements of a 5.0 micromol l(-1) ascorbic acid solution. Furthermore, the electroactivity was maintained over a long period (e.g., 92% after 100 determinations).