Double-chained cationic surfactant modification of SU-8/Pyrex® microchips for electrochemical sensing of carboxylic ferrocene after reverse electrophoresis

Abstract

This paper describes the effect of the modification of microchip microchannels with two different cationic surfactants on the electrochemical behavior of ferrocene carboxylic acid (FCA), common redoxprobe in bioanalysis. Cetyltrimethylammonium bromide (CTAB), a single-chain surfactant, and didecyldimethylammonium bromide (DDAB), double-chained, were evaluated. The purpose was to obtain a reversal of the electroosmotic flow for allowing precise determination of FCA, an anionic probe that is employed in electrochemical bioassays. Although this was possible in both cases, modification of the microchannel with a high concentration of CTAB produced a differentiation between the free CTAB fraction and the CTAB-combined FCA. DDAB is presented as a good alternative for this modification because this double-chained cationic surfactant forms a more stable quasi-permanent coating on the microchannel surface, avoiding these surfactant-probe interactions. Linear relationship was found between the analytical signal and the concentration of FCA (evaluated between 10 and 150μM) for a modification with 0.1mM of DDAB.