Development of novel surfaces for enhancement of sensitivity and selectivity with carbon fiber electrodes

The development of novel surfaces for enhancement of sensitivity and selectivity of uric acid (UA) determinations with carbon fiber electrodes (CFE) has been the goal in our research. To achieve this goal, different approaches have been taken. First, a nanostructured CFE was prepared by a combination of mechanical polishing and electrochemical pretreatment, which involves moderate oxidation of the surface, followed by reduction. The effects of the treatment parameters such as polishing time, potential window, composition of the buffer and cycling time at the carbon fiber electrode surface were investigated.; Electrochemical parameters such as capacitance, roughness factor, area of electrode, kinetics of different probes were used to follow and validate structural changes at the CFE surface before and after electrochemical pretreatment.; An ultrathin film of overoxidized polypyrrole (OPPY) was used as another new strategy to increase the signal-to-noise ratio and the sensitivity of nanostructured carbon fiber electrode for UA determination. The film decreased the background current and enhanced sensitivity in fast scan voltammetry (FSV) because the electroactive area is large while the area that undergoes charging decreased. Electrochemical characterization of the film and the polymerization process were studied. Experimental results suggest that the electropolymerization. of pyrrole is a diffusion-controlled process.; One of the major problems of in vivo determinations of UA comes from electrochemical interferences such as ascorbic acid (AA). We present here the results of fast scan voltammetry (FSV) which show improved selectivity and sensitivity in UA determination in the presence of 100 fold excess of AA at a bare CFE. Signal-to-noise (S/N) ratios at bare nanostructured CFE in FSV are improved because high temporal resolution of the technique allows acquisition of a large number of scans that can be averaged in a short period of time.; Preliminary results in biological systems show that the nanostructured CFE can be applied in in vivo UA determinations. The pH effect in uric acid determinations at the bare nanostructured CFE was also evaluated. The nanostructured CFE and OPPy modified CFE were used for UA determination in 70 mM phosphate buffer (pH 7.4). The OPPy modified CFE increases the sensitivity and S/N ratios for UA determinations.; Other strategy used to increase the sensitivity in UA detection was the modification of CFE with phosphotungstic acid. Phosphotungstic acid modified electrodes enhance UA response due to catalysis of UA oxidation reaction.