Voltammetric detection of ofloxacin in human urine at a Congo red functionalized water-soluble carbon nanotube film electrode

A simple physical method was developed for the surface modification and the solubilization of MWNTs in water by Congo red. The resulting water-soluble MWNTs (MWNTs-CR) can form stable and uniform films on solid supports when dried, which was used to fabricate MWNTs-CR modified glassy carbon electrodes (MWNTs-CR/GCE). Voltammetric studies showed that MWNTs-CR/GCE exhibited a strong enhancement effect on the electrooxidation of ofloxacin. MWNTs-CR films were also proved to possess overwhelming advantages as electrochemical sensing films over other commonly used MWNTs composite films (e.g., MWNTs-DHP and MWNTs-Nafion), reflected by the higher oxidation current, lower background and stronger accumulation capacity towards less soluble species. The sensitive oxidation of ofloxacin at MWNTs-CR/GCE was used for the determination of ofloxacin. Under optimal conditions, the oxidation current was proportional to ofloxacin concentration in the ranges of 5 x 10(-8)-3.0 x 10(-5) M. The detection limit of 9 x 10(-9) M was obtained for 350 s accumulation at open circuit (S/N= 3). This method was applied to the determination of ofloxacin in human urine and the result was satisfying.