Simultaneous Detection of Two Analytes Using a Spectroelectrochemical Sensor

Spectroelectrochemical sensors developed in our group achieve three modes of selectivity by combining electrochemistry, spectroscopy, and a chemically selective membrane in a single device. Analyte detection is based upon a change in the optical response due to the conversion of the analyte between two oxidation states that results from the cycling or stepping of the applied potential. We have demonstrated a novel approach to simultaneously detect two metals by combining optical stripping voltammetry for one metal (Pb2+) and the in situ ligand complexation in a film for the other metal (Fe2+). Using an indium tin oxide (ITO) sensor platform with a 50 nm Nafion film to preconcentrate the analytes, equimolar mixtures of Pb2+ and Fe2+ in 0.1 M sodium acetate buffer (pH 5) were detected. Pb2+ was detected by optical stripping voltammetry, in which lead was deposited as metal on the ITO and detected by the optical change as it was removed by stripping. The ferrous ion was detected by the in situ ligand complexation method in which Fe2+ was complexed with 2,2'-bipyridyl in the Nafion in the film to form ail intense red complex that was detected by absorbance at 520 nm. Detection limits of 300 and 400 nM were obtained for Pb2+ and Fe2+, respectively. The presence of the film had no effect on the optical signal that results from the deposition and stripping of the Pb2+. In addition, competition between the Pb2+ and Fe2+ for sites in the film and for the organic ligand was investigated.