Ultrasensitive Electroanalysis: Femtomolar Determination of Lead, Cobalt, and Nickel

We demonstrate the feasibility of attaining femtomolar limits of quantitation in electroanalysis. The method employed is based on electrocatalytic amplification, where small quantities of metal deposit performed on a carbon electrode causes a large increase in the observed current, for example, for the oxidation of water. We show calibration curves at the femtomolar level for cobalt, nickel, and lead ions on carbon ultramicroelectrodes (CUMEs), ca. 500 nm radii. The CUME was biased at a potential where the ion would deposit as the metal oxide, MOx, and a high concentration of species that is oxidized at the deposit is present in solution. Blips were observed in the amperometric i-t response, and their frequency scaled linearly with the concentration of ions at the femtomolar level. From these results, the limits of quantitation for cobalt, nickel, and lead ions were reported at 10 s of femtomolar level for the first time.