(153d) Detection of Pyocyanin and Methylene Blue Using Electrochemical Impedance Spectroscopy (EIS) with Electrodeposited Nickel-Iron-Carbon Composite Electrodes

The detection of pyocyanin (PYO), a metabolite of Pseudomonas aeruginosa, a gram-negative bacterium, is of interest due to its association with disease responsible for chronic infection in people with cystic fibrosis and in burn patients. Methylene blue (MB) can serve as a comparable model for PYO due to similar structure and redox potential. Methylene blue is a dye and because it is a pollutant its detection is also of interest in its own right. Both PYO and MB can be detected at redox potentials under diffusion control by conventional voltammetry, where the generated current is directly proportional to concentration. In contrast to reactions controlled by diffusion, the capacitance can also be used at the electrode-electrolyte interface to avoid the diffusion limit at low concentration. Electrochemical impedance spectroscopy (EIS) can capture the different behavior. EIS was used in a three-electrode cell configuration in a phosphate buffer solution (PBS) containing various concentrations of MB and/or PYO. Electrodeposited nickel-iron nanoclusters onto a glassy carbon electrode was fabricated to enhance charge transfer while at the same time permitting adsorption of the organic molecules to a glassy carbon surface. The Ni–Fe nanoclusters were prepared from a sulfate-boric acid electrolyte by a pulse galvanostatic method. Linear EIS equivalent circuit models were used to characterize the signal over a wide frequency range at different steady state potentials. The models included constant phase elements (CPE) that were used to determine an average, effective capacitance of the interface, resistances to represent charge transfer, and a Warburg diffusion impedance. The capacitance component of the equivalent circuits resulted in a larger signal as the analyte concentration decreased, in contrast to conventional voltammetry techniques under a diffusion control, enabling a much lower detection limit, below 1 mM. The controlling phenomena that altered the electrode-electrolyte capacitance was attributed to adsorption.