(680d) Integrated Palladium Reference Microelectrode for Use in Electrochemical Detection of Bacterial Toxins

The miniaturization and integration of components for electrochemical detection in micro- and nano-fluidic devices is of great interest as it directly yields an electrical signal that provides information about the chemical composition of a sample. We have developed a device that integrates a palladium and a gold electrode inside of a nanoscale constriction for use as an electrochemical sensor. We first tested the stability of the palladium pseudo-reference electrode and compared its performance against a commercially available external silver/silver chloride reference electrode, using the gold as a working electrode.

Palladium is capable of absorbing hydrogen up to several hundred times its volume.  It functions in a similar fashion to the standard hydrogen reference electrode in that the potential is set by the hydrogen ion concentration versus the amount of absorbed hydrogen molecules. The potential remains constant as the amount of absorbed hydrogen changes over a wide range of values. The potential is affected by the concentration of protons, but for a buffered solution, this also does not change significantly, making it very useful in biological experiments.

We used the device to measure pyocyanin production by Pseudomonas aeruginosa in growth media. The oxidation potential of pyocyanin was measured to be approximately -0.5 volts against the miniaturized palladium reference. By utilizing square wave voltammetry, the concentration of pyocyanin was selectively measured in a complex solution.