Simple microfluidic device for spectroelectrochemistry

Abstract

The design, fabrication, and performance of a simple microfluidic device permitting spectroelectrochemical measurements on submicroliter samples are described. Planar electrode chips were prepared from cast epoxy and assembled to yield a device with a single flow channel of approximate dimensions 25 mm × 1.3 mm × 0.2 mm. Spectral measurements were made by passing the light beam parallel to the 1.3-mm channel dimension, resulting in a relatively high optical sensitivity. Bare disk electrodes embedded in opposing channel walls permit spectroelectrochemical measurements on sample volumes as low as approximately 3 µL, corresponding to a solution plug just long enough to contact all three electrodes. Adding a solution-cast ionomeric film to the channel wall containing reference and auxiliary electrodes provided an effective salt bridge to significantly smaller sample volumes in contact with a bare working electrode on the opposite channel wall. As demonstration of submicroliter sample analysis, spectroelectrochemical measurements were carried out on a ∼ 0.3 µL aqueous ferricyanide solution and showed near exhaustive electrolysis of the optically sampled volume is achieved in approximately 3 min.