Electrochemical detection in paper-based analytical devices using microwire electrodes

Microwire electrodes are presented as an alternative to screen-printed electrodes for detection in electrochemical paper-based analytical devices (ePADs). Compared to carbon ink electrodes, microwire electrodes offer lower resistance and a significant increase in current density relative to carbon ink electrodes. Various microwire compositions and diameters, including 30 μm Pt, 25 μm Au, 18 μm Pt with 8% W, and 15 μm Pt with 20% Ir, were tested and compared to theoretically predicted behavior. The measured current in static solution was below predicted levels for cylindrical microelectrodes but greater than levels predicted for hemi-cylindrical electrodes most likely as a result of the proximity of the electrode to the paper surface. Furthermore, the current response was indicative of semi-thin layer behavior, likely due to the confined solution volume in the paper. After electrode characterization, a device was developed for the non-enzymatic detection of glucose, fructose, and sucrose using a Cu electrode in alkaline solution. The limits of detection for glucose, fructose, and sucrose were 270 nM, 340 nM, and 430 nM, respectively, which are significantly below sugar concentrations found in sweetened beverages or glucose levels in serum.