In this work we have fabricated sensors using both commercial gold disc electrodes and custom, e-beam deposited, thin-film gold electrodes, both of which have advantages and disadvantages. Disc electrodes can be conveniently built using commercially available tools. Thin-film electrodes, in contrast, require more specialized tools to create but they enable the placement of the entire 3-electrode reference/counter/working system on a single, small chip. A second concern is that, even when the geometric surface area of the two is identical (3.14 mm 2 ) the peak currents associated with the thin-film electrodes are less than half those of the disk electrodes when they are free in solution (figure ). We believe this arises due to differences in the surface microstructure of the two electrode types. Disc electrodes, being reusable, are mechanically polished as part of preparation, which increases their roughness and thus their microscopic surface area. Consistent with this, cyclic voltammetry of the gold oxidation peak indicates that the electrochemically active surface area of disc electrodes is 49.5±0.3% larger than that of thin-film electrode of the same macroscopic dimensions (SI figure ). Unfortunately, our attempts to increase the microscopic surface area of the thinfilm electrodes via, for example mechanical polishing and electrochemical roughening , lead to poor reproducibility and increased sensor degradation (data not shown). The peak currents of both disk and thin-film electrodes become poorer when these are integrated into microneedle devices. Specifically, the peak currents of sensors fabricated on disc electrodes decreased by 30% to 40% and those fabricated on thin-film electrodes by 66% to 78% when these were integrated into microneedle devices. This may arise because the placement of electrodes in our microneedle devices limits the cross section of the solution available to pass current, which, which, when combined with the microneedle's acting as a capacitor, creates an RC circuit charging current. The stored charge in such a circuit cannot be measured, leading to lower current measurements.