  We demonstrate a flexible sensor for ascorbic acid detection in sweat based
on single-step modified gold microelectrodes. The modification consists on the
electrodeposition of alginate membrane with trapped CuO nanoparticles on top of
the electrodes. The electrodes are fabricated at a thin polyimide support and
the soft nature of the membrane can withstand mechanical stress far beyond the
requirements for skin monitoring. We further show the efficient detection of
ascorbic acid at the micromolar levels in both, a neutral buffer and acidic
artificial sweat, at ultra-low applied potential (-5 mV). The effect of
possible interfering species present in sweat is minimized, with no observable
cross-reaction, thus maintaining a high degree of selectivity despite absence
of enzymes in the fabrication scheme. This sensor is envisioned as a promising
component of a wearable device for e.g. non-invasive monitoring of
micronutrient loss through sweat.
