Resettable sweat-powered wearable electrochromic biosensor

Wearable biofuel cells (BFCs) are being widely studied as self-powered sensors to monitor one's physiological status non-invasively. However, the energy generated by such devices is often insufficient to power accompanying measurement read-out systems and communication protocols. Here, we report a reversible fully printed electrochromic self-powered sensor (ESPS) toward on-body sweat lactate monitoring. The device was realized by integrating a lactate-oxidizable BFC anode, oxygen-reducible BFC cathode, and a reversible Prussian blue (PB) electrochromic display on a single wearable patch. Through modification of the BFC electrodes, the formal potential of the PB display (0.14 V) could be positioned in between the potentials of the lactate oxidation (-0.05 V) and oxygen reduction (0.35 V). Based on this system, the ESPS enables reversible and robust color changes with distinct time- and concentration-dependent profiles. The results demonstrate that the self-powered device has practical on-body applications for continual lactate monitoring with several advantages, including facile reversibility, ease of fabrication, and naked-eye colorimetric read-out.