Abstract

The signal quality of a sensing device is largely determined at the interface between the device and its target, a region typically less than a few hundred nm thick. In wearable electrophysiology, this interface must maintain contact with skin that deforms and perspires, whereas in trace-level chemical sensing it must discriminate analytes with few reactive functional groups. In both cases, the thickness and surface chemistry of the interface are usually dictated by the choice of material. This reserach presents two nanoscale interface platforms in which both parameters are defined at the design stage.

The first platform is an ultrathin skin-conformal nano-electrode composed of Ti₃C₂T_x MXene (50 nm), poly-L-lysine, and parylene (≈300 nm), with the parylene thickness determined from a work-of-adhesion analysis of contact with skin texture. The hydrophilic MXene side and hydrophobic parylene side allow the film to be transferred onto skin by water-assisted capillary flow and to remain attached without gel or adhesive. Compared with commercial gel electrodes, the nano-electrode showed approximately 35% lower skin interfacial impedance and up to threefold higher signal-to-noise ratio in ECG and EMG. ECG was recorded in a sauna and a swimming pool, where gel electrodes detached within minutes, and stable recording was maintained over 30 h of continuous wear.