  Epidermal skin sensors have emerged as a promising approach for continuous
and noninvasive monitoring of vital health signals, but to maximize their
performance, these sensors must integrate seamlessly with the skin, minimizing
impedance while maintaining the skin's natural protective and regulatory
functions.In this study, we introduce an imperceptible sweat sensor that
achieves this seamless skin integration through interpenetrating networks
formed by a porous, ultra-thin, ultra-high molecular weight polyethylene
(UHMWPE) nanomembrane. Upon attachment to the skin by van der Waals force, the
amphiphilic sweat extrudates infuse into the interconnected nanopores inside
the hydrophobic UHWMPE nanomembrane, forming "pseudo skin" nanochannels for
continuous sweat perspiration. This integration is further enhanced by the
osmotic pressure generated during water evaporation. Leveraging the efficient
transport of biomarkers through the "skin" channels within the porous membrane,
we developed an organic electrochemical transducer (OECT) cortisol sensor via
in-situ synthesis of a molecularly imprinted polymer (MIP) and poly(3,4
ethylenedioxythiophene) (PEDOT) within the nanomembrane. This demonstrates the
capability to detect cortisol concentrations from 0.05 to 0.5 {\mu}M for
seamless monitoring of stress levels. This work represents a significant
advancement in self-adhesive sweat sensors that offer imperceptible and
real-time non-invasive health monitoring capabilities.
