Silver Nanowire-Based Stretchable Transparent Electrodes for Precise Biosignal Sensing from Small Skin Areas

Large-area stretchable transparent electrodes (STEs) are essential in wearable biosignal sensors to achieve high signal-to-noise ratios (SNRs), primarily due to the low electrical conductivity of traditional stretchable materials. Silver nanowires (AgNWs) offer excellent conductivity and transparency; however, their poor mechanical compliance restricts their use in stretchable electronics. To overcome this challenge, we developed an STE by creating a grid-like AgNW network using a bar-coating method. This structured arrangement improves the connectivity of electrical pathways while maintaining high optical transmittance, resulting in a superior Haacke figure of merit of 23.3 × 10^-3 Ω^-1, which surpasses that of the traditional isotropic AgNW networks. The AgNW grid was embedded in a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) matrix and transferred onto a thermoplastic polyurethane substrate, yielding an STE with exceptional optoelectronic and mechanical performance. The resulting electrode demonstrated a low sheet resistance of ∼25 Ω sq^-1, ∼85% transmittance at 550 nm, minimal resistance change under 50% strain, and excellent durability over 500 stretch-release cycles. Notably, the STE enabled reliable acquisition of electrocardiogram, electromyogram, and electroencephalogram signals with a high SNR, even from areas smaller than 1 cm². Moreover, this work provides a scalable approach for engineering high-performance AgNW-based stretchable electrodes, enhancing their potential in next-generation wearable health monitoring technologies.