A Miniaturized Flexible Patch Based on CNT Fiber Sensors and Highly Integrated SoC for Analysis of Sweat

The existing wearable sweat monitoring systems still face drawbacks in poor breathability, high power consumption, and bulky size. Herein, a miniaturized flexible sweat analysis patch based on carbon nanotube (CNT) fiber sensors and highly integrated SoC for potassium ions (K+) and lactate monitoring is proposed. CNT fiber-based sensors are developed to ensure good breathability and flexibility. The customized SoC integrates signal processing, wireless power delivery, wireless communication, and power management onto a single chip, which enjoys a miniaturized dimension (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4\times 4$ </tex-math></inline-formula> mm), requires few off-the-chip components (one pull-down resistor and one decoupling capacitor), and has low power consumption (typically <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$33~\mu $ </tex-math></inline-formula>W in operational mode). The patch has a compact size of only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.4\times 1.2$ </tex-math></inline-formula> cm for the main body, accompanied by 3.4 cm2 for the antenna, which is designed as a hollow shape to further improve breathability. The patch achieves a lactate sensitivity of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.10~\mu $ </tex-math></inline-formula>A<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cdot $ </tex-math></inline-formula>mM<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-{1}}$ </tex-math></inline-formula> and a K+ sensitivity of 47.23 mV per decade. Successful human trials were conducted to monitor K+ and lactate concentrations in sweat during exercise. Overall, the proposed patch is breathable, power efficient, miniaturized, and thus suitable for long-term sweat monitoring applications.