Laser-Processed All-Paper-Based Wearable and Biodegradable Electrochemical Sensor for Continuous Sweat pH Detection

Flexible and wearable electronics have attracted widespread attention in human healthcare and medical applications owing to their inherent flexibility, skin conformability, and continuous real-time operating capabilities. However, conventional petroleum-based polymer wearable electronics lack environmental sustainability as their disposal generates hazardous e-waste with significant ecological impacts. Herein, we fabricated a biodegradable and wearable electrochemical sensor with typical cellulose-based paper for continuous monitoring of sweat pH. The paper was hydrophobically modified, and etched by CO2 laser, then layer–layer assembled to integrate an all-paper-based electrochemical (APEC) sensor. The APEC sensor consists a paper-based pH sensor and a microfluidic patch for sweat sampling. We constructed MXene-supported polyaniline:poly(styrenesulfonate) (PANI:PSS) nanoparticles for detecting H+, which are water-soluble because of the introduction of PSS, rendering them compatible for fabricating paper-based sensors. The APEC sensors demonstrate biodegradability in both aqueous and soil media. Their waterproof characteristics enable reliable operation during in situ sweat sampling and real-time sweat analysis. These sensors exhibit an ultrawide linear pH detection range (pH 1.53–13.46) with excellent reversibility and high sensitivity (46.01 mV pH–1). On-body measurements demonstrated that the APEC sensors can continuously detect the pH of human sweat and have the potential to detect muscle fatigue. The fabrication and demonstration of the APEC sensors is expected to facilitate the development of flexible and wearable electronics and contribute to a sustainable electronics future.