Multipurpose biosensing electronics enabled by ultrasoft and durable hydrogel via ions pre-incorporation

Abstract

Fast-growing flexible electronics bring technological innovation to all industries, including personal health management, clinical diagnosis, and smart agriculture. However, conventional synthesis strategy fails to reconcile the divergent mechanical property demands for monitoring disparate targets (such as humans and plants), impeding the development of a universal strain sensor. In this work, a universal ions pre-incorporation strategy is first proposed to develop ultrasoft and durable ionic hydrogels for multipurpose biosensing. Through iron-mediated Fenton-like reactions and Cl⁻-dominated radical scavenging effects, the glycerin-doped PAAM/PVA hydrogel pre-incorporated with Fe ions (GPPFe) exhibits ultrasoft mechanical properties (Young’s modulus = 41.7 kPa, 84.8% softer than post-incorporated samples), effectively avoiding the excessive stiffness of ionic hydrogels prepared by the conventional ions post-incorporation strategy, which can be well applied for the monitoring of plant growth considering its good conformal contact with the plant surface and less pressure on the plant tissues. The reversible and sacrificial bonds formed between Fe³⁺ and polymers ensure excellent mechanical stability of the GPPFe hydrogel (1.12% permanent deformation after successive loading–unloading 50 cycles test at a tensile strain of 150%, 94.7% lower than post-incorporation strategy), thus ensuring its utilization as a comfortable and durable human wearable strain sensor. Additionally, this strategy can be extended to design various types of synthetic hydrogels, providing an innovative approach for designing the multipurpose wearable electronic devices oriented to various target objects.