Anti-Freezing Janus Hydrogels for Non-Invasive Sweat Glucose and Motion Monitoring in Subzero Environments.

Wearable flexible sweat sensors offer a powerful platform for noninvasive health monitoring, yet their stable operation at low temperatures remains a critical challenge. Herein, we design an antifreezing, self-healing bilayer Janus hydrogel comprising a NiTPP/BSA/CFs/PA-PVA sensing layer and a Collagen-PVA self-healing layer. In the sensing layer, phytic acid (PA) converts free water into bound water via hydrogen bonding, lowering the freezing point to -21.4 °C. This enables the hydrogel to maintain high stretchability (623.4%) and strain sensitivity (GF = 1.11) even at -20 °C. Furthermore, bovine serum albumin (BSA)-modified carbon fibers loaded with nickel(II) tetraphenylporphyrin (NiTPP) provide robust electrocatalytic selectivity, achieving a low detection limit of 0.68 μM for sweat glucose. The adjacent Collagen-PVA layer exploits dynamic hydrogen bonds and physical entanglements to endow the hydrogel with an 87.5% self-healing efficiency and excellent skin affinity. United by stable physical cross-linking at the interface, this Janus architecture integrates antifreezing, self-healing, and multimodal sensing capabilities, offering a promising strategy for robust wearable biosensing in extremely cold environments.