Functionalized Au@Ag nanorod-embedded triple-network hydrogel for wearable SERS analysis of azelaic acid, H2O2 and pH in sweat

Functionalized Au@Ag NRs were immobilized in a triple-network hydrogel for wearable SERS sweat sensing. • Three reporter-functionalized hydrogel channels enabled ratiometric SERS detection of azelaic acid, H 2 O 2 , and pH. • The ATPPZn hydrogel showed good signal uniformity, reproducibility, 100-day storage stability, and skin-contact adaptability. • Sensitive detection of azelaic acid and H 2 O 2 was achieved with detection limits of 7.8 × 10 −13  M and 66.1 μM, respectively. • Real sweat analysis confirmed the feasibility of the platform for monitoring skin-inflammation-related molecular changes. Skin inflammation is commonly accompanied by oxidative stress and changes in the local acid–base microenvironment, whereas molecular indicators reflecting inflammation-associated metabolic changes remain less explored in wearable sensing. Azelaic acid, a dicarboxylic acid associated with inflammatory skin conditions, represents a potential small-molecule target, yet its non-invasive analysis in sweat remains challenging. Herein, a wearable-compatible ratiometric surface-enhanced Raman scattering (SERS) platform was constructed by embedding functionalized Au@Ag nanorods into a TEMPO-oxidized cellulose nanofibers (TOCNF)/poly(vinyl alcohol) (PVA)/poly(acrylamide-co-acrylic acid) [P(AM-co-AA)]-Zn 2+ triple-network hydrogel. The hydrogel architecture promoted nanoprobe dispersion and immobilization while maintaining flexibility and signal stability, yielding a spatial SERS relative standard deviation (RSD) of 5.19% and 77% signal retention after 100 days. Using Au@4-ATP@Ag nanorods (NRs) containing 4-ATP as a Raman-responsive reporter, azelaic acid was quantified through the ratiometric I 1194 /I 1073 response over 1 × 10 −12 –1 × 10 −7  M, with a detection limit of 7.8 × 10 −13  M, and its analytical feasibility in sweat was further evaluated by spike-recovery analysis. To provide complementary information on inflammation-related microenvironmental changes, the same hydrogel architecture was further adapted for H 2 O 2 and pH sensing using Au@4-MPBA@Ag and Au@4-MBA@Ag NRs, respectively. The H 2 O 2 channel exhibited a concentration-dependent response over 1-500 μM, while the pH response agreed well with pH-meter measurements, with deviations within 0.07 pH units. These results demonstrate the analytical feasibility of azelaic acid as an underexplored inflammation-related sweat target and highlight the potential of the triple-network SERS hydrogel for integrating molecular and microenvironmental information in skin-related sweat analysis. Download: Download high-res image (313KB) Download: Download full-size image