Wearable optical patches for non-invasive sweat sensing

As a non-invasive and information-rich diagnostic biofluid, sweat offers a promising alternative to conventional blood analysis, circumventing issues of invasiveness, patient discomfort, and complex laboratory processing. Wearable optical patches for non-invasive sweat sensing are emerging as a transformative platform in personalized and preventive healthcare, enabling real-time, continuous monitoring of metabolic and electrolyte biomarkers. This review comprehensively summarizes recent advances in wearable flexible optical sweat sensors, focusing on the following primary optical mechanisms: colorimetry, surface-enhanced Raman scattering (SERS), fluorescence, electrochemiluminescence (ECL) and other optical approaches. First, we discuss the integration of these sensing modalities with soft, stretchable substrates, such as hydrogels, textiles, paper, and polymer films, and highlight key innovations in sweat collection, fabrication techniques, adhesion, and encapsulation that enable robust wearable operation. Second, we examine performance metrics, current challenges, and future perspectives for translating these technologies from laboratory prototypes to clinical and commercial applications. Finally, the challenges and future perspectives of the next-generation wearable optical platforms for continuous sweat analysis and personalized health monitoring are discussed.