Hybrid Organic-Inorganic Sol-Gel-Based Textile Finishing for Real-Time Sweat pH Monitoring in Wearable Health Systems

Flexible wearable sweat sensors are advancing health monitoring by enabling continuous, non-invasive analysis of biomarkers. Advances in chemistry, materials science, and electronics have enabled the development of skinconformal devices with significant potential in diagnostics, athletic performance, and personalized care. Cellulosic textiles are optimal substrates due to their softness, breathability, and compatibility with functional coatings. This study reports the development of a durable, pH-responsive smart textile obtained by covalently grafting a halochromic dye onto cotton through sol-gel chemistry. Litmus, a naturally derived, non-toxic halochromic dye, was chemically functionalized via epoxy ring-opening of 3-glycidoxypropyltrimethoxysilane to produce a hybrid silane-dye molecule. The functionalized dye was placed onto cotton using a paddry-cure sol-gel process optimized for coating stability and laundering durability. Morphological and spectroscopic analyses implied uniform deposition and chemical integrity. FTIR and UV-vis spectroscopy verified the formation of siloxane linkages and the retention of the dye’s pH responsiveness within the physiological range (pH 4–8). SEM imaging revealed a continuous xerogel layer, indicating robust chemical anchoring. Colorimetric measurements demonstrated a pronounced and reversible chromatic transition, with ΔE values exceeding 20 units between acidic and slightly basic condition. The obtained coating maintained its pH responsiveness after a one washing cycle and demonstrated high repeatability, with colour deviation of less than 5% across five pH cycles. These findings highlight the potential of this halochromic textile platform for reliable, reusable, and wearable sensing applications.