Durable silk fiber-based colorimetric sensor via laccase-catalyzed grafting of butterfly pea anthocyanins: Performance, characterization, and theoretical mechanism

Monitoring the pH of human body fluids is crucial for health assessment. This study develops a durable, textile-based colorimetric sensor via laccase-catalyzed covalent grafting of edible butterfly pea anthocyanins onto silk fabric. The functionalized silk exhibits distinct, reversible color transitions across a broad pH range (2−12), enabling direct visual discrimination of simulated human sweat (purple at pH 4.5, blue at 6.0, turquoise at 8.0), urine (blue at pH 6.0), and vaginal secretions (purple at pH 4.5). The sensor demonstrates robust durability, with good wash and abrasion fastness (grade 4) and stable performance over 10 reuse cycles (all ΔE < 2). It also exhibits significant antioxidant activity (DPPH scavenging rate ~ 73%). A comprehensive multi-stage DFT investigation provides a fundamental molecular-level explanation for the sensor's function and stability. The calculations identify the key acidic site (δ-OH) with a pKa of 4.96, responsible for the primary purple-to-blue transition, and reveal a high kinetic barrier (~28 kcal/mol) for the competing color-fading pathway, rationalizing the observed durability and irreversible degradation under strong alkali. This work presents a complete “fabrication-to-mechanism” study, integrating a high-performance wearable sensor with fundamental theoretical validation for potential applications in personal health monitoring and smart textiles.