A portable platform integrated with smartphones for rapid lactic acid analysis via ratiometric fluorescent imaging

This study presents a smartphone-integrated portable platform for rapid lactic acid (LA) analysis using ratiometric fluorescent imaging. The system employs a dual-emission probe composed of glutathione-modified gold nanoclusters (GSH-AuNCs) and carbon quantum dots (CDs), enabling visual detection via fluorescence color transitions under 365 nm UV excitation. As LA concentration increases, the fluorescence shifts from blue to orange. Smartphone photography and RGB color analysis reveal a nonlinear sigmoidal correlation between the red-to-blue intensity ratio (R/B) and LA concentration, modeled with a coefficient of determination (R² = 0.998). The method exhibits high selectivity and achieves recovery rates of 94.5-104.8 % in sweat samples, validated against LC-MS. This technology offers a novel, on-site solution for food quality assessment and health monitoring applications.