Smartphone-based colorimetric sensing of cadmium in milk for food safety monitoring

This study presents a smartphone-based colorimetric imaging system combined with a paper-based sensor on a 3D-printed platform for the sensitive and selective detection of cadmium ions (Cd²⁺) in milk and water samples. The sensing probe utilizes sucrose-capped silver nanoparticles (AgNPs/sucrose), which exhibit a visible color change from yellow to reddish and a shift in localized surface plasmon resonance (LSPR) upon interaction with Cd²⁺. This was validated by UV-Vis, TEM, DLS, FTIR, and XPS analyses. Additionally, density functional theory (DFT) using Gaussian 16 confirmed coordination between Cd²⁺ and AgNPs. Quantification was achieved via smartphone-assisted RGB image analysis, correlating Cd²⁺ concentration with color intensity. The method showed a linear range of 0.05–3 µg/mL and detection limits of 0.02 µg/mL (imaging) and 0.03 µg/mL (paper-based assay). Non-carcinogenic and carcinogenic health risk assessments for milk samples were also performed. This eco-friendly, low-cost approach enables on-site food safety and environmental monitoring.