Development of paper-based detection methods for aqueous Cr(III) utilizing label-free plasmonic AgNPs

This study presents a paper-based plasmonic detection mechanism that relies on a distinct colorimetric change in silver nanoparticles (AgNPs), triggered by aggregation-induced plasmonic shifts. Spherical AgNPs are synthesized using the stem bark extract of Ceriops decandra (C. decandra), which serves as both a reducing and capping agent. The extract's strong reducing properties and high affinity for Ag(I) ions enable the formation of a highly selective Cr(III) sensor. The aggregation-based sensing mechanism and its sensitivity and selectivity have been systematically validated using UV-Vis spectroscopy, SERS, FESEM, TEM, and DLS analyses. The optimized sensor exhibits a linear response to Cr(III) concentrations from 0.1 to 20 nM, achieving a detection limit of 0.1 nM with a regression coefficient (R²) of 0.9832. Kinetic and thermodynamic studies further elucidate the sensor's performance and specificity. Overall, this label-free plasmonic sensing method provides a reliable, portable, and efficient solution for on-site detection of Cr(III) in real-world aquatic samples.