Carrageenan-stabilized silver nanoparticle gel probe kit for colorimetric sensing of mercury (II) using digital image analysis

Hydrophilic gelling kit consisting of carrageenan-stabilized silver nanoparticles (AgNPs) is described herein as a selective probe for the colorimetric detection of Hg2+. Spherical AgNPs with surface plasmon resonance (SPR) at 430 nm and TEM size of less than 100 nm were synthesized using κ-carrageenan to give a dark brown gelling mixture (Carr-AgNP) that were used directly for colorimetric reaction with various metal ions. The reaction is selective only to Hg2+. The dark brown color of the Carr-AgNP was found to fade as the concentration of Hg2+ increases until the mixture turns white. It can detect Hg2+ at a concentration of ≥350 ppm with limits of detection at 2.92 × 10−4 M. Quantification of the color change was established using digital photometry with strong correlation observed for L*, R and G color parameters. The role of chlorides in the colorimetric sensing is critical to detecting Hg2+ as excess chlorides promote the formation of AgCl as well as the dissolution of AgNP. The utility of the gelling kit was successfully applied for the detection of mercury(II) in a cosmetic cream sample.