Dual functionalized Ag plasmonic sensor for colorimetric detection of Cr (III)/Hg(II)-carboxyl complexes: Mechanism and its sensing based on the interference of organic ligand

Heavy metal-organic complexes are prevalent in contaminated waters but decontamination of these complexes is far more challenging than free ions. The existing analytical methods cannot determine these complexes which greatly affects the development of decontamination mechanisms for metal-organic complexes. A highly sensitive and selective colorimetric sensor of Cr3+/Hg2+-organic complexes is developed. In this study, tween-80 and citrate functionalized zero-valent silver nanoparticles (Ag NPs) for the detection of metal-organic complexes is reported. On the addition of Cr-organic complexes (Cr-EDTA, Cr-tartrate, Cr-citrate, Cr-acetate, Hg-EDTA, Hg -tartrate, Hg-citrate, and Hg-acetate), Cr3+ ions coordinate with citrate causing the aggregation of Ag NPs (excluding Cr-citrate complex), and on Hg-organic complexes addition, Hg2+ ions are bound to Ag ions and form Ag-Hg amalgam. The changes in absorbance were due to the conformational changes and coordination of Cr(III) ions. In the case of Hg-Ag amalgam formation, coordination changes occur in carboxylate compounds. The interference of organic ligands in the detection mechanism was explained. Different optimization studies were carried out at different pH, temperature, and interference. The nanosensor is highly sensitive with nanomolar scale detection. The study will greatly forward the application of instant colorimetric detection of heavy metals in any form that may exist in the environment.

Automated summary

Heavy metal-organic complexes are widespread in contaminated waters and pose a greater challenge for decontamination compared to free ions. Current analytical methods are unable to determine these complexes, impeding the development of decontamination mechanisms. A highly sensitive and selective colorimetric sensor for detecting Cr3+/Hg2+-organic complexes using citrate functionalized silver nanoparticles (Ag NPs) has been developed. The sensor exhibits nanomolar scale detection and its application could greatly advance the instant colorimetric detection of heavy metals in the environment.