An integrated, portable sensing platform made with surface-immobilized fluorophore-appended silver nanotriangles for bimodal detection of mercury(II) ions

A novel, yet simple and portable, sensing platform has been developed by using silver nanotriangles immobilized on a glass substrate and capped with an optical marker, which, just by dipping in an analyte solution in presence of iodide, can detect mercury (Hg²⁺) ions by both colorimetric and fluorometric detection modes. This method, which is highly selective for the Hg²⁺ ions, relies on the superior binding affinity of the Hg²⁺ with the thiolated ligand, whereby the ligands were extracted from the nanotriangle surfaces exposing them to etching by iodides present in solution. The resulting change in morphology of the surface-bound nanotriangles was manifested in terms of the optical responses by nanoparticles, leading to the colorimetric detection of the analyte in the nanomolar level. The ligands released in solution due to abstraction by Hg²⁺ allowed fluorometric detection due to the change in emission spectra of these free ligands, offering a unique bimodal sensing of the analyte. A comparison of the substrate-based sensing protocol with conventional solution-based study gave a better insight into the sensing event, helped in optimizing the sensing conditions and emphasized the diverse application potential of the current surface-immobilized sensing system. Our developed sensory platform not only offers easy portability and a bimodal sensing detection, it also the demonstrates an unprecedented wide-range of detection (0.1–10 μM) of Hg²⁺ ions while maintaining high sensitivity and selectivity for the analyte.