Tyndall-Effect-inspired assay with gold nanoparticles for the colorimetric discrimination and quantification of mercury ions and glutathione.

This work initially reports a new nanosening method for simple, sensitive, specific, visual detection of mercury (II) (Hg) and glutathione (GSH) using the Tyndall Effect (TE) of the same colloidal gold nanoparticle (GNP) probes for efficient colorimetric signaling amplification. For the TE-inspired assay (TEA) method, arginine (Arg) molecules are pre-modified on the GNPs' surfaces (Arg-GNPs). Upon the Hg introduction, it can be specifically coordinated with the terminal -NH and -COOH groups of the Arg molecules to make the Arg-GNPs aggregate, producing a significantly-enhanced TE signal in the reaction solution after its irradiation by a 635-nm red laser pointer pen. On the other hand, the introduction of the GSH results in the production of the original Arg-GNPs' weak TE response, as it is able to bind such metal ion via mercury-thiol reactions to inhibit the above aggregation. Under the optimal conditions, the utility of the new TEA method is well demonstrated to quantitatively detect the Hg and GSH with the aid of a smartphone as a portable TE reader during the linear concentration ranges of 50-3000 and 10-3000 nM, respectively. The detection limits for the Hg and GSH are estimated to be as low as ∼3.5 and ∼0.3 nM, respectively. The recovery results obtained from the detection of Hg in the complex tap and pond water samples and the assay of GSH in real human serum and urine samples are also satisfactory.