Heterocyclic thiol protected supramolecular self-assembly of silver nanoclusters for ultrasensitive detection of toxic Hg (II) ions in nanomolar range

Abstract

Supramolecular self-assembly of heterocyclic thiolate protected silver nanoclusters (AgNCs) formed via non-covalent binding interactions exhibits a unique physicochemical property. Herein we demonstrate a facile synthesis of 2-mercaptobenzothiazole (MBT) protected self-assembled AgNCs (SA-AgNCs) in acetone–water medium. The existence of hydrophobic and bridging type coordination interactions describes the direct formation of SA-AgNCs. The photo stability of as obtained SA-AgNCs at 630 nm with orange emission is attributed to the cumulative electron-hole hopping interactions of individual Agn(MBT)m clusters present in supramolecular network of SA-AgNCs. The synergetic effect of self-assembly induced emission (SAIE) and ligand–metal-metal charge transfer (LMMCT) interactions of SA-AgNCs leads to the enhancement of photoluminescence properties. The SA-AgNCs serves as a fluorescent turn-off probe for the ultrasensitive detection of toxic Hg(II) ions at nanomolar ranges of 3.5–100 nM via quenching dynamics resulting from the metallophilic affinity of Hg2+-Ag+ ions. The favourable mechanism for the quenching dynamics was validated from the spectroscopic studies, that reveals as the Hg2+ ions approaches SA-AgNCs network, the combined effect of Hg2+-Ag+ alloying property and the detachment of Agn(MBT)m staple motifs from core silver clusters decreases the luminescence proportionality. The real sample analysis for the detection of Hg2+ ions in tap water and lactating mother’s milk samples were found satisfactorily.