Oxacalix[4]arene templated silver nanoparticles as dual readout sensor: Developing portable kit for rapid detection of methylmercury and its speciation

Abstract

Simultaneous detection, speciation and removal of mercury from contaminated water is a dire necessity in recent times. In this direction, a novel oxacalix[4]arene derivative viz. Di-acetamido-oxacalix[4]arene (DAOC) was synthesized for stabilization of silver nanoparticle (DAOC-AgNPs). To induce fluorescence activity, the surface of DAOC-AgNPs was modified with Rhodamine B (RhB) yielding RhB@DAOC-AgNPs. Both DAOC-AgNPs and RhB@DAOC-AgNPs were found to be highly selective and sensitive chromogenic sensor towards methylmercury (CH3Hg+) with a limit of detection (LOD) of 1.7 nM and 7 nM respectively. The mechanistic study discloses that the color change is due to mercury-induced oxidation of DAOC-AgNPs, ultimately leading to the formation of Ag-Hg nanoalloy. Cysteine, a semi-essential amino acid, was also selectively detected with the aid of DAOC-AgNPs and methylmercury. Considering the masking effect of ethylenediaminetetraacetic acid (EDTA), a multilevel INHIBIT-OR logic gate assembly was designed to discriminate organic and inorganic mercury (Hg2+) ions. Moreover, three types of portable sensors (cellulose fiber strip, ZIF-8 based nanocomposite, hybrid alginate bead) were fabricated and successfully tested for the on-spot detection of mercury in contaminated water. Simultaneously, in-vivo detection of methylmercury using RhB@DAOC-AgNPs was done in brine shrimp showcasing replicable activity in the living system as well.