A new Eosin Y-based 'turnon' fluorescent sensor for ratiometric sensing of toxic mercury ion (Hg2+) offering unaided eye detection and its antibacterial activity.

A unique fluorescent molecule (ND-S) was obtained from Eosin Y in two simple yet high yielding steps (1). ND-S has special metal ion sensing ability, such that it can selectively detect toxic Hg2+ present in very low concentration in aqueous solutions in the presence of other competing metal ions. The host-guest complexation is ratiometric and is associated with significant increase in fluorescence during the process. Isothermal titration calorimetry (ITC) experiments provided thermodynamic parameters related to interaction between ND-S and Hg2+. Using inductively coupled plasma mass spectrometry (ICP-MS), the Hg2+(aq) removal efficiency of ND-S was estimated to be 99.88%. Appreciable limit of detection (LOD = 7.4 nM) was observed. Other competing ions did not interfere with the sensing of Hg2+ by ND-S. The effects of external stimuli (temperature and pH) were studied. Besides, the complex (ND-M), formed by 1:1 coordination of ND-S and Hg2+ was found to be effective against the survival of Gram-positive bacteria (S. aureus and B. subtilis) with a high selectivity index. Moreover, bacterial cell death mechanism was studied systematically. Overall, we have shown the transformation of a toxic species (Hg2+), extracted from polluted water by a biocompatible sensor (ND-S), into an effective and potent antibacterial agent (ND-M).

Rationally Designed Ionic Covalent Organic Networks (iCONs) with Efficient Antimicrobial Activities.

Two unique ionic covalent organic networks (iCONs) incorporated with guanidinium motifs were obtained and characterized by various techniques. Upon 8 h of treatment with iCON-HCCP (250 µg/mL), >97% killing of Staphylococcus aureus, Candida albicans, and Candida glabrata strains was observed. Antimicrobial efficacies against bacteria and fungi were also evident from FE-SEM studies. High antifungal efficacies also correlated well with >60% reduction of ergosterol content, high lipid peroxidation, and membrane damage leading to necrosis.