N-methyl isatin nanoparticles as a novel probe for selective detection of Cd2+ ion in aqueous medium based on chelation enhanced fluorescence and application to environmental sample

The fluorescent N-methyl isatin nanoparticles (N-MINPs) were prepared by a simple reprecipitation method. The prepared N-MINPs examined by dynamic light scattering (DLS) show narrower particle size distribution having an average particle size of 112 nm. The scanning electron microphotograph shows distinct spherical shaped morphology of nanoparticles. The UV-absorption and fluorescence spectra of aqueous suspension of N-MINPs are blue shifted from the corresponding spectra of N-methyl isatin solution in acetone. The blue shift indicates the H-aggregates and Aggregation Induced Enhanced Emission (AIEE) from nanoparticles. The nanoparticles have high stability without any stabilizer and functional keto moiety recognized Cd2+ ions selectively by enhancing the fluorescence preference to Ni2+, Cu2+, Hg2+, Sn2+, Pb2+, Ca2+, Zn2+, Na+, Co2+ and Mg2+ ions which actually seem to quench the fluorescence of nanoparticles. The studies on fluorescence lifetime of N-MINPs and its fluorescence titration with and without Cd2+ helped to propose a suitable mechanism of fluorescence enhancement of nanoparticles by Cd2+ and their binding ability during complexation. The fluorescence enhancement effect of N-MINPs induced by Cd2+ is further used to develop analytical method for detection of Cd2+ from aqueous medium in environmental samples based on chelation enhanced fluorescence approach. (C) 2015 Elsevier B.V. All rights reserved.