A novel isatin-based probe for ratiometric and selective detection of Hg2+ and Cu2+ ions present in aqueous and environmental samples.

Abstract

A novel isatin derivative (1) is UV-Visible active and displays about 90 nm bathochromic shift upon interaction with only Hg2+ and Cu2+, but not with other common metal ions. Also, the colorless probe 1 turns to brick-red and yellow in the presence of Hg2+ and Cu2+, respectively. Addition of increasing amounts of Hg2+ or Cu2+ to 1 leads to the emergence of a new absorption at ~470 nm (due to LMCT), with a concomitant decrease in the intensity of absorption of 1 at ~380 nm, and thereby provides a ratiometric response. Common metal ions and anions do not interfere with the interactions of 1 with Hg2+or Cu2+ ions. Probe 1 shows very high sensitivity and selectivity towards Hg2+ and Cu2+ as revealed by their very low detection limits 0.95 × 10-9 M and 1.5 × 10-9 M, respectively. Formation of 1:1 complex with Hg2+ and 2:1 complex with Cu2+ is confirmed using NMR, ESI-MS and FT-IR techniques, Job plot and DFT calculations. Selective detection of Hg2+ from Cu2+ is established from the ratiometric response caused by β-mercaptoethanol. Advantages of the probe 1 in terms of high sensitivity, stability in the physiological pH and suitability for dual detection are presented. Probe impregnated silica plates for onsite detection of Hg2+ and Cu2+ present in environmental samples is also demonstrated.