A novel isatin-based probe for ratiometric and selective detection of Hg and Cu ions present in aqueous and environmental samples.

A novel isatin derivative (1) is UV-Visible active and displays about 90 nm bathochromic shift upon interaction with only Hg and Cu, but not with other common metal ions. Also, the colorless probe 1 turns to brick-red and yellow in the presence of Hg and Cu, respectively. Addition of increasing amounts of Hg or Cu 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 Hgor Cu ions. Probe 1 shows very high sensitivity and selectivity towards Hg and Cu as revealed by their very low detection limits 0.95 × 10 M and 1.5 × 10 M, respectively. Formation of 1:1 complex with Hg and 2:1 complex with Cu is confirmed using NMR, ESI-MS and FT-IR techniques, Job plot and DFT calculations. Selective detection of Hg from Cu 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 Hg and Cu present in environmental samples is also demonstrated.