Manipulation of monomer-aggregate transformation of a heptamethine cyanine ligand: near infrared chromogenic recognition of Hg2+

Abstract

A novel near infrared optical molecular probe (CyL) derived from heptamethine cyanine dye was developed for the selective detection of Hg²⁺ over other metal ions in aqueous solutions. The detection conditions for Hg²⁺ were optimized. A linear range from 1.0 × 10⁻⁷ M to 5.0 × 10⁻⁶ M and a detection limit of 1.93 × 10⁻⁸ M with a correlation coefficient of 0.9992 were achieved under the optimal conditions. In the recognition of Hg²⁺, CyL alone peaks at 760 nm and exhibits a shoulder at 690 nm. Hg²⁺ can modulate the aggregation state of CyL through coordination of thiosemicarbazide on CyL and Hg²⁺, and thus results in an obvious shift in the maximal absorption wavelength of CyL in the NIR region. The ESI mass spectra of CyL–Hg²⁺ solution have been used to prove the conversion of CyL from monomers to aggregates. Finally, the proposed method has been successfully applied to the determination of Hg²⁺ in cosmetic samples.