Si-rhodamine B thiolactone: A simple long wavelength operating chemosensor for direct visual recognition of Hg2+

A novel long wavelength operating colorimetric and fluorescent chemosensor, Si-rhodamine B thiolactone (Si-RBS), has been successfully synthesized and characterized. Si-RBS demonstrated high selectivity towards Hg2+ with about 670-fold enhancement in fluorescence emission intensity at 687 nm over various environmentally relevant metal cations such as Ag+, Al3+, Ca2+, Cd2+, Cr3+, Cu2+, Fe3+, K+, Mg2+, Mn2+, Ni2+, Pb2+ and Zn2+ in pH 5.2 media. The addition of Hg2+ induced a significant change in color of Si-RBS solution from colorless to light blue, making the "naked-eye" recognition of mercury ions possible. Importantly, high sensitivity (detection limit down to 0.25 nM) and a rapid response time (<1 min) were noted for the feasibility in real-time quantitative recognition of Hg2+.