A thiol-containing colorimetric chemosensor for relay recognition of Cu2+ and S2- in aqueous media with a low detection limit

A thiol-containing chemosensor MPT was prepared and used to relay recognition of Cu2+ and S2-. Addition of Cu2+ to MPT caused the obvious appearance of a red-shifted absorption with a color change from colorless to pale yellow. MPT for detecting Cu2+ could be used in real samples and test strips. Sequentially, MPT-Cu2+ recognized S2- through the appearance of a blue-shifted absorption with a color change from pale yellow to colorless. Detection limits for copper(II) ion and sulfide turned out to be 0.11 mu M and 0.23 mu M, which were significantly below WHO standards (31.4 mu M for Cu2+ and 14.8 mu M for S2-) for drinking water. The binding processes of MPT toward copper(II) ion and sulfide were demonstrated by UV-visible, ESI-mass, FT-IR and H-1 NMR titrations, and understood by DFT calculations.