Bispyrene/surfactant assemblies as fluorescent sensor platform: detection and identification of Cu2+ and Co2+ in aqueous solution

A cationic bis-pyrene derivative was prepared and its assemblies with anionic surfactant to function as fluorescent sensor platforms for heavy metal ions in aqueous solution were evaluated. Optical spectroscopy measurements illustrated that both UV-vis absorption and fluorescence emission spectra of bis-pyrene could be well enhanced in the assemblies with the anionic surfactant, SDS. Moreover, fluorescence quenching studies revealed that the sensitivity of bis-pyrene/SDS assemblies is highly dependent on the concentration of SDS. The optimized sensor platform exhibited not only a high sensitivity towards both Cu2+ and Co2+ in aqueous solution with detection limits lower than 100 nM but also a high selectivity towards these two metal ions over a series of divalent metal ions including Ba2+, Ca2+, Hg2+, Mg2+, Ni2+, Pb2+, Zn2+, Cd2+, and Fe3+. The high sensitivity was demonstrated to be due to the electrostatic interaction between the metal cations and the anionic surfactants, which dramatically increases the local concentration of metal ions in the near vicinity of pyrene moieties. Moreover, the metal ion target could be identified by addition of glycine to the quenched system, where a dramatic turn-on fluorescence was observed for the Cu2+-quenched system whereas a further turn-off fluorescence was found for the Co2+-quenched system. Furthermore, the recovery of Cu2+-quenched fluorescence could be utilized to provide a turn-on fluorescence sensor for neutral amino acids.