A surfactant-modulated fluorescent sensor with pattern recognition capability: sensing and discriminating multiple heavy metal ions in aqueous solution

Pattern recognition has been widely used to detect and identify multiple analytes. The strategies for realizing pattern recognition of a single sensor are in significant demand. In the present work, a particular bispyrene-based fluorophore containing a hydrophilic spacer, Py-TOA-Py, was synthesized, and it was observed that its mixture with anionic surfactant assemblies realizes multiple fluorescence responses to different metal ions. The combination of fluorescence variation at four emission wavelengths enables the fluorophore/surfactant sensor system to provide specific recognition patterns to different metal ions. Principle component analysis shows that the present single sensor system could discriminate 6 metal ions, namely Fe3+, Co2+, Ni2+, Cu2+, Pb2+, and Hg2+, 5 of which are heavy metal ions. Results from UV-vis measurements rule out the possibility of the bispyrene fluorophore binding with metal ions. Fluorescence titration of metal ions with two other bispyrene fluorophores reveals that the ones with similar hydrophilic spacer, Py-EOA-Py, exhibit similar multiple fluorescence responses, whereas, the ones with hydrophobic spacer, Py-DDA-Py, display no cross-reactive responses. Time-resolved emission spectra measurements reveal that the spacer polarity plays an important role in determining the location of bispyrene in surfactant assemblies, which further influences its cross-reactive responses to metal ions. The present work provides a new strategy for developing fluorescent sensors with pattern recognition abilities.