Bispyrene/surfactant-assembly-based fluorescent sensor array for discriminating lanthanide ions in aqueous solution

Lanthanides are valuable nonrenewable resources and widely used in a variety of industries. Detection and identification of lanthanide ions are in high demand but challenging because of the similarity among lanthanide ions. In the present work, a fluorescent sensor array of three cationic bispyrene derivatives mixed with anionic surfactant assemblies was developed. The sensor array exhibits cross-reactive responses to lanthanide ions when tested in aqueous solution. The combination of fluorescence variations at both monomer and excimer emission of each of the bispyrene sensor elements provides a six-signal recognition pattern for lanthanide ions. Principle component analysis illustrates that the sensor array could at least identify 6 of the 14 similar lanthanide ions including La(3+), Pr(3+), Nd(3+), Eu(3+), Ho(3+), and Er(3+). UV-vis absorption measurements rule out the possibility of binding lanthanides with fluorophores. Fluorescence titration experiments in both cationic and neutral surfactant aqueous solutions reveal that the three fluorophores show slight fluorescence responses to the lanthanide ions, indicating that electrostatic attraction between lanthanide ions and anionic surfactant plays an important role in the sensing behavior of the sensor array. Control experiments with divalent metal ions find no cross-reactive responses, suggesting that the stronger electrostatic interaction with trivalent lanthanide ions is responsible for the multiple fluorescence responses.