A halide sensor based on the quenching of fluorescence of an immobilised indolium salt

A halide sensitive indolium salt has been produced by the quaternisation of Harmane with 1,3-propane sultone. The product, 1-methyl-2(sulfonatopropyl)-9H-pyrido[3,4-b] indolium (SPI), is readily water soluble and in the presence of aqueous halide ions is fluorescence quenched, enabling halide concentrations to be determined using Stern-Volmer kinetics. The fluorophore has been immobilised within a hydrophilic Quattro copolymer, so-called due to its four constituent co-monomers, to produce a halide sensor. The sensor film is sensitive to modest bromide and iodide concentrations with a 90% response time to molar halide of approximate to2 min. The sensor film is completely reversible, which can potentially allow for the continuous monitoring of halide in industrial and medical applications, where the 90% fluorescence recovery time to distilled water is similar to5 min. The interference of other aqueous anions on sensor performance is discussed. The sensor film was found to have a shelf life in excess of 2 years. Opportunities for multiphoton transdermal halide sensing are discussed. (C) 2000 Elsevier Science B.V. All rights reserved.