A metal ion sensor may be prepared by immobilizing a fluorogenic ligand on the common end of a bifurcated fiber optic. Fluorescence is excited through one arm of the fiber optic and observed through the other. When the immobilized ligand is placed in a solution of metal ion, some of the metal associates with the ligand causing its fluorescence characteristics to change. Equations are derived for the response of a sensor for systems where a 1:1 complex is formed.
We have successfully immobilized several ligands including morin, quercetin, and calcein to cellulose using cyanuric chloride as a coupling reagent. Immobilized morin is only very weakly fluorescent but forms fluorescent complexes with Al+3 and Be+2 and can be used to sense these ions. Immobilized calcein is fluorescent by itself but is quenched by several metal ions. We have also immobilized hydroxy napthol blue and 8-hydroxyquinoline-5-sulfonate on anion exchangers. In addition 2, 2′, 4-trihydroxy-azobenzene and p-tosyl-8-aminoquinoline have been immobilized to silica gel.