A highly Li+-selective glass optode based on fluorescence ratiometry

This paper presents the preparation and characterization of a single-excitation, dual-emission ratiometric optical Li+-sensing device using a newly designed and synthesized highly Li+-selective fluoroionophore (KBL-01) carrying 14-crown-4 ether with tetramethyl and benzene blocking subunits as Li+-binding site and boron-dipyrromethene as fluorophore. The indicator dye was covalently immobilized on the surface of a porous glass support having a large internal surface area using a silane-coupling agent. The resulting Li+-selective glass optode shows dual fluorescence emission response in pseudo-serum at varying Li+ concentrations, allowing ratiometric signal processing. The obtained signal is independent of the presence of possibly interfering cations (Na+, K+, Mg-2+ and Ca2+) and pH. The sensor response was found to be reversible within the Li+ concentration range from 10(-4) to 10(-1) M, and showed good repeatability and light stability. The plots of the ratiometric signal versus the Li+ concentrations in spiked real human serum go along with the response curve in pseudo-serum. These results indicate that the novel Li+-selective glass optode can be employed as a Li+-sensing device with high durability, sensitivity and accuracy for medical analyses.