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⁺, Mg²⁺ 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.