A ratiometric fluorescent sensor for zinc ions based on covalently immobilized derivative of benzoxazole

In the present paper, we describe the fabrication and analytical characteristics of fluorescence-based zinc ion-sensing glass slides. To construct the sensor, a benzoxazole derivative 4-benzoxazol-2′-yl-3-hydroxyphenyl allyl ether (1) with a terminal double bond was synthesized and copolymerized with 2-hydroxyethyl methacrylate (HEMA) on the activated surface of glass slides by UV irradiation. In the absence of Zn2+ at pH 7.24, the resulting optical sensor emitted fluorescence at 450 nm via excited-state intramolecular proton transfer (ESIPT). Upon binding with Zn2+, the ESIPT process was inhibited resulting in a 46 nm blue-shift of fluorescence emission. Thus, the proposed sensor can behave as a ratiometric fluorescent sensor for the selective detection of Zn2+. In addition, the sensor shows nice selectivity, good reproducibility and fast response time. Cd2+ did not interfere with Zn2+ sensing. The sensing membrane demonstrates a good stability with a lifetime of at least 3 months. The linear response range covers a concentration range of Zn2+ from 8.0 × 10−5 to 4.0 × 10−3 mol/L and the detection limit is 4.0 × 10−5 mol/L. The determination of Zn2+ in both tap and river water samples shows satisfactory results.