Molecularly imprinted fluorescent polymers as chemosensors for the detection of mercury ions in aqueous media

This article describes the investigation of molecularly imprinted fluorescent polymer membranes as sensing receptors for Hg²⁺ detection by an optical approach. The polymers were synthesized with 4-vinyl- pyridine as a functional monomer and Hg²⁺ as a template; 9-vinylcarbazole was used as both a complex-forming agent and a fluorescence probe. The free-radical polymerization was performed within a semicylindrical Teflon mold and was initiated by 2,2′-azobisisobutyronitrile at 60°C. The template, ion-bonded to pyridine and carbazole groups in the polymer membrane, was removed by acid treatment. Attenuated total reflectance-Fourier transform infrared (FTIR) spectroscopic measurements and scanning electron microscopy images were used to compare the chemistry and surface morphology, respectively, of both imprinted and nonimprinted polymer materials. The final polymer membranes with semicylindrical shapes were used directly to determine Hg²⁺ concentration in aqueous solutions by the monitoring of the fluorescence intensity of the carbazole groups quenched upon complex formation with metal ions. The values of the Hg²⁺ binding ratio for the imprinted and nonimprinted polymeric membranes were compared, and the results indicate the superior sensitivity and selectivity of the imprinted membranes.