Preperation of turn on fluorescent chemosensor based on rhodamine hydrazide anchored poly vinyl amine microbeads for selective detection of Fe(III) cation

Fluorescent chemosensors have mechanism which can make relation between fluorophore unit and binding site which show selectivity towards analyte. In the literature, first developed chemosensor by F. Goppelsröder shows selectivity for Al3+ cation in 1867. Development of new fluorescent chemosensors has gained a lot attention for the detection of anions cations and neutral molecules because of their simplicity and being easy applicable in aqeous media. A simple and efficient chemosensor has been designed for detection of Fe (III) ions via fluorescence turn on mechanism. For this purpose, poly (vinyl formamide-co-ethylene glycol dimethacrylate) microbeads poly (VFA-co-EGDMA) was prepared via precipitation polymerization in the presence of AIBN, vinyl formamide and ethylene glycol methacrylate in acetonitrile. After hydrolysis of P(VFA-EGDMA) microbeads, terephthalaldehyde was tethered onto the microbeads via imine linkages via catalytic amount of glacial acetic acid in EtOH. Then, Rhodamine 6G hydrazide was attached onto the resulting aldehyde functional microbeads in the same manner. All the reaction steps were characterized by FTIR . Also, the resulting microbeads which are naked and rhodamine 6G hydrazide modified microbeads (rhod-beads) were pictured. SEM images show that their shapes were not affected thorought the reaction. For detection properties of the resulting rhod-microbeads (25 mg/100 mL) were investigated with metal ions (Na+, K+, Al3+, Fe3+, Cd2+, Ba2+, Cu2+, Hg2+, Fe2+, Pb2+, Zn2+, Ni2+, Co2+, Mg2+). It was observed that prepared chemosensor beads show the best fluorescent response to the Fe3+ cation. Moreover, detection limit was found as 95.2 and 98.5 µm by fluorescence and UV-Vis spectra. Also, Job's Plot proves the 1:1 stoichiometry between rhod-beads and Fe3+. Furthermore, the Benesi-Hildebrand Plot shows the binding constant (Ka) as 7x104 mol/L by using 1:1 stoichiometric ratio from Job's Plot. Fluorescence life time was measured as 48.9 ± 3.0 ns. Then, to investigate the fluorescence properties of interacted and not interacted rhod-beads with Fe3+ fluorescence microsope images were taken.