ZnO-based imine-linked coupled biocompatible chemosensor for nanomolar detection of Co2+

Abstract

A sol-gel process is developed for the synthesis of ZnO crystals at room temperature using organic receptors (bearing imine linkages) as the capping agents to control the size and shape of ZnO. The size and morphology of ZnO are characterized with X-ray diffraction, TEM, SEM, and DLS studies. The decoration of imine-linked receptors on the surface of ZnO is characterized with IR and NMR spectroscopy and confirmed with EDX analysis. The XRD results show that the average crystallite size of ZnO is 13.8 nm with a hexagonal wurtzite structure. Fluorescence spectroscopy revealed that surface-coated ZnO possesses fewer surface defects than the usual bulk ZnO. The imine-linked receptor-coated ZnO (sensor) was tested for recognition of various metal ions; however, the sensor was found to be selective for Co2+ in the DMSO/H2O (8:2; v/v) solvent system. The successive addition of Co2+ to the solution of the sensor quenches the fluorescence intensity at 445 nm with enhancement at 353 nm. This leads to the development of a ratiometric fluorescence sensor for the recognition of Co2+ in a semi-aqueous solvent system with a detection limit of 0.4 nM. To the best of our knowledge, this manuscript represents the first ZnO-based imine-linked coupled biocompatible chemosensor for nanomolar detection of Co2+.