A fluorometric assay is described for the determination of Cd(II) in environmental and agricultural samples. It is making use of a molecularly imprinted polymer (MIP) and aptamer as dual recognition units, while carbon quantum dots (co-doped with sulphur and nitrogen) and gold nanoparticles (SN-CQD/Au) act as the fluorophores. The aptamer-modified MIP was placed on an SN-CQD/Au-modified indium tin oxide glass electrode. Cd(II) was detected with high selectivity by the recognition sites of the aptamer in the MIP. Fluorescence, with excitation/emission peaks at 370/430 nm, is quenched by Cd(II). Response is linear in the 20 pM to 12 nM concentration range. The detection limit is 1.2 pM. The sensor is selective for Cd(II), and recoveries from spiked waters, soils and vegetables real-world samples range between 82.1 and 113.9%. Graphical abstractA fluorescence sensor composed of a molecularly imprinted polymer and an aptamer as a dual identification system for Cd2+ coupled with and carbon quantum dots (co-doped with sulphur and nitrogen) and gold nanoparticles (SN-CQDs/Au) as fluorescent element that can detect Cd2+ with high selectivity by a dual-recognition mechanism.
Keywords: Cyclic voltammetry; Fluorescence spectra; Transmission electron microscopy; UV-visible spectroscopy; X-ray photoelectron spectroscopy.