Molecularly imprinted polymers on CdS quantum dots for sensitive determination of cefixime after its preconcentration by magnetic graphene oxide

Abstract

A sensitive and selective method was developed for the simple monitoring of cefixime based on its preconcentration by magnetic Fe₃O₄@SiO₂ modified graphene oxide (Fe₃O₄@SiO₂-GO) and fluorimetric detection using molecularly imprinted polymer coated CdS quantum dots (MIP-CdS QDs). GO was simply synthesized using the Hummers method and then was modified using Fe₃O₄@SiO₂ nanoparticles. MIP-CdS QDs were obtained by copolymerization of certain monomers in the presence of CdS QDs as fluorescent materials and cefixime as a template molecule. The obtained nanomaterials were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray powder diffraction (XRD). MIP-CdS QDs showed a high tendency towards cefixime, and the adsorbed cefixime molecules led to a linear increase in the emission intensity of QDs. Based on this effect, a selective determination method was designed for cefixime. To detect lower cefixime concentrations, a preconcentration step was applied. In this regard, the dispersed Fe₃O₄@SiO₂-GO displayed good efficiency to extract low amounts of cefixime as a model analyte. Important parameters including pH, buffer type and concentration, reagent amounts, ionic buffer, incubation time, eluent, etc. were optimized for both the extraction and detection steps. A calibration graph in the concentration range of 0.001–0.7 μg mL⁻¹ was obtained for cefixime with a detection limit (3 s) of 0.54 ng mL⁻¹. The present method was satisfactorily used for cefixime determination in pharmaceutical and urine samples. The results were shown to possess adequate features compared with previous methods.