CeO₂ quantum dots for highly selective and ultrasensitive fluorescence detection of 4-nitrophenol via the fluorescence resonance energy transfer mechanism

A rapid and simple fluorescence probe based on CeO₂ quantum dots (QDs) was developed for highly selective and ultrasensitive direct determination of 4-nitrophenol (4-NP). CeO₂ QDs were prepared using the sol-gelmethod with the precursor of Ce(NO₃)₃·6H₂O as a cerium source. The products were characterized through high-resolution electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy. The fluorescent probe based on CeO₂ QDs exhibited a broad linear response to the concentration of 4-NP in the range of 0.005-75.00 μM and provided a low detection limit of 1.50 nM. The fluorescence of CeO₂ QDs was quenched by 4-NP through the fluorescence resonance energy transfer mechanism owing to the well overlaps between the fluorescence emission spectrum of CeO₂ QDs with the ultraviolet absorption spectrum of 4-NP. This result was confirmed by the time-resolved fluorescence spectra and the evaluation of the interaction distance between CeO₂ QDs and 4-NP. The prepared CeO₂ QDs are successfully applied to the determination of 4-NP in real water samples, where the spiked recoveries range from 98.2% to 102.4%.