Determination of cobalt(II) using β-cyclodextrin-capped ZnO quantum dots as a fluorescent probe

The authors describe a method for the determination of cobalt(II) ions based on the use of luminescent and water-soluble ZnO quantum dots capped with β-cyclodextrin (β-CD@ZnO QDs). The modified QDs display strong yellow-green fluorescence with a peak at 537 nm under 360 nm excitation. High-resolution transmission electron microscopy, Fourier transform infrared spectroscopy, luminescence, and UV-visible absorption spectroscopy were used to characterize the β-CD@ZnO QDs. The fluorescence of the QDs is quenched by Co(II) ions. This finding was exploited to design a quenchometric assay designed for the detection of Co(II) in water solution. The detection limit is 0.34 μM (based on the 3σ/slope criterion), and the linear range extends from 1.0 to 10 μM. The method was applied to quantify Co(II) in spiked real samples. The quenching mechanism was studied, and this showed that aggregation-induced quenching causes the main effect. Graphical abstract The fluorescence of β-cyclodextrin-capped ZnO quantum dots (β-CD@ZnO QDs) is quenched by cobalt ions, and this finding is exploited in a fluorescence assay for cobalt ions in aqueous solutions.