β-Cyclodextrin-capped ZnO-doped carbon dot as an advanced fluorescent probe for selective detection of dopamine

Selective and sensitive detection of dopamine (DA) in the presence of other interfering biomolecules is very challenging in biomedical analysis. Here, we have reported the one-pot synthesis strategy of water-soluble beta-cyclodextrin-capped ZnO-doped carbon dot (ZnO-CD) via a simple hydrothermal treatment of beta-cyclodextrin (beta-CD) and zinc acetate. The as-synthesized ZnO-CDs have a very small size, similar to 2-3 nm, and are used as an efficient sensing probe. The aqueous solution of ZnO-CDs exhibits excitation-dependent emission properties. They exhibit the maximum intensity in the blue region of the visible spectrum under excitation at similar to 360 nm with the emission maximum at similar to 443 nm. The blue emissive ZnO-CDs have shown a high quantum yield (similar to 18%), good colloidal stability, and photostability under UV light exposure. ZnO-CDs have been used for selective sensing of DA in the presence of other interfering biomolecules with a detection limit of similar to 285 nM. Interestingly, DA sensing has also been performed in a mixture of interfering biomolecules. To explore their practical significance as a sensing probe, this fluorescent probe has been used to determine the DA content in spiked blood samples with remarkable accuracy, selectivity, and sensitivity. Based on our results, we propose that selective sensing of DA occurs via the host-guest interaction of DA with beta-CD on the ZnO-CD surface, followed by electron transfer through the oxidized form of DA under excitation. Thus, the fluorescence of ZnO-CDs is "turned-off" selectively in the presence of DA.