Highly sensitive detection of CB[7] based on fluorescence resonance energy transfer between RhB and gold nanoparticles

Background: Cucurbit[n]uril (CB[n], n=5, 6, 7, 8 and 10）is a type of macrocyclic compounds formed by n glycerol units and 2n methylene. The different size of the cavity led the different chemical characteristics of CB[n]. Therefore, it was very important to distinguish and detect CB[n]. Methods: At room temperature, Rhodamine B was added with gold nanoparticles solution. The above mixture was respectively mixed with different concentrations of Cucurbituril [n] or β-cyclodextrin solutions. The fluorescence spectra and ultraviolet-visible spectra of samples were determined. Results: It was found that 1.2nM gold nanoparticles could quench the fluorescence of 1μM Rhodamine B completely. After adding a certain amount of Cucurbituril[7], the fluorescence intensity of Rhodamine B was restored. Compared with other macrocyclic compounds, such as Cucurbituril[5], Cucurbituril[6] and β-cyclodextrin, we found that this method had unique selectivity for Cucurbituril[7]. Under the optimal conditions, the fluorescence recovery efficiency was linearly proportional to the concentration of Cucurbituril[7] in the range of 0.8-8 μg·mL-1. The detection limit was 0.21 μg·mL-1. Conclusion: We have established an effective and practical FRET-based detection method for CB[7] with RhB as donor and the gold nanoparticles as the acceptor. The system has unique and extensively selectivity for CB[7].