Novel upconversion fluorescence sensor for the detection and imaging of procyanidins in foods by NaYF4:Yb/Tm@NaYF4:Yb-Cit-CD

In this paper, a β-cyclodextrin (CD)-modified citric acid (Cit)-stabilized blue-emitting upconversion nanocomposite NaYF4:Yb/Tm@NaYF4:Yb-Cit-CD (abbreviated as Y/Yb/Tm@Y/Yb-Cit-CD) has been prepared. Under 980 nm laser excitation, the fluorophore Y/Yb/Tm@Y/Yb of the nanocomposite emits blue fluorescence, and the spectral peak is approximately 482 nm. The emission spectrum partly overlaps with the absorption spectrum of procyanidins, which will lead to the upconversion fluorescence intensity of Y/Yb/Tm@Y/Yb decreasing by the fluorescence resonance energy transfer between Y/Yb/Tm@Y/Yb and procyanidins. Thus, the Y/Yb/Tm@Y/Yb-Cit-CD nanocomposite can be used as an upconversion fluorescence probe to detect procyanidins. The quantitative analysis of procyanidins has displayed a linear range of 0.1–1000 μM, with a detection limit of 0.06718 μM (S/N = 3). Furthermore, this probe has shown potential for detection of procyanidins in biological samples and upconversion luminescence imaging analysis in vivo.