Silicon Doped Carbon Dots as an New Ratiometric Fluorescence Probe for Proanthocyanidins Assay Based on the Redox Reaction Between Cr(VI) and Proanthocyanidins

In the study, silicon doped carbon quantum dots (Si-CQDs) was prepared by one-pot hydrothermal method with (3-aminopropyl) triethoxysilane (APTES) and o-phenylenediamine (OPD) as raw materials. Then a new ratiometric fluorescent probe (RF-probe) was successfully established for sensitively and selectively monitoring proanthocyanidins (PAs) with a linear range of 10–500 nM and limit of detection (LOD) of 5.6 nM. that is, the fluorescence (FL) intensity of Si-CQDs at 570 nm was used as the built-in reference, while dopamine (DA) reacting with 4-hexylresorcinol (4-HR) could produce a new fluorescent substance (named as azamonardine, AZMON), and its FL intensity at 480 nm was reduced because Cr(VI) could oxidize DA to generate quinone without fluorescence. In the presence of PAs, Cr(VI) was reduced to Cr(III), which caused that the amount of DA reacting with 4-HR was increased, thus the FL intensity of AZMON was recovered. Furthermore, the RF-probe was successfully used for the determination of PAs in black goji berry from two different areas and PAs capsule with satisfactory results compared to the standard HPLC method.