Synthesis of intrinsic fluorescent dopamine/quercetin copolymer nanoparticles and their application as a dual-mode assay for detection of quercetin

Originally, intrinsic fluorescent dopamine/quercetin copolymer nanoparticles (DA/QCT-CPNPs) were synthesized via oxidation and spontaneous copolymerization of dopamine (DA) and quercetin (QCT). Manganese oxide nanosheets (MnO2) were utilized as an oxidant agent. Quercetin was rapidly oxidized to quinone derivatives in the presence of MnO2 and subsequently self-polymerized and formed non-fluorescent polyquercetin nanoparticles (PQCT). Then by adding DA, MnO2 oxidized the nanoparticles and subsequently caused DA/QCT-CPNPs generation via copolymerization of oxidized DA and PQCT. The color and the fluorescent intensity of the synthesized DA/QCT-CPNPs were significantly influenced by the systematic variation in the QCT concentration. In this regard, the synthesized DA/QCT-CPNPs were successfully applied as a new QCT dual-sensing assay. Dynamic ranges of 0.5–300 µM and 0.5–250 µM were obtained for colorimetric and fluorometric determination of QCT, respectively. The experimental detection limit of 0.1 µM and 0.3 µM were evaluated for fluorometric and colorimetric determination methods, respectively. The designed dual-sensing system was successfully utilized to assess the QCT contents in biological (urine) and food samples (red and yellow onions).