Determination of quercetin in pharmaceuticals by digital colorimetry using assemblable microfluidic systems based on paper modified with gold and silver nanoparticles

One of the actual fields of application of paper-based microfluidic systems (µPADs) is the determination of biologically active substances in various objects, including pharmaceuticals. Often such determination is carried out as a variant of screening analysis to identify samples that should be investigated in more detail by highly informative but relatively expensive methods. In this work, an original method for the colorometric determination of quercetin using microfluidic analytical systems based on paper modified with gold and silver nanoparticles of different morphologies is proposed. It is based on the reduction of silver(I) ions to metallic silver under the action of quercetin, which leads to a contrast color change of the BMFS detection zones. The possibility of using a monitor calibrator and a smartphone camera to record the analytical signal was demonstrated. Optimal conditions of the analysis have been selected. It is shown that the type of nanoparticles affects the sensitivity coefficient of quercetin detection, which is promising for the creation of multisensor systems for discrimination of samples of complex composition. The limits of quercetin detection under the selected conditions are 70-120 ng depending on the nature of the analytical reagent and the method of analytical signal registration. The range of detectable contents is 2-10 µg. Sufficient sample volume for analysis does not exceed 25 µl. The selectivity of the proposed method for the determination of quercetin in relation to a series of common inorganic ions and organic substances was evaluated. The applicability of the developed approach for the determination of quercetin in three pharmaceutical preparations is shown.