Green synthesis and characterization of gold nanoparticles and their application for the rapid detection of glycyrrhizin with immunochromatographic strips.

In this study, a facile and environmentally friendly synthesis process was proposed without regular chemical additives. We successfully synthesized spherical gold nanoparticles (AuNPs) coated with glycyrrhizin (GL) by using GL as both a reductant and a stabilizer to reduce chloroauric acid. The obtained NPs were approximately 35 nm in size. The formation of these GL-AuNPs was verified by the presence of a surface plasmon resonance band at 526 nm. We also experimentally determined that in terms of chemical structure, GL can be used as a reducing agent to obtain colloidal gold. The d-glucuronic acid structure, rather than glycyrrhetinic acid (GA), plays an important reducing role in colloidal gold production. From this, we hypothesized that other compounds with sugar structures in Glycyrrhiza may also have the ability to reduce chloroauric acid. To mitigate the high cost and low efficiency of current GL detection methods, we applied AuNPs to the immunochromatographic system. Then, a colloidal gold immunochromatographic test strip based on the indirect competition method was developed for the rapid detection of GL, and the detection limit of this strip was 25 ng mL. The cross-test showed that the strip has high specificity. The test results are consistent with the data obtained by high-performance liquid chromatography (HPLC) with a coincidence rate of up to 100%. The rapid test strip is simple, fast, highly efficient and inexpensive, making it suitable for large-scale, rapid glycyrrhizin content determination.