Hexaphenyl-butadiene derivative with aggregation-induced emission characteristic for high-sensitive detection of ursolic acid, oleanolic acid, and glycyrrhizic acid

Plant natural products (PNPs) have a wide range of pharmacological effects and biological activities, including antitumor, antiinflammatory, antibacterial, and antiviral properties. These properties can be beneficial for their use in the health care industry. As representative PNPs, ursolic acid (UA), oleanolic acid (OA), and glycyrrhizic acid (GA) have been efficiently biosynthesized in microbial cells. In this study, hexaphenyl-butadiene methylpyridine salt (HPB-I) with an aggregation-induced emission characteristic (AIE) was developed as a simple, real-time, and efficient quantitative probe for detection of PNPs. Experimental results showed that HPB-I has a highly selective fluorescence response to UA, OA, and GA among 18 PNPs. Three detection methods were employed. Dilution of a PNP aqueous solution with dimethyl sulfoxide was optimal with low limits of detection of 0.16 (UA), 0.23 (OA), and 0.066 (GA) nmol/mL. Scanning electron microscopy, dynamic light scattering, and zeta potential analyses revealed that the PNPs were effectively adsorbed on the surface of HPB-I aggregates, which resulted in an increase in the fluorescence response based on restriction of intramolecular motion. HPB-I could also effectively and quantitatively detect the three PNPs in a synthetic dropout (SD) culture medium. This study provides a valuable approach toward the development of a real-time low-cost method for in-situ PNP detection of biosynthesis processes in microbial cells.