Development of a lateral flow dipstick immunoassay for the rapid detection of glycyrrhizic acid

A sensitive antibody-based lateral flow dipstick was developed for glycyrrhizic acid (GL) detection. The stick consisted of a sample pad, a conjugate pad, membrane and an absorbent pad. The membrane was coated with two capture reagents, GL-BSA conjugate and goat anti-mouse antibodies, forming a test line and a control line, respectively. The conjugate pad was saturated with colloidal gold particles coated with affinity purified monoclonal anti-GL antibody. The visual detection limit was 20–50 ng ml^–1 of GL and the reaction time was 10 min. The dipstick was used for the detection of GL in roots, leaves and stems of liquorice plant samples. The results were compared with those obtained using an indirect competitive enzyme-linked immunosorbent assay (icELISA). After sample extraction with tap water for 30 min at room temperature, it also can be used for identifying liquorice roots and measuring their quality. The dipstick assay proved to be a sensitive and rapid tool for quality control of liquorice herbs.