Recombinant single-chain variable fragment-based immunoassay for the authentication of Vietnamese ginseng via quantitative detection of majonoside R2

Majonoside R2 (MR2) is an ocotillol-type saponin found at 3%–5% (w/w) in Panax vietnamensis that serves as a critical biomarker for authenticating sought-after Vietnamese ginseng varieties, such as Ngoc Linh and Lai Chau. However, widespread adulteration with morphologically similar species has created an urgent need for high-throughput, cost-effective authentication methods beyond chromatographic or deoxyribonucleic acid-based techniques. A single-chain variable fragment (scFv) antibody against MR2 was recombinantly expressed in Escherichia coli , purified, and functionally validated. Using this antibody, an indirect competitive enzyme-linked immunosorbent assays (icELISA) approach was optimized for MR2 quantification in complex herbal matrices. The performance of this novel assay was benchmarked against that of a previously validated method using monoclonal antibody (mAb)-based ELISA and verified using authentic Panax spp. and Randia siamensis samples. The scFv-based icELISA demonstrated a detection range of 31.25–1000 ng/mL for MR2, with high reproducibility and accuracy (CV