Development of a VL domain antibody for congeneric detection of cobra (Naja spp.) venom

Snakebite envenoming by the monocled cobra (Naja kaouthia) is a major health burden in Southeast Asia, driven largely by the tissue-damaging effects of cytotoxin-II (CTX-II). This study identifies a human light-chain monoclonal antibody, clone E1, with dose-dependent binding and good selectivity for CTX-II using phage display biopanning. While pairing E1 with a heavy-chain domain to form an scFv (clone E1-H2) slightly optimized binding at high concentrations, it significantly reduced protein solubility and expression yield compared to the standalone domain. The antibody demonstrated broad, genus-specific recognition across various Asiatic and African cobras while showing no cross-reactivity with non-cobra elapid or viperid venoms. These results suggest that the smaller, more stable architecture is better suited for accessing epitopes on compact toxins like CTX-II. Consequently, the E1 VL domain antibody is a promising, high-stability candidate for developing regional point-of-care diagnostics for cobra envenoming.