A 78-mer ss DNA library was synthesized in vitro. The tetrodotoxin (TTX) specific monoclonal DNA aptamer A3 was prepared using systematic evolution of ligands by exponential enrichment(SELEX) combined with mutagenic PCR by screening, enrichment, cloning and sequencing. The secondary structure of the DNA aptamer A3 mainly contained stem ring structure, and the affinity for tetrodotoxin was 1.254. The PBS buffer p H and fluorochrome-binding time were optimized. The results showed that the optimum p H was 7.5 ...