Locked　nucleic　acid　(LNA)　is　applied　in　toehold-mediated　strand　displacement　reaction　(TMSDR)　to　develop　a　junction-probe　electro-chemiluminescence　(ECL)　biosensor　for　single-nucleotide　polymorphism　(SNP)　detection　in　the　BRCA1　gene　related　to　breast　cancer.　More　than　65-fold　signal　difference　can　be　observed　with　perfectly　matched　target　sequence　to　single-base　mismatched　sequence　under　the　same　conditions,　indicating　good　selectivity　of　the　ECL　biosensor.