A　new　signal　amplification　strategy　based　on　target-induced　proximity　ligation　assay　accompanying　three-way　junction-based　rolling　chain　amplification　was　designed　for　ultrasensitive　detection　of　concanavalin　A　(Con　A)　by　coupling　with　a　sequential　injection　mode.　To　construct　such　a　proximity　ligation　assay　system,　two　types　of　magnetic　sensing　probes　including　glucosamine/DNA(1)-conjugated　magnetic　bead　(GA-MB-DNA(1))　and　glucosamine/DNA(2)-labeled　magnetic　bead　(GA-MB-DNA(2))　were　first　synthesized　and　prepared　through　a　typical　carbodiimide　coupling.　In　the　presence　of　target　Con　A,　GA-MB-DNA,　and　GA-MB-DNA(2)　were　ligated　together　based　on　the　interaction　between　Con　A　and　the　conjugated　glucosamine　on　the　MB,　thereby　resulting　in　the　formation　of　a　three-way　DNA　junction　because　of　partial　base　pairing　on　the　DNA(1)/DNA(2).　With　the　aid　of　ligase　and　polymerase,　the　formed　three-way　DNA　junction　could　be　used　as　the　primer　to　produce　numerous　repeated　oligonucleotide　sequences　through　rolling　circle　amplification　(RCA)　reaction.　The　formed　long　oligonucleotide　strand　could　cause　the　intercalation　of　numerous　positively　charged　methylene　blue　molecules　with　a　negatively　charged　DNA　backbone.　During　the　electrochemical　measurement,　each　of　the　intercalated　indicators　could　produce　an　electrochemical　signal　within　the　applied　potentials,　resulting　in　the　amplification　of　detectable　electronic　signal.　By　monitoring　the　change　in　the　signal,　we　could　indirectly　determine　the　concentration　of　target　Con　A　in　the　sample.　Under　the　optimal　conditions,　the　developed　sensing　platform　exhibited　high　sensitivity　for　detection　of　Con　A　with　a　wide　dynamic　range　of　1.96　pM　to　98　nM　and　a　low　limit　of　detection　(LOD)　of　1.5　pM　at　the　3(SB)　level.　Intra-assay　and　interassay　coefficients　of　variation　were　less　than　8.9%　and　9.7%,　respectively.　In　addition,　the　methodology　was　validated　by　assaying　Con　A　spiked　samples　including　newborn　cattle　serum　and　peanuts,　and　the　recovery　in　all　cases　was　88.8-134.7%.