Nuclear　factor　kappa　B　p50　(NF-κB　p50)　induces　various　biological　processes.　In　this　study,　a　highly　selective　and　sensitive　electrochemiluminescence　(ECL)　biosensor　for　the　detection　of　NF-κB　p50　has　been　developed,　which　combines　the　high　selectivity　of　the　proximity　hybridization　assay　(PHA)　with　the　high　efficiency　of　the　hybridization　chain　reaction　(HCR).　This　journal　is　©　The　Royal　Society　of　Chemistry.