A　label-free　and　sensitive　electrochemical　biosensing　strategy　for　a　hepatocellular　carcinoma　biomarker　of　miRNA-122　has　been　proposed　based　on　hybridization　induced　ion-barrier　effect　on　the　electroactive　sensing　interface.　First,　a　bifunctional　electroactive　electrode　with　the　nanocomposite　of　Prussian　blue　(PB)　and　gold　nanoparticles　(AuNPs)　was　prepared　through　a　two-step　electrodeposition　process.　The　PB　endows　the　electrode　excellent　K+-dependent　voltammetric　signal　and　the　AuNPs　act　as　the　matrix　for　the　self-assembly　immobilization　of　the　thiolated　probe　DNA.　Upon　specific　hybridization　of　probe　DNA　with　the　target　miRNA-122,　the　formed　double　duplex　induced　the　ion-barrier　effect,　which　blocked　the　diffusion　of　the　K+　from　the　bulk　solution　to　the　electrode　surface.　As　a　result,　the　voltammetric　signal　of　the　PB　on　the　electrode　was　surpressed,　and　thus　the　target　miRNA-122　was　monitored.　The　sensing　assay　showed　that　the　miRNA-122　could　be　analyzed　in　the　concentration　range　from　0.1　fmol/L　to　1.0　nmol/L,　with　a　detection　limit　of　0.021　fmol/L.　The　practical　applicability　of　the　biosensor　was　also　verified　by　the　spiking　serum　assay.　(C)　2021　Chinese　Chemical　Society　and　Institute　of　Materia　Medica,　Chinese　Academy　of　Medical　Sciences.　Published　by　Elsevier　B.V.　All　rights　reserved.