A responsive electrical detection technique of nucleic acids has been demonstrated on submicrogapped biosensor. This method contain immobilizing of Peptide Nucleic Acid (PNA) probes in the gap areas of a pair of interdigited microelectrodes and subsequently hybridizing with their complementary target RNA. After hybridization, hemin molecules were introduced into the RNA strand via zirconium-phosphate and zirconium-carbonate chemistries. The newly attached hemin molecules act as a catalyst to accelerate reducing ammoniacal Ag ion to form Ag nanoparticles, which span the gap of the interdigitated microelectrode. The conductance of the Ag nanoparticles directly correlated with the number of the hybridized RNA molecules. Nearly 1 fM sensitivity was achieved under optimal conditions.