A gene-sensing system has been developed using actinomycin D-functionalized magnetic nano-microspheres, which can interact with double-stranded DNAs (dsDNAs) anchored on the gold film electrode of all electrochemical quartz crystal microbalance (EQCM). Actinomycin D acts as a guide that leads heavy microspheres onto the dsDNAs at the EQCM film. A magnetic separation shelf could separate unreacted microspheres conveniently. The modification and DNA hybridization at EQCM electrodes were examined by microgravimetric and electrochemical methods. In this way, an outstanding change in frequency decrease has been monitored owing to the mass increase on the EQCM electrodes. The limit for the determination of target DNA could be improved from 6.2 x 10(-8) to 2.0 x 10(-12) mol l(-1) by the amplifying technique.