PML/RARα fusion gene (P/R) is the characteristic signature genetic variation of acute promyelocytic leukemia (APL). Here, by integrating triple-stranded DNA hybridization-triggered strand displacement amplification (tri-HT SDA) and cobalt oxyhydroxide nanosheets/quantum dots (CoOOH/QD)-based amplification, we constructed a novel biosensor of easy-operating, time-saving and high sensitivity for detecting P/R to meet clinical needs. Owing to the specific recognition and efficient amplification of tri-HT SDA as well as impressive anti-interference and considerable amplification of CoOOH/QD, this biosensor demonstrated a wide dynamic range (10 fM to 10nM) with a low limit of detection (5.50 fM) in P/R detection. Additionally, this biosensor could detectP/R spiked into human serum with good recoveries and relative standard deviation (RSD), thus potentially exhibiting ultrasensitive and specific nuclear acid sequence detection ability in clinical diagnosis owing to combing isothermal amplification and nanomaterials.