RARA and acute promyelocytic leukemia: Subsequently, using targeted switching DNA nanotweezers as a hemin concentration controller and combining a G-quadruplex structure in which the rich-G bases of the different strands are stabilized together by hydrogen bonding to form a tetrameric structure, an ultrasensitive “on-off” ECL biosensor was developed for the detection of PML/RARα, the important biomarker for acute promyelocytic leukemia (APL) [60].