Rapid and colorimetric detection of nucleic acids based on entropy-driven circuit and DNAzyme-mediated autocatalytic reactions.

In this work, a novel, rapid and enzyme-free colorimetric biosensor for the detection of nucleic acids has been developed based on entropy-driven (EDC) circuit and DNAzyme-mediated autocatalytic reactions. On sensing the target DNA, the EDC reaction could be initiated and the intact Mg2+-dependent DNAzyme was formed in the reaction product; then, a "mimic target" DNA was generated during the cleavage process of DNAzyme, which in turn catalyzed the EDC reaction corresponding to an autocatalytic process. Meanwhile, numerous G-quadruplex structures were released and further interacted with hemin to form peroxidase-mimicking DNAzyme, inducing a remarkably amplified colorimetric signal. This autocatalytic EDC (AEDC) sensing system exhibited a linear relationship in the range from 20 pM to 10 nM with a detection limit of 10.2 pM. More importantly, benefitting from the Mg2+-dependent DNAzyme-mediated autocatalytic reaction, the detection time (20 min) was significantly reduced compared to that for the reported EDC strategies. In addition, this sensing system has been applied for the detection of target DNA in human serum samples, indicating that it is promising for the on-site and real-time detection of nucleic acids in biomedical research and disease diagnosis.