Label-free and ultrasensitive colorimetric detection of DNA based on target-triggered quadratic amplification strategy

Highly sensitive detection of DNA plays a crucial role in biomedical research and clinical diagnosis. Herein, we developed a simple, label-free, isothermal, and ultrasensitive colorimetric method for amplified detection of DNA on the basis of a new quadratic amplification strategy. With the presence of three ingeniously designed hairpin structures and Exonuclease III (Exo III), the target DNA can trigger two independent cycles of reactions: hairpin assembly reaction and Exo III cleavage reaction, which are designed to initiate target DNA recycling amplification and reporter DNA amplification, respectively. Therefore, the proposed method exhibits a high sensitivity toward target DNA with a detection limit of as low as 81 fM, and it can discriminate mismatched DNA from completely matched target DNA. Furthermore, this method could be used as a universal tool for the detection of various DNA sequences and might be further extended for the detection of aptamer-binding molecules.