DNA nanomachines as evolved molecular beacons for in vitro and in vivo detection.

Modern biosensors require high sensitivity, great signal enhancement and extensive applicability for detection and diagnostic purposes. Traditional molecular beacons (MBs) do not meet these requirements because of the lack of signal amplification. The current amplification pathways using enzymes, DNAzymes and nanoparticles are usually quite sophisticated and are limited to specific applications. Herein, we developed simple biosensors based on the structure of kissing-hairpin. Through hybridization amplification of these nanomachines, the evolved MBs could greatly enhance the detected signals (approximately 10-fold higher than the signals generated by traditional molecular beacons), reduce the sensing limits for targets and, remarkably, distinguish single-base mismatches specifically for nucleic acid detection. In addition, these new MBs can be directly applied in living cells. By introducing aptamer sequences, these novel sensors can also detect proteins and small molecules. These properties were exemplified by the detection of both the β-actin gene and thrombin. The simplicity, sensitivity and flexibility of these devices make them appropriate for more expansive applications.