Localized Bicirculating DNAzyme Self-Feedback Amplification Strategy for Ultra-Sensitive Fluorescence Biosensing of MicroRNA

DNAzyme-based cascade networks are effective tools to achieve ultrasensitive detection of low-abundance miRNAs. However, their designs are complicated and costly, and the operation is time-consuming. Herein, a novel simple noncascade DNAzyme network is designed and its amplification effect is comparable to or even better than many cascading ones. It is a nonenzymatic, isothermal, bicirculating amplification network consisting of two toehold-mediated strand-displacement reactions and a localized DNAzyme amplification strategy. Taking microRNA-122 as a target model, this ultrasensitive fluorescence biosensor has a detection limit of 84 zmol L–1, which is 8-orders of magnitude lower than that of the nonamplification one. The ultrasensitivity mainly benefits from the exclusive design and positive self-feedback mechanism of the ingenious bicirculating DNAzyme amplification network. In addition, the utilization of superparamagnetic Fe3O4@SiO2 particles not only helps for the localization of DNAzymes but also facilitates the rapid separation of signal probes (output DNA-CdTe QDs). This fluorescent biosensor also has the advantages of specificity, speed, thermal stability, and low cost. This novel design paves a new way to simple and effective bioamplification strategy, which may be very attractive for biosensors, DNA logic gates, and DNA computers.