AuNPs-DNAzyme molecular motor biosensor mediated by neighborhood click chemistry reactions for the ultrasensitive detection of microRNA-155

As an important biomarker of cancers and some ischemic diseases, the rapid and ultrasensitive detection of microRNAs (miRNAs) holds great promise for the early diagnosis and treatment of high rates of morbidity and mortal diseases. We prepared optimum gold nanoparticles (AuNPs) as the ideal miRNA detection platform. Utilizing these, an AuNPs-DNAzyme molecular motor biosensor was developed for the detection of miRNA-155. Initially, the click chemistry reaction empowered by miRNA-155 certified by experiments converts the intermolecular hybridization of Mg2+ DNAzyme two strands into an intramolecular hybridization on the surface of AuNPs. In the presence of Mg2+, the DNAzyme is activated to cleave the substrate strands, generating fluorescence group contained fragments and releasing them from AuNPs surface. The catalysis strands subsequently hybridize with other substrate strands, accomplishing the movement of AuNPs-DNAzyme molecular motor. The long catalysis strands allowing free cleavage for most substrate strands and the stepwise movement on AuNPs surface is fueled by the target-empowered neighborhood click chemistry reaction. As such, the AuNPs-DNAzyme molecular motor movement can be monitored in real time through the fluorescence signal. In addition, we optimized crucial parameters to realize highly efficient cyclic cleavage and signal amplification. As an ultrasensitive detection platform for miRNA-155, it has a limit of detection (LOD) as low as 50 fM. The molecular motor is a thermostabilized, cyclic and enzyme-free nanomachine. Due to the empowering role of miRNA-155 independent to the specific sequences, the molecular motor possesses universality and can, thus, be used for the detection of various kinds of miRNAs.