A microfluidic-based SERS biosensor with multifunctional nanosurface immobilized nanoparticles for sensitive detection of MicroRNA

Developing sensitive and miniaturized biosensors for the detection of microRNAs (miRNAs) is highly desirable due to their association with early cancer diagnosis and prognosis. Here, a new microfluidic-based biosensor, combined with multifunctional nanosurface and DSN-assisted target recycle amplification strategy, is designed for the detection of miRNA-21. The design of nanosurface includes gold nanoparticles on porous anodic aluminum oxide (AAO) for surface enhanced Raman scattering (SERS) substrate, AuMBA@Ag core-shell nanoparticles for SERS nanotags and single-stranded DNA (ssDNA) in between for miRNA capture and nanotags immobilization. When the target miRNA is present near the nanosurface, it will be captured by ssDNA via hybridization reaction. Then, triggered by the DSN-assisted target recycle process, the freshly formed DNA/miRNA heteroduplexes are cleaved by DSN enzyme into DNA fragments and single-strand miRNA. The SERS nanotags are also dissociated from the nanosurface, leading to decrease of SERS signal. The cleaved target miRNA can be captured and SERS nanotags are released again in the next cycle, resulting in amplification of detection signal. To improve the accuracy of this biosensor, the functionalized AAO membrane is subdivided into two groups - AAO/Au array linked with encoded core-shell SERS nanotags acting as a reactor and primary detector and AAO/Au@Ag array serving as a collector and secondary detector for the dissociative SERS nanotags from the reactor. The decrease of SERS signal in primary detector and increase of signal in secondary detector ensures the accuracy and it is called dual-SERS detection strategy. The detection of miRNA-21 can be achieved with only 30 μL sample and 10 μL enzyme and a wide linear range of 10 fM∼10 nM is obtained. In addition, the microfluidic dual-SERS detection strategy can greatly reduce the possibility of false positive or false negative in single detection mode and it can be applied to the simultaneous detection of multiple miRNAs via integrating different probes.