Iodide-modified Ag nanoparticles coupled with DSN-Assisted cycling amplification for label-free and ultrasensitive SERS detection of MicroRNA-21.

With the emergence of microRNA (miRNA) as a key player in early clinical disease diagnosis, development of rapidly sensitive and quantitative miRNA detection methods are imperative. Herein, a label-free SERS assay coupled with duplex-specific nuclease (DSN) signal amplification strategy was proposed for facilely ultrasensitive and quantitative analysis of miRNA-21. Firstly, magnetic beads assembled with excessive capture DNA were utilized to hybridize the target miRNA-21. These DNA-RNA heteroduplexes were cleaved by DSN to generate small nucleotide fragments into the supernatant and the miRNA-21 released and rehybridized another DNA, going to the next DSN cycle. Consequently, numerous of small nucleotide fragments of capture DNA were released from magnetic beads and the miRNA-21 signal was transferred and amplified by the SERS signals of total phosphate backbones which are abundant in nucleotide. Furthermore, iodide-modified Ag nanoparticles (AgINPs) was employed to generate a strong and reproducible SERS signal. The proposed method displayed excellent performance for miRNA-21 detection with the linear range from 0.33 fM to 3.3 pM, and a lower detection limit of 42 aM. Moreover, this strategy exhibited effectively base discrimination capability and was successfully applied for monitoring the expression levels of miRNA-21 in different cancer cell lines and human serum.