Label-Free Detection of miRNA Using Surface-Enhanced Raman Spectroscopy.

miRNA plays a vital role in many biological processes by regulating the expression of target genes and is considered to be a promising disease biomarker. Although surface-enhanced Raman spectroscopy (SERS) has been widely used for the detection of nucleic acid molecules, obtaining a characteristic SERS signal of unlabeled RNA in a nondestructive state still remains a challenge. Herein, titanium ions were used as aggregating agents to induce the aggregation of silver nanoparticles, forming hot spots, and the fingerprint information on miRNAs was successfully obtained. This method was used to determine the RNA sequence of homopolymeric bases and the peak position of each base in the Raman spectrum. The obtained RNA spectrum was normalized with the signal intensity of ribose at 959 cm-1, and the base contents of a series of mature miRNA sequences were quantified. Subsequently, the characteristic SERS signal of the RNA hybridization event was obtained by studying the process of RNA hairpin structure formation, and the role of the precursor mir-21 in regulating the target streptomycin sulfate was successfully analyzed. The changes in the SERS signal intensity at the interaction site were accurately identified. This method has potential applications in biological functions of miRNAs, molecular diagnosis, disease treatment, and targeted drug design.