Recent advances in surface plasmon resonance biosensors for microRNAs detection.

miRNAs are a large family of non-coding RNAs which play important roles in translational and post-transcriptional regulation of gene expression and biological processes. Abnormal expression of miRNAs is related to the initiation and progression of different diseases which make them be promising candidates for early medical diagnostics. Thus, accurate detection of miRNAs has great significance for disorder diagnosis. Nevertheless, their intrinsic characteristics such as short sequence, low concentration and sequence homology challenge routine techniques. The detection assays need to be extremely sensitive and selective in small value of intricate RNA samples. Biosensor-based strategies have emerged as potential alternatives to conventional methods in miRNA quantification. The surface plasmon resonance (SPR), an optical biosensor, possessing various advantages including excellent reliability, selectivity and reproducibility represents a wide range of applications in real-time monitoring of biomolecular interactions and detection of biological and chemical analytes with label-based or label free form. Various signal amplification methods can overcome the limitation of SPR methods for detection of small molecules, making it suitable for clinical diagnosis. This review discusses main concepts and performance characteristics of SPR biosensor. Mainly, it focuses on newly emerged enhanced SPR biosensors towards high-throughput and ultrasensitive screening of miRNAs using labeling processes with focusing on the future application in biomedical research and clinical diagnosis. Actually, label-based signal amplification strategies of SPR platforms including nanoparticle enhancement, supersandwich assembly, streptavidin/biotin complex, antibody amplification, enzymatic reactions, triplex structure formation and catalytic hairpin assembly are discussed. Finally label free detection of miRNAs and advantages of SPR-based method was presented.