A Nanobiosensor Based on Fluorescent DNA-Hosted Silver Nanocluster and HCR Amplification for Detection of MicroRNA Involved in Progression of Multiple Sclerosis.

MicroRNAs (miRNA) are a novel class of small noncoding RNAs with roles in RNA silencing and post transcriptional regulation of gene expression. Due to their roles, miRNA can be considered as new biomarkers for prognosis of diseases such as Multiple sclerosis (MS). Herein, we report a miRNA nanobiosensor based on nucleic acid hybridization chain reaction and highly fluorescent DNA hosted silver nanoclusters (NC). In our method, two types of hairpin oligonucleotide probes, MB1 and MB2, were employed as hybridization chain reaction (HCR) monomers, where MB1 acted as a template for in situ synthesis of fluorescent Ag NC. These monomers were stable in solution but they triggered a cascade of hybridization events once miR-145 (a biomarker of MS in blood) was added to the solution. The process yielded nicked double stranded DNA. The nanobiosensor showed great sensitivity for the detection of target microRNA and excellent limit of detection of about 0.1 nM with high specificity to differentiate sharply between complementary, mismatch, and non-complementary target miRNAs. Alongside the outstanding sensitivity and selectivity, the nanobiosensor exhibited great reproducibility, stability and a decent response in real sample analysis with blood plasma. In conclusion, this simple and highly responsive nanobiosensor can clinically be used for the early detection of MS by direct detection of the plasma miR-145 in real clinical samples, without a need for sample preparation, RNA extraction and/or amplification.