Quantitative Detection of MicroRNA in One Step via Next Generation Magnetic Relaxation Switch Sensing.

One-step, quantitative and rapid detection of microRNA (miRNA) in tumor cells or tissues can provide critical information for clinical diagnosis and cancer treatment. In this work, we develop a magnetic relaxation switch sensing (MRS)-based miRNA sensor using magnetic microparticle (1 μm in diameter, MM1000)-DNA probe-magnetic nanoparticle (30 nm in diameter, MN30) conjugates (MM1000-DNA-MN30). In the presence of target miRNA, DSN enzyme selectively cleaves the DNA tether after miRNA/DNA hybridization to release MN30 and leaves the miRNA intact to lead to the declustering of more MN30 than before. In contrast to conventional MRS by measuring the change of transverse relaxation time (ΔT2) induced by the aggregation or dissociation of magnetic particles in the presence of target, we use the cleaved MN30 from conjugates as the direct readout of ΔT2, which is more sensitive and stable. This MRS-based assay allows for one-step detection of 5 fM of miR-21 in urine samples, quantification of miR-21 from 100 cancer cells, and differentiation of the expression of miR-21 in tumor and surrounding tissues. The merits of this assay, rapidity, ability for quantitation, high sensitivity, and one-step operation, ensure a promising future in diagnostic technology.