MicroRNAs (miRNAs) have emerged as promising diagnostic biomarkers. We introduce a kinetic fingerprinting approach called Single Molecule Recognition through Equilibrium Poisson Sampling (SiMREPS) for the amplification-free counting of single unlabeled miRNA molecules, which circumvents thermodynamic limits of specificity and virtually eliminates false positives. We demonstrate high-confidence single-molecule detection of synthetic and endogenous miRNAs in both buffer and minimally treated biological liquids, as well as >500-fold discrimination between single nucleotide polymorphisms.
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