Single-MicroRNA Detection on High-Selectivity Metasurface Fluorescence Biosensors.

Next-generation diagnostics is expected to use the abundant data on living bodies and provide sufficiently useful healthcare information. A significant portion of the data are considered to be collected from microRNAs (miRNAs), which play crucial roles in various activities inside the body. Here, we demonstrate single-miRNA detection using metasurface fluorescence (FL) biosensors, which are optimized all-dielectric nanostructured surfaces featuring excellent FL detection capability. Ultimate high-sensitivity discrimination of one miRNA from zero miRNA is achieved at the subattomolar level by employing optimized reverse transcription (RT) of miRNAs, polymerase chain reaction (PCR) suppressing false reactions, and highly efficient and target-selective FL detection of the miRNA amplicons on the metasurface biosensors using appropriately designed oligo DNA probes. This degree of precision has never been obtained using any other technique, such as digital PCR, which is currently one of the most efficient techniques. Furthermore, we demonstrate the specific detection of a cancer-correlated miRNA that is deeply mixed with another miRNA. We also examine and discuss other methods that possibly work for miRNA detection at femtomolar or lower concentrations, such as chromatography and different amplification methods, including handy one-step RT-PCR.