Metasurface Biosensors Enabling Single-Molecule Sensing of Cell-Free DNA

In this study, we have revealed that highly fluorescence (FL)-enhancing all-dielectric metasurface biosensors are capable of detecting single-target DNA, which is cell-free DNA (cfDNA) specific to the human practice effect. The ultimately high-precision detection was achieved in a scheme combining the metasurface biosensors with a short-time nucleic acid amplification technique, that is, a reduced-cycle polymerase chain reaction (PCR). In this combined scheme, we obtained a series of FL signals at a single-molecule concentration, reflecting the Poisson distribution, and moreover elucidated that the FL signals exhibit the single-molecule cfDNA detection with more than 84% statistical confidence in an automated FL detection system and with 99.9% statistical confidence in confocal FL microscopy. As a result, we have found a simple and practical test to discriminate the target of 1 copy/test from zero using metasurface biosensors, which has not been realized by other elaborate techniques such as digital PCR.