A upconverting nanoparticle-based DNA biosensor with the femtomolar detection limit

Abstract

Lowering the limit of detection remains challenging in biosensors due to the false positive signals. The false positive signals, originated from the non-specific binding of molecules, are the critical source of the background noise. We aimed to selectively exclude the false positive signals in our measurement by implementing a two-reporter system composed of upconverting nanoparticles (UCNPs) and fluorescence dyes. The rationale for the designed system is that the probability of non-specific binding of target molecules to two independently labeled probes should be lower compared to a single labeled probe. The UCNPs can be used together with the conventional fluorescence dyes, since the UCNPs have unique upconversion process which the photoluminescence of Tm3+-doped UCNPs lies in the NIR (~800 nm) spectral range (~800 nm) upon NIR (980 nm) excitation. Based on the rationale, we developed a DNA biosensor platform which can detect Middle East Respiratory Syndrome Coronavirus (MERS-CoV) cDNA in femtomolar range. It consists of a capture DNA (with a UCNP tag immobilized on surface) and a reporter DNA (with a fluorescence tag). The capture DNA partially hybridizes with the half of the target DNA while the reporter DNA hybridizes with the other half. We could distinguish the true positive signals from the false positive signals through the co-localization of UCNPs and fluorescent dyes resulted from the specific binding of the target DNA. We believe that our DNA biosensor can be widely adapted to the detection of various infection diseases.