DNA-Coated Upconversion Nanoparticles for Sensitive Nucleic Acid FRET Biosensing

Despite the significant advancements of developing upconversion nanoparticles (UCNPs) for high performance biosensing and bioimaging, the development of DNA-functionalized UCNPs with thin coatings, efficient surface passivation, and fully functional DNAs for hybridization sensing in biological media remains extremely challenging. Here, a straightforward concept of labeling DNA to a thin polysulfonate polymer layer on UCNPs is presented. Both UCNPs and DNA preserve their full functionality as demonstrated by Forster resonance energy transfer (FRET) hybridization assays with a Cy3-conjugated complementary DNA. The important bioanalytical benefits of the UCNP-DNA nanohybrids are demonstrated by their implementation into rapid and wash-free microRNA hybridization FRET assays. Using a simple fiber-coupled USB-spectrometer and 980 nm diode laser excitation in a 96-well microplate, ratiometric FRET from UCNP-to-Cy3 can quantify miR20a in a 0.01-10 x 10(-9) m concentration range with a detection limit of 30 x 10(-12) m (4.5 fmol of miR20a), which is more than 20-fold lower compared to quantum dot-based FRET assays. The functional thin-coating DNA-UCNP nanohybrids have a strong potential for translating UCNPs into advanced DNA-based biosensing, bioimaging, and high-throughput and point-of-care clinical diagnostics.