Long-range Energy Transfer Between Dye-loaded Nanoparticles: Observation and Amplified Detection of Nucleic Acids.

Förster resonance energy transfer (FRET) is essential in optical materials for light-harvesting, photovoltaics and biosensing, but its operating range is fundamentally limited by the Förster radius of ∼5 nm. Here, FRET between fluorescent organic nanoparticles (NPs) is studied for the first time in order to break this limit. The donor and acceptor NPs are built from charged hydrophobic polymers loaded with cationic dyes and bulky hydrophobic counterions. Their surface is functionalized with DNA in order to control surface-to-surface distance. It is found that the FRET efficiency does not follow the canonic Förster law, reaching 0.70 and 0.45 values for NP-NP distance of 15 and 20 nm, respectively. This corresponds to the FRET efficiency decay as power four of the surface-to-surface NP-NP distance. Based on this long-distance FRET, a DNA nanoprobe is developed, where a target DNA fragment, encoding cancer marker survivin, brings together donor and acceptor NPs at ∼15 nm distance. In this nanoprobe, a single molecular recognition results in unprecedented color switch for >5000 dyes, yielding a simple and fast assay with 18 attomoles limit of detection. Breaking the Förster distance limit for ultrabright NPs opens the route to advanced optical nanomaterials for amplified FRET-based sensing of biomolecules. This article is protected by copyright. All rights reserved.