Recent developments in lanthanide-to-quantum dot FRET using time-gated fluorescence detection and photon upconversion

Lanthanide (Ln) ions and quantum dots (QD) provide us with exceptional photophysical properties that cannot be found in any other luminescent material. Long luminescence lifetimes of supramolecular Ln complexes, combination of near infrared excitation and visible luminescence of Ln-doped upconversion nanoparticles, and color-tunability and high brightness of QDs have therefore been widely exploited for bioanalytical applications. One of the most frequently used techniques for analyzing biomolecular interactions is FRET (Förster resonance energy transfer), and the Ln-QD donor-acceptor FRET pair is one of the most versatile tools for FRET biosensing. Progress of technology development in biology, chemistry, and physics has significantly advanced Ln-to-QD FRET over the last five years, and current biosensing approaches include multiplexed detection of microRNAs, homogeneous clinical immunoassays, analysis of QD-bioconjugate morphology, and intra- and extracellular biosensing. Here, we will highlight the concepts and advantages of Ln-to-QD FRET and discuss recent progress and emerging applications.