Europium-quantum dot nanobioconjugates as luminescent probes for time-gated biosensing

Abstract. Nanobioconjugates have been synthesized using cadmium selenide quantum dots (QDs), europiumcomplexes (EuCs), and biotin. In those conjugates, long-lived photoluminescence (PL) is provided by the euro-pium complexes, which efficiently transfer energy via Forster resonance energy transfer (FRET) to the QDs inclose spatial proximity. As a result, the conjugates have a PL emission spectrum characteristic for QDs com-binedwiththe longPLdecaytimecharacteristicforEuCs.Thenanobioconjugatessynthesisstrategyandphoto-physical properties are described aswell as their performance in a time-resolved streptavidin-biotin PL assay.Inorder to prepare the QD-EuC-biotin conjugates, first an amphiphilic polymer has been functionalized with theEuC and biotin. Then, the polymer has been brought onto the surface of the QDs (either QD655 or QD705) toprovide functionality and to make the QDs water dispersible. Due to a short distance between EuC and QD, anefficient FRET can be observed. Additionally, the QD-EuC-biotin conjugates’ functionality has been demon-strated in a PL assay yielding good signal discrimination, both from autofluorescence and directly excitedQDs. These newly designed QD-EuC-biotin conjugates expand the class of highly sensitive tools for bioana-lytical optical detection methods for diagnostic and imaging applications.