No abstract

Quantum dots (QDs) are attractive photoluminescence probes for biomedical imaging due to their unique photophysical properties. However, the potential toxicity of QDs has remained a major obstacle to their clinical use because they commonly incorporate the toxic heavy metal cadmium within the core of the QDs. In this work, we have evaluated a novel type of heavy metal-free/cadmium-free and biocompatible QD nanoparticles (bio CFQD® nanoparticles) with a good photoluminescence quantum yield. Sentinel lymph node mapping is an increasingly important treatment option in the management of breast cancer. We have demonstrated their potential for lymph node mapping by ex vivo imaging of regional lymph nodes after subcutaneous injection in the paw of rats. Using photoluminescence imaging and chemical extraction measurements based on elemental analysis by inductively coupled plasma mass spectroscopy, the quantum dots are shown to accumulate quickly and selectively in the axillary and thoracic regional lymph nodes. In addition, lifetime imaging microscopy of the QD photoluminescence indicates minimal perturbation to their photoluminescence properties in biological systems.

The ability to control Förster Resonance Energy Transfer (FRET) between emitters via the design of nanostructured materials with appropriate electromagnetic properties is important in the development of fast and enhanced sources of illumination, high-efficiency photovoltaic devices and biomedical applications, such as nanorulers. While the engineering of the local density of states allows an efficient control over the spontaneous emission rate, its influence on the FRET process has been an ongoing debate and has led to disparate experimental and theoretical results. In particular, hyperbolic metamaterials have recently been shown to drastically increase the fluorescence decay rate. Here, we experimentally demonstrate an increase in the FRET rate for Donor-Acceptor (D-A) pairs separated by fixed distances (3.4, 6.8 and 10.2 nm) located inside a hyperbolic metamaterial comprised of an array of gold nanorods. While the modification of the local density of states surrounding the D-A pairs strongly influences the FRET rate, leading to a 13-fold increase inside the metamaterial, the FRET efficiency is shown to remain mostly unaffected. For comparison, we also study the modification of energy transfer rate and efficiencies of D-A pairs placed on top of a gold film, on top of a nanorod-based metamaterial and inside a nanorod-based metamaterial coated with polymer in order to prevent quenching. The free-space emission intensities of the acceptor were also investigated, leading up to an 18-fold increase in the emission intensity. The designed

We perform wide-field time-correlated single photon counting-based fluorescence lifetime imaging (FLIM) with a crossed delay line anode image intensifier, where the pulse propagation time yields the photon position. This microchannel plate-based detector was read out with conventional fast timing electronics and mounted on a fluorescence microscope with total internal reflection (TIR) illumination. The picosecond time resolution of this detection system combines low illumination intensity of microwatts with wide-field data collection. This is ideal for fluorescence lifetime imaging of cell membranes using TIR. We show that fluorescence lifetime images of living HeLa cells stained with membrane dye di-4-ANEPPDHQ exhibit a reduced lifetime near the coverslip in TIR compared to epifluorescence FLIM.