Impact of surface chemistry of upconversion nanoparticles on time-dependent cytotoxicity in non-cancerous epithelial cells.

The application of upconversion nanoparticles (UCNPs) for cell and tissue analysis requires a comprehensive understanding of their interactions with biological entities to prevent toxicity or harmful effects. Whereas most studies focus on cancer cells, this work addresses non-cancerous cells with their regular in vitro physiology. Since it is generally accepted that surface chemistry largely determines biocompatibility in general and uptake of nanomaterials in particular, two bilayer surface coatings with different surface shielding properties have been studied: (i) a phospholipid bilayer membrane (PLM) and (ii) an amphiphilic polymer (AP).

Targeted Single Particle Tracking with Upconverting Nanoparticles.

Single particle tracking (SPT) is a powerful technique for real-time microscopic visualization of the movement of individual biomolecules within or on the surface of living cells. However, SPT often suffers from the suboptimal performance of the photon-emitting labels used to tag the biomolecules of interest. For example, fluorescent dyes have poor photostability, while quantum dots suffer from blinking that hampers track acquisition and interpretation.

Upconversion in a d-f [RuYb] Supramolecular Assembly.

We have prepared a hetero-tetrametallic assembly consisting of three ytterbium ions coordinated to a central [Ru(bpm)] (bpm = 2,2'-bipyrimidine) motif. Irradiation into the absorption band of the peripheral ytterbium ions at 980 nm engenders emission of the MLCT state of the central [Ru(bpm)] core at 636 nm, which represents the first example of f → d molecular upconversion (UC). Time-resolved measurements reveal a slow rise of the UC emission, which was modeled with a mathematical treatment of the observed kinetics according to a cooperative photosensitization mechanism using a virtual Yb centered doubly excited state followed by energy transfer to the Ru centered MLCT state.

Structural basis for DNA recognition and allosteric control of the retinoic acid receptors RAR-RXR.

Retinoic acid receptors (RARs) as a functional heterodimer with retinoid X receptors (RXRs), bind a diverse series of RA-response elements (RAREs) in regulated genes. Among them, the non-canonical DR0 elements are bound by RXR-RAR with comparable affinities to DR5 elements but DR0 elements do not act transcriptionally as independent RAREs. In this work, we present structural insights for the recognition of DR5 and DR0 elements by RXR-RAR heterodimer using x-ray crystallography, small angle x-ray scattering, and hydrogen/deuterium exchange coupled to mass spectrometry.

Molecular Upconversion in Water in Heteropolynuclear Supramolecular Tb/Yb Assemblies.

Piling up excited states to reach upconversion (UC) is severely restricted by vibrational quenching mechanisms, especially when one looks at discrete molecular entities in solution. By carefully controlling the supramolecular assembly processes resulting from the strong electrostatic interactions between negatively charged Yb complexes and Tb cations in aqueous solutions, we engineered the formation of heteropolynuclear complexes of [(YbL)Tb ] compositions ( x = 1 and 2). These edifices display a phenomenon of cooperative photosensitization UC with green emission of the Tb cations upon NIR excitation at 980 nm in the Yb absorption band.

Time-dependent luminescence loss for individual upconversion nanoparticles upon dilution in aqueous solution.

Single-particle luminescence microscopy is a powerful method to extract information on biological systems that is not accessible by ensemble-level methods. Upconversion nanoparticles (UCNPs) are a particularly promising luminophore for single-particle microscopy as they provide stable, non-blinking luminescence and allow the avoidance of biological autofluorescence by their anti-Stokes emission. Recently, ensemble measurements of diluted aqueous dispersions of UCNPs have shown the instability of luminescence over time due to particle dissolution-related effects.

Quantitative assessment of energy transfer in upconverting nanoparticles grafted with organic dyes.

Upconverting nanoparticles (UCNPs) are luminophores that have been investigated for a multitude of biological applications, notably low-background imaging, high-sensitivity assays, and cancer theranostics. In these applications, they are frequently used as a donor in resonance energy transfer (RET) pairs. However, because of the peculiarity and non-linearity of their luminescence mechanism, their behavior as a RET pair component has been difficult to predict quantitatively, preventing their optimization for subsequent applications.

FRET-based assay to screen inhibitors of HIV-1 reverse transcriptase and nucleocapsid protein.

During HIV-1 reverse transcription, the single-stranded RNA genome is converted into proviral double stranded DNA by Reverse Transcriptase (RT) within a reverse transcription complex composed of the genomic RNA and a number of HIV-1 encoded proteins, including the nucleocapsid protein NCp7. Here, we developed a one-step and one-pot RT polymerization assay. In this in vitro assay, RT polymerization is monitored in real-time by Förster resonance energy transfer (FRET) using a commercially available doubly-labeled primer/template DNA.

Reverse Transcriptase in Action: FRET-Based Assay for Monitoring Flipping and Polymerase Activity in Real Time.

Reverse transcriptase (RT) of human immunodeficiency virus-1 (HIV-1) is a multifunctional enzyme that catalyzes the conversion of the single stranded viral RNA genome into double-stranded DNA, competent for host-cell integration. RT is endowed with RNA- and DNA-dependent DNA polymerase activity and DNA-directed RNA hydrolysis (RNase H activity). As a key enzyme of reverse transcription, RT is a key target of currently used highly active antiretroviral therapy (HAART), though RT inhibitors offer generally a poor resistance profile, urging new RT inhibitors to be developed.

Large parallelization of STED nanoscopy using optical lattices.

As a scanning microscope, STimulated Emission Depletion (STED) nanoscopy needs parallelization for fast wide-field imaging. Using well-designed optical lattices for depletion together with wide-field excitation and a fast camera for detection, we achieve large parallelization of STED nanoscopy. Wide field of view super-resolved images are acquired by scanning over a single unit cell of the optical lattice, which can be as small as 290 nm * 290 nm.

Site-selective probing of cTAR destabilization highlights the necessary plasticity of the HIV-1 nucleocapsid protein to chaperone the first strand transfer.

The HIV-1 nucleocapsid protein (NCp7) is a nucleic acid chaperone required during reverse transcription. During the first strand transfer, NCp7 is thought to destabilize cTAR, the (-)DNA copy of the TAR RNA hairpin, and subsequently direct the TAR/cTAR annealing through the zipping of their destabilized stem ends. To further characterize the destabilizing activity of NCp7, we locally probe the structure and dynamics of cTAR by steady-state and time resolved fluorescence spectroscopy.

Long vs. short-range orders in random subwavelength hole arrays.

We analyze the progressive introduction of disorder in periodic subwavelength hole arrays. Two models of disorder are discussed from their associated Fourier transforms and correlation functions. The optical transmission properties of the corresponding arrays are closely related with the evolutions of structure factors, as experimentally detailed.

Efficiency and finite size effects in enhanced transmission through subwavelength apertures.

We investigate transmission efficiency and finite size effects for the subwavelength hole arrays. Experiments and simulations show how the finite size effects depend strongly on the hole diameter. The transmission efficiency reaches an asymptotic upper value when the array is larger than the surface plasmon propagation length on the corrugated surface.