J Fluorescence

The scope of this paper is to illustrate the need for an improved quality assurance in fluorometry. For this purpose, instrumental sources of error and their influences on the reliability and comparability of fluorescence data are highlighted for frequently used photoluminescence techniques ranging from conventional macro- and microfluorometry over fluorescence microscopy and flow cytometry to microarray technology as well as in vivo fluorescence imaging. Particularly, the need for and requirements on fluorescence standards for the characterization and performance validation of fluorescence instruments, to enhance the comparability of fluorescence data, and to enable quantitative fluorescence analysis are discussed. Special emphasis is dedicated to spectral fluorescence standards and fluorescence intensity standards

Influence of the stabilizing ligand on the quality, signal-relevant optical properties, and stability of near-infrared emitting Cd1₁₋ₓHgₓTe nanocrystals

Bright and stable near-infrared (NIR) and infrared (IR) emitting chromophores are in high demand for applications in telecommunication, solar cells, security barcodes, and as fluorescent reporters in bioimaging studies. The best choice for wavelengths >750 nm are semiconductor nanocrystals, especially ternary or alloy nanocrystals like CdHgTe, which enable size and composition control of their optical properties. Here, we report on the influence of growth time and surface chemistry on the composition and optical properties of colloidal CdHgTe. Up to now, these are the only NIR and IR emissive quantum dots, which can be synthesized in high quality in water, using a simple one-pot reaction. For this study we utilized and compared three different thiol ligands, thioglycolic acid (TGA), 3-mercaptopropionic acid (MPA), and glutathione (GSH). Aiming at the rational design of bright NIR- and IR-emissive alloy materials, special emphasis was dedicated to a better understanding of the role of the surface ligand and adsorption–desorption equilibria on the photoluminescence quantum yield and stability. In this respect, dilution and protonation studies were performed. Our results show that with this simple synthetic procedure, strongly fluorescent CdHgTe colloids can be obtained with MPA as stabilizing ligand revealing quantum yields as high as 45% independent of particle concentration

Metasurface enhanced sensitized photon upconversion towards highly efficient low power upconversion applications and nano scale E field sensors

Large scale nanoimprinted metasurfaces based on silicon photonic crystal slabs were produced and coated with a NaYF4 Yb3 Er3 upconversion nanoparticle UCNP layer. UCNPs on these metasurfaces yield a more than 500 fold enhanced upconversion emission compared to UCNPs on planar surfaces. It is also demonstrated how the optical response of the UCNPs can be used to estimate the local field energy in the coating layer. Optical simulations using the finite element method validate the experimental results and the calculated spatial three dimensional field energy distribution helps to understand the emission enhancement mechanism of the UCNPs closely attached to the metasurface. In addition, we analyzed the spectral shifts of the resonances for uncoated and coated metasurfaces and metasurfaces submerged in water to enable a prediction of the optimum layer thicknesses for different excitation wavelengths paving the way to applications such as electromagnetic field sensors or bioassay

Quantification of the Activator and Sensitizer Ion Distributions in NaYF4 Yb3 , Er3 Upconverting Nanoparticles Via Depth Profiling with Tender X Ray Photoemission

The spatial distribution and concentration of lanthanide activator and sensitizer dopant ions are of key importance for the luminescence color and efficiency of upconverting nanoparticles UCNPs . Quantifying dopant ion distributions and intermixing, and correlating them with synthesis methods require suitable analytical techniques. Here, X ray photoelectron spectroscopy depth profiling with tender X rays 2000 6000 eV , providing probe depths ideally matched to UCNP sizes, is used to measure the depth dependent concentration ratios of Er3 to Yb3 , [Er3 ] [Yb3 ], in three types of UCNPs prepared using different reagents and synthesis methods. This is combined with data simulations and inductively coupled plasma optical emission spectroscopy ICP OES measurements of the lanthanide ion concentrations to construct models of the UCNPs dopant ion distributions. The UCNP sizes and architectures are chosen to demonstrate the potential of this approach. Core only UCNPs synthesized with XCl3 6H2O precursors amp; 946; phase exhibit a homogeneous distribution of lanthanide ions, but a slightly surface enhanced [Er3 ] [Yb3 ] is observed for UCNPs prepared with trifluroacetate precursors amp; 945; phase . Examination of Yb core Er shell UCNPs reveals a co doped, intermixed region between the single doped core and shell. The impact of these different dopant ion distributions on the UCNP s optical properties is discussed to highlight their importance for UCNP functionality and the design of efficient UCNP

Photoluminescent diamond nanoparticles for cell labeling: study of the uptake mechanism in mammalian cells

Diamond nanoparticles (nanodiamonds) have been recently proposed as new labels for cellular imaging. For small nanodiamonds (size <40 nm) resonant laser scattering and Raman scattering cross-sections are too small to allow single nanoparticle observation. Nanodiamonds can however be rendered photoluminescent with a perfect photostability at room temperature. Such a remarkable property allows easier single-particle tracking over long time-scales. In this work we use photoluminescent nanodiamonds of size <50 nm for intracellular labeling and investigate the mechanism of their uptake by living cells . By blocking selectively different uptake processes we show that nanodiamonds enter cells mainly by endocytosis and converging data indicate that it is clathrin mediated. We also examine nanodiamonds intracellular localization in endocytic vesicles using immunofluorescence and transmission electron microscopy. We find a high degree of colocalization between vesicles and the biggest nanoparticles or aggregates, while the smallest particles appear free in the cytosol. Our results pave the way for the use of photoluminescent nanodiamonds in targeted intracellular labeling or biomolecule deliver

Photo-antagonism of the GABAA receptor

Neurotransmitter receptor trafficking is fundamentally important for synaptic transmission and neural network activity. GABAA receptors and inhibitory synapses are vital components of brain function, yet much of our knowledge regarding receptor mobility and function at inhibitory synapses is derived indirectly from using recombinant receptors, antibody-tagged native receptors and pharmacological treatments. Here we describe the use of a set of research tools that can irreversibly bind to and affect the function of recombinant and neuronal GABAA receptors following ultraviolet photoactivation. These compounds are based on the competitive antagonist gabazine and incorporate a variety of photoactive groups. By using site-directed mutagenesis and ligand-docking studies, they reveal new areas of the GABA binding site at the interface between receptor β and α subunits. These compounds enable the selected inactivation of native GABAA receptor populations providing new insight into the function of inhibitory synapses and extrasynaptic receptors in controlling neuronal excitation

Probing quantum confinement within single core-multishell nanowires

Theoretically core-multishell nanowires under a cross-section of hexagonal geometry should exhibit peculiar confinement effects. Using a hard X-ray nanobeam, here we show experimental evidence for carrier localization phenomena at the hexagon corners by combining synchrotron excited optical luminescence with simultaneous X-ray fluorescence spectroscopy. Applied to single coaxial n-GaN/InGaN multiquantum-well/p-GaN nanowires, our experiment narrows the gap between optical microscopy and high-resolution X-ray imaging and calls for further studies on the underlying mechanisms of optoelectronic nanodevices. © 2012 American Chemical Society.The authors thank Irina Snigireva and Armando Vicente Sole for their assistance with the SEM measurements and data processing using PyMca, respectively. We thank Remi Tocoulou and Peter Cloetens for their help and the ESRF for the beam time allocated. We also thank Andrei Rogalev for the valuable discussions and Gary Admans for the critical reading of the manuscript. This work has been partially supported by the NANOWIRING Marie Curie ITN (EU project no. PITN-GA-2010-265073), as well as by the EPIC-NANOTICS (TEC2011-29120-C05-04) and Q&C-LIGHT (S2009ESP-1503) from Spanish MEC and CAM, respectively.Martínez Criado, G.; Homs Puron, AA.; Alen, B.; Sans Tresserras, JÁ.; Segura Ruiz, J.; Molina Sánchez, A.; Susini, J.... (2012). Probing quantum confinement within single core-multishell nanowires. Nano Letters. 12(11):5829-5834. https://doi.org/10.1021/nl303178uS58295834121

Set Pseudophasors to Stun for Flow Cytometry

Study of signal transduction in live cells benefits from the ability to visualize and quantify light emitted by fluorescent proteins (XFPs) fused to different signaling proteins. However, because cell signaling proteins are often present in small numbers, and because the XFPs themselves are poor fluorophores, the amount of emitted light, and the observable signal in these studies, is often small. An XFP's fluorescence lifetime contains additional information about the immediate environment of the fluorophore that can augment the information from its weak light signal. Here, we constructed and expressed in Saccharomyces cerevisiae variants of Teal Fluorescent Protein (TFP) and Citrine that were isospectral but had shorter fluorescence lifetimes, ∼ 1.5 ns vs ∼ 3 ns. We modified microscopic and flow cytometric instruments to measure fluorescence lifetimes in live cells. We developed digital hardware and a measure of lifetime called a "pseudophasor" that we could compute quickly enough to permit sorting by lifetime in flow. We used these abilities to sort mixtures of cells expressing TFP and the short-lifetime TFP variant into subpopulations that were respectively 97% and 94% pure. This work demonstrates the feasibility of using information about fluorescence lifetime to help quantify cell signaling in living cells at the high throughput provided by flow cytometry. Moreover, it demonstrates the feasibility of isolating and recovering subpopulations of cells with different XFP lifetimes for subsequent experimentation

Plasmonic Control of Radiative Properties of Semiconductor Quantum Dots Coupled to Plasmonic Ring Cavities

In recent years, a lot of effort has been made to achieve controlled delivery of target particles to the hotspots of plasmonic nanoantennas, in order to probe and/or exploit the extremely large field enhancements produced by such structures. While in many cases such high fields are advantageous, there are instances where they should be avoided. In this work, we consider the implications of using the standard nanoantenna geometries when colloidal quantum dots are employed as target entities. We show that in this case, and for various reasons, dimer antennas are not the optimum choice. Plasmonic ring cavities are a better option despite low field enhancements, as they allow collective coupling of many quantum dots in a reproducible and predictable manner. In cases where larger field enhancements are required, or for larger quantum dots, nonconcentric ring-disk cavities can be employed instead