Single-photon emission from a single InAs quantum dot

Excitation power-dependent micro-photoluminescence spectra and photon-correlation measurement are used to study the optical properties and photon statistics of single InAs quantum dots. Exciton and biexciton emissions, whose photoluminescence intensities have linear and quadratic excitation power dependences, respectively, are identified. Under pulsed laser excitation, the zero time delay peak of second order correlation function corresponding to exciton emission is well suppressed, which is a clear evidence of single photon emission.

Zur Kooperativität des Vogelspinnen-Hämocyanins

Zusammenfassung Kooperativität bei Atmungsproteinen bedeutet eine Änderung der O2-Affinität während der Beladung mit O2 und läßt sich durch die Wechselbeziehung zwischen O2-Beladung und Konformation beschreiben. In dieser Arbeit wurde das 24-mere Hämocyanin der Vogelspinne Eurypelma californicum bzgl. Beladung und Konformationen sowohl auf der Ensemble- wie auch auf der Einzel-Molekül-Ebene charakterisiert. EnsembleDie Bindung von O2 an Hämocyanine ist mit einer drastischen Abnahme der Fluoreszenz-Quantenausbeute verbunden. Durch Vergleich von theoretisch und experimentell bestimmten Quantenausbeuten konnte gezeigt werden, daß die Löschung auf Förster-Transfer zurückzuführen ist, und daß kein Einfluß der Oligomerisierung, Protein-Konformation, Beweglichkeit oder Tierart besteht. Die Konformation von Hämocyaninen konnte mit Crosslinkern im oxy- und deoxy-Zustand fixiert werden. Die Charakterisierung der Produkte führte zu einer neuen Vorstellung, wie unterschiedliche Affinitäten realisiert sein können. Hierbei kommt der Dynamik der Protein-Matrix eine entscheidende Rolle zu. Einzel-MoleküleMittels Zwei-Photonen-Anregung konnten erstmalig einzelne Proteine über ihre intrinsische Tryptophan-Fluoreszenz nachgewiesen werden. Zum einen gelang es, Modellsysteme mit nur 340 Trp abzubilden, andererseits konnte die Diffusion einzelner Hämocyanine (148 Trp) mit Hilfe der Fluoreszenz-Korrelationsspektroskopie nachgewiesen werden.Einzelne Hämocyanine konnten durch Adsorption und mildes Eintrocknen an verschiedenen Oberflächen immobilisiert werden. Mittels Atomarer Kraft-Mikroskopie (AFM) ließen sich individuelle Hämocyanine abgebilden, wobei Details der Quarärstruktur aufgelöst werden konnten.

Nuclear charge radius of the halo nucleus lithium-11

Nuclear charge radii of short-lived isotopes can be probed in a nuclear-model independent way via isotope shift measurements. For this purpose a novel technique was developed at GSI, Darmstadt. It combines two-photon laser spectroscopy in the 2s-3s electronic transition of lithium, resonance ionization, and detection via quadrupole mass spectrometry. In this way an accuracy of 5e-5 which is necessary for the extraction of nuclear charge radii, and an overall detection efficiency of 1e-4 is reached. This allowed an isotope shift measurement of Li-11 for the first time at the TRIUMF facility in Vancouver. Additionally, uncertainties in the isotope shift for all other lithium isotopes were reduced by about a factor of four compared to previous measurements at GSI. Results were combined with recent theoretical mass shift calculations in three-electron systems and root-mean-square nuclear charge radii of all lithium isotopes, particulary of the two-neutron halo nucleus Li-11, were determined. Obtained charge radii decrease continuously from Li-6 to Li-9, while a strong increase between Li-9 and Li-11 is observed. This is compared to predictions of various nuclear models and it is found that a multicluster model gives the best overall agreement. Within this model, the increase in charge radius between Li-9 and Li-11is to a large extend caused by intrinsic excitation of the Li-9-like core while the neutron-halo correlation contributes only to a small extend.

Fluctuation spectroscopy of single plasmonic nanostructures

Plasmonic nanoparticles are great candidates for sensing applications with optical read-out. Plasmon sensing is based on the interaction of the nanoparticle with electromagnetic waves where the particle scatters light at its resonance wavelength. This wavelength depends on several intrinsic factors like material, shape and size of the nanoparticle as well as extrinsic factors like the refractive index of the surrounding medium. The latter allows the nanoparticle to be used as a sensor; changes in the proximate environment can be directly monitored by the wavelength of the emitted light. Due to their minuscule size and high sensitivity this allows individual nanoparticles to report on changes in particle coverage.rnrnTo use this single particle plasmon sensor for future sensing applications it has to meet the demand for detection of incidents on the single molecule level, such as single molecule sensing or even the detection of conformational changes of a single molecule. Therefore, time resolution and sensitivity have to be enhanced as today’s measurement methods for signal read-out are too slow and not sensitive enough to resolve these processes. This thesis presents a new experimental setup, the 'Plasmon Fluctuation Setup', that leads to tremendous improvements in time resolution and sensitivity. This is achieved by implementation of a stronger light source and a more sensitive detector. The new setup has a time resolution in the microsecond regime, an advancement of 4-6 orders of magnitude to previous setups. Its resonance wavelength stability of 0.03 nm, measured with an exposure time of 10 ms, is an improvement of a factor of 20 even though the exposure time is 3000 times shorter than in previous reports. Thus, previously unresolvable wavelength changes of the plasmon sensor induced by minor local environmental alteration can be monitored with extremely high temporal resolution.rnrnUsing the 'Plasmon Fluctuation Setup', I can resolve adsorption events of single unlabeled proteins on an individual nanorod. Additionally, I monitored the dynamic evolution of a single protein binding event on a millisecond time scale. This feasibility is of high interest as the role of certain domains in the protein can be probed by a study of modified analytes without the need for labels possibly introducing conformational or characteristic changes to the target. The technique also resolves equilibrium fluctuations in the coverage, opening a window into observing Brownian dynamics of unlabeled macromolecules. rnrnA further topic addressed in this thesis is the usability of the nanoruler, two nanospheres connected with a spacer molecule, as a stiffness sensor for the interparticle linker under strong illumination. Here, I discover a light induced collapse of the nanoruler. Furthermore, I exploit the sensing volume of a fixed nanorod to study unlabeled analytes diffusing around the nanorod at concentrations that are too high for fluorescence correlation spectroscopy but realistic for biological systems. Additionally, local pH sensing with nanoparticles is achieved.

Fluorescence correlation analysis of probe diffusion simplifies quantitative pathogen detection by PCR

A sensitive, labor-saving, and easily automatable nonradioactive procedure named APEX-FCS (amplified probe extension detected by fluorescence correlation spectroscopy) has been established to detect specific in vitro amplification of pathogen genomic sequences. As an example, Mycobacterium tuberculosis genomic DNA was subjected to PCR amplification with the Stoffel fragment of Thermus aquaticus DNA polymerase in the presence of nanomolar concentrations of a rhodamine-labeled probe (third primer), binding to the target in between the micromolar amplification primers. The probe becomes extended only when specific amplification occurs. Its low concentration avoids false-positives due to unspecific hybridization under PCR conditions. With increasing portion of extended probe molecules, the probe’s average translational diffusion properties gradually change over the course of the reaction, reflecting amplification kinetics. Following PCR, this change from a stage of high to a stage of low mobility can directly be monitored during a 30-s measurement using a fluorescence correlation spectroscopy device. Quantitation down to 10 target molecules in a background of 2.5 μg unspecific DNA without post-PCR probe manipulations could be achieved with different primer/probe combinations. The assay holds the promise to concurrently perform amplification, probe hybridization, and specific detection without opening the reaction chamber, if sealable foils are used.

Conformational transitions monitored for single molecules in solution.

Phenomena that can be observed for a large number of molecules may not be understood if it is not possible to observe the events on the single-molecule level. We measured the fluorescence lifetimes of individual tetramethylrhodamine molecules, linked to an 18-mer deoxyribonucleotide sequence specific for M13 DNA, by time-resolved, single-photon counting in a confocal fluorescence microscope during Brownian motion in solution. When many molecules were observed, a biexponential fluorescence decay was observed with equal amplitudes. However, on the single-molecule level, the fraction of one of the amplitudes spanned from 0 to unity for a collection of single-molecule detections. Further analysis by fluorescence correlation spectroscopy made on many molecules revealed a process that obeys a stretched exponential relaxation law. These facts, combined with previous evidence of the quenching effect of guanosine on rhodamines, indicate that the tetramethylrhodamine molecule senses conformational transitions as it associates and dissociates to a guanosine-rich area. Thus, our results reveal conformational transitions in a single molecule in solution under conditions that are relevant for biological processes.

Oxidation Of Spiroalcohols With 2,3-Dichloro-5,6-Dicyano-1,4-Benzoquinone (Ddq) .4. Structure Of A Novel Dioxepin Derivative

DDQ oxidation of the spiroalcohol 7a gives exclusively a compound to which the 13a-methyl-13aH-7a, 15-methano-15H-dinaphtho[2,1-b:2',1'-e][1,4]-dioxepin structure 8a has been assigned on the basis of two-dimensional homonuclear (H-1-H-1) and heteronuclear (H-1-C-13; FUCOUP) correlation spectroscopy experiments. Similar oxidation of spiroalcohols 7b-h gives the dioxepin derivatives 8b-h.

J-Edited Pure Shift NMR for the Facile Measurement of (n)J(HH) for Specific Protons

We report a novel 1D J-edited pure shift NMR experiment (J-PSHIFT) that was constructed from a pseudo 2D experiment for the direct measurement of proton-proton scalar couplings. The experiment gives homonuclear broad-band H-1-decoupled H-1 NMR spectra, which provide a single peak for chemically distinct protons, and only retain the homonuclear-scalar-coupled doublet pattern at the chemical-shift positions of the protons in the coupled network of a specific proton. This permits the direct and unambiguous measurement of the magnitudes of the couplings. The incorporation of a 1D selective correlation spectroscopy (COSY)/ total correlation spectroscopy (TOCSY) block in lieu of the initial selective pulse, results in the exclusive detection of the correlated spectrum of a specific proton.

Quantitative metabolic profiling of NMR spectral signatures of branched chain amino acids in blood serum

Branched Chain Amino Acids (BCAAs) are related to different aspects of diseases like pathogenesis, diagnosis and even prognosis. While in some diseases, levels of all the BCAAs are perturbed; in some cases, perturbation occurs in one or two while the rest remain unaltered. In case of ischemic heart disease, there is an enhanced level of plasma leucine and isoleucine but valine level remains unaltered. In `Hypervalinemia', valine is elevated in serum and urine, but not leucine and isoleucine. Therefore, identification of these metabolites and profiling of individual BCAA in a quantitative manner in body-fluid like blood plasma/serum have long been in demand. H-1 NMR resonances of the BCAAs overlap with each other which complicates quantification of individual BCAAs. Further, the situation is limited by the overlap of broad resonances of lipoprotein with the resonances of BCAAs. The widely used commercially available kits cannot differentially estimate the BCAAs. Here, we have achieved proper identification and characterization of these BCAAs in serum in a quantitative manner employing a Nuclear Magnetic Resonance-based technique namely T-2-edited Correlation Spectroscopy (COSY). This approach can easily be extended to other body fluids like bile, follicular fluids, saliva, etc.

Reversible addition-fragmentation chain transfer mediated radical polymerization of asymmetrical divinyl monomers targeting hyperbranched vinyl polymers

Reversible addition-fragmentation chain transfer (RAFT) mediated radical polymerizations of allyl methacrylate and undecenyl methacrylate, compounds containing two types of vinyl groups with different reactivities, were investigated to provide hyperbranched polymers. The RAFT agent benzyl dithiobenzoate was demonstrated to be an appropriate chain-transfer agent to inhibit crosslinking and obtain polymers with moderate-to-high conversions. The polymerization of allyl methacrylate led to a polymer without branches but with five- or six-membered rings. However, poly(undecenyl methacrylate) showed an indication of branching rather than intramolecular cycles. The hyperbranched structure of poly(undecenyl methacrylate) was confirmed by a combination of H-1, C-13, H-1-H-1 correlation spectroscopy, and distortionless enhancement by polarization transfer 135 NMR spectra. The branching topology of the polymers was controlled by the variation of the reaction temperature, chain-transfer-agent concentration, and monomer conversion. The significantly lower inherent viscosities of the resulting polymers, compared with those of linear analogues, demonstrated their compact structure,

Chemical bonding and electronic structure of 4d-metal monocarbides

Bond distances, vibrational frequencies, dissociation energies, electron affinities, ionization potentials and dipole moments of the title molecules in neutral and charged ions were studied by use of density functional method. Ground states for each molecule were assigned. For neutral and cationic molecules, the bond distance decreases from YC (YC+) to RhC (RhC+), then increases, while for anionic molecules, the bond distance decreases from YC- to RuC-, then increases. Opposite trend was observed for vibrational frequency. The bond ionic character decreases from ZrC to PdC for neutral molecules. The bonding patterns are discussed and compared with the available studies.

Synteza i charakterystyka wybranych nanocząstek o potencjalnych zastosowaniach w medycynie

Zakład Biofizyki Molekularnej, Centrum NanoBioMedyczne UAM

The Superresolution Problem in Doppler Difference Laser Anemometry

info:eu-repo/semantics/published

Charge exchange emission from solar wind helium ions

Charge exchange X-ray and far-ultraviolet (FUV) aurorae can provide detailed insight into the interaction between solar system plasmas. Using the two complementary experimental techniques of photon emission spectroscopy and translation energy spectroscopy, we have studied state-selective charge exchange in collisions between fully ionized helium and target gasses characteristic of cometary and planetary atmospheres (H2O, CO2, CO, and CH4). The experiments were performed at velocities typical for the solar wind (200-1500 km s(-1)). Data sets are produced that can be used for modeling the interaction of solar wind alpha particles with cometary and planetary atmospheres. These data sets are used to demonstrate the diagnostic potential of helium line emission. Existing Extreme Ultraviolet Explorer (EUVE) observations of comets Hyakutake and Hale-Bopp are analyzed in terms of solar wind and coma characteristics. The case of Hale-Bopp illustrates well the dependence of the helium line emission to the collision velocity. For Hale-Bopp, our model requires low velocities in the interaction zone. We interpret this as the effect of severe post-bow shock cooling in this extraordinary large comet.

Charge exchange and dissociative processes in collisions of slow He2+ ions with H2O molecules

Experimental and theoretical studies of one-electron capture in collisions of He2+ ions with H2O molecules have been carried out in the range 0.025-12 keV amu(-1) corresponding to typical solar wind velocities of 70-1523 km s(-1). Translational energy spectroscopy (TES), photon emission spectroscopy (PES), and fragment ion spectroscopy were employed to identify and quantify the collision mechanisms involved. Cross sections for selective single electron capture into n=1, 2, and 3 states of the He+ ion were obtained using TES while PES provided cross sections for capture into the He+(2p) and He+(3p) states. Our model calculations show that He+(n=2) and He+(n=3) formation proceeds via a single-electron process governed by the nucleus-electron interaction. In contrast, the He+(1s) formation mechanism involves an exothermic two-electron process driven by the electron-electron interaction, where the potential energy released by the electron capture is used to remove a second electron thereby resulting in fragmentation of the H2O molecule. This process is found to become increasingly important as the collision energy decreases. The experimental cross sections are found to be in reasonable agreement with cross sections calculated using the Demkov and Landau-Zener models.