89 research outputs found
Polymer dynamics, fluorescence correlation spectroscopy, and the limits of optical resolution
In recent years, fluorescence correlation spectroscopy has been increasingly
applied for the study of polymer dynamics on the nanometer scale. The core idea
is to extract, from a measured autocorrelation curve, an effective mean-square
displacement function that contains information about the underlying
conformational dynamics. The paper presents a fundamental study of the
applicability of fluorescence correlation spectroscopy for the investigation of
nanoscale conformational and diffusional dynamics. We find that fluorescence
correlation spectroscopy cannot reliably elucidate processes on length scales
much smaller than the resolution limit of the optics used and that its improper
use can yield spurious results for the observed dynamics.Comment: 4 pages, 4 figures, accepted by Physical Review Letter
Graphene-Induced Energy Transfer for Quantitative Membrane Biophysics at Sub-Nanometer Resolution
Graphene-induced energy transfer (GIET) is a recently developed
fluorescence-spectroscopic technique that achieves sub-nanometric optical
localization of fluorophores along the optical axis of a microscope. GIET is
based on the near-field energy transfer from an optically excited fluorescent
molecule to a single sheet of graphene. It has been successfully used for
estimating inter-leaflet distances of single lipid bilayers, and for
investigating the membrane organization of living mitochondria. In this study,
we use GIET to measure the cholesterol-induced subtle changes of membrane
thickness at the nanoscale. We quantify membrane thickness variations in
supported lipid bilayers (SLBs) as a function of lipid composition and
increasing cholesterol content. Our findings demonstrate that GIET is an
extremely sensitive tool for investigating nanometric structural changes in
bio-membranes.Comment: 6 pages, 4 figure
Repair and Prepare: Strengthening Europe's Economies after the Crisis. Bertelsmann Studies
Europe is often portrayed as a ship with sails of different colours from different countries pushing the common boat in the right direction. From 2010 to 2012, that ship faced the perfect storm: The euro area almost caused the ship to sink, there was massive disagreement on how to get out of the storm, and it was unclear who was steering the ship. However, Euro-Europe eventually
managed to buoy the ship while in the eye of the storm, and the decisive action by ECB President Mario Draghi, arguably not the captain of the ship, managed to steer the common project away from imminent danger
An axon initial segment is required for temporal precision in action potential encoding by neuronal populations
Central neurons initiate action potentials (APs) in the axon initial segment
(AIS), a compartment characterized by a high concentration of voltage-dependent
ion channels and specialized cytoskeletal anchoring proteins arranged in a
regular nanoscale pattern. Although the AIS was a key evolutionary innovation
in neurons, the functional benefits it confers are not clear. Using a mutation
of the AIS cytoskeletal protein \beta IV-spectrin, we here establish an in
vitro model of neurons with a perturbed AIS architecture that retains nanoscale
order but loses the ability to maintain a high NaV density. Combining
experiments and simulations we show that a high NaV density in the AIS is not
required for axonal AP initiation; it is however crucial for a high bandwidth
of information encoding and AP timing precision. Our results provide the first
experimental demonstration of axonal AP initiation without high axonal channel
density and suggest that increasing the bandwidth of the neuronal code and
hence the computational efficiency of network function was a major benefit of
the evolution of the AIS.Comment: Title adjusted, no other change
Electrodynamic coupling of electric dipole emitters to a fluctuating mode density within a nano-cavity
We investigate the impact of rotational diffusion on the electrodynamic
coupling of fluorescent dye molecules (oscillating electric dipoles) to a
tunable planar metallic nanocavity. Fast rotational diffusion of the molecules
leads to a rapidly fluctuating mode density of the electromagnetic field along
the molecules' dipole axis, which significantly changes their coupling to the
field as compared to the opposite limit of fixed dipole orientation. We derive
a theoretical treatment of the problem and present experimental results for
rhodamine 6G molecules in cavities filled with low and high viscosity liquids.
The derived theory and presented experimental method is a powerful tool for
determining absolute quantum yield values of fluorescence.Comment: 5 pages, 3 figures, accepted by Physical Review Letter
photoluminescence of a single quantum emitter in a strongly inhomogeneous chemical environment
A comprehensive photoluminescence study of defect centers in single SiO2 nanoparticles provides new insight into the complex photo-physics of single quantum emitters embedded into a random chemical environment
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