48 research outputs found
Calibrating evanescent-wave penetration depths for biological TIRF microscopy
Roughly half of a cells proteins are located at or near the plasma membrane.
In this restricted space the cell senses its environment, signals to its
neighbors and ex-changes cargo through exo- and endocytotic mechanisms. Ligands
bind to receptors, ions flow across channel pores, and transmitters and
metabolites are transported against con-centration gradients. Receptors, ion
channels, pumps and transporters are the molecular substrates of these
biological processes and they constitute important targets for drug discovery.
Total internal reflection fluorescence microscopy suppresses background from
cell deeper layers and provides contrast for selectively imaging dynamic
processes near the basal membrane of live-cells. The optical sectioning of
total internal reflection fluorescence is based on the excitation confinement
of the evanescent wave generated at the glass-cell interface. How deep the
excitation light actually penetrates the sample is difficult to know, making
the quantitative interpretation of total internal reflection fluorescence data
problematic. Nevertheless, many applications like super-resolution microscopy,
colocalization, fluorescence recovery after photobleaching, near-membrane
fluorescence recovery after photobleaching, uncaging or
photo-activation-switching, as well as single-particle tracking require the
quantitative interpretation of evanescent-wave excited images. Here, we review
existing techniques for characterizing evanescent fields and we provide a
roadmap for comparing total internal reflection fluorescence data across
images, experiments, and laboratories.Comment: 18 text pages, 7 figures and one supplemental figur
Molecular Plasmonics: strong coupling at the low molecular density limit
We study the strong coupling between the molecular excited state and the
plasmonic modes of silver hole arrays with a resonant frequency very close to
the asymptotic line of the plasmonic dispersion relation, at the nonlinear
regime. We demonstrate that the strong coupling regime can be achieved between
the two sub-systems at low molecular densities with negligible damping of the
electromagnetic field. Our results are supported by rigorous numerical
simulations showing that the strong coupling is observed when the molecular
transition lies within the nonlinear regime of the dispersion relation rather
than the linear regime.Comment: submitted to PCCP, 7 pages and 3 pages supporting informatio
Collective Plasmonic-Molecular Modes in the Strong Coupling Regime
We demonstrate strong coupling between molecular excited states and surface
plasmon modes of a slit array in a thin metal film. The coupling manifests
itself as an anti-crossing behavior of the two newly formed polaritons. As the
coupling strength grows, a new mode emerges, which is attributed to long range
molecular interactions mediated by the plasmonic field. The new, molecular-like
mode repels the polariton states, and leads to an opening of energy gaps both
below and above the asymptotic free molecule energy.Comment: 8 pages, 6 figures, submitted to PR
How do electronic carriers cross Si-bound alkyl monolayers?
Electron transport through Si-C bound alkyl chains, sandwiched between n-Si
and Hg, is characterized by two distinct types of barriers, each dominating in
a different voltage range. At low voltage, current depends strongly on
temperature but not on molecular length, suggesting transport by thermionic
emission over a barrier in the Si. At higher voltage, the current decreases
exponentially with molecular length, suggesting tunneling through the
molecules. The tunnel barrier is estimated, from transport and photoemission
data, to be ~1.5 eV with a 0.25me effective mass.Comment: 13 pages, 3 figure