The emission properties of most fluorescent emitters, such as dye molecules or solid-state color ... more The emission properties of most fluorescent emitters, such as dye molecules or solid-state color centers, can be well described by the model of an oscillating electric dipole. However, the orientations of their excitation and emission dipoles are, in most cases, not parallel. Although single molecule excitation and emission dipole orientation measurements have been performed in the past, no experimental method has so far looked at the three-dimensional excitation and emission dipole geometry of individual emitters simultaneously. We present the first experimental study, using defocused imaging in conjunction with radially polarized excitation scanning, to measure both the excitation as well as emission dipole orientations of single molecules, which allows us to sample the distribution of their mutual orientation. We find an unexpectedly broad distribution of the angle between both dipoles which we attribute to the interaction between the observed molecules and the substrate they are immobilized on.
Mutations within the epidermal growth factor receptor (EGFR/erbB1/Her1) are often associated with... more Mutations within the epidermal growth factor receptor (EGFR/erbB1/Her1) are often associated with tumorigenesis. In particular, a number of EGFR mutants that demonstrate ligand-independent signaling are common in non-small cell lung cancer (NSCLC), including kinase domain mutations L858R (also called L834R) and exon 19 deletions (e.g. ΔL747-P753insS) which collectively make up nearly 90% of mutations in NSCLC. The molecular mechanisms by which these mutations confer constitutive activity remain unresolved. Using multiple subdiffraction-limit imaging modalities, we reveal the altered receptor structure and interaction kinetics of NSCLC-associated EGFR mutants. We applied two-color single quantum dot tracking to quantify receptor dimerization kinetics on living cells and show that, in contrast to wild type EGFR, mutants are capable of forming stable, ligand-independent dimers. Two-color super-resolution localization microscopy confirmed ligand-independent aggregation of EGFR mutants. ...
Inorganic carbon nanomaterials, also called carbon nanodots, exhibit a strong photoluminescence w... more Inorganic carbon nanomaterials, also called carbon nanodots, exhibit a strong photoluminescence with unusual properties and, thus, have been the focus of intense research. Nonetheless, the origin of their photoluminescence is still unclear and the subject of scientific debates. Here, we present a single particle comprehensive study of carbon nanodot photoluminescence, which combines emission and lifetime spectroscopy, defocused emission dipole imaging, azimuthally polarized excitation dipole scanning, nanocavity-based quantum yield measurements, high resolution transmission electron microscopy, and atomic force microscopy. We find that photoluminescent carbon nanodots behave as electric dipoles, both in absorption and emission, and that their emission originates from the recombination of photogenerated charges on defect centers involving a strong coupling between the electronic transition and collective vibrations of the lattice structure.
Using a metal nanocavity, we measure absolute values of the photoluminescence quantum yield in a ... more Using a metal nanocavity, we measure absolute values of the photoluminescence quantum yield in a mixture of different types of chromophores (dye molecules and semiconductor nanocrystals). We show that measurements can be performed in an attoliter volume, both in liquid and solid phases, even if both types of chromophores absorb and emit light in the same spectral range. The method is based on recording photoluminescence decay curves of the chromophore mixture as a function of the cavity length. Changing the distance between the cavity mirrors modifies the local density of states of the electromagnetic field and thus, the radiative transition rate of the enclosed emitters. By extracting individual decay components, corresponding to the different types of the emitters, we determine their quantum yield values separately and simultaneously. The nanocavity-based method opens up new perspectives for studying quantum emitters in complex photophysical systems, for instance, multichromophoric thin films, fluorescent proteins, or dyes incorporated into a lipid bilayer.
We present a new concept for measuring distance values of single molecules from a surface with na... more We present a new concept for measuring distance values of single molecules from a surface with nanometer accuracy using the energy transfer from the excited molecule to surface plasmons of a metal film. We measure the fluorescence lifetime of individual dye molecules deposited on a dielectric spacer as a function of a spacer thickness. By using our theoretical model, we convert the lifetime values into the axial distance of individual molecules. Similar to Förster resonance energy transfer (FRET), this allows emitters to be localized with nanometer accuracy, but in contrast to FRET the distance range at which efficient energy transfer takes place is an order of magnitude larger. Our technique can be potentially used as a tool for measuring intramolecular distances of biomolecules and complexes.
The emission properties of most fluorescent emitters, such as dye molecules or solid-state color ... more The emission properties of most fluorescent emitters, such as dye molecules or solid-state color centers, can be well described by the model of an oscillating electric dipole. However, the orientations of their excitation and emission dipoles are, in most cases, not parallel. Although single molecule excitation and emission dipole orientation measurements have been performed in the past, no experimental method has so far looked at the three-dimensional excitation and emission dipole geometry of individual emitters simultaneously. We present the first experimental study, using defocused imaging in conjunction with radially polarized excitation scanning, to measure both the excitation as well as emission dipole orientations of single molecules, which allows us to sample the distribution of their mutual orientation. We find an unexpectedly broad distribution of the angle between both dipoles which we attribute to the interaction between the observed molecules and the substrate they are immobilized on.
Mutations within the epidermal growth factor receptor (EGFR/erbB1/Her1) are often associated with... more Mutations within the epidermal growth factor receptor (EGFR/erbB1/Her1) are often associated with tumorigenesis. In particular, a number of EGFR mutants that demonstrate ligand-independent signaling are common in non-small cell lung cancer (NSCLC), including kinase domain mutations L858R (also called L834R) and exon 19 deletions (e.g. ΔL747-P753insS) which collectively make up nearly 90% of mutations in NSCLC. The molecular mechanisms by which these mutations confer constitutive activity remain unresolved. Using multiple subdiffraction-limit imaging modalities, we reveal the altered receptor structure and interaction kinetics of NSCLC-associated EGFR mutants. We applied two-color single quantum dot tracking to quantify receptor dimerization kinetics on living cells and show that, in contrast to wild type EGFR, mutants are capable of forming stable, ligand-independent dimers. Two-color super-resolution localization microscopy confirmed ligand-independent aggregation of EGFR mutants. ...
Inorganic carbon nanomaterials, also called carbon nanodots, exhibit a strong photoluminescence w... more Inorganic carbon nanomaterials, also called carbon nanodots, exhibit a strong photoluminescence with unusual properties and, thus, have been the focus of intense research. Nonetheless, the origin of their photoluminescence is still unclear and the subject of scientific debates. Here, we present a single particle comprehensive study of carbon nanodot photoluminescence, which combines emission and lifetime spectroscopy, defocused emission dipole imaging, azimuthally polarized excitation dipole scanning, nanocavity-based quantum yield measurements, high resolution transmission electron microscopy, and atomic force microscopy. We find that photoluminescent carbon nanodots behave as electric dipoles, both in absorption and emission, and that their emission originates from the recombination of photogenerated charges on defect centers involving a strong coupling between the electronic transition and collective vibrations of the lattice structure.
Using a metal nanocavity, we measure absolute values of the photoluminescence quantum yield in a ... more Using a metal nanocavity, we measure absolute values of the photoluminescence quantum yield in a mixture of different types of chromophores (dye molecules and semiconductor nanocrystals). We show that measurements can be performed in an attoliter volume, both in liquid and solid phases, even if both types of chromophores absorb and emit light in the same spectral range. The method is based on recording photoluminescence decay curves of the chromophore mixture as a function of the cavity length. Changing the distance between the cavity mirrors modifies the local density of states of the electromagnetic field and thus, the radiative transition rate of the enclosed emitters. By extracting individual decay components, corresponding to the different types of the emitters, we determine their quantum yield values separately and simultaneously. The nanocavity-based method opens up new perspectives for studying quantum emitters in complex photophysical systems, for instance, multichromophoric thin films, fluorescent proteins, or dyes incorporated into a lipid bilayer.
We present a new concept for measuring distance values of single molecules from a surface with na... more We present a new concept for measuring distance values of single molecules from a surface with nanometer accuracy using the energy transfer from the excited molecule to surface plasmons of a metal film. We measure the fluorescence lifetime of individual dye molecules deposited on a dielectric spacer as a function of a spacer thickness. By using our theoretical model, we convert the lifetime values into the axial distance of individual molecules. Similar to Förster resonance energy transfer (FRET), this allows emitters to be localized with nanometer accuracy, but in contrast to FRET the distance range at which efficient energy transfer takes place is an order of magnitude larger. Our technique can be potentially used as a tool for measuring intramolecular distances of biomolecules and complexes.
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Papers by Narain Karedla