Publications by Iwan Märki | EPFL Graph Search

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Research on synthetic delivery vectors is of major interest for cell imaging and manipulation, as they allow an efficient transfer of nucleic acids, therapeutic proteins or small drugs into the cells. We have developed a library of L-lysine analogues that allow for highly efficient gene delivery with low cytotoxicity. However little is known on the exact mechanism of uptake and the final intracellular destination of the synthetic carriers. Therefore we have developed a novel optical technique based on a mod

The measurement of tissue and cell oxygenation is important for understanding cell metabolism. We have addressed this problem with a novel optical technique, called triplet imaging, that exploits oxygen-induced triplet lifetime changes and is compatible with a variety of fluorophores. A modulated excitation of varying pulse widths allows the extraction of the lifetime of the essentially dark triplet state using a high-fluorescence signal intensity. This enables the monitoring of fast kinetics of oxygen conc

Fluorescence localization microscopy (i.e., PALM, STORM) has enabled optical imaging at nanometer-scale resolutions. The localization algorithms used in these techniques rely on fitting a 2-D Gaussian to the in-focus image of individual fluorophores. For f ...

We present a functional imaging method based on triplet state kinetics. The triplet state of many known fluorophores shows a triplet lifetime typically in the order of ~10e-6 – 10e-3 s, 3-6 orders of magnitude longer than the associated fluorescence singlet lifetime. As a consequence triplet state sensing is more exposed to the microenvironment of fluorophores and can be used as a functional molecular antenna. By means of a modulated excitation scheme of pulses with varying duty cycles, the triplet state po

We report results on two-photon total-internal-reflection fluorescence correlation spectroscopy with radially polarized light. The combination of liquid crystal spatial light modulator, providing radial polarization, with ultrafast laser (picosecond Nd:GdV ...

The use of fluorescence light for far-field imaging at the nanometer scale has drawn much attention worldwide. Example techniques include STED microscopy and localization microscopy (PALM, STORM). Typically, nanoscopy approaches have been focused on the manipulation and detection of the intensity of fluorescence light leading to lateral accuracy of a few nanometers. However, three-dimensional nanometer accuracy, in particular axial accuracy of the same order, remains a challenge. The phase of fluorescence l

Fluorophores that are fixed during image acquisition produce a diffraction pattern that is characteristic of the orientation of the fluorophore’s underlying dipole. Fluorescence localization microscopy techniques such as PALM and STORM achieve super-resolution by applying Gaussian-based fitting algorithms to in-focus images of individual fluorophores; when applied to fixed dipoles, this can lead to a bias in the range of 5-20 nm.We introduce a method for the joint estimation of position and orientation of d

We introduce a photoswitchable O6-benzylguanine derivative and demonstrate its use for super-resolution microscopy of SNAP-tagged proteins based on single fluorophore localization. Stochastic Optical Reconstruction Microscopy (STORM) reveals SNAP-tagged mi ...

Triplet imaging is a novel optical technique that allows investigating oxy- gen metabolism at the single cell and the sub-cellular level. The method combines high temporal and spatial resolution, which are required for the monitoring of fast kinetics of ox ...

The present invention relates to a functional optical coherent imaging (fOCI) platform comprising at least one active camera unit (ACU) comprising a coherent and/or a partially coherent light source, and means for spectral filtering and imaging a selected ...

Fluorescence localization microscopy techniques such as PALM and STORM achieve super-resolution by sequentially imaging sparse subsets of fluorophores, which are localized by means of Gaussian-based localization. Applied to fixed fluorophores, with dipole radiation characteristics, this can lead to an estimation bias in the range of 5-20nm. We introduce a method for the joint estimation of position and orientation of single fluorophores, based on an accurate image formation model expressed as a 3-D steerabl

We present a combination of self-interference microscopy with lateral super-resolution microscopy and introduce a novel approach for localizing a single nano-emitter to within a few nanometers in all three dimensions over a large axial range. We demonstrat ...

We present theoretical and experimental results on switching and tuning of a two-dimensional photonic crystal resonant microcavity by means of a silicon AFM tip, probing the highly localized optical field in the vicinity of the cavity. On-off switching and ...

We present the results on two-photon total-internal-reflection fluorescence correlation spectroscopy. The combination of liquid crystal spatial light modulator, providing radial polarization, with ultrafast laser (picosecond Nd:GdVO4 laser) allowed us to take the advantage of nonlinear optical contrast mechanisms to suppress the side-lobe energy specific for radial polarization and reduce the effective excited volume twice compared to one-photon evanescent wave excitation in fluorescence correlation spectro

We present a novel concept for optical spectroscopy called nonlinear correlation spectroscopy (NLCS). NLCS analyses coherent field fluctuations of the second and third harmonic light generated by diffusing nanoparticles. Particles based on noncentrosymmetr ...

We demonstrate nanometer-level localization accuracy of a single fluorescent emitter in three dimensions. Our super resolution microscopy technique is based on spectral self-interference for axial localization and two-dimensional diffraction pattern analysis for lateral localization.

We show nanometer-level localization accuracy of a single quantum-dot in three dimensions by self-interference and diffraction-pattern analysis. We believe that this approach has the capacity to push optical microscopy to the molecular level.

Nanoparticles are interesting for biomedical imaging as novel non- fluorescent non-bleaching labels. We present the characterization of freely diffusing nanoparticles using third harmonic generation correlation spectroscopy by illumination with a focussed pulsed femtosecond laser. We present the optical system as well as first spectroscopic results on nanoparticles.

Iwan Märki

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Assessing the cellular uptake pathway for poly-Lysine analogues using triplet lifetime imaging

Super-resolution orientation estimation and localization of fluorescent dipoles using 3-D steerable filters

Triplet imaging of oxygen consumption during the contraction of a single smooth muscle cell (A7r5)

Steerable filters for orientation estimation and localization of fluorescent dipoles

Triplet State Imaging

High volume confinement in two-photon total-internal- reflection fluorescence correlation spectroscopy

Three-dimensional Nano-Localization of Fluroescent Emitters

Super-resolved position and orientation from defocused images of fluorescent dipoles

Targeted Photoswitchable Probe for Nanoscopy of Biological Structures

Triplet imaging of oxygen consumption during the contraction of a single smooth muscle cell (A7r5)

Functional optical coherent imaging platform for medical application e.g. neurosurgery, has active camera unit that captures image of specific region of test subject after transmitting stimulus signals

Super-resolved position and orientation estimation of fluorescent dipoles using 3D steerable filters

Three-dimensional nano-localization of single fluorescent emitters

Tuning the resonance of a photonic crystal microcavity with an AFM probe

High volume confinement in two-photon fluorescence correlation spectroscopy with radially polarized light

Nonlinear Correlation Spectroscopy (NLCS)

Three-dimensional Localization of Fluorescent Emitters at the Nano-scale

Three-Dimensional Localization of Nano-Emitters with Nanometer-Level Precision

Characterization of Nanoparticles Using Non-linear Correlation Spectroscopy

Three-Dimensional Localization of Nano-Emitters with Nanometer-Level Precision