Biology subjects

Kessler, L. F.

Publications and source records attributed to Kessler, L. F..

5 recordsLinked to original sources

bioRxiv2026

Wash-Free Multi-Target Super-Resolution Microscopy with Photocaged DNA Labels

Super-resolution microscopy with DNA-fluorophore labels is primed for multi-target imaging of cell biological samples. However, direct interaction with the sample is required to exchange or add DNA-fluorophore labels in each imaging round, which can impair the accuracy of the imaging data at the nanometer scale. To bypass this requirement, we introduce a wash-free method that employs DNA oligonucleotides equipped with photocaging groups. Irradiation with light removes these photo-modulatable groups and changes the hybridization properties of DNA labels, enabling light-modulated targeting. We demonstrate this concept by imaging various cellular targets with confocal microscopy, single-molecule localization microscopy, and stimulated emission depletion (STED) microscopy.

biophysics↗

bioRxiv2025

Quantitative STED microscopy with DNA-fluorophore labels

Stimulated emission depletion (STED) microscopy enables super-resolution imaging of complex biological samples in 3D, in large volumes, and live. However, molecular quantification with STED has remained underexplored. Here, we present a straightforward approach for quantitative STED that enables molecule counting. For this purpose, we designed DNA-fluorophore labels that enable signal amplification and allow for reliable intensity-based quantitative imaging. We demonstrate accurate molecule counting on DNA origami. Furthermore, we visualized and quantified EGF receptor monomers and dimers in cells. In summary, we introduce a robust, fast, and easy-to-implement tool for quantitative STED microscopy with single-protein resolution.

biophysics↗

bioRxiv2024

Smart 3D super-resolution microscopy reveals the architecture of the RNA scaffold in a nuclear body

Small subcellular organelles orchestrate key cellular functions. How biomolecules are spatially organized within these assemblies is poorly understood. Here, we report an automated super- resolution imaging and analysis workflow that integrates confocal microscopy, morphological object screening, targeted 3D super-resolution STED microscopy and quantitative image analysis. Using this smart microscopy workflow, we targeted the 3D organization of an architectural RNA that constitutes the structural backbone of paraspeckles, a membraneless nuclear organelle. Using site-specific labeling, morphological sorting and particle averaging, we reconstructed the morphological space of paraspeckles along their development cycle from over 10,000 individual particles. Applying spherical harmonics analysis, we report so-far unknown heterotypes of RNA organization. By integrating multi- positional labeling, we determined the coarse conformation of the RNA within the organelle and found the 3 end forming a loop-like structure at the surface of the paraspeckle. Our study reveals key structural features of nuclear paraspeckle structure and growth, as well as on the molecular organization of the scaffold RNA.

biophysics↗

bioRxiv2024

Fast and long-term super-resolution imaging of ER nano-structural dynamics in living cells using a neural network

Stimulated emission depletion (STED) microscopy is a super-resolution technique that surpasses the diffraction limit and has contributed to the study of dynamic processes in living cells. However, high laser intensities induce fluorophore photobleaching and sample phototoxicity, limiting the number of fluorescence images obtainable from a living cell. Here, we address these challenges by using ultra-low irradiation intensities and a neural network for image restoration, enabling extensive imaging of single living cells. The endoplasmic reticulum (ER) was chosen as the target structure due to its dynamic nature over short and long timescales. The reduced irradiation intensity combined with denoising permitted continuous ER dynamics observation in living cells for up to 7 hours with a temporal resolution of seconds. This allowed for quantitative analysis of ER structural features over short (seconds) and long (hours) timescales within the same cell, and enabled fast 3D live-cell STED microscopy. Overall, the combination of ultra-low irradiation with image restoration enables comprehensive analysis of organelle dynamics over extended periods in living cells.

biophysics↗

bioRxiv2024

Self-quenched fluorophore-DNA labels for super-resolution fluorescence microscopy

Protein labeling through transient and repetitive hybridization of short, fluorophore-labeled DNA oligonucleotides has become widely applied in various optical super-resolution microscopy methods. The main advantages are multi-target imaging and molecular quantification. A challenge is the high background signal originating from the presence of unbound fluorophore-DNA labels in solution. Here, we report self-quenching of fluorophore dimers conjugated to DNA oligonucleotides as a general concept to reduce the fluorescence background. Upon hybridization, the fluorescence signal of both fluorophores is fully restored. Here, we expand the toolbox of fluorophores suitable for self-quenching and report their spectra and hybridization equilibria. We apply self-quenched fluorophore-DNA labels to stimulated emission depletion (STED) microscopy and single-molecule localization microscopy (SMLM) and report improved imaging performances.

biophysics↗