Biology subjects

Mojiri, S.

Publications and source records attributed to Mojiri, S..

5 recordsLinked to original sources

bioRxiv2026

Cryo-FIB lamellae enable ultra-high excitation laser intensities for cryogenic super-resolution fluorescence imaging

Super-resolution cryogenic correlative light and electron microscopy (SR-cryo-CLEM) integrates molecular specificity and structure on the single-molecule level, but contemporary approaches require low laser powers to preserve specimen vitrification. Here, we perform SR-cryo-CLEM via single molecule localization microscopy (SMLM) on thin biological lamellae and demonstrate that their geometry and minimally-absorbent composition permit excitation laser powers three orders of magnitude higher than standard cryo-EM grids, allowing improved localization precision and imaging speeds.

molecular biology↗

bioRxiv2026

A stable cryogenic fluorescence microscope for correlative super-resolution light and electron microscopy

Cryogenic correlative light and electron microscopy (cryo-CLEM) enables visualization of biological specimens with molecular specificity while preserving near-native macromolecular structure. However, the severely limited resolution of conventional cryo-fluorescence microscopes restricts the accuracy of correlation with cryo-electron microscopy. Super-resolution cryogenic CLEM (SR-cryo-CLEM) offers a potential solution, but presents substantial technical challenges, including mechanical instability and ice contamination. Here, we introduce a modular cryogenic light microscope optimized for single-molecule localization microscopy (cryo-SMLM) that mitigates such limitations. The system is constructed primarily from off-the-shelf components, enabling straightforward and cost-effective assembly, and is operated using fully open-source Python software for flexible and customizable control. The mechanically and thermally stabilized architecture, combined with an axial focus-lock system, maintains sample positioning within a standard deviation of 40 nm. Ice contamination is minimized by imaging inside a purged enclosure, enabling prolonged acquisitions. Together, the platform provides robust localization precision, reproducible imaging performance, and an accessible solution for SR-cryo-CLEM.

molecular biology↗

bioRxiv2025

Effects of base temperature, immersion medium, and EM grid material on devitrification thresholds in cryogenic optical super-resolution microscopy

Cryogenic correlative light and electron microscopy (cryo-CLEM) is an imaging strategy that integrates specific molecular labeling and molecular resolution structural information. However, there is a resolution gap of more than two orders of magnitude between diffraction-limited fluorescence microscopy and electron microscopy (EM). Single-molecule localization microscopy (SMLM) performed at cryogenic temperatures promises to bridge this resolution gap. Nevertheless, the high excitation laser powers required for SMLM risk the devitrification of frozen biological samples, leading to perturbation of their native-like state. Here, we investigate how base cooling temperature, immersion medium, and EM grid support materials influence sample devitrification. Using finite element simulations and experimental validation, we show that a cryo-immersion medium enhances heat dissipation for carbon supports, while metallic supports in a cold nitrogen gas medium tolerate higher laser intensities due to lower base temperatures. Gold supports illuminated at 640 nm exhibit markedly high laser thresholds, similar to silver-coated grids. Additionally, metallic supports maintain efficient heat dissipation in vacuum-based cryostats. Our findings provide quantitative insights that aid in optimization of cryo-SMLM setups for improved cryo-CLEM imaging.

molecular biology↗

bioRxiv2021

Instant three color multi-plane fluorescence microscopy

One of the most widely used microscopy techniques in biology and medicine is fluorescence microscopy, offering high specificity in labeling as well as maximum sensitivity. For live cell imaging, the ideal fluorescence microscope should offer high spatial resolution, fast image acquisition, three-dimensional sectioning, and multi-color detection. However, most existing fluorescence microscopes have to compromise between these different requirements. Here, we present a multi-plane multi-color wide-field microscope that uses a dedicated beam-splitter for recording volumetric data in eight focal planes and for three emission colors with frame rates of hundreds of volumes per second. We demonstrate the efficiency and performance of our system by three-dimensional imaging of multiply labeled fixed and living cells.

biophysics↗

bioRxiv2020

Three-dimensional beating dynamics of Chlamydomonas flagella

Axonemes are the basic structure of motile cilia and flagella, and the investigation of how they function and move requires rapid three-dimensional imaging. We built a multi-plane phase-contrast microscope for imaging the three-dimensional motion of unlabeled flagella of the model organism Chlamydomonas reinhardtii with sub-m spatial and 4 ms temporal resolution. This allows us to observe not only bending but also the three-dimensional torsional dynamics of these small structures. We observe that flagella swim counter-clockwise close to a surface, with negatively-valued torsion at their basal and positively-valued torsion at their distal tips. To explain the torsional dynamics and signature, we suggest the existence of an intrinsic negative twist at the basal end that is untwisted by active positive-twist-inducing dynein motor proteins. Moreover, dyneins walking towards the basal induce an opposite twist at the distal tip. Bending of the whole axoneme structure then translates this twist into an observable torsion. This interconnection between chiral structure, twist, curvature, and torsion is fundamental for understanding flagellar mechanics.

biophysics↗