Biology subjects

Tortarolo, G.

Publications and source records attributed to Tortarolo, G..

11 recordsLinked to original sources

bioRxiv2025

Smart hybrid microscopy for cell-friendlydetection of rare events

Fluorescence microscopy offers unparalleled access to the spatial organization and dynamics of biological events in living samples, yet capturing rare processes over extended durations remains challenging due to tradeoffs between exposure to excitation light and sample health. Here, we introduce hybrid-EDA, an event-driven acquisition (EDA) framework that combines the gentleness and contextual richness of phase contrast with the functional specificity of fluorescence. We developed surveillance for events of interest in label-free microscopy by novel dynamics-informed neural networks that trigger smart acquisitions in fluorescence upon detection. This allows us to dramatically reduce phototoxic damage while obtaining specific and functional information from fluorescence when beneficial. We demonstrate how hybrid-EDA enables improved imaging acquisitions of organelle contacts and mitochondrial divisions. We envision that hybrid-EDA will enable new insights into a range of dynamic and rare biological processes, providing a powerful and general strategy for cell-friendly imaging.

cell biology↗

bioRxiv2023

4D Single-Particle Tracking with Asynchronous Read-Out SPAD-Array Detector

Single-particle tracking (SPT) techniques are essential for investigating the com-plex functions and interactions of individual, specifically labelled particles in biological environments. Many SPT techniques exist, each optimised towards a different balance between spatiotemporal resolution and range, technical com-plexity, and information content. This bargain is exemplified by the contrast between wide-field camera-based and real-time SPT approaches, with the latter being generally more advanced but at the cost of high complexity. Further-more, the fluorescence lifetime, a powerful tool for investigating the particles interactions and nano-environment, has yet to be measured consistently. To overcome these limitations, we propose a novel real-time three-dimensional SPT technique based on a hybrid approach. In our implementation, we equip a confocal laser-scanning microscope with an asynchronous read-out single-photon avalanche diode (SPAD) array detector and few other optics. Each sensitive detector element acts as a confocal pinhole, and the recorded intensity distribu-tion reflects the particles position in three dimensions relative to the excitation volume. This localization is used in a real-time feedback system to keep the par-ticle in the centre of the excitation volume. Importantly, as each pixel is an independent single-photon detector, SPT is combined with fluorescence lifetime measurement. Our system achieves a localization precision of up to 30 nm with 100 photons and microsecond time resolution, while also performing fluorescence lifetime mea-surements. First, we validated the technique by tracking fluorescent particles in artificial environments. Secondly, as further validation, we investigated the move-ment of lysosomes in living SK-N-BE cells and measured the fluorescence lifetime of the GFP marker expressed on a membrane protein. We observed an unprece-dented correlation between the changes in fluorescence lifetime and the motion state of the lysosomes. Thanks to its simplicity and the great momentum of confocal microscopy based on SPAD array detector, we expect that this implementation will open to many information-rich correlative imaging and tracking studies.

biophysics↗

bioRxiv2023

A Compact and Effective Photon-Resolved Image Scanning Microscope

Fluorescence confocal laser-scanning microscopy (LSM) is one of the most popular tools for life science research. This popularity is expected to grow thanks to single-photon array detectors tailored for LSM. These detectors offer unique single-photon spatiotemporal information, opening new perspectives for gentle and quantitative super-resolution imaging. However, a flawless recording of this information poses significant challenges for the microscope data-acquisition system. Here, we present a data-acquisition module based on the digital frequency domain principle, able to record photons essential spatial and temporal features. We use this module to extend the capabilities of established imaging techniques based on single-photon avalanche diode (SPAD) array detectors, such as fluorescence lifetime image scanning microscopy. Furthermore, we use the module to introduce a robust multi-species approach encoding the fluorophores excitation spectra in the time domain. Lastly, we combine time-resolved stimulated emission depletion microscopy with image scanning microscopy, boosting spatial resolution. Our results demonstrate how a conventional fluorescence laser scanning microscope can transform into a simple, information-rich, super-resolved imaging system with the simple addition of a SPAD array detector with a tailored data acquisition system. We expected a blooming of advanced single-photon imaging techniques which effectively harness all the sample information encoded in each photon.

biophysics↗

bioRxiv2022

Focus-ISM for Sharp and Gentle Super-Resolved Microscopy

Super-resolution microscopy is routinely used for fixed and thin samples, while its feasibility for imaging live and thick samples is still limited. In the case of stimulated emission depletion (STED) microscopy, the high-intensity illumination required to achieve effective sub-diffraction resolution can introduce photo-damage, thus reducing the compatibility of the technique with live-cell imaging. Moreover, the out-of-focus fluorescence background may overcome the often faint signal stemming from the focal point, thus constraining imaging to thin samples. Here, we combined STED microscopy with image-scanning microscopy (ISM) to mitigate these limitations without any practical disadvantages. We first enhanced a laser scanning microscope (LSM) by introducing a detector array, hence providing access to a set of additional spatial information that is not available with a typical single-element detector. Then, we exploited this extended dataset to implement focus-ISM, a novel method that relaxes the high-intensity requirement of STED microscopy and removes the out-of-focus background. Additionally, we generalized the focus-ISM method to conventional LSM, namely without a STED beam. The proposed approach requires minimal architectural changes compared with conventional STED microscopes but provides substantial advantages for live and thick sample imaging while maintaining all compatibility with all recent advances in STED and confocal microscopy. As such, focus-ISM represents an essential step towards a universal super-resolved LSM technique for subcellular imaging.

biophysics↗

bioRxiv2021

The BrightEyes-TTM: an Open-Source Time-Tagging Module for Single-Photon Microscopy

Fluorescence laser-scanning microscopy (LSM) is experiencing a revolution thanks to the introduction of new asynchronous read-out single-photon (SP) array detectors. These detectors give access to an entirely new set of single-photon information typically lost in conventional fluorescence LSM, thus triggering a new imaging/spectroscopy paradigm - the so-called singlephoton LSM (SP-LSM). The revolutions outcomes are, from one side, the blooming of new SP-LSM techniques and tailored SP array detectors; from the other side, the need for data-acquisition (DAQ) systems effectively supporting such innovations. In particular, there is a growing need for DAQ systems capable of handling the high throughput and high temporal resolution information generated by the single-photon detectors. To fill this gap, we developed an open-source multi-channel timetagging module (TTM) based on a field-programmable-gatearray (FPGA), that can temporally tag single-photon events - with 30 ps precision - and synchronisation events - with 4 ns precision. Furthermore, being an open-access project, the TTM can be upgraded, modified, and customized by the microscopy-makers. We connected the TTM to a fluorescence LSM equipped with a single-photon avalanche diode (SPAD) bi-dimensional array detector, and we implemented fluorescence lifetime image scanning microscopy (FLISM) and, for the first time, fluorescence lifetime fluctuation spectroscopy (FLFS). We expect that our BrigthEyes-TTM will support the microscopy community to spread SP-LSM in many life science labs.

bioengineering↗

bioRxiv2021

Cooled SPAD array detector for low light-dose fluorescence laser scanning microscopy

The single-photon timing and sensitivity performance and the imaging ability of asynchronous-readout single-photon avalanche diode (SPAD) array detectors have opened up enormous perspectives in fluorescence (lifetime) laser scanning microscopy (FLSM), such as super-resolution image scanning microscopy and high-information content fluorescence fluctuation spectroscopy (FFS). However, the strengths of these FLSM techniques depend on the many different characteristics of the detector, such as dark-noise, photon-detection efficiency, after-pulsing probability, and optical-cross talk, whose overall optimization is typically a trade-off between these characteristics. To mitigate this trade-off, we present a novel SPAD array detector with an active cooling system, which substantially reduces the dark-noise without significantly deteriorating any other detector characteristics. In particular, we show that lowering the temperature of the sensor to -15{degrees}C significantly improves the signal-to-noise ratio due to a 10-fold decrease in the dark-count rate compared to room temperature. As a result, for imaging, the laser power can be decreased by more than a factor of three, which is particularly beneficial for live-cell super-resolution imaging, as demonstrated in fixed and living cells expressing GFP-tagged proteins. For FFS, together with the benefit of the reduced laser power, we show that cooling the detector is necessary to remove artifacts in the correlation function, such as spurious negative correlations observed in the hot elements of the detector, i.e., elements whose dark-noise is substantially higher than the median value. Overall, this detector represents a further step towards the integration of SPAD array detectors in any FLSM system. SIGNIFICANCESingle-photon avalanche diode (SPAD) array detectors are revolutionizing fluorescence laser-scanning microscopy (FLSM). Thanks to their single-photon timing and sensitivity ability and their imaging faculty, a SPAD array detector transforms any FLSM into a super-resolution microscope, and opens a whole range of possibilities for the study of sample dynamics by means of fluorescence fluctuation spectroscopy (FFS). However, dark-noise can be a severe problem for both imaging and FFS. For imaging, the signal overcomes noise only for a relatively high illumination intensity, which can be detrimental for live-cell experiments. For FFS, the noise leads to artifacts in the correlation curves, potentially leading to wrong conclusions about the sample. We show that lowering the temperature of the detector to -15{degrees}C solves both problems

biophysics↗

bioRxiv2019

Synergic Combination of Stimulated Emission Depletion Microscopy with Image Scanning Microscopy to Reduce Light Dosage

Stimulated emission depletion (STED) microscopy is one of the most influential nanoscopy techniques; by increasing the STED beam intensity, it theoretically improves the spatial resolution to any desired value. However, the higher is the dose of stimulating photons, the stronger are the photo-bleaching and photo-toxicity effects, which potentially compromise live-cell and long-term imaging. For this reason the scientific community is looking for strategies to reduce the STED beam intensity needed to achieve a target resolution. Here, we show how the combination of STED microscopy with image scanning microscopy (ISM) meets this request. In particular, we introduce a new STED-ISM architecture - based on our recent single-photon-avalanche-diode (SPAD) detector array - which allows covering the near-diffraction limit resolution range with reduced STED beam intensity. We demonstrate this ability both with simulated data and in live-cell experiments. Because of (i) the minimal changes in the optical architecture of the typical point-scanning STED microscope; (ii) the parameter-free, robust and real-time pixel-reassignment method to obtain the STED-ISM image; (iii) the compatibility with all the recent progresses in STED microscopy, we envisage a natural and rapid upgrade of any STED microscope to the proposed STED-ISM architecture.

bioengineering↗

bioRxiv2019

Easy Two-Photon Image Scanning Microscopy with SPAD Array and Blind Image Reconstruction

Two-photon excitation (2PE) microscopy is the imaging modality of choice, when one desires to work with thick biological samples, possibly in-vivo. However, the resolution in two-photon microscopy is poor, below confocal microscopy, and the lack of an optical pinhole becomes apparent in complex samples as reduced quality of optical sectioning. Here, we propose a straightforward implementation of 2PE image scanning microscopy (2PE-ISM) that, by leveraging our recently introduced ISM platform - based on a new single-photon avalanche diode array detector - coupled with a novel blind image reconstruction method, is shown to improve the optical resolution, as well as the overall image quality in various test samples. Most importantly, our 2PE-ISM implementation requires no calibration or other input from the user - it works like any old and familiar two-photon system, but simply produces higher resolution images (in real-time). Making the complexity disappear, in our view, is the biggest novelty here, and the key for making 2PE-ISM mainstream.

bioengineering↗

bioRxiv2019

Fourier ring correlation simplifies image restoration in fluorescence microscopy

Fourier ring correlation (FRC) has recently gained some popularity among (super-resolution) fluorescence microscopists as a straightforward and objective method to measure the effective resolution of a microscopy image. While the knowledge of the numeric resolution value is helpful in e.g. interpreting imaging results, much more practical use can be made of FRC analysis - in this article we propose novel blind image restoration methods enabled by it. We apply FRC to perform image de-noising by frequency domain filtering. We propose novel blind linear and non-linear image deconvolution methods that use FRC to estimate the effective point-spread-function, directly from the images, with no need for prior knowledge of the instrument or sample characteristics. The deconvolution is shown to work exquisitely with both two- and three-dimensional images. We also show how FRC can be used as a powerful metric to observe the progress of iterative deconvolution. While developing the image restoration methods, we also addressed two important limitations in FRC that are of more general interest: how to make FRC work with single images and with three-dimensional images with anisotropic resolution.

bioinformatics↗

bioRxiv2018

Photon-separation to enhance the spatial resolution in pulsed STED microscopy

Stimulated emission depletion microscopy (STED) is one of the pivotal super-resolution techniques. It overcomes the spatial resolution limit imposed by the diffraction by using an additional laser beam, the STED beam, whose intensity is directly related to the achievable resolution. Despite achieving nanometer resolution, much effort in recent years has been devoted to reduce the STED beam intensity because it may lead to photo-damaging effects. Exploring the temporal dynamics of the detected fluorescence photons and accessing the encoded spatial information has proven to be a powerful strategy, and has contributed to the separation by lifetime tuning (SPLIT) technique. The SPLIT technique uses the phasor analysis to efficiently distinguish photons emitted from the center and the periphery of the excitation spot. It thus improves the resolution without increasing the STED beam intensity. This method was proposed for architectures based on STED beam running in continuous wave (CW-STED microscopy). Here, we extend it to architectures based on pulsed STED beam (pSTED microscopy). We show, through simulated and experimental data, that the SPLIT-pSTED method reduces the detection volume of the pSTED microscope without significantly reducing the signal-to-noise ratio of the final image, thus effectively improving the resolution without increasing the STED beam intensity.

biophysics↗

bioRxiv2018

Image Scanning Microscopy with Single-Photon Detector Array

Image scanning microscopy (ISM) improves the spatial resolution of conventional confocal laser-scanning microscopy (CLSM), but current implementations reduce versatility and restrict its combination with fluorescence spectroscopy techniques, such as fluorescence lifetime. Here, we describe a natural design of ISM based on a fast single-photon detector array, which allows straightforward upgrade of an existing confocal microscope, without compromising any of its functionalities. In contrast to all-optical ISM implementations, our approach provides access to the raw scanned images, opening the way to adaptive reconstruction methods, capable of considering different imaging conditions and distortions. We demonstrate its utility in the context of fluorescence lifetime, deep, multicolor and live-cell imaging. This implementation will pave the way for a transparent and massive transition from conventional CLSM to ISM.\n\nconfocal microscopy | time-resolved spectroscopy | image scanning microscopy | single-photon detector array

bioengineering↗