Eli Slenders

Short Bio

Eli Slenders has a bachelor’s and master’s degree in physics from Hasselt University (Hasselt, Belgium) and KU Leuven (Leuven, Belgium), respectively. He graduated in 2013. From 2014 to 2018, he worked as a PhD student at Hasselt University in the Biophysics group of prof. M. Ameloot. His PhD thesis was entitled “Resolution in coherent and incoherent optical imaging with two-photon excitation microscopy”. From 2019 to 2021, Eli worked as a post-doctoral researcher under the supervision of Giuseppe Vicidomini in the Molecular Microscopy and Spectroscopy research line at the Italian Institute of Technology (IIT, Genoa, Italy) where he developed SPAD-FFS, an optical tool to study biomolecular dynamics. Since March 2021, Eli is a Marie Skłodowska-Curie Actions research fellow in dr. Vicidomini’s group, working on time-resolved low light-dose single molecule imaging with SPAD array detectors.

Projects Description

SPAD-FFS: Over the last decades, fluorescence fluctuation spectroscopy (FFS) has been successfully applied to many biological systems to study molecular transports, dynamic behavior of macromolecules, membrane structures, and organization of chromatin. By measuring and analyzing the fluorescence intensity fluctuations generated by biomolecules moving in-and-out of the microscope detection volume(s), parameters such as diffusion coefficients, molecular concentrations, and the fluorescence brightness can be calculated. The (sub)microsecond temporal resolution and the low background typically needed for FFS are usually obtained by employing a point-detector - such as a photomultiplier tube or an avalanche photodiode - in a confocal microscope system. The detector integrates all photons in the detection volume, thus ignoring all information encoded in the spatial distribution of the photons. Consequently, FFS has a limited value when studying more complex situations, e.g. FFS is not able to measure the direction of active transport in a sample undergoing anomalous diffusion. Adaptations of FFS that do register spatial information with a camera, such as spatiotemporal image scanning correlation spectroscopy, exist, but at the cost of a very poor temporal resolution.

The trade-off between recording spatial and temporal information can be removed by using an asynchronous-readout single photon avalanche diode (SPAD) array detector placed at the image plane of a laser scanning microscope. Each pixel of the detector can register the arrival time of a photon with sub-nanosecond temporal resolution. In combination with a pulsed laser source and a time-correlated photon registration platform, such a setup offers the additional advantage of being able to simultaneously measure the fluorescence lifetime.

In this project, we built a platform for recording and analyzing FFS data with a novel 5x5 SPAD array detector installed in a custom-built confocal microscope. We explored how the diffusion parameters can be retreived from analysing the autocorrelation and cross-correlation functions of the 25 intensity traces. In addition, we were able to exploit the system’s capability of simultaneously measuring the fluorescence lifetime during an FFS experiment by time-tagging each fluorescence photon. Our platform opens up a new way of accurately quantifying fast local dynamics and studying the structural organization of complex biological samples.

SM-SPAD: Conventional optical microscopes achieve a maximum resolution of about 250 nm, posing significant limitations to structural biology efforts. The main goal of the EU-funded SM-SPAD project is to develop a 3D single-molecule fluorescence lifetime imaging technique to visualise macromolecules smaller than 100 nm. The proposed approach circumvents size restrictions by stochastically switching on single fluorescent molecules and determining their position in the image plane by exciting the molecule multiple times with different illumination patterns and recording the corresponding fluorescence with a SPAD array detector. This technique combines a very high spatial and temporal resolution, perfectly suitable for studying complex biological samples. Application of this technique in neuroscience will enable the visualization of large protein complexes responsible for the development of neurodegenerative diseases, such as Alzheimer’s and Parkinson’s. More information on https://cordis.europa.eu/project/id/890923.

Publications with our group