The Frontiers in Neurophotonics Symposium is a biennial event that brings together neurobiologists and physicists/engineers who share interest in the development of leading-edge photonics-based approaches to understand and manipulate the nervous system, from its individual molecular components to complex networks in the intact brain. In this Community paper, we highlight several topics that have been featured at the symposium that took place in October 2022 in Québec City, Canada.
Progress achieved in the field of stem-cell technology allows the reprogramming of patient-derived cells, obtained from urine or skin biopsies, into induced pluripotent stem cells that can then be differentiated into any cell types. Within this framework, techniques, being able to accurately and non-invasively characterize cell structure, morphology, and dynamics, represent very promising approaches to identify disease-specific cell phenotypes. Consequently, we will present how a label-free optofluidic platform, based on quantitative-phase digital holographic microscopy along with various experimental developments in microfluidics, constitutes a very appealing cell imaging methodology to identify, through the measurement of biophysical properties, specific cell phenotypes.
Digital holographic microscopy (DHM), provides an extremely sensitive quantitative-phase signal (QPS), which is nevertheless affected by coherent noise. The recent development of polychromatic DHM (P-DHM) enables us to provide quasi-coherent-noise-free quantitative-phase images. The implementation of P-DHM remains, however, demanding. We propose a convolutional neural network architecture, using for the first time an experimental ground-truth dataset, performing the P-DHM denoising from conventional DHM images. The results highlight, a strong efficiency, fine subcellular structures are made visible without loss of QPS accuracy, an interest in comparison to state-of-the-art learning methods and the possibility of a more widespread use of the P-DHM.
KEYWORDS: Digital holography, Microfluidics, Microscopy, Holography, Microfluidic imaging, Refractive index, Modulation, Environmental sensing, Control systems
Biophysical properties (BPs) of a cell depend drastically on its physiological or pathological state. Thus, being able to accurately and non-invasively measure a set of cell BPs, that reflect these cellular states, is of major importance. To this end, we propose an approach that combines customized fluidic devices with digital holographic microscopy (DHM). Specifically, we have developed several low-cost 3D-printed millifluidic devices which when combined with DHM allow to measure in a controlled physiological environment specific cell BPs including intracellular refractive index, absolute cell volume, membrane flickering as well as cell elasticity and viscosity moduli.
Digital holographic microscopy (DHM) has been used in numerous successful studies in materials and life sciences. It is well known that the light source coherence, useful to generate high-quality interference patterns that encode the phase in an extremely accurate manner, generates coherent noise (CN), which precludes to adequately address some important applications, especially when single-shot fast recording is required. We propose an original approach, called polychromatic DHM, which thanks to the reconstruction of several holograms acquired at different wavelengths provides quasi-CN-free optical path difference images. Preliminary results concerning materials and life sciences will be presented.
Quantitative Phase Signal (QPS) stems from the difference between the refractive indices of the observed specimen and that of its surrounding environment (ne). Therefore, any change in ne will drastically affect the QPS. We have developed an original approach, based on both the manipulation and the measurement of ne that allows from the QPS the visualization of various structures inside the observed specimen as well as accurate measurements of their respective refractive indices. Such an approach performed with digital holographic microscopy on living cells reveals internal cell structures including organelles (nucleus, nucleolus, vesicles, etc.) and some components of the cytoskeleton.
Recently, interest in the biophysics of cells has been stimulated by evidence from many studies that external force applied to a cell generates signals that are as potent as those of biochemical stimuli for cell growth, differentiation, migration and function. Furthermore, living cells as open systems maintain their homeostasis, i.e. the internal condition necessary for physiological functioning, by exchanging substances with their environments including energy substrate, ions and water across their membrane. Consequently, the objective is to develop milli/microfluidic assays to measure biophysical properties of human cells with a multi-modality imaging system combining digital holographic microscopy and fluorescence microscopy.
KEYWORDS: Digital holography, Chemical mechanical planarization, Microscopy, Holography, Microfluidics, Signal generators, Neurons, Imaging systems, Environmental sensing, Control systems
Many studies suggest that external forces applied to cells generate signals that are as potent as those of biochemical stimuli. To understand how these forces are transmitted to the molecular structures of cells, and how they might be transduced into biochemical reactions, require measuring both cell mechanical properties (CMPs) and biological pathways in a physiological environment. For this purpose, we will present measurements, through rheological approaches, of CMPs in a label-free manner performed thanks to an automated imaging system devoted to live cells combining digital holographic microscopy, environmental control, and microfluidic assays.
The recent developments in stem cell biology especially the generation of induced pluripotent stem cells (iPSCs) has made possible the development of in vitro cellular models of developmental brain disorders including schizophrenia. Within this framework, we will present how quantitative phase imaging and in particular quantitative phase digital holographic microscopy (QP-DHM), as a label-free technique is able to study these in vitro cellular models and identify both some pathophysiological processes and cell biomarkers related to developmental brain disorders. This will be illustrated by the exploration with QP-DHM of human neuronal networks derived from iPSCs coming from patients suffering from schizophrenia.
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