Cells on video
The movement of the cells was captured on ultra-high resolution video with a frequency of 200 frames per second
Alexander Dubov, N+1
Scientists have developed a method of ultra-high-resolution optical microscopy, which can be used to obtain video images of moving cells with a frequency of up to 200 frames per second. The spatial resolution of the method reaches 110 nanometers, scientists write in Nature Photonics (Descloux et al., Combined multi-plane phase retrieval and super-resolution optical fluctuation imaging for 4D cell microscopy).
To obtain three-dimensional images of cells with nanometer resolution, as a rule, either electron microscopy or special optical microscopy techniques are used (in very rare cases, atomic force microscopy is also proposed for this). At the same time, unlike electron microscopy, which requires covering cells with a conductive material to obtain an image, freezing them and keeping them in vacuum conditions, optical microscopy allows measurements to be made at room conditions and even allows you to observe cells in dynamics. Typically, ultra-high resolution optical microscopy, the spatial resolution of which is below the diffraction limit, is based either on the analysis of the interference pattern that is formed when a luminescent sample is illuminated at different angles, or using near-field methods.
The main problem of ultra–high resolution microscopes for obtaining video images is a rather low frame rate. In order to increase spatial resolution, it is necessary to sacrifice time resolution, and even in the best implementations of the method it is not possible to achieve a frequency of more than a few frames per second.
Scientists from Switzerland, the USA and Germany, led by Theo Lasser from the Federal Polytechnic School of Lausanne, have developed a new method of ultra-high resolution optical microscopy, with which it is possible to obtain video images of cells with a frequency of up to 200 frames per second. Scientists were able to achieve this by combining in one device an ultra-high-resolution microscope based on the measurement of optical fluctuations, and devices for obtaining images with phase contrast, in which the phase shift of light is converted into a change in the reflection coefficient of the image. And in order to get not a flat image, but a three-dimensional one, each frame was shot for eight different horizontal slices.
Using the proposed method, scientists were able to obtain three-dimensional images of moving objects in a volume of 2.5 ×50×50 micrometers with a frequency of 50 to 200 frames per second. The spatial resolution of the images was 110 nanometers in the image plane and less than 500 nanometers along the vertical axis.
The authors managed to show that the method they developed works on several model systems with different dynamics: scientists obtained images of living human fibroblasts, dividing cancer cells of the HeLa line, mouse hippocampal neurons and muscle macrophages. At the same time, it is possible to obtain volumetric videos of moving and dividing cells both with the use of special fluorescent labels and without them.
From left to right: HeLa cancer cell, mouse hippocampal neuron axon, muscle macrophage cells (images from an article in Nature Photonics).
Movement of a human fibroblast cell on a glass surface. The video was received at 200 frames per second.
HeLa cancer cell division: transition from the metaphase stage of mitosis to the telophase stage.
As a result, the proposed technique allowed not only to obtain images of different types of cells, but also to trace the movement of cellular organoids in them and the dynamics of changes in the cytoskeleton. The results obtained allow us to expect that in the near future the developed approach will be widely used to obtain three-dimensional photographs and videos with living cells for biological and medical research.
The development of microscopic methods that make it possible to obtain three-dimensional video images is relevant not only for the study of biological objects, but also for the study of dynamic processes in inanimate nature, for example, the diffusion of nanoparticles or the propagation of defects inside crystals.
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