Without contrast dyes or fluorophores, a new device can image and track living cells’ reactions to various stimuli and create 3-D images of biological tissue at the nanoscale in just minutes. The system, developed by Yann Cotte and Fatih Toy of Ecole Polytechnique Fédérale de Lausanne (EPFL), combines holographic microscopy and computational image processing to obtain 3-D images of living cells from every angle at a resolution of less than 100 nm. Because the tissue can be imaged without using contrast dyes or fluorescents, foreign substances will not distort the experimental results. Yann Cotte (left) and Fatih Toy are using their setup — a holographic microscope (rear) and visualization computer — to get accurate 3-D models of live cells. Courtesy of Alain Herzog/EPFL. “We can observe in real time the reaction of a cell that is subjected to any kind of stimulus,” Cotte said. “This opens up all kinds of new opportunities, such as studying the effects of pharmaceutical substances at the scale of the individual cell.” The researchers demonstrated the potential of their system by capturing one image per minute to show the growth of a neuron and the birth of a synapse over the course of an hour. The work was done in collaboration with the Neuroenergetics and cellular dynamics laboratory in EPFL’s Brain Mind Institute. "Because we used a low-intensity laser, the influence of the light or heat on the cell is minimal," Cotte said. "Our technique thus allows us to observe a cell while still keeping it alive for a long period of time." Numerous images extracted by holography are captured by a digital camera while the laser scans the sample. These images are assembled by a computer and “deconvoluted” to eliminate noise. To develop their algorithm, the scientists designed and built a “calibration” system using a thin layer of aluminum pierced with 70-nm-diameter nanoholes spaced 70 nm apart. Thanks to this setup, a “cold” laser beam hits a sample at the center; a camera then analyzes the phase (holographic technique), and a computer builds a 3-D image of the sample, including its interior. Courtesy of Yann Cotte and Fatih Toy, EPFL. The assembled 3-D image of the cell, which looks as focused as an encyclopedia drawing, can be virtually “sliced” to expose its internal elements, such as the nucleus, genetic material and organelles. Cotte and Toy are now working in collaboration with the startup Lyncée SA to develop a system that could be used to observe cells in vivo. Their research is being carried out under the supervision of Christian Depeursinge, head of the Microvision and Microdiagnostics Group in EPFL's School of Engineering. Findings were reported in Nature Photonics (doi: 10.1038/nphoton.2012.329). For more information, visit: www.epfl.ch