Live cell imaging is made possible by a confluence of advances in imaging, computing, microscopy, and reagent technologies, connected by a deeper understanding and appreciation for cellular processes.
Cell imaging has become one of the most exciting subcategories of biological microscopy. During the past decade, cell imaging has evolved from the study primarily of fixed cells to time-lapse photos of events in living cells to real-time videos of cellular processes.
“Working with living systems is much more indicative of what’s going on in the cellular physiology,” says Ian Clements, product manager at Applied Precision (Issaquah, WA), a GE Healthcare company. “We have reached the point where we can follow the same event in the same cell over a period of time rather than simply taking snapshots.”
Expanding visualization horizons
New imaging techniques typically develop in the fixed-sample world, where sequential still photomicrographs still dominate. Researchers apply these methods to living cells as the techniques improve and become faster and more robust. That was the case with optical superresolution (OSR) techniques, which enable imaging within a narrow window below the diffraction limit of visible light (about 300 nm) and the upper limit of electron microscopy (20 nm).
One approach to OSR, termed STED (stimulated emission depletion), was discovered at the Max Planck Institute in 1994, and commercialized by Leica (the original licensee), Nikon, and Zeiss. Other OSR methods include photoactivated localization microscopy (PALM); ground state depletion individual molecule return (GSDIM); and stochastic optical reconstruction microscopy (STORM), which was developed at Harvard University during the late 2000s.
The oldest and arguably most widely adopted OSR technique is threedimensional structured illumination microscopy (3D-SIM) — invented at the University of California, San Francisco — and was licensed to Applied Precision, which continues to improve the technique and implement it in its product line. An ultrafast version of 3D-SIM can capture videos of very rapid cellular events. Twenty-four top research institutions worldwide have adopted 3DSIM in their OSR core facilities.
Although routine laboratory instrumentation tends toward simplicity and ease of use (think MS, LC), high-end experimentation (e.g., flow cytometry, cell imaging) increasingly requires a type of “renaissance” researcher, according to Mr. Clements. Because cell imaging is so novel, investigators must confirm what they see on-screen with “molecular” assays. “Ten years ago journal papers often had 20 or more authors, each of whom played a small role. Today, scientists must wear many hats and be prepared to use several high-end instrumental methods as well as more traditional tests to confirm their results.”
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