World’s smallest periscopes offer 3D views

VANDERBILT (US)—A periscope no wider than a human hair is yielding 3D images at the microscopic level and offering scientists an unprecedented look at cells and very small organisms from multiple vantage points—top, bottom, and all sides—like the single grain of pollen from a sunflower pictured here.

Chris Janetopoulos, part of the team at Vanderbilt University that developed the tiny devices, says viewing the top and sides of cells is a perspective biologists “almost never see.”

“The method is particularly well suited for studying dynamic processes within cells because it can follow them in three dimensions,” says Janetopoulos. The Vanderbilt researchers are using the micropyramids to examine how protozoa swim and how cells divide.

Ron Reiserer, a lab manager at the Vanderbilt Institute for Integrative Biosystems Research and Education, predicts the devices could become as common as microscope slides and even replace more expensive methods used to position individual cells.

The researchers have dubbed their devices “mirrored pyramidal wells.” As the name implies, they consist of pyramidal-shaped cavities molded into silicon whose interior surfaces are coated with a reflective layer of gold or platinum. When a cell is placed in such a well and viewed with a regular optical microscope, the researcher can see several sides simultaneously.

“This technology is exciting because these mirrored wells can be made at very low cost, unlike other, more complex methods for 3D microscopy,” says Kevin Seale, an assistant professor of biomedical engineering at Vanderbilt.

The Vanderbilt group is not the first to make microscopic pyramidal wells, but it is the first to apply them to make 3D images of microorganisms. In 2006, scientists in England applied the imaging technology to trap atoms, and last spring researchers at the National Institute of Standards and Technology used similar structures to track nanoparticles.

The mirrored pyramidal wells provide a high-resolution, multi-vantage-point form of microscopy that also makes it easier for researchers to measure a number of important cell properties. A popular method for studying biological processes uses genetic engineering to attach genes that produce fluorescent molecules to different cell structures such as specific surface receptors. This procedure makes the targeted cell structures light up when illuminated by ultraviolet light, but strong UV light also has the potential to damage the structures. If the engineered cell structures are put in a micropyramidal well, the fluorescent light that is emitted toward the mirrored sides is reflected upward toward the microscope, allowing the researchers to reduce the intensity of the UV light and its potential for damaging the engineered cells.

According to Janetopoulos, the micropyramids also have a major advantage for single molecule studies. Optical noise is a constant problem when working at the low light levels involved. Being able to pinpoint actual light sources in two or three dimensions allows the researchers to reject spurious signals. This should be useful in quantitative fluorescence or bioluminescence studies: Cells can be genetically modified to glow in the dark to provide a measure of cellular metabolic activity or the expression of a specific gene.

Vanderbilt University  is hoping to patent the use of the micropyramids for simultaneous, multi-vantage-point imaging.

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