Articles
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Advanced microscopic cameras use sophisticated sensors. Colin Coates, PhD, product manager for imaging at Andor Technology (Belfast, Northern Ireland), says, “The dominant technology has been the interline CCD from Sony, which has been great for the past 12 or 15 years. Its pixel size—6.5 microns—is the sweet spot for cell microscopy, especially fluorescence imaging of live cells.” Nonetheless, Coates sees a new “gun” in town.
Andor Technology’s Neo sCMOS Camera, launched in November 2010, uses a sensor based on a complementary metal-oxide semiconductor, CMOS. “This new scientific-grade CMOS technology combines a lot of performance parameters, without trade-offs,” Coates says. That includes just one electron of read noise, whereas the interline usually runs at about six. “For previous generation CMOS cameras, the noise was about 30 electrons,” Coates explains, “and that couldn’t compete with CCD technology. Now we have actually surpassed CCDs.”
The Neo sCMOS also works fast, grabbing 30 to 100 frames per second, while still maintaining extremely low read noise. “Faster frame rates yield shorter exposures and fewer photons, meaning ideally, fast cameras should also be extra sensitive,” Coates points out.
The Neo sCMOS sticks with the 6.5-micron pixel, but its large 5.5 megapixel sensor provides images that are “matched to the natural field of view of the microscope,” Coates says. “What you see through the eyepiece, you can see on the sensor as well.”
Although Coates admits that the interline continues to dominate live-cell imaging and high-content screening, he believes that the Neo sCMOS will soon take the lead based on performance superiority. He says, “We’ve already shipped hundreds of these cameras to academic labs. The price is between an electron-multiplying CCD, or EMCCD, and an interline.” Andor Technology manufactures interline CCDs, EMCCDs, and sCMOS, and does not expect the interline to disappear just yet, primarily because it remains a less expensive option. Andor also acknowledges that back-illuminated EMCCD technology maintains a raw sensitivity advantage under extremely low light conditions, typical of single-molecule microscopy. Still, sCMOS sensors provide many useful advances.
Expanding the view
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EMCCDs continue to possess optimal characteristics for sensitivity, with greater than 90% maximum quantum efficiency and around 0.3 electrons of read noise. Aiming to expand the available imaging range and speed, in November 2010, Photometrics(Tucson, Ariz.) rolled out its Evolve 128 EMCCD camera with eXcelon, an exclusive technology that drastically improves imaging in the blue and near infrared (NIR) wavelengths. This EMCCD sensor is available for Photometrics’ Evolve 512 and 128 cameras. Rachit Mohindra, associate product manager at Photometrics, says, “The Evolve 128 provides an ultrafast 530 frames per second with extraordinary sensitivity.” The eXcelon Evolves also reduce etaloning—a fringe pattern that arises in NIR images—while still providing quantitative photoelectron measurements first pioneered in the Evolve camera platform.
In addition, QImaging (Surrey, B.C., Canada) offers its Rolera EM-C2 EMCCD camera, designed for high speed and sensitivity. With megapixel resolution, says Chris Ryan, associate product manager at QImaging, “you can have a bigger field of view to track multiple sample areas.” The camera can also allow scientists to capture high-resolution images of single cells at greater than 120 frames per second with less than half an electron of read noise.
This camera offers an Easy-EM mode that sets the EM gain to enhance dynamic range and the low light signal-to-noise ratio. As Ryan explains: “This optimal camera setting is programmed during manufacture; a simple software command switches on this setting.” He adds, “This allows researchers to confidently compare thousands of different experiments.”
About the Author
Mike May is a publishing consultant for science and technology based in Houston, Texas.
