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“People are doing live cell experiments on samples with things like HIV or cholera toxins that are fluorescently labeled, and they’re observing how the cells take these things in and how they’re processed,” Sharma says. “They’re measuring the effects of certain drugs on these things. So ideally you want to do that with a very low amount of label in there to see what really happens in real life, rather than overloading it with stuff.”
But when low labeling amounts are used, camera noise interferes. The EMCCD camera takes the tiny bit of signal and multiplies it before it’s measured. All of a sudden, Sharma says, the incoming signal is larger while noise remains the same and you begin to see the cell’s reaction in real time.
“The problem that’s been solved here is that you can detect things in a much more realistic and native form in live cell research that you weren’t able to detect before,” he says. “And if you did use alternative detection methods, they weren’t as efficient at gathering the light. You didn’t have the same dynamic range, which means you couldn’t see bright things and dim things at the same time. So the previous technologies had all these little negative aspects to them, which electron multiplying technology overcomes and provides the researcher with a way to detect things and see things that were hard to see before.”
One of the major methods that has been used, and still is in some applications, is intensified cameras, in which an intensifier is placed before the CCD, so there is a multiplying signal before it hits the camera.
“The problem with those,” says Sharma, “is [that] the quantum efficiency, which is a measurement of how efficient the detector picks up incoming light, is actually lower on those cameras than they are on EMCCDs. So the quantum efficiency on an intensified camera, for instance, is you’d be doing well to be in the 40 percent [range], which means four of 10 photons actually are seen by the CCD. So the quantum efficiency in general can be lower.”