Researchers with Stanford University have come up with a solution, referred to as "multi-pass microscopy," to produce images of biological specimens in greater clarity than ever before.
As proteins and living cells tend to work in low light, images of these specimens are likely grainy and fuzzy because of an effect known as shot noise, making it hard to distinguish the intricate proteins and internal structures.
"If you work at low-light intensities, shot noise limits the maximum amount of information you can get from your image," said Thomas Juffmann, a postdoctoral research fellow in Stanford Professor Mark Kasevich's research group and co-author of a paper published this week in Nature Communications. "But there's a way around that; the shot-noise limit is not fundamental."
The researchers at the university in northern California on the U.S. west coast have found that they get better results from the optical detector if each photon, or individual unit of light, interacts with the sample multiple times. To implement this in a microscope, instead of sending light through a specimen and then directly capturing the resulting image, the Stanford team repeatedly reflects the image back onto the specimen.
"In a sense, it's like you're taking a picture of multiple times your object," explained co-author Brannon Klopfer, a graduate student in the Kasevich group. "You first take an image of the specimen, you then illuminate it with an image of itself, and the image you get, you again send back to illuminate the sample. This leads to contrast enhancement."
As a general signal-enhancing technique, multi-pass microscopy is expected to increase the sensitivity of various microscopy techniques, so long as a source of image noise doesn't build up with the recycling of photons. "While multi-passing builds up the signal in your image, the noise is hardly affected," Klopfer noted.
While multi-passing is restricted to optical microscopes for now, the Stanford team is also working on multi-pass electron microscopy, where damage prevents the atomic-scale imaging of single proteins or deoxyribonucleic acid (DNA), the molecule that carries the genetic instructions used in the growth, development, functioning and reproduction of all known living organisms. According to a news release from Stanford, recycling the electrons in electron microscopy would improve image quality just as the recycling of photons does in the optical microscopes.
