A Nature paper co-authored by Steven Chu, Nobel laureate and Energy Secretary of the United States, describes a big breakthrough in the science of the very small: a method of optical microscopy that can image at resolutions as small as half a nanometer, a full order of magnitude smaller than the previous finest optical resolution.
Conventional optics are generally restrained by a law of physics known as the diffraction limit, which dictates that optical systems can only resolve images down to abut half the wavelength of the light used to produce the image, or down to about 200 nanometers for most standard optics. That’s pretty small, but not small enough to, say, measure the gaps between proteins or look at a DNA molecule up close. In order to perform such tasks, researchers have had to rely on non-optical options like electron microscopy.
CCDs, or charge-coupled devices, can resolve down to about five nanometers, still twice as large as the width of a single DNA molecule. But they suffer from a non-uniformity that can occur depending on where on the chip a photon lands; sometimes it dislodges an electron, and sometimes it’s not measurable. This results in a blurring of the picture, making it difficult to bring into focus two points that are within a few nanometers of one another.
Chu and company found a way to correct this non-uniformity, using both additional optical beams to stabilize the entire system and an active feedback system that corrects for the non-uniformity. Doing so allows the optical system to reduce the error due to non-uniformity down to just 0.5 nanometers, letting researchers see at subnanometer resolutions using conventional optical microscopes.
The breakthrough has the potential to drastically enhance biological studies, letting researchers observe the structure of the tiniest and most complex elements of life in focus for the first time. The team is already at work studying the human RNA polymerase II system, which initiates DNA transcription, and will also use the technique to study signaling molecules and proteins that have been linked to various cancers.