Zooming in on the nanoscale

Researchers have created the highest resolution optical image ever, revealing structures as small as just tens of billionths of a metre across.

Carbon filaments: The technique can resolve detail down to about 25 billionths of a metre

Enlarge image

"This is the highest resolution optical spectroscopic measurement ever made," said Lukas Novotny, professor of optics at Rochester University, US.

The novel technique should allow a new insight into the world of the small, for example examining the proteins embedded in a cell's membrane.

"There are other methods that can see smaller structures, but none use light, which is rich in information," said Professor Novotny.

"With this technique, we have a detailed spectrum for every point on a surface."

Gold point
Other ultra-high resolution imaging techniques, such as atomic force microscopes, only detect the presence of objects. But they don't actually see them.

The laws of physics make very high magnifications extremely difficult because the wavelength of light is a limitation in itself.

To tackle this problem, Professor Novotny's team sharpened a gold wire to a point that was just a few tens of nanometres across.

A laser was then shone against the side of the gold tip, inciting electrons inside it to oscillate.

These oscillations created a tiny bubble of electromagnetic energy at the tip, which interacts with the vibrations of the atoms in the sample.

Designer medicines

This interaction, called Raman scattering, releases packets of light from the sample at specific frequencies that can be detected and used to identify the chemical composition of the material.

The first images taken with the new technique are of so-called carbon nanotubes, filaments of carbon atoms strung together.

One prospect for this technique is determining exactly how cell membranes work, opening the door to designer medicines that could kill harmful cells or repair damaged ones.

Currently, Professor Novotny and colleagues can achieve a resolution of about 25 nanometres. In a few years, they expect to be capable of seeing proteins, which are little more than five nanometres wide.

To do this, they will have to get the point of the gold tip sharper still.