The researchers characterise their new technique as a neat solution to the "needle in a haystack" problem of nanoscale microscopy, but it's more like the difference between finding the coffee table in a darkened room either by walking around until you fall over it, or using a flashlight.
"Laser targeting" for nanoscale microscopy: On left, typical 900 square micrometer view, using focused laser beam, shows potentially interesting purple membrane patch, which is marked with the square. Right top, closer optical image of patch; bottom, same target imaged with AFM revealing topological detail. Credit: Churnside, CU
In a new paper,* a group from JILA - a joint venture of the National Institute of Standards and Technology (NIST) and the University of Colorado - finds tiny assemblies of biomolecules for subsequent detailed imaging by combining precision laser optics with atomic force microscopy.(* A.B. Churnside, G.M. King and T.T. Perkins. Label-free optical imaging of membrane patches for atomic force microscopy. Optics Express. Vol. 18, No. 23. Nov. 8, 2010.
The atomic force microscope (AFM) has become one of the standard tools of nanotechnology. The concept is deceptively simple. A needle - not unlike an old-fashioned phonograph stylus, but much smaller with a tip at most only a couple of atoms wide - moves across the surface of the specimen.
A laser measures tiny deflections of the tip as it is pushed or pulled by atomic scale forces, such as electrostatic forces or chemical attraction. Scanning the tip back and forth across the sample yields a three-dimensional image of the surface.
The resolution can be astonishing - in some cases showing individual atoms, a resolution a thousand times smaller than the best optical microscopes can achieve.
Such amazing sensitivity raisesd a technical problem: if your probe can image an object of, say, 100 square nanometers, how exactly do you find that object if it could be nearly anywhere on a microscope stage a million times that size? That's not an unusual case in biological applications.