Researchers' imaging technique trolls in quiet cellular seas

Experienced anglers know that choppy waters make for difficult fishing, so they try not to rock the boat. Thanks to a new microscopy technique, cell biology researchers can heed that same advice.

University of Illinois researchers developed a method they call ''trolling AFM,'' which allows them to study soft biological samples in liquid with high resolution and high quality. Led by mechanical science and engineering professor Min-Feng Yu, the group published its findings in the journal Nanotechnology.
 
''We developed a highly sensitive method for high-resolution imaging of soft biological samples, such as living cells, in their physiological condition,'' said Majid Minary, a recent graduate of Yu's group and first author of the paper. Minary now is a professor at the University of Texas-Dallas. ''We improved the quality factor of common atomic force microscopy imaging methods by two orders of magnitude,'' Minary said.

The widely used atomic force microscope provides images of tiny structures with high resolution at the atomic scale. The AFM has a sharp probe at the end of an arm, called a cantilever. The tip of the probe skims the surface of a sample to measure mechanical, electrical or chemical properties.

When scientists want to study cells, tissue or other live biological materials, the samples must be submerged in a liquid to keep them alive. This poses difficulties for atomic force microscopy, because the cantilever has to be submerged as well.

Cells and tissues are so soft that if the AFM probe were simply dragged across the surface, it would damage or displace the sample instead of reading it. Therefore, scientists have to operate the AFM in oscillation mode – with the probe gently tapping along the sample and detecting resistance.

But oscillation in liquid brings a tide of complications in its wake.