Under dry conditions, a conventional AFM set-up typically delivers a sharp image at high scan rates. However, when the sample is submerged under liquid it's a different story.

"As the scanning rate increases, the sample image soon becomes distorted," Inhee Choi of Seoul National University (SNU) told nanotechweb.org. "Looking at the effect in detail, we found that the distortion correlates strongly with the kinematic viscosity of the fluid."

One way to get around the problem is to apply a loading force to the scanning probe, which counterbalances the force generated by the flow of viscous liquid between the tip and the sample.

To determine the ideal loading force, the researchers input a set of readily obtainable parameters including the viscosity and density of the fluid and the dimensions of the AFM's cantilever probe into their model.

The results are impressive. Under ordinary conditions, images of bacterial cells in 2-propanol showed signs of blurring at scan rates of 50 µm/s. When the team applied its loading factor, it was possible to generate undistorted images at scan rates in excess of 200 µm/s.

Dubbed variable-controlled fast scanning, the method allows the team from SNU and Kwangwoon University to examine biological systems in real-time and opens the door to studying the effect of nanomaterials on cell behaviour.

The researchers presented their work in Nanotechnology.