PNAS: Nanoscale imaging works differently in water

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Researchers have found that the atomic force microscope, a tool widely used in nanoscale imaging, works differently in liquid environments, it was reported online in last week's Proceeedings of the National Academy of Sciences.

The atomic force microscope uses a tiny vibrating probe, which researchers from Purdue University in West Lafayette, Ind., and three Spanish universities report behaves differently when in water as opposed to air.

Since it is preferable to study biological structures such as cell membranes in wet environments, Arvind Raman, MD, Purdue professor of mechanical engineering said this knowledge will help researchers understand how the microscope works in a watery environment and help them interpret images.

The atomic force microscope’s vibrating probe is caused to oscillate by the vibrating source at its base. But there is a different level of oscillation between the probe’s tip and its base, which is called a phase contrast. According to Raman, the differences in phase contrast give researchers information about the material they are studying, but they will need to understand exactly how the phase changes differ depending on whether the microscope is operating in water or air.

The researchers demonstrated this by showing how the microscope showed the detailed properties of the Phi29 virus. "The findings suggest that phase contrast in liquids can be used to reveal rapidly the intrinsic variations in local stiffness with molecular resolution, for example, by showing that the head and the collar of an individual virus particle have different stiffness," said Raman.