Origins of phase contrast in the atomic force microscope in liquids.
We study the physical origins of phase contrast in dynamic atomic force microscopy (dAFM) in liquids where low-stiffness microcantilever probes are often used for nanoscale imaging of soft biological samples with gentle forces. Under these conditions, we show that the phase contrast derives primarily from a unique energy flow channel that opens up in liquids due to the momentary excitation of higher eigenmodes. Contrary to the common assumption, phase-contrast images in liquids using soft microcantilevers are often maps of short-range conservative interactions, such as local elastic response, rather than tip-sample dissipation. The theory is used to demonstrate variations in local elasticity of purple membrane and bacteriophage 29 virions in buffer solutions using the phase-contrast images.
Melcher
John
J
School of Mechanical Engineering and Birck Nanotechnology Center, Purdue University, West Lafayette, IN 47907, USA.
Carrasco
Carolina
C
Xu
Xin
X
Carrascosa
José L
JL
Gómez-Herrero
Julio
J
José de Pablo
Pedro
P
Raman
Arvind
A
D000465:Algorithms; D017103:Bacillus Phages / Q000737:chemistry; D002021:Buffers; D002138:Calibration; D020285:Cryoelectron Microscopy / Q000379:methods; D003593:Cytoplasm / Q000378:metabolism; D004548:Elasticity; D007700:Kinetics; D018625:Microscopy, Atomic Force / Q000379:methods*; D008858:Microscopy, Phase-Contrast / Q000379:methods*; D015233:Models, Statistical; D008962:Models, Theoretical; D009991:Oscillometry; D018717:Purple Membrane / Q000378:metabolism; D013314:Stress, Mechanical
D002021:Buffers