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Open AccessArticle

Photothermal Off-Resonance Tapping for Rapid and Gentle Atomic Force Imaging of Live Cells

1
Laboratory for Bio- and Nano-Instrumentation, Swiss Federal Institute of Technology Lausanne (EPFL), 1015 Lausanne, Switzerland
2
UPKIN, Swiss Federal Institute of Technology Lausanne (EPFL), 1015 Lausanne, Switzerland
*
Author to whom correspondence should be addressed.
Int. J. Mol. Sci. 2018, 19(10), 2984; https://doi.org/10.3390/ijms19102984
Received: 4 September 2018 / Revised: 21 September 2018 / Accepted: 24 September 2018 / Published: 30 September 2018
(This article belongs to the Special Issue Atomic Force Microscopy for Biological Applications)
Imaging living cells by atomic force microscopy (AFM) promises not only high-resolution topographical data, but additionally, mechanical contrast, both of which are not obtainable with other microscopy techniques. Such imaging is however challenging, as cells need to be measured with low interaction forces to prevent either deformation or detachment from the surface. Off-resonance modes which periodically probe the surface have been shown to be advantageous, as they provide excellent force control combined with large amplitudes, which help reduce lateral force interactions. However, the low actuation frequency in traditional off-resonance techniques limits the imaging speed significantly. Using photothermal actuation, we probe the surface by directly actuating the cantilever. Due to the much smaller mass that needs to be actuated, the achievable measurement frequency is increased by two orders of magnitude. Additionally, photothermal off-resonance tapping (PORT) retains the precise force control of conventional off-resonance modes and is therefore well suited to gentle imaging. Here, we show how photothermal off-resonance tapping can be used to study live cells by AFM. As an example of imaging mammalian cells, the initial attachment, as well as long-term detachment, of human thrombocytes is presented. The membrane disrupting effect of the antimicrobial peptide CM-15 is shown on the cell wall of Escherichia coli. Finally, the dissolution of the cell wall of Bacillus subtilis by lysozyme is shown. Taken together, these evolutionarily disparate forms of life exemplify the usefulness of PORT for live cell imaging in a multitude of biological disciplines. View Full-Text
Keywords: high-speed atomic force microscopy; photothermal off-resonance tapping; live cell imaging; antimicrobial peptide; thrombocytes; bacterial imaging; cell lysis high-speed atomic force microscopy; photothermal off-resonance tapping; live cell imaging; antimicrobial peptide; thrombocytes; bacterial imaging; cell lysis
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Nievergelt, A.P.; Brillard, C.; Eskandarian, H.A.; McKinney, J.D.; Fantner, G.E. Photothermal Off-Resonance Tapping for Rapid and Gentle Atomic Force Imaging of Live Cells. Int. J. Mol. Sci. 2018, 19, 2984.

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