Applications

Measuring forces on cells with AFM

The unique feature of atomic force microscopy (AFM) in life sciences is its ability to measure forces in liquids to probe cells or molecules from micro to nano.

Cells are dynamic systems packed with force-generating machines. From adhesion, migration and cell division to molecular processes, everything is linked to force generation and binding between molecules. AFMs can quantify these at the cellular and molecular level with micro to nanoscale spatial resolution, providing a deeper understanding of how living systems utilize forces.

AFM setups

There are almost unlimited variations of AFM experiments for which supply two AFM setups depending on the application.

The HR-AFM is a sample scanning AFM, where the sample moves on XYZ piezoelectric elements. This system differentiates itself by a very low noise floor of <35 pm and is ideal for imaging very small features such as molecules, either dry or in liquid at room temperature. The HR-AFM uses a video tube microscope and light reflected from the sample surface to identify areas of interest and can be equipped with a dunk and scan probe holder for measurements in liquids under ambient conditions.

HR-AFM setup for molecular imaging in liquid at ambient conditions.

The LS-AFM is a tip scanning AFM, where the tip moves on XYZ piezoelectric elements. This system is typically mounted on an inverted light microscope (bright field and fluorescence correlation) and is ideal for imaging live systems such cells in liquid using a heated stage. The LS-AFM can also be purchased separately and integrated with other laboratory instruments.

LS-AFM setup for correlative light microscopy – AFM of live cells in liquid.
Brightfield image of a Caco-2 cell in buffer, showing the shadow of the probe and two nuclei in the boxed region. This image is from an LS-AFM with heated stage and a 63x LWD objective.
Corresponding topography of the boxed region by AFM showing the height of the condensed chromatin.

Force measurements

AFM force measurements encompass a wide range of complexities depending on the imaging conditions (dry vs. liquid), mode (non-vibrating or vibrating), and the forces to be measured. Stiffness measurements combine accurate force measurements with scanning in liquids. Measurements of interaction forces such as antibody-antigen require one binding partner to be attached to the tip typically using biochemical crosslinking strategies.1 Other applications extend from force measurements of bacterial cell adhesion2 to the stretching of individual collagen fibrils.3

Force measurements use the AFMs ability to measure the bending of the cantilever which is proportional to the applied force and can be calibrated accurately. The recording of a force-distance curve is straightforward using the included software.4 The interpretation of the data on the other hand can be more complex, as it needs to take into account several parameters of the probe and sample.5

AFMWorkshop AFMs have been used for force-distance measurements of yeast cell clusters6, cardiomyocytes7, tumor cells8, and aorta tissue9.

Advanced force-distance measurement on an HR-AFM equipped with a dunk and scan liquid setup.

References

  • 1

    Lower, B. H.; Yongsunthon, R.; Shi, L.; Wildling, L.; Gruber, H. J.; Wigginton, N. S.; Reardon, C. L.; Pinchuk, G. E.; Droubay, T. C.; Boily, J.-F.; Lower, S. K. Antibody Recognition Force Microscopy Shows That Outer Membrane Cytochromes OmcA and MtrC Are Expressed on the Exterior Surface of Shewanella Oneidensis MR-1. Appl. Environ. Microbiol. 2009, 75 (9), 2931–2935. https://doi.org/10.1128/AEM.02108-08.

  • 2
    Aguayo, S.; Donos, N.; Spratt, D.; Bozec, L. Single-Bacterium Nanomechanics in Biomedicine: Unravelling the Dynamics of Bacterial Cells. Nanotechnology 2015, 26 (6), 062001. https://doi.org/10.1088/0957-4484/26/6/062001.
  • 3

    Quigley, A. S.; Veres, S. P.; Kreplak, L. Bowstring Stretching and Quantitative Imaging of Single Collagen Fibrils via Atomic Force Microscopy. PLOS ONE 2016, 11 (9), e0161951. https://doi.org/10.1371/journal.pone.0161951.

  • 4

    Measuring and Analyzing Force-Distance Curves with AFM. https://www.afmworkshop.com/newsletter/measuring-and-analyzing-force-distance-curves-with-atomic-force-microscopy (accessed 2023-12-29).

  • 5
    Dufrêne, Y. F.; Martínez-Martín, D.; Medalsy, I.; Alsteens, D.; Müller, D. J. Multiparametric Imaging of Biological Systems by Force-Distance Curve–Based AFM. Nat. Methods 2013, 10 (9), 847–854. https://doi.org/10.1038/nmeth.2602.
  • 6
    Bozdag, G. O.; Zamani-Dahaj, S. A.; Day, T. C.; Kahn, P. C.; Burnetti, A. J.; Lac, D. T.; Tong, K.; Conlin, P. L.; Balwani, A. H.; Dyer, E. L.; Yunker, P. J.; Ratcliff, W. C. De Novo Evolution of Macroscopic Multicellularity. Nature 2023, 617 (7962), 747–754. https://doi.org/10.1038/s41586-023-06052-1.
  • 7
    Peyronnet, R.; Desai, A.; Edelmann, J.-C.; Cameron, B. A.; Emig, R.; Kohl, P.; Dean, D. Simultaneous Assessment of Radial and Axial Myocyte Mechanics by Combining Atomic Force Microscopy and Carbon Fibre Techniques. Philos. Trans. R. Soc. Lond. B. Biol. Sci. 2022, 377 (1864), 20210326. https://doi.org/10.1098/rstb.2021.0326.
  • 8
    Deliorman, M.; Janahi, F. K.; Sukumar, P.; Glia, A.; Alnemari, R.; Fadl, S.; Chen, W.; Qasaimeh, M. A. AFM-Compatible Microfluidic Platform for Affinity-Based Capture and Nanomechanical Characterization of Circulating Tumor Cells. Microsyst. Nanoeng. 2020, 6 (1), 1–15. https://doi.org/10.1038/s41378-020-0131-9.
  • 9

    Canugovi, C.; Stevenson, M. D.; Vendrov, A. E.; Hayami, T.; Robidoux, J.; Xiao, H.; Zhang, Y.-Y.; Eitzman, D. T.; Runge, M. S.; Madamanchi, N. R. Increased Mitochondrial NADPH Oxidase 4 (NOX4) Expression in Aging Is a Causative Factor in Aortic Stiffening. Redox Biol. 2019, 26, 101288. https://doi.org/10.1016/j.redox.2019.101288.