Combined High-Speed Atomic Force and Optical Microscopy Shows That Viscoelastic Properties of Melanoma Cancer Cells Change during the Cell Cycle

Current high-speed atomic force microscopy (HS-AFM) setups reach imaging speeds of several images per second but often have limited options for imaging live cells because of a small scan range, a lack of environmental control, or a missing combination with optical phase-contrast or fluorescence microscopy. A HS-AFM setup is therefore developed with a large scan range optimized for imaging live cells. The setup is equipped with temperature and CO2 control and is mounted on an inverted optical microscope providing high-quality phase-contrast and fluorescence microscopy. To demonstrate the capabilities of the setup, fast force mapping on live human platelets is performed. Further, HS-AFM images and optical phase-contrast and actin fluorescence images of live cancer cells are simultaneously recorded, and two state-of-the-art AFM modes for imaging viscoelastic sample properties, force clamp force mapping and resonance compensating chirp mode, are compared. The setup is then applied to the investigation of viscoelastic material properties of cells in different cell cycle states. Using a melanoma cell line with a fluorescent cell cycle sensor, it is found that during the cell cycle not only cell volume and morphology, but also viscoelastic material properties significantly change, with increasing stiffness and decreasing fluidity from the G1 through the G1/S to the S/G2/M phases.

Automated summary

A high-speed atomic force microscopy setup optimized for imaging live cells has been developed and demonstrated in experiments on live human platelets and cancer cells. Additionally, the study explores the changes in viscoelastic material properties of cells in different cell cycle states.