High Resolution Imaging of Living Cells with Microsecond Force Spectroscopy

Abstract

Mapping cell mechanical properties down to molecular level can both refine our knowledge about cellular structures and reveal information about biological functions like cell adhesion, proliferation and survival. Atomic force microscopy (AFM) is a powerful method to probe materials at the nanoscale. Although AFM has been used to image live cells and probe their mechanical properties1, its resolution on cells is much lower than on stiffer materials. To address this, we adapted Microsecond Force Spectroscopy2 to rapidly image mechanical properties of live and cross-linked fibroblasts, neurons and Human Umbilical Vein Endothelial Cells in culture media or buffer.Mechanical properties images showed cellular features as small as 50nm, representing an unprecedented resolution over a wide variation of cell types. The enhanced resolution and speed of our method allowed the identification of dynamic changes in elastic modulus of fine cellular structures, which did not appear to be reflected in optical images of fluorescently-labeled actin, acquired from the same cells. These changes might reflect a loss of tension in the actin network underneath the cell membrane. Preliminary data further suggest that our platform might allow the label-free recognition of stress fibers, retraction fibers, Weibel-Palade bodies and microvilli solely based on nanomechanical contrast. These developments extend the cell imaging capabilities of AFM and highlight the value of mechanics in the delineation of cellular physiological states. The compatibility of our method with human cells suggests that it can be further developed as a diagnostic tool for the detection of disease-specific cellular mechanical responses.1-Casuso et al. J.Mol.Recogn. 2011; 24:406-413.2-Dong et al. Nature Nanotechnology 2009; 4:514-517.