Nanomechanical and topographical imaging of living cells by Atomic Force Microscopy with colloidal probes

Atomic Force Microscopy (AFM) has a great potential as a tool to characterize me-chanical and morphological properties of living cells; these properties have been shown to correlate with cells ’ fate and patho-physiological state in view of the development of novel early-diagnostic strategies. Although several reports have described experi-mental and technical approaches for the characterization of cell elasticity by means of AFM, a robust and commonly accepted methodology is still lacking. Here we show that micrometric spherical probes (also known as colloidal probes) are well suited for performing a combined topographic and mechanical analysis of living cells, with spatial resolution suitable for a complete and accurate mapping of cell morphological and elastic properties, and superior reliability and accuracy in the mechanical mea-surements with respect to conventional and widely used sharp AFM tips. We address a number of issues concerning the nanomechanical analysis, including the applicabil-ity of contact mechanical models and the impact of a constrained contact geometry on the measured elastic modulus (the finite-thickness effect). We have tested our protocol by imaging living PC12 and MDA-MB-231 cells, in order to demonstrate the importance of the correction of the finite-thickness effect and the change in cell elasticity induced by the action of a cytoskeleton-targeting drug