Contactless measurements of the elastic modulus of living cells using thermal fluctuations of atomic force microscope cantilever

We present a contactless method for measuring the elastic modulus of living human triple-negative breast cancer cells (MDA-MB-231) using the thermal fluctuations of an atomic force microscope (AFM) cantilever. By analyzing the power spectral density (PSD) of the cantilever's thermal fluctuations, we obtain the resonance frequencies of its first three modes at various cell to cantilever separation distances. By comparing measurements on living cells with those on a rigid borosilicate sphere of the same size, we extract the frequency shift caused by the elasto-hydrodynamic coupling between the cantilever fluctuations and the deformations of the cells. We then fit this frequency shift using an elasto-hydrodynamic model that integrates hydrodynamic forces and cell deformation. This approach allows us to determine the elastic modulus values of the living cells for the first three resonant frequencies of the cantilever.