Atomic force microscopy (AFM) employs a very sharp tip to mechanically scan a sample resulting in a 3D representation of its surface. Under ideal conditions, even single atoms can made visisble. Because scanning can also be performed in liquid at ambient temperature, AFM has gained popularity for the investigation of biological samples, still at nanometer resolution. Besides high-resolution imaging, AFM can be used to measure mechanical characteristics of samples. For this, the tip is used to deform the sample and properties such as elasticity, viscosity and adhesion can be measured. The ESRIC AFM has been used to study the roughness and elasticity of surfaces and gels, to image protein complexes and to study the morphology and stiffness of living cells. The latter can be indicative of a cell’s health and allow the measurement of any changes that might occur in disease states.
Figure 1 Left: A wing is showed at macroscale with two different angle-view and distinct colors are seen. In a), the wings appear green but they turn black in b). Right: The nanoscale structure start to be visible in the 25 x 25 μm AFM image d) representing an unique scale. Finally the 10 x 10 μm AFM image e) reveals the approx. 200 nm vertical periodic pattern partly responsible for the apparent color of the butterfly wings.
The ESCRIC AFM is optimized for scanning of larger biological samples (tens of micrometers) in liquid and is combined with an optical and fluorescence microscope. Nevertheless, the AFM still provides nanometer resolution on smaller samples such as amyloid fibrils and can be operated in air too.
In addition to creating a quantitative 3D image of your cell surface it is possible to use AFM Force Spectroscopy, which enables you to measure on the nanoscale, properties such as visco-elasticity by recording the response of the cell upon the applied forces
AFM is being used at Heriot-Watt University by Maryam Mohammad Zadeh to measure the mechanical properties of cells.
“Cell elasticity (E) is one of the important mechanical properties, which can be used to determine the state of cell’s health or disease. Cell elasticity can be measured by indenting the cell with a probe of an AFM by applying nano-Newton forces. For a quantitative study of the cell elasticity by AFM, force vs. cell deformation curves are recorded and analysed. These curves contain information about the mechanics of the cell and provide a basis for Young’s elastic modulus estimation (E). An appropriate mechanical model is required to calculate the value of the elastic modulus from the experimental data.”