Fabrication of atomic force microscope spherical tips and its application in determining the mechanical property of cancer cells

The process of cancer metastasis is closely related to the mechanical property of cells. Using the atomic force microscope (AFM)-based nanoindentation technique, the mechanical properties of cancer cells can be measured in liquid and at 37 degrees C. However, the conventional AFM tip is too sharp to finish this process. The AFM tip with a microsphere at the end is usually used. How to adhere a microsphere to the tip apex has become a big concern up to now. In this work, an easy and simple method based on the employment of carbon nanotube bundles is presented. The microsphere is successfully adhered to the tip and the elastic constant of the cantilever is calibrated with the Cleveland method. Using the developed tip, the nanoindentation tests on two kinds of lung cancer cells (Anip-973 and AGZY-83a), which exhibit different metastatic properties, are carried out in liquid and at 37 degrees C. Based on the Hertz contact equation between the spherical tip and the cell, the stress relaxation model is used to calculate the Young's modulus and viscoelastic properties of the cells. Experimental results confirm the feasibility of the method proposed in this work.