Investigation of the mechanical property of individual cell using axial optical tweezers

摘要

Optical tweezers is a technique that can trap and manipulate small objects using a highly focused laser beam. Because optical tweezers can also be used to measure small forces, it has been extensively used for the measurement of the mechanical forces of cells. Previous research works typically study particle manipulation and cell force measurement in the lateral direction, hence excluding valuable insights about the axial mechanical properties of cells. Other works that investigate axial cell force measurements utilize spatial light modulators and other devices that are expensive and complicate the setup. Thus, in our study, we designed a simple scheme that can axially manipulate particles by adjusting the position of one lens, called L1-lens, in our setup. Image processing techniques were utilized to determine the changes in the axial particle translation, providing nanometer sensitivity. We investigated the capability of our system using two different-sized particles and results show that for a given L1-lens default position and movement, a 2-micron particle and a 4.26-micron particle were moved axially for 7.68 μm and 4.83 μm, respectively. Axial trapping stiffness was also measured for the stated bead sizes in different magnification. Using the computed trapping stiffness, we will investigate the axial reactive forces of cells.