Cell diagnosis based on optical forces

In this article, we report the development of a novel system for distinguishing various types of cell based on the differences in the values of optical forces experienced by them. The laser induced optical forces arise when molecules comprising the cell interact with the photons of the laser beam resulting in an exchange of momentum. The basic principle is based on the phenomenon of laser cell guidance: a cell, in proximity of a weakly focused laser beam experiences a net force which attracts it to the centre of the beam and propels it along the axis of the beam. The 'guidance' is thus a direct result of the optical forces experienced by the cell. The guidance force experienced by the cell is directly related to the amount of momentum exchange, which in turn depends on factors such as the cell shape and size, the refractive index difference between the materials composing the cell and the materials in the culture media, and the properties of the beam. Since different cell types have different physical properties, they experience different optical (guiding) forces when they interact with the same laser beam. Since guidance force causes the cells to be propelled along the axis of the beam, the force with which the cell is propelled will directly determine the velocity with which the cell will move along the beam. Hence different types of cells will move with different velocities. Thus by studying this motion of cell, we in turn study the forces experienced by the cell. We propose that by analyzing the velocity with which cells are being guided by a laser beam, we can develop a technique to distinguish various cell types. Extensive GLMT theories calculate and predict theoretically the forces experienced by particles of a given size and refractive index for a given set of beam parameters. These theories are used as the basis to make judgments about the validity of our velocity and force calculation. The velocity assessments are conducted for a statistically significant number of cells from various cell types to explore the systematic difference among various groups of cells and, accordingly, the reliability of the developed method is discussed.