Feeling for cells with light

In an optical stretcher, infrared laser light is used to exert surface stress on biological cells, causing an elongation of the trapped cell body along the laser beam axis. These optically induced deformations characterize individual cells and cell lines. When integrated within a microfluidic chamber with high throughput, this enables diagnosis of diseases, on a cellular level, that are associated with cytoskeletal processes. Additionally, it allows sorting of cells with high accuracy in a non-contact manner. To determine the surface stress on the cell, ray optics calculations as well as the system transfer operator (T-matrix) approach with an appropriate incident field are used. The latter approach allows a more accurate modeling of the cell in the optical stretcher and reveals a more detailed stress profile acting on the cell surface. Analyzing the deformation behavior of normal and malignantly transformed fibroblasts, significant differences in axial elongation even for sample sizes as low as 30 cells are already measurable on a time scale of 0.1s. Here, malignant transformation of cells is discussed as an example of how any process that affects the cell's optical or mechanical properties allows classification with the optical stretcher.