The optical stretcher is a novel laser tool to micromanipulate single biological cells and to probe their viscoelastic properties in suspension [1].



A cell is trapped by two opposing laser beams, which hold it and pull on both sides of it. Higher laser powers are used to deform the cell. The cell deformations are recorded by a CCD camera and evaluated by a custom designed software. The measurement chamber of the Optical Stretcher is integrated into a microfluidic system, such that cells can be easily delivered one after the other. High throughput rates of about 250 cells per hour can be achieved, allowing for better statistics compared to other tools such as atomic force microscopy (AFM).


3D Stretcher Skizze

Sketch of an Optical Stretcher Measurement Chamber


The forces to deform the cells originate from the laser light. When the light is refracted at the surfaces of the cells there is a change in momentum of the photons. Since overall momentum must always be conserved there is a momentum transfer to the cell surface in form of a force acting perpendicular to it.

Momentum transfer at the cell surface in a dual beam optical trap

Momentum transfer at the cell surface


Cell mechanics as a disease marker

The physical mechanics of cells are important for their regular, biological functioning and are regulated by a structure called the cytoskeleton. It is involved in many vital processes of the cell. If these are changes this naturally results also in changes of the biomechanical properties, which can be measured with the Optical Stretcher. There is already published data for cancer [2, 3] and for the effect of cell aging [4].
Several ongoing studies examine the ability of the Optical Stretcher to differentiate between the stages of a cancer tumor, making it a valuable tool for both scientific research and clinical diagnosis [5].

Cell types can be differentiated by their deformation in the optical stretcher

Cell types can be differentiated by their deformation in the optical stretcher