Optical deformation of red blood cells trapped on a narrow waveguide

Reduced blood deformability is clinically linked to several diseases. It is important to develop sensitive tools to measure the loss of blood deformability. The evanescent field of an optical waveguide can trap and propel red blood cells along the waveguide. Here we propose to use the evanescent field from a narrow optical waveguide to trap and deform red blood cells. We demonstrate that the intensity gradient of the evanescent field at the edge of narrow waveguides (1-3 mu m) can be used to squeeze a blood cell. The RBCs are squeezed to a size comparable to the waveguide width. When the laser is switched on the cell is attracted towards the waveguide and is held in place. Subsequently, the part of the cell not on the waveguide is pulled in across the waveguide. The result is a cell (7-8 mu m in diameter) squeezed down to a significantly smaller width (typically 3 mu m). The cell regains its original shape when laser is switched-off.