Cell elongation via intrinsic antipodal stretching forces.

To probe the mechanical properties of cells, we investigate a technique to perform deformability-based cytometry that inherently induces normal antipodal surface forces using a single line-shaped optical trap. We show theoretically that these opposing forces are generated simultaneously over curved microscopic object surfaces with optimal magnitude at low numerical apertures, allowing the directed stretching of elastic cells with a single, weakly focused laser source. Matching these findings with concomitant experimental observations, we elongate red blood cells, effectively stretching them within the narrow confines of a steep, optically induced potential well.