Using an optical trap to fold and align single red blood cells

We report on the trapping dynamics of single red blood cells (RBCs) in an optical trap. The optical trap was constructed using linearly polarized, infrared laser light (1064 nm). The trapped RBC shows folding behaviour due to the elastic nature of the cell membrane. On removal of the trap, the RBC regains its original shape, indicating that there is no cell damage induced by the optical field. The folding time for the RBC is less than 1 s, while the relaxation time is 6 s. The folded RBC aligns itself along the direction of the electric field of the laser due to the action of polarization-induced forces; introducing a half-wave plate in the trap and forcing the trapped RBC to follow the direction of the electric field vector of the laser confirms this