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Understanding the deformability and associated biomechanical properties of red blood cells (RBCs) is crucial for many pathological analysis and diagnosis of human diseases. In such endeavors, optical tweezers have played an active role over the past decades. Here, we study the RBC deformability by employing a novel “tug of war” (TOW) optical tweezers consist of a pair of elongated diverging accelerating beams that can stably trap and stretch a single RBC under different osmotic conditions without any tethering or mechanical movement. With a viscous drag method, we compare directly the trapping force at different states of RBCs, and find that even one arm of the TOW tweezers can apply a force of over 18pN with only 100mW laser power, more than 2 times stronger than that from the Gaussian trap at the same condition. Without the need of two independent controls as in a conventional dual trap, the spacing between the two TOW traps can be increased conveniently from 0 to over 9m, resulting in nearly 15% of cell deformation. We obtain the shear modulus of the RBCs in different osmotic conditions, with the largest value of 3.36±0.95pN/μm in the hypertonic case, and compare with those previously reported results. Our work may bring about a new photonic tool for the study of biomechanical properties of living cells, promising for applications such as distinguishing healthy and diseased cells.
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