Optical Tweezers Based Bio-Microrheology

Viscoelastic properties of a myriad of biological cells and bio-fluids are strongly correlated to their physiological functions; a change in their viscoelastic properties, even at a very small fraction on the order of a few percents, is often concomitant with related diseases. A classical example is the red blood cells (RBCs) whose deformability is critical to their oxgen-carrying and delivery function through veins and arteries. In the case of biological fluids, the viscosity of blood is closely related to cerebral vascular disease and coronary artery disease, and the liquefaction of vitreous humor can lead to retinal detachment. The relation of viscoelastic alterations of cerebral-spinal fluid and hydrocephalus has also been reported. Accurate measurement of the viscoelastic properties of biological samples at either single cell resolution (for the case of biological cells) or with sample volume on the order of micro-liter (for the case of biological fluids) may hence shed light on clinically-relevant mechano-biology at the molecular lever. From the practical point of view, the requirement of only a very small amount of sample is particularly important since many biological fluids such as synovial fluid and vitreous humor are available only in limited amount. Optical-Tweezers Based Micro-Rheology has emerged in recent years as one of the critical techniques capable of fulfilling the needs elucidated above.