Optical stretching on chip with acoustophoretic prefocusing

We demonstrate the use of a two-beam optical trap (an optical stretcher) in a low-cost microuidic system with the purpose of measuring the mechanical properties of cells and vesicles. Delivery of micrometer-sized particles and cells to the optical stretcher is obtained by acoustophoretic prefocusing. This focusing mechanism aims for target particles to always ow in the correct height relative to the optical stretcher, and is induced by a piezo-electric ultrasound transducer attached underneath the chip and driven at a frequency leading to a vertical standing ultrasound wave in the microchannel. Trapping and manipulation is demonstrated for dielectric beads. In addition, we show trapping, manipulation and stretching of red blood cells and vesicles, whereby we extract the elastic properties of these objects. Our design points towards the construction of a low-cost, high-throughput lab-on-a-chip device for measurement of mechanical properties of cells and vesicles.