Opto-acousto-fluidic microscopy for three-dimensional imaging of droplets and cells

摘要

This paper reports a novel method, opto-acousto-fluidic microscopy, for label free detection of droplets and cells in microfluidic networks. Leveraging the optoacoustic effect, the microscopic system possesses capabilities of visualizing flowing droplets, analyzing droplet contents, and detecting cell populations encapsulated in droplets via the sensing of acoustic waves induced by intrinsic light-absorbance of matters. The opto-acousto-fluidic chip was fabricated using standard soft-lithography with a channel width of 200 μm and height of 120 μm. Fluid samples were injected into chips using syringe pumps via plastic tubings. A T-junction was used to produce aqueous droplets which consisted of light-absorbing molecule species or cells and buffer fluids. A pulse laser beam (repetition rate 50 kHz) steered by a galvanometer mirror and focused by an objective (4X) transmits through and converges with a focal spot size of 3.2μm in the microfluidic channels. For each scanning line, 250 sampling was made with a spatial interval of 1 μm across the channel with a width of 200μm in the experiment, and thus the 50kHz repetition rate of the laser provides a 200Hz B-scan rate. In the cell research, arterial blood was draw from a rat and buffered with saline. Droplets with different volumes but same density of red blood cell population were generated, and the cytometric measurement shows that the number of detected RBCs increases proportionally with the volume of the droplet.