Simultaneous imaging and manipulation of microparticles in horizontal and vertical planes of microchannels using a single objective lens

In this Letter, we present an experimental method that allows simultaneous imaging of microparticles in horizontal and vertical planes of a microchannel using a single objective lens to be achieved. This is done by implementing a specialized dual-prism arrangement, i.e., by placing two 67.5 degrees right triangular prisms between the objective and the microfluidic channel. Apart from demonstrating simultaneous imaging of microparticles in orthogonal planes of a microchannel and discussing the applicability of the dual-prism configuration for efficient microchannel imaging, examples are also given for the imaging of microparticle alignment and motion in an acousto-microfluidic channel, where microparticles were found to be rapidly focused to the channel center under ultrasonic excitations. It is demonstrated here that, compared to the optical measurements using conventional microscopy, which generally can only ensure one plane of a microchannel in focus, the optical platform presented here enables more convenient and superior optical characterization of microparticles and acoustophoresis.