In this paper, we present a fluorescence activated sorter realized in a continuous flow microfluidic chip. Sorting is achieved by deflecting a focused particle stream with short acoustic bursts (2.5 ms), in a fluorescence activated configuration. The system utilizes two-dimensional acoustic pre-focusing, using a single actuation frequency, to position all particles in the same fluid velocity regime at flow rates up to 1.7 mL min(-1). Particles were sorted based on their fluorescence intensities at throughputs up to 150 particles s(-1). The highest purity reached was 80% when sorting at an average rate of 50 particles s(-1). The average recovery of a sort was 93.2 ± 2.6%. The presented system enables fluorescence activated cell sorting in a continuous flow microfluidic format that allows aseptic integration of downstream microfluidic functionalities, opening for medical and clinical applications.
The ability to concentrate cells from dilute samples into smaller volumes is an essential process step for most biological assays. Volumetric concentration is typically achieved via centrifugation, but this technique is not well suited for handling small number of cells, especially outside of the laboratory setting. In this work, we describe a novel device that combines acoustofluidics with a recirculating architecture to achieve >1000-fold enrichment of cells in a label-free manner, at high volumetric throughput (>500 μL min(-1)) and with high recovery (>98.7%). We demonstrate that our device can be used with a wide variety of different cell types and show that this concentration strategy does not affect cell viability. Importantly, our device could be readily adopted to serve as a "sample preparation" module that can be integrated with other microfluidic devices to allow analysis of dilute cellular samples in large volumes.
Flow cytometry is a frequently used method when it comes to cell sorting and analysis. Nonspherical cells, such as red blood cells or sperm cells, however, pose a challenge as they reduce the precision of light scatter measurements which interfere with the analysis of these and other cell populations in the same sample. Here, we present a microfluidic chip for acoustophoresis utilizing ultrasonic standing waves to focus and orient red blood cells in two dimensions in the channel center. The cells can be oriented to show either their flat or up-ended side toward the optical axis and the observer. In an acoustic standing wave field the cells will be rotated until the direction of the smallest dimension is parallel with the direction where the acoustic energy is strongest. While keeping the cells focused in the channel center utilizing acoustic resonances in two dimensions, the orientation can be controlled by increasing the acoustic energy in either the horizontal or vertical resonance mode. It was shown that 87.8 ± 3.8% of the red blood cells could be horizontally oriented while 98.7 ± 0.3% could be vertically oriented. The ability to control the orientation of nonspherical cells with high accuracy is a beneficial feature and potential contribution to the rapidly growing field of flow and image cytometry.
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