Acoustofluidic rare cell sample preparation

Abstract: Acoustofluidics utilizes a combination of acoustics, in the form of ultrasound, and microfluidics to manipulate cells and particles. This has proven to be a versatile method that is gentle to the cells. In this thesis acoustofluidics has been used for processing rare cells in continuous flow. Rare cells are within this thesis defined as cells that are present in numbers of 1-1000 per mL in a much larger population of background cells. Rare cells present in blood have been of particular interest, and cancer cells and bacteria have been used as model cells. In this thesis acoustofluidics has first been used to concentrate cells. This was done by using two-dimensional focusing and a multistage acoustofluidic device where sequential concentration steps, generating moderate concentration factors, could be multiplied into large concentration factors. The usefulness of the method was then extended as the critical particle focusing size was lowered to also allow focusing of bacteria. This was done through using two-dimensional focusing, which was shown to change the acoustic streaming pattern to no longer counteract the primary acoustic radiation force. The new critical particle focusing size was determined to be between 0.5 μm and 0.24 μm in particle diameter for polystyrene-like particles. In the third paper a simplyfied acoustofluidic device, that does not rely on a clean fluid sheath flow to prealign the cells or particles before the separation, was presented. To be able to do this the device used only two-dimensional focusing to prealign the cells. The usefulness of the device was in turn demonstrated with the separation of cancer cells from white blood cells where it was shown to perform comparably to previously presented devices. In the fourth paper a separation method was combined with the concentration method presented in the first paper on an integrated device. The device was shown to be able to simultaneously separate and concentrate cancer cells from white blood cells. Finally, the previously proposed concentration device was integrated with a DEP single cell trapping device further showing the usefulness of the acoustofluidic method. Standing alone, the DEP trapping device could only process sample at a flow rate of 4 μL/min while still maintaining a high trapping efficiency.By integrating the DEP trapping device with the acoustofluidic concentrator device a higher sample inflow rate could be used as the acoustofluidic device could gear down the flow rate before the sample entered the DEP trapping device. Together samples could be processed ~10 times faster than using the DEP trapping device alone, while still recovering over 90% of the cells.