A microfluidic approach for raw milk sample preconditioning prior to protein and lipid content analysis has been developed. The system utilizes microchip acoustophoresis and is a further extension of our previously reported multiple node ultrasonic standing wave focusing platform (Grenvall, C., Augustsson, P., Matsuoka, H. and Laurell, T. Proc. Micro Total Anal. Syst. 2008, 1, 161-163). The microfluidic approach offers a method for rapid raw milk quality control using Fourier transform infrared spectroscopy (FT-IR). Two acoustophoresis modes are explored, 2 lambda/2 and 3 lambda/2, offering lipid content enrichment or depletion, respectively. Lipid content depletion above 90% was accomplished. FT-IR data on microchip-processed raw milk samples, enabling direct lipid and protein content analysis, are reported. Most importantly, the harmonic operational modes bypass the problem of lipid aggregation and subsequent clogging, inherent in lambda/2 acoustophoresis systems.

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 field of cytometry has grown in scope and importance ever since the early 20th century with leaps in technology introducing the Coulter counter and the flow cytometer. Cytometry methods have brought about a revolution for the medical and biotechnology industry by providing fast and accurate analysis of cell and particle suspensions. Recent developments in the field aim at improving current cytometers and to provide miniaturized low-cost cytometry systems for point-of-care clinical diagnostics or research. In an attempt to address the need for particle positioning which is important for both impedance and optically based cytometers we present a microfluidic system which precisely positions cells and particles, using acoustic forces and subsequently performs measurements using an integrated and simple planar electrode Coulter-type impedance cytometer without the need for sheath flows. Data is presented to show how the acoustic method improves the accuracy of the impedance cytometer when prefocusing is employed to particles and cells (diluted whole blood). Confocal imaging and simulations support the findings and provide the basis for further improvements. The acoustophoretic prefocusing technique opens a path towards small, low cost cytometers while also providing an easy way to improve current systems.

Microchip-based free flow acoustophoresis (FFA) in combination with two-dimensional cell prefocusing enables concurrent multiple target outlet fractionation of leukocytes into subpopulations (lymphocytes, monocytes and granulocytes); we report on this method here. We also observed significantly increased accuracy in size-based fractionation of microbeads as compared to previously presented FFA multiple outlet systems. Fluorescence microscopy illustrates the importance of two-dimensional prefocusing where a sample mixture of 3-, 7- and 10-micrometer beads are separated into well-confined particle streams and collected in their respective target outlets. Flow cytometry data for lymphocytes and granulocytes, respectively, in their corresponding outlets verify concurrent isolation of leukocyte subpopulations with high purity (95.2 ± 0.6% and 98.5 ± 0.7%) and high recovery (86.5 ± 10.9% and 68.4 ± 10.6%). A relatively low purity and high recovery of monocytes (25.2% ± 5.4% and 83.1 ± 4.3%) was obtained in the third target outlet. No subpopulation bias was observed. These data demonstrate an unprecedented separation of leukocyte subpopulations at flow rates of ~100 μl/min and ~1M cells/ml sample concentrations, not previously reported in acoustofluidic systems. Two-dimensional prefocusing FFA with multiple target outlets is a viable alternative to current methods for particle fractionation and cell isolation, requiring a minimum of sample preparation, and lowering analysis time and cost.

A microfluidic system for cell enumeration in raw milk was developed. The new method, preconditions the milk sample using acoustophoresis that removes lipid particles which are larger than a few micrometers. The acoustophoretic preprocessing eliminates the need for conventional sample preparation techniques, which include chemical solvents, cell labeling and centrifugation, and facilitates rapid cell enumeration using microscopy or coulter counter measurements. By introducing an acoustic standing wave with three pressure nodes in a microchannel at the same time as the milk sample is laminated to the channel center, lipids are acoustically driven to the closest pressure antinode at each side of the channel center and the cells in the milk sample are focused in the central pressure node. The extracted center fraction with cells becomes sufficiently clean from lipid vesicles to enable enumeration of somatic cells without any labeling step either by direct light microscopy or by coulter counting. Obtained lipid free milk fractions clearly revealed the cell fraction when analyzed by Coulter Counting.

Correction for 'Acoustic actuated fluorescence activated sorting of microparticles' by Ola Jakobsson et al., Lab Chip, 2014, 14, 1943-1950.

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