Microfluidic sedimentation cytometer for milk quality and bovine mastitis monitoring
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We report a rapid, low-cost, portable microfluidic sedimentation cytometer (SeCy) for assessing the somatic cell count and fat content of milk in 15 min using a “sample-in, answer-out” approach. The system consists of 12 independent microfluidic devices, essentially flattened funnel structures, fabricated on the footprint of a single plastic compact disc (CD). Each funnel structure holds 150 μL of milk, has an inlet for milk filling and an outlet for air to escape, and ends in a narrow, closed-end microfluidic channel that facilitates packing of the cells into a column whose length is proportional to cell count. The closed-end channel provides accurate cell counts over the range 50,000–>3,000,000 cells per mL. The assay separates cells and fat globules based on their densities (by differential sedimentation), concentrating white cells in the closed-end channel near the outer rim of the CD for estimation of total “cell pellet” volume, while fat globules move toward the center of disc rotation, forming a fat “band” in the funnel. After adding milk to two or more microfluidic devices, the CD is loaded onto a custom-built reader unit that spins the disc for 15 min. Two low-cost microscopes in the reader image the centrifuged cell pellet and the fat band, providing a sufficiently accurate cell count to diagnose mastitis and measuring fat content as an indication of health and nutritional status.
KeywordsBovine mastitis Milk Cytometer Centrifugal microfluidics Sedimentation Cell-counter Somatic cells Sample-to-answer device
This work was supported by Science Foundation Ireland under Grant No. 05/CE3/B754. We are grateful to Jim Flynn and Brendan Kavanagh in Teagasc, MoorePark for providing and analyzing milk samples in the MilkoScan system. We also acknowledge Lorcan Kent for help with SEM images and Caroline Viguier for help during initial experiments. We thank Prof. Luke P. Lee for helpful discussions and Ivan Dimov for helping with image analysis. We also thank Dr. Holger Becker of Microfluidic ChipShop for helpful discussions in adapting our CD design to the injection molding process.
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