Here are some microfluidic videos from our research lab :
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We show the basis of Sorting using Interfacial Tension (SIFT) to sort droplets of different pH. We use specific surfactant conditions where surface tension is highly sensitive to pH. The device uses a rail oriented diagonally relative to the oil flow (left to right). Droplets are less confined (expand in height) when on the rail.
Here is how it works: white droplets at higher pH (pH = 7.48) of low surface tension are only slightly deflected by the rail and leave near the bottom. However, clear droplets at lower pH (pH = 7.01) of higher surface tension follow the rail upwards and leave near the top. Video slowed 10X. Read more here. |
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Here is sorting of droplets containing cells. Droplets that do not contain cells are only slightly deflected by the sorting rail and exit the rail near the bottom. Droplets containing a live cell ride ride the rail laterally up and leave the rail near the top. Cells are bright (labelled with a fluorescent viability marker). Fluorescent excitation is localized in a hexagonal central region of the imaging field. Video slowed 10X. The technology enables the selection of only droplets containing a single live cell. Read the details here.
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We show here that SIFT can select cells that have higher metabolism after been exposed to different conditions. Hypoxia conditions promotes cellular glycolysis and acid secretion. Hence, a droplet containing a cell exposed to hypoxia will achieve a lower pH then a droplet grown in ambient oxygen. The droplets containing the hypoxia cell rides the rail laterally up and leaves the rail near the top. Higher glycolysis is an indicator of malignancy in cancer. Hence this technology presents a way to isolate more dangerous cells for study or therapy. Read the details here.
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We show how you can select any desired droplet in an array (and write "S" "C" in droplets!), For droplets containing a fluorescent dye, light is used to provoke a decrease in droplet pH. In the right chemical conditions the interfacial tension increases at lower pH. Hence, when the flow of oil is increased only photoexcited droplets remain as all other droplets are pushed out. This technique enables the selection of droplets by any user-defined criteria. Read the details here.
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Here, we show that water microdroplets in oil be pinned into specific locations in the microfluidic chip. We use a technique called "Rails and Anchors": The droplet are not spheres but rather "pancake" shaped, squeezed by the top and bottom surface of the channel. They expand into the deeper wells and remain in place. In this case, three droplets fit into each anchor. This method allows us to quickly prepare an array of droplets of arbitrary size and shape.
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Two aqueous droplets are placed in each anchor. One containing FeCl3,, the other KSCN. Surfactants at the droplet inhibits droplet fusion. However by flowing oil without surfactant outside the droplet, the surfactant concentration at the interface is gradually depleted eventually triggering droplet fusion. The rows are droplets are fused sequentially by controlling the oil flow within the channel. The mixing of FeCl3 and KSCN produces a dark product. Find out more in our paper.
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The fusion of large droplet containing FeCl3 with three small droplets containing KSCN by the introduction of external oil without surfactant.
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In this video, a method developed in our lab to determine single-cell lactate release rates is shown. Droplets containing cells are positioned into an array. At the beginning of the video, cells are circled in red in the bright field image. In the time-lapse fluorescence video that follows, droplets containing cells get brighter as lactate released from the cells is enzymatically converted to a fluorescence product. The fluorescence increase is then used to make an accurate determination of the single-cell lactate release rate. Read more about the technique in our paper.
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