Department of Biomedical Engineering, McGill University
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Perrault, C. M., Qasaimeh, M. A., Juncker, D. The Microfluidic Probe: Operation and Use for Localized Surface Processing. J. Vis. Exp. (28), e1418, doi:10.3791/1418 (2009).
Microfluidic devices allow assays to be performed using minute amounts of sample and have recently been used to control the microenvironment of cells. Microfluidics is commonly associated with closed microchannels which limit their use to samples that can be introduced, and cultured in the case of cells, within a confined volume. On the other hand, micropipetting system have been used to locally perfuse cells and surfaces, notably using push-pull setups where one pipette acts as source and the other one as sink, but the confinement of the flow is difficult in three dimensions. Furthermore, pipettes are fragile and difficult to position and hence are used in static configuration only.
The microfluidic probe (MFP) circumvents the constraints imposed by the construction of closed microfluidic channels and instead of enclosing the sample into the microfluidic system, the microfluidic flow can be directly delivered onto the sample, and scanned across the sample, using the MFP. . The injection and aspiration openings are located within a few tens of micrometers of one another so that a microjet injected into the gap is confined by the hydrodynamic forces of the surrounding liquid and entirely aspirated back into the other opening. The microjet can be flushed across the substrate surface and provides a precise tool for localized deposition/delivery of reagents which can be used over large areas by scanning the probe across the surface. In this video we present the microfluidic probe1 (MFP). We explain in detail how to assemble the MFP, mount it atop an inverted microscope, and align it relative to the substrate surface, and finally show how to use it to process a substrate surface immersed in a buffer.
1. Microfabrication of the probe head ( process not shown in the video)
2. Assembly of the MFP
3. Set-up of the MFP
4. Operation of the MFP
The microfluidic probe (MFP) is versatile because it is (i) mobile, (ii) adaptable for use with different types of reagents and substrate and it can (iii) be operated over large areas.
Unwanted bubbles can lead to disruption of the flow To avoid bubbles, all components need to be filled with liquids prior to assembly. The gap between the probe and the surface is only a few micrometers, yet the mesa is several hundred micrometers wide, and distances in the range of centimeters are scanned. Therefore both horizontality of the scanned surface and the parallelism between the MFP mesa and the substrate need to be adjusted with great care. Finally, the ratio between aspiration and injection has to be large enough to capture all of the reagent injected into the gap between the MFP and the substrate.
The MFP may be used for patterning surfaces with proteins under mild conditions, to process tissues or individual cells immersed in physiological buffers, or to etch patterns into a surface.
This work was funded by the Fonds de Recherche sur la Nature et les Technologies de Quebec, the Canada fundation for Innovation and the Canadian Institutes of Health Research ( CIHR).
|microfluidic connectors||Upchurch Scientific||Micro- and Nano-tight fittings and sleeves|
|2-component manual dispenser||Conprotec Inc.||DM400||To dispense and mix PDMS mixture|
|LabVIEW||National Instruments||Version 8.0|
|Mechanical Convection Oven||VWR international||1330FM|
|Glass syringes||Hamilton Co|
|Capillary tubing||Polymicro Technologies|
|Plasma Chamber||Tegal Corporation||Plasmaline 415|
|Inverted Microscope||Nikon Instruments||TE2000-E|
|Sylgard 184||Ellsworth Adhesives||184 Sil Elast Kit|
|Microfluidic probe holder goniometers||Melles Griot||07GON504|
|Linear stage||Applied Scientific Instrumentation||LS-50||For z-control of the MFP|
|Manual linear stage||Newport Corp.||443-4 Series||For x- and y- axis control of the MFP|
|Microscope stage||Applied Scientific Instrumentation||PZ-2000||With x-, y- and z- control|