Blood cell trapping
I have been working on using the membranes to trap blood cells so that I can take force measurements with the AFM. It is impossible to perform AFM on blood cells resting on a coverslip because the water displaced by the tip on the approach pushes them away, so I am trying to use a pressure gradient across a membrane to draw cells down onto the surface and hold them in place against any fluid flow in the chamber. The device is a PDMS gasket bonded to a coverslip and a membrane connected to a reservoir to apply a pressure.
I have had some success using this device to trap blood cells.
Video:
In the test I have placed blood cells in the chamber and drawn a pressure down into the reservoir and the cells stick to the surface when they get close, despite the flows circulating around the chamber. When the pressure is reversed the cells float off of the surface and return to flowing around the chamber, with the exception of a few cells that have stuck to the surface. The illumination in this video is quite bad and there are shadows.
In the AFM video the cells are drawn down onto the surface with a similar pressure to the test video with a chip from wafer 130, and the AFM cantilever is used to approach a leukocyte in the center of the window. It looks like I was able to position the tip above the cell, perform a slow force curve, and retract without moving the cell. The cantilever blocks the illumination source, so I have been working on rebuilding the illumination path of the microscope so that I can illuminate from below to see the exact position of the tip to the cells so that I can be sure I am centered when doing force curves, and it looks like the microscope is ready to go for experiments tomorrow afternoon.
Note in the second video there are more cells around the edge of the membrane than in the middle. This was true of all 9 windows on this chip.