The fluid in my case is blood with suspended elements like RBCs etc. i.e. a non-Newtonian fluid.
Could you be a bit specific?
There are special materials to stain the biological cells. It makes special kind of cells distinguishable, and maybe you could follow the rotation that specific particles.
Thank you for your reply, Sir.
I am not using any stains. The infected RBCs have a different morphology than the normal ones and they are very clearly visible under 40X magnification in bright field with an Olympus IX71 microscope. The lab where I am working on my MS project is a very new one and it would take some time before we get a high speed camera. So what I do is i fill 1000 times diluted blood sample into the reservoir in my chip, rotate it at a set rpm for a set period of time. Then take it out from the setup used to rotate and observe under the microscope. So there's a definite time-lag between my expt. and my observation that enhances the capillary effect and some inertial effects for obvious. So I wished to ask if there is some other way I could do the observations more accurately, in the absence of a high speed camera?
There are a number of optical techniques which can do so pointwi. We are working, for instance in a low cost approach to laser feedback interferometry. But it is not immediate or easy. Focus a laser spot on the fluid and amplify the signal at the monitor photodiode output. If you Fourier-transform the signal you will get a peak proportional to the speed of the fluid flow.
However, it is harder than it sounds to set up for the first time so depending on the available time you have for your MS project mybe it is not the perfect. There are some commercial systems, I believe, but not sure of their performance and cost.
Thank you Sir for your reply.
I have about 7 months more for my MS thesis. So I could possibly try out the technique as we have good laser setups in our lab. Well, if I understood it correctly, can this laser which I focus on my flow dynamically capture the fluid motion (maybe if I could focus it at the meniscus)? What is the time lag? It is a rotating platform (lab-on-a-CD), so fluid velocity (linear) would not be the same at all points along the flow as it depends on the interplay of centrifugal force and capillary action. But depending on the time L.C of the system, I could take an average about two surrounding points. Moreover the flow is also not maintained continuously. I just add a measured quantity of fluid into the reservoir and drain it to the sink by rotating the platform. Had it been a continuous flow, the temporal response wouldn't have been an issue.
No: it can capture the flow speed at the point where it is focused. If you need the full speed profile across the radius of the CD you either need an array of laser diodes or scan mechanically (not really useful n your approach, apparenty) and assume stationary conditions. If you estimate the volume where the laser is being focused (a cylinder with the spot radius) you will be able to model (in a basic way) the flow as the product of volume and speed.
The RBC's in your channel will deform depending on the shear forces. This deformation can be visualized by the diffraction patter of laser light shining through. Diffraction is larger in the direction of the smaller sizes. This can easily be observes with a relatively simple camera.
Next to your cells under investigation you could add an additional small population with known elongation for calibration. I would be interested in your results.
Thanks Jan for the suggestion. I am not very sure how effective the use of lasers would be to study such differences in optical behaviour (diffraction patterns) of normal and infected cells. I suspect further damage to the cells because of the focussed laser beam which might aberrate my results. What do you say on this issue? Is controlling the laser power and maintaining the exposure time duration, a sufficiently safe way to do such tests on biological cells?
LoRRca is an instrument we sell that measures RBC deformation in a rotating couette system. With such a laser setup of 1 mm2 beam no harm is done to the cells, and it can identify the difference between normal and malaria infected blood from its diference in elongation. The diffaction pattern is large enough (20 mm) to be recorded with a camera. Baskurt, Hardeman, Meiselman and Dobbe probably have publications that would be of interest to you. Also you could google LoRRca RBC to find some pictures of a setup.
Article Comparison of three commercially available ektacytometers wi...
That's a cool instrument. Thanks for letting me know. Jan de Zoeten. I shall keep you posted with my results.
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