Index of refraction based detection

I had an idea to build an index of refraction-based detector for an electrophoresis set-up. When light passes through a prism, it bends. That’s how prisms cast rainbows. The angle at which the rainbow shows up depends on the material of the prism. If the prism is made of glass, you get a rainbow at one angle. If the prism is made of water, you get a different angle. We can use this phenomenon to detect changes in the material. We need a prism that we can fill with different materials. Then we can see how the angle changes. I built such a prism out of acrylic with my laser cutter. It looks like this:

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I haven’t started flowing things through the prism yet. I’m still figuring out how to detect the angle change. But there definitely is an angle change. I can see the difference in angle between when I have air in the prism and when I have water in the prism. Have a look – that’s air on the left and water on the right:

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So now the question is how tiny a difference can I detect? Adding small amounts of sugar to the water will change the index of refraction a tiny bit. That should change the angle by a small amount as well. If I can measure the angle very precisely, I should be able to detect very small changes in the sugar content of the water.

I’ll try to get my students to build generation 2 of the device. Design, build, test learn. The work will teach them.