Urea by Polarized Light Microscopy


Urea (also known as carbamide) is an organic compound, that has the chemical formula of CO(NH2)2. This consists of two NH2 groups which are joined by a carbonyl (C=O) functional group. It has an important role in the metabolism of nitrogen-containing compounds by animals, and is the main nitrogen containing substance in the urine of mammals.

I chose to image Urea because after some web searching I discovered it exhibits strong birefringence. This means that as the polarization of light changes, and the angle of the Urea crystal so to does the optical property, in short it leads to wonderful rainbow colors as per the image below.

Another important feature is that Urea was easily obtainable for me (already in a prepared slide kit), but also that it is relatively non-toxic which means it is far easier to work with than some of the other chemicals which may be dissolved in acid solvents or otherwise.


How it was done:

Since Urea was already mounted in a pre-prepared slide it required no additional work for me to image, however it is easily dissolved in water so should I need to prepare another slide, it would be done by dissolving urea in a water solvent, and slowly evaporating the water from the urea (at lower temperatures) which would leave the urea in place to crystallize.

The image(s) were captured using my typical microscope kit as per the below, with the addition of a geology polarizing retrofit;

Images (click to enlarge):