Wednesday, August 10, 2011

Contrast enhancement for plant cell viewing

It’s difficult to see cells under a regular brightfield microscope when they don’t have pigment or stained with color.  The reason is that the light source of a brightfield microscope was placed directly underneath the specimen.  The light penetrate the specimen to illuminate the specimen and finally reach your retina.  There is very little deflection of the light to create the contrast.  Some simple filters can be added to the optical train to create the contrast.


Figure 1.  Onion epidermis cell under regular brightfield microscope.

Onion_DarkField DarkField


Figure 2.  adding a darkfield filter to the light path, the cell wall can be easier to see.

Onion_Rheinberg_two_color Rheinberg

Figure 3. Based on the darkfield technique,  The Rheinberg illumination, a form a optical staining, can stain the specimen without chemical stain.  The method used a color filter consists of two or more colors to allow the light with different color come from different direction which create the structure to be “Stained” with different color.  The above image was viewed under a Rheinberg filter with green center and red peripheral.


Figure 4. Of course, it is inevitable to use chemical staining if the structure of interest has very different chemical composition but very little in deflecting light.  The above picture is an onion epidermis cell with the nucleus in the center.  The specimen was stained with Methylene blue.  The nucleus was darker because methylene blue has stronger binding to nucleic acid than cytoplasm.

The steps for making the filters was described earlier at Laboratory and Home Science Resources.


1 comment:

  1. Great Post!!
    Thanks for sharing such a useful information on Microscopes!!