Heat-fixing and staining human cheek cells

Observing human cells is a good introductory activity to learn heat-fixing and staining. I will not waste many introductory words here. Here is the method:

Heat fixing

Heat fixing essentially “bakes” the cells to the glass slide much like a fried egg sticking to a frying pan. Heat fixing is absolutely essential before staining. Otherwise the staining procedure will wash away the cells.

• Take a cotton swab and rub the inside of your cheeks to collect epithelium cells.
• Smear these cells on a microscopy slide
• Completely air-dry the slide, without applying heat. This should not take long because there is not much liquid on the slide anyway. If you heat the slide before it is completely dry, then you end up “boiling apart” the cells. The vapor pressure inside the cells will burst them…
• Heat fix the dried slide by quickly pulling it through a Bunsen burner (2x), but in a way that the cells do not touch the flame. Pull it through the flame with the cells on top and the flame below. The slide should be pretty hot but you should still be capable of holding it in the palm of your hand without burning yourself. You should just be capable of holding the slide. Too high a temperature and you destroy the cells on the slide (and on your skin!). Too low a temperature and the cells will not stick to the glass slide.

Staining

Apply a drop of the stain (eg. methylene blue) to the heat fixed but cold specimen slide. Allow the stain to work for a few minutes and then carefully rinse away the stain with water. Do not apply the water stream to the cells directly. Allow the water to run over the cells from the top of the slide. Air dry the slide and observe in the microscope.