04 Oct

Phase Contrast Microscopy

There are many techniques that are used to enhance images in a compound biological microscope. One of the most common as well as one of the most useful is phase contrast. This technique was developed by Frits Zernike (a Danish physicist) in the 1930′s and he was awarded the Nobel Prize in physics in 1953 for this significant contribution to the field of optics. As light passes through a medium of varying density, a phase shift or contrast change occurs as a result of the retardation or slowing of the illuminating wave front. Z ernike developed a method to take advantage of this change. It allows one to view cells in liquid suspension without the addition of stains or other chemical additives that might alter the nature of the sample. The image may be further enhanced with the addition of a green filter since this is the color to which the human eye is most sensitive. This remarkable change in contrast is easily appreciated in the included illustration of two epithelial cells. A microscope equipped with phase contrast allows sample viewing in both brightfield and phase without any additional specimen preparation. Common applications of the phase contrast technique include the examination of spinal fluid, urine, naturally occurring water sources and any other solution in which suspended particulate matter is suspected or needs to be evaluated..