Through polarized light interacting with samples, imaging ellipsometry
is capable of aiding in the study of semitransparent biological cells
microscopically; it is also possible to find applications in
marker-free nondestructive disease diagnosis. Often a living
biological cell is sensitive to environmental conditions, and fast
measurement is preferred. Fast and accurate locating of the focal
plane is important for biosensing. By analyzing our previous published
through-focus ellipsometry images for S.
mutans cells on Au film, we have found an efficient method of
locating the focal plane position, i.e., through edge detection of
cells in ellipsometry images. The method is not sample-dependent. As
the edges are decided only by a sample’s own features, the method is
robust against noise or small shifts of images. It is also easy to use
without the need to choose a threshold value as in the Laplace
filtering method. The method can be further useful for biosensing
applications.