A Method for Investigating the Thickness, Chemical Properties, and Surface Structure of Thin Biological Objects1

Abstract

A method is described for determining thickness, refractive index, and chemical properties of objects which are submicroscopic in one dimension and microscopic in the other dimensions. Designed primarily for use in biology, the method depends upon the modifications in reflectivity of a glass surface produced by the deposition of a thin transparent film. The object is viewed with a microscope fitted with a vertical illuminator. Thickness is determined by matching the intensity of light reflected from the object with that reflected from a standard step film of barium stearate viewed in an identical companion system. The sensitivity is approximately ±12A. The method finds application in the biological field particularly in the investigation of thin cellular structures. In such cases information may also be obtained regarding the relative chemical composition by the use of solvents which remove certain of the components. The existence of patterns due to surface discontinuities (differences in optical thickness) may be detected and structure of this sort has been observed in the case of the limiting envelope of the mammalian red blood corpuscle.