X-ray Microanalysis of Cultured Cells in the Scanning Electron Microscope and in the Scanning Transmission Electron Microscope: a Comparison

X-ray microanalysis of cultured cells as “whole mounts” (i.e., not sectioned) is used frequently e.g., to study mechanisms of ion transport. Cells can be cultured either on solid substrates or on thin plastic films on grids. Cells cultured on solid substrates are analyzed in the scanning electron microscope at relatively low accelerating voltage, cells cultured on thin films can be analyzed in the (scanning) transmission electron microscope at high accelerating voltage. The main advantage of culturing the cells on a solid substrate is that the specimen is less easily damaged during preparation. Analysis of cells on thin films is more sensitive, and subcellular resolution is possible. The main problem here is the correction for extraneous background that has to be applied in quantitative analysis. The following test systems were used in this study: HT29 human colon carcinoma cells, primary cultures of human sweat gland coil cells, and normal bronchial human epithelial (NHBE) cells. The spread in the data is similar for cells grown and analyzed on a solid substrate compared to cells grown and analyzed on a thin substrate. The spread is much larger than expected on the basis of counting statistics, and is not reduced by using elemental ratios rather than net peak intensities. This means that the spread is not mainly caused by overpenetration or extraneous background, but that likely biological variation between the cells is responsible.