Anomalous diffraction spectra of biological cells

Abstract

Anomalous diffraction spectra of monolayers of biological cells dried on a quartz plate were observed between 0.25 and 2.5 μ. The possibility of using the positions of the diffraction maxima and minima for the determination of cell dimensions was examined on the basis of a simple theory of anomalous diffraction for spherical or discoidal cells. In the spectra region used, yeast and Chlorella cells showed two diffraction maxima, and spinach chloroplasts and human erythrocytes a single maximum. The relative wavelengths of the two maxima and the minimum between them were in the ratios calculated from the theory, so that it was possible to evaluate a term proportional to the cell diameter or thickness. The proportionality between the evaluated quantity and the diameter was examined with yeast, Chlorella cells, cloroplasts, and erythrocytes, and was approximately constant. A semi-empirical formula for the determination of cell dimensions was obtained by assuming the average of the proportionality constants for these different species of cells. The maximum error due to this assumption and due to the variation of the content of solid materials in cells was estimated to be 13% in diameter. The diffraction method was compared with other optical or microscopic methods for the determination of cell dimensions.