Application of a laser self-beat spectroscopic technique to the study of solutions of human plasma lipoproteins

Abstract

The technique of self-beat or homodyne spectroscopy in conjunction with a He–Ne (50 mW) laser has been applied to the determination of the translational diffusion constants of human plasma lipoproteins. The photo power spectrum of the laser light scattered by the particles was analyzed in the frequency domain by noise power spectrum analysis and in the time domain by autocorrelation. The results were corroborated by the spectral analysis of polystyrene latex spheres of known diameters. The precision of these measurements was 3 % and accuracy 5 %. The following results were obtained, for the very low density lipoproteins, D of 5.4 × 10^–7 cm² s^–1, and a mean diameter of 792 ± 30 Å, for the low density lipoproteins, D of 1.8 × 10^–7 cm^–2 s^–1 and a mean diameter of 265 ± 13 Å, for the high density lipoprotein, D of 0.72 × 10^–7 cm² s^–1, and a mean diameter of 110 ± 10 Å. Results from the two methods of analysis were in good agreement and were comparable to those reported previously in the literature. Whereas the noise power spectrum required recording in the order of hours, autocorrelation can be conveniently done in minutes. As compared with more conventional methods, autocorrelation in conjunction with laser self-beat spectroscopy provides a rapid technique for the physical characterization of lipoprotein particles in solution.