The adhesion of colloidal gold on membranes was examined with an electron microscope with protein on the membrane, on the colloidal particles and present on both membrane and particles. The conditions for best adhesion were determined. Quantitative measurements were caNied out using adhesion to the membrane to monitor diffusion, centrifugation and electrophoresis of colloidal particles. Electrophoresis in a centrifugal field was used as a nul method to determine the charge on the colloidal

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... cle. Inorganic colloidal particles play an interesting role in biological systems. Thus colloidal gold has been used for disease diagnosis by examination of its interaction with spinal fluids. 1 It is also used for treatment of arthr itis. 2 Radioactive colloidal gold, phosphorus and technicium on colloidal sulfur are used extensively for cancer diagnosis and treatment 3-5 • With this in mind it was of interest to investigate the adhesion of mono-disperse colloidal gold on surfaces covered with proteins. This investigation is an extension of work on colloidal particles carried out in the Chemistry Department of Princeton University.G-14 Conditions were found under which adhesion took place under every collision of the particle with the surface. This permitted development of new techniques for quantitative study of diffusion, centrifugation and electropho-resis. Electrophoresis carried out in the electric field was used to calculate t hE charge on the colloidal particle much in the way Millikan determined t he charge on the electron. 1 5 Methods were devised for uniform mounting of particulate matter for examination in the electron microscope. EXPERIMENTAL Standard 200 A Colloidal Gold 100 ml of HAuC1 4 solution containing 50 mg of gold is added to 850 ml of distilled water, boiling in a two-liter flask. When the solution comes to boiling after this addition, 50 ml of 10/o sodium citrate solution is added with good mechanical stirring. The solution is brought back to boiling. It undergoes a series of color changes, the yellow color disappears, a greying-blue color appears which changes into deep wine red coior in the course of fifteen minutes. After thirty minutes boiling, the solution is allowed to cool.