PARTICLE-SURFACE INTERACTION IN THIN VITRIFIED FILMS FOR CRYOELECTRON MICROSCOPY

The concentration of particles in thin vitrified films of suspensions is described as a function of various parameters such as the type of particles observed, the time the sample is left on the grid and the effect of different washing procedures. The thin films are prepared for cryo-electron microscopy by the classical, single-side blotting method or by blotting both sides of the grid simultaneously. The two-side blotting method gives the most faithful representation of the bulk solution. The single-side blotting method results in particles preferentially adsorbing to the non-blotted surface. This has the advantage that the concentration of particles in the thin vitrified film is higher than in the original suspension. The energy involved in adhesion of particles to the surface seems to be generally small. In most cases, it does not cause significant deformation of the particles or of the surface of the film. However, there are cases, as for example with lipid vesicles, where the particles are broken as a result of adsorption. Since particles remain adsorbed to the air-liquid interface, it is possible to wash or dialyse the solution directly on the grid with negligible loss of particles. This represents a very rapid and handy method for micro-dialysis. A thin film is then formed by blotting the specimen and vitrified by rapid cooling.