PARTICLE-SURFACE INTERACTION IN THIN VITRIFIED FILMS FOR CRYOELECTRONMICROSCOPY

The concentration of particles in thin vitrified films of suspensions is described as a function of various parameters such as the type of p articles observed, the time the sample is left on the grid and the eff ect of different washing procedures. The thin films are prepared for c ryo-electron microscopy by the classical, single-side blotting method or by blotting both sides of the grid simultaneously. The two-side blo tting method gives the most faithful representation of the bulk soluti on. The single-side blotting method results in particles preferentiall y adsorbing to the non-blotted surface. This has the advantage that th e concentration of particles in the thin vitrified film is higher than in the original suspension. The energy involved in adhesion of partic les 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 vesic les, where the particles are broken as a result of adsorption. Since p articles remain adsorbed to the air-liquid interface, it is possible t o wash or dialyse the solution directly on the grid with negligible lo ss of particles. This represents a very rapid and handy method for mic ro-dialysis. A thin film is then formed by blotting the specimen and v itrified by rapid cooling.