Methods

Formvar coating specimen grids

1. Clean 100 mesh, hexagonal specimen grids. Place them in a 200 ml glass flask, rinse with 2% aqueous acetic acid, multiple washes with distilled water and finally with 3 changes in acetone. Dry over a warm plate.
2. Clean a glass slide by immersing it in ethanol, instantly removing it and drying with lens tissue. Use "precleaned 25 x 75mm micro slides selected" Catalogue #48312-002 from VWR Scientific Inc.
3. Dip slide into a solution of formvar dissolved in chloroform (2% w/v) and withdraw carefully. The speed of withdrawal will affect film thickness. Alternatively, semi-automated withdrawl devices can be purchased from EM supply companies.
4. Leave slide to dry vertically.
5. Score around slide on all four sides with a razor blade to define limits of film to be dislodged from slide.
6. Fill a deep glass dish with distilled water and place a light so that it reflects on the water surface.
7. Clean the water surface by passing a piece of lens tissue over the surface.
8. Hold the formvar coated slide at a 45¡ angle at the edge of the glass dish, with the water just touching the bottom of the slide. The formvar film should start to come away from the glass.
9. Slowly push the slide into the water, watching as the film as it lifts off the glass and floats on the water surface.
10. Remove the glass slide from the water and examine the floating film. The incident light should show interference colors in the film. These should be silver or gray. Yellow, purple or green colors indicate that the formvar solution should be diluted more by adding chloroform. Films that are too thin mean that the formvar solution is too dilute. To increase the thickness either remove the glass slide from the solution more slowly or increase the concentration of formvar.
11. Place cleaned specimen grids onto the floating film until it is filled. Place the grids so that the shiny surface of the grid is facing up and the dull side is on the film.
12. Dry the glass slide used for casting the film and attach a 1" by 2.5" white address label to it.
13. Hold the glass slide vertically over one edge of the floating film and push it into the water so that the film, with grids attached, stick to the address label.
14. Once the glass slide has been totally immersed remove it, with the grids attached and leave to dry.
15. Coat the grids with carbon using a vacuum evaporator.
16. Although not essential, the grids can be made hydrophilic prior to use using a glow discharge apparatus in a vacuum evaporator.