Making Lacey Carbon Coated Grids in Your Own Laboratory
We've been asked how we make lacey carbon coated grids. There may be as many methods as there are people making lacey carbon; a number of methods may be found in textbooks. All of them work to some extent, and all of them involve some art that can only be learned through the experience of doing it. The problem with instructions like these is that the devil is in the details, and times, temperatures and concentrations all vary with the season.
How it is done:
Take a glass slide. Clean it thoroughly. The best cleaning method seems to be wiping the slide vigorously with either SPI Supplies® Brand lens tissue.
Dip the now cleaned slide into a solution of Formvar® in ethylene dichloride or some other film forming polymer (we know that some people prefer Butvar® in chloroform, despite the added risks) in the appropriate solvent. Remove the slide from the Formvar solution and allow it to dry briefly; our current time is about one second, but there is a "feel" for this step, and it is important to observe the way that the excess solution flows off the slide; if the solution is too thick, the film will be lumpy; it it is too thin, the film will be too thin. Insert the slide into the "steam chamber" for several seconds, remove the slide and allow it to dry thoroughly. "Score" the film at the edges of the slide using a fresh GEM® single edge razor blade and float the film off the slide onto freshly filtered, deionized water.
Some people hold the slide over a beaker or a flask of boiling water. Others breathe on the slide (Caution: do not breathe in; these solvents are not good for you).
The "steam chamber" which we use consists of a beaker of water, sitting on a hot plate and covered with an empty one pound (or 500g) size coffee can which has a hole cut in the side about 4 cm square. The temperature of the water in the beaker is maintained so that there is visible condensation on the side of the beaker, but the water is not actively boiling.
When the film has been floated onto the water, look at it. If it looks clear, it is probably good. If it looks cloudy, or if wrinkles can be seen, you might as well discard it now. Lay a pattern of the grids of your choice onto the film, and pick the film and the grids up using a piece of filter paper. Allow the film, the grids and the filter paper to dry thoroughly. What you now have is grids which have a damaged Formvar film. The grids are made "lacey" by exposing them to the ethylene dichloride vapors above ethylene dichloride-soaked filter paper in a covered Petri dish for several seconds. The exact time of exposure is determined using a stop watch and inspecting sample grids in the TEM; there is no substitute for this inspection step and the feedback of checking sample grids as you process each batch.
The lacey grids can now be carbon coated; carbon coating is an art in itself, and it requires a good carbon evaporator (with diffusion pump or better) and suitable carbon or graphite rods. You will need a good sharp "tip" at the end of one of the carbon rods and we recommend the SPI Supplies® Brand carbon rod sharpener.
After carbon coating, the Formvar film is removed by placing the grids on chloroform-soaked filter paper overnight. Example grids are examined in the TEM to assure that the film is beam stable and free from artifacts. The finished grids are inspected under a low power light microscope and packaged for storage in a grid storage box, such as the SPI Slide-A-Grid™ box.
At each step, it is necessary for the specific laboratory to determine the precise concentration, time, temperature, etc. which is required for each step; there is no universal recipe, and the recipe for our laboratory varies from day to day. There is no substitute for inspection of sample grids at each step of the process using a TEM; you simply can't see what you need to see by light microscopy. The cornerstone of our quality assurance program for lacey carbon and other custom coated grids is inspecting example grids from each batch in our own TEM. If the grids do not meet our quality standards, the customer never sees them. This may explain why we have virtually no returns of coated grids from customers.
And it helps to have been doing the process for several decades. This is a skilled art, and the only substitute for going through the learning curve yourself is to ask someone who has "been there" before you to make the grids you need. What we are really saying is, you have to keep at it, you won't make good grids the first time out, but with time, most people can master the art. The real question asked of our customers is simply one of how they would prefer to be using their valuable time: Doing grids or doing the research.
So if you are one who will be our customer for our Formvar and our grids and will elect to try your hand at doing your own grid coating, you can depend on us to help you. And if you should be one who prefers to purchase their grids already coated with the best custom coated grids in the world, then we sure to learn more about the customer grid coating services of SPI Supplies.