Sterile procedure is used in biochemistry
and molecular biology
to protect samples from contamination
by living material, particularly bacteria
in the air and on surfaces. The general idea is to make sure that every item contacting samples is REALLY FUCKING CLEAN
, without damaging, denaturing or killing the samples themselves.
Firstly, identify all the tools that will come into contact with the samples. These include toothpicks, test tube
s, petri dish
es and lids, graduated cylinder
s, beakers, flasks, jars, bottles, etc. etc. etc.
- Before these are used, they should be autoclaved, that is, subjected to tremendous heat and pressure in a machine that looks like a submarine. I believe that all metal, glass and wood is autoclavable, but all plastic is definitely not. Check the manufacturer's labeling to make sure that the material you are autoclaving is autoclavable, or it will degenerate under pressure into a soupy puddle.
- Anything that's going to be autoclaved should be wrapped in aluminum foil, and shouldn't be unwrapped until immediately prior to its use.
- Once containers are sterile, keep them that way, by flaming the lip of a given container with a blowtorch both before and after pouring liquid out of it.
- Very small items can also be sterilized on the spot by dipping them in glycerol, then setting the glycerol on fire using a small oil lamp. This is really exciting, I promise. Except that the glycerol itself needs to be sterile prior to its use here as a fuel. To sterilize the glycerol, pour it from a stock supply into an autoclaved beaker, flaming the lip of the stock supply jar before and after pouring. Never pour any liquid that you're trying to keep sterile back into the stock supply; if you've got glycerol left over in the beaker, cover it with saran wrap and save it separately.
Secondly, identify all the surfaces that may come into contact with the samples, either intentionally or by accident (such as if an instrument is dropped).
- Your hands: The latex or nitrile gloves that protect hands from chemicals are not sterile. And even if they were sterile in the box, they would not longer be after a minute of two of use. Anti-bacterial hand foam (the kind for laboratories and hospitals, not the kind sold in convenience stores) will keep hands clean, in fact if you use it repeatedly, you don't not even need gloves.
- Lids from petri dishes and centifuge tubes: Don't put these down on the lab bench. Don't even put them up-side down; the inside of the lid won't contact the bench but it will catch all the bacteria in the air. Instead, hold lids that you aren't using right-side up. This creates some difficulty, as it permanently ties up one hand.
- The counter itself: Truly sterile work is done inside of a fume hood, which is a stainless steel counter covered by a hutch, with a fan in the back that sucks air back, up, and out of the building, and a UV lamp at the top. Don't keep the UV light on while work is being done, but turn it on for 15 minutes prior to placing samples on the counter to sterilize this surface.