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We don't know who we are until we see what we can do.
Martha Grimes

Some Tips for Molecular Biologists

Aseptic technique

Aseptic technnique refers to laboratory practices to avoid exposing preparations to bacteria, mold, and other contaminants. We apply aseptic technique in a conventional laboratory environment when working with bacterial plates, DNA or protein preparations, etc. Materials are frequently sterilized before use, but sterile conditions are not necessarily maintained during use. The phrase "sterile technique" refers to more stringent practices to prevent the slightest contamination whatsoever. Surgeons apply sterile technique, as to researchers who culture cells and tissues.

General Guidelines

  1. Maintain a clean work area
  2. Use a fresh pipet tip for every transfer (tips should be DNase/RNase free)
  3. Wear gloves to prevent contamination (of yourself as well as your experiment)
  4. Sterilize solids and liquids by autoclaving 20 minutes at 121°C at 15 psi

Microcentrifuge/conical centrifuge tubes can easily be contaminated by contact with non-sterile surfaces (e.g., your fingers) or by air borne particles. Be careful when transferring solutions from one tube to another. Also, keep the lids closed when you're not working with the samples.

Media can be also contaminated by contact with non-sterile surfaces or by air borne organisms. Remove lids and coverings carefully avoiding contact with any part of the cover that may contact the media; minimize the amount of time the container is exposed to air. Lids and coverings should be held with media side down at all times. Air borne contaminants are usually falling downward. Replace the coverings carefully so that the rim of the container makes contact only with sterile surface of the inside of the cap.

The use of a flame helps maintain aseptic materials. Working near a flame can decrease air borne contamination. The flame is also used to singe surfaces to maintain sterility. The mouth of the tube or flasks is passed through the flame before and after pouring. The cap or cover is also passed through the flame prior to replacing on the container.

Caution: The flame is used to singe the surfaces only. Do not hold the items in the flame to make them hot.Glass flasks, even Pyrex, can break from the heat or when the cooler media hits the hot surface.

Notes on Molecular Biological Procedures


  2. ALWAYS balance the load in the centrifuge
  3. Capless 1.5 ml vials serve as holders for 0.2 and 0.5 ml tubes in the rotors
  4. Pulse spin ALL tubes of aliquots to bring the liquid to the bottom of the tube -- in the microcentrifuge hold the "SHORT" key for about 5-10 seconds
  5. DO NOT SLAM THE LIDS! (this action breaks the latch mechanisms)

Pipetting Small Volumes

  1. Before beginning the procedure, thaw all frozen reagents and mix well
  2. Pulse spin ALL tubes of aliquots to bring the liquid to the bottom of the tube as described above
  3. Touch only the very tip to the surface of the solution (i.e., do NOT submerge the pipet tip into the solution)
  4. Most enzyme stocks are in 50% glycerol; these solutions are quite viscous and liquid will stick to the outside of the pipet tip so touch only the surface

We would like to thank New England Biolabs for their generous support of our laboratory program

New England Biolabs

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Created by David R. Caprette (caprette@rice.edu), Rice University 22 Jul 08
Authored by Beth Beason Abmayr, Ph.D., Rice University