3.1 Things to Consider

3.1.1 Contamination

When preforming any type of experiment, it’s always important to prevent cross contamination. For cell culture experiments, it’s bacterial or fungal cells, and for many molecular experiments it’s DNA or RNA contamination from other samples. Reagent contamination is another dangerous and often overlooked type of cross contamination that can affect current and future experiments. This is why it’s necessary to make working solutions of your stock reagents. It may seem like it takes a lot of time, but in the end working solutions save time and money that would otherwise be spent troubleshooting an experiment that is behaving abnormally.

Having a pre-measured or pre-diluted working solution is the best way to prevent mathematical, pipetting, and contamination errors. Working solutions also help with the calculations that need to be made before an experiment takes place, which saves valuable time. If and when mistakes are made, contaminated reagents can easily be discarded and new working solutions can be retrieved from storage. (Always check the lab’s inventory before discarding a sample/reagent. Some samples and reagents have limited availability.)

3.1.2 Centrifugation

When working through a protocol, gentle centrifugation of various tubes or plates is usually necessary. Air bubbles, liquid on the sides, or liquid on the top of your plates or tubes is not only annoying, but it also frequently leads to contamination, evaporation, improper volume, or improper concentration. These issues can be avoided by additionally checking to make sure your plates or tubes are sealed before centrifugation. If you end up contaminating some of your reagents, then clean your workspace thoroughly and dispose of anything that you suspect to be contaminated (check your inventory first). Proceed by creating more aliquots with the pseudo-stock solution or retrieving another working solution from storage.

3.1.3 Pipetting

Pipetting is one of the very basic techniques that you will need to know for most labs. This lab in particular relies heavily on pipetting for molecular and cell culture experiments. So developing good pipetting skills is vital for success and efficiency.

There are many special techniques that you can use in order to pipette like a seasoned professional. Gilson has a very comprehensive manual that I would suggest going over. It’s mentioned in this Bitesize Bio blog post on pipetting techniques.

While preference often plays a huge role in what pipette tips are purchased, some specialized tips have use-cases that go beyond user preference. For instance, some pipettors can only be used with certain tips, and some tips can only be used with certain pipettors. Other special properties, such as being sterile (rnase, dnase, and protease free), or having filtered tips, also makes a difference when selecting pipette tips. Filtered tips are useful for preventing pipettor contamination. They are vital in certain situations such as DNA or RNA isolation and cell culture. In these situations it’s usually important to utilize filter tips that are also dnase/rnase/protease free.