While real estate depends on location, location, location, molecular biology requires pipetting, pipetting, pipetting. Sure, there’s more to molecular biology than that, but there is no denying that these labs do tons of pipetting every day. To get the right results, those devices must stay clean and contamination free.
“There are two main contaminant classes: biological and chemical,” says Paulus Artimo—product manager, pipetting and dispensing at Sartorius. A lab’s pipetting practices must guard against both classes.
“Common biological contaminants include DNA and microbes, and the chemical contaminants are corrosive and volatile substances,” Artimo explains. “These spread due to rapid and irregular liquid movement in and out of the pipette tip that creates droplets and aerosols that can reach the insides of the pipette and spread across the working area.”
Image: Only a combination of the right technology and technique fights pipette contamination. Image courtesy of Sartorius.
Beyond the sources of contamination, there are several pathways to contaminating a pipette. As described by Tommy Bui, business development manager at Thermo Fisher Scientific, the steps in contamination come in three forms: pipette-to-sample; sample-to-pipette; and sample-to-sample. In the first category, “the pipette tip or the pipette carries the contaminants forward to the samples,” Bui says. “This kind of contamination also gets carried forward due to the types of tips that are used since it is difficult to remove contaminants such as DNase, Rnase, and endotoxins by any sterilization method.” Sample-to-pipette contamination arises if a contaminated sample touches the pipette body or aerosol particles formed from the sample enter the pipette handle. The last category, Bui says, comes from “carryover contamination when the same pipette is used across multiple samples and multiple users.” In that case, “either liquid residue or an aerosol may be carried over from one sample to another sample through the pipette,” he adds.
The kind of equipment being used and how scientists use the equipment impact the odds of contaminating a pipette. Here’s what some experts recommend.
Technology and technique
To reduce the odds of contamination, scientists should match the equipment to the task. As Bui notes: “Pipetting equipment unsuitable for the specific application is another common factor behind pipette contamination.”
Just getting the right equipment, though, is not enough, because it must be properly maintained. “Regular maintenance makes sure that there is nothing jamming the piston and that the movement through the seal is smooth,” Artimo says.
Last, even the right equipment, all properly maintained, plus the needed options will not ensure contamination-free pipetting. Don’t forget the user. As Artimo says, “Preventing contamination of the working area is mainly dependent on best pipetting practices.”
Bui agrees on the user’s role in keeping a pipette clean. As he says, “The last factor affecting pipette contamination is always the person conducting the pipetting.” Then, he adds, “The good news is that the human factor can be notably minimized with the correct pipetting equipment.
Types of tips
A pipette’s tip creates a key pathway from the environment to a pipette. So, scientists should think about the right tip to use. “In critical applications like cell culture, microbiology, and PCR, the best pipetting practice also includes the use of filters or so-called aerosol barriers to prevent these contaminants from entering the pipette,” Artimo explains. “Most commonly, the filters are passive, and they physically absorb the droplets or aerosols, so they never reach the inside of the pipette.”
Bui agrees that filter tips can prevent pipette contamination. “Filter tips work in two ways as they also protect the samples from cross-contamination,” he says. That is, “if the pipette has gotten contaminated, but used with the filter tips, the pipette won’t contaminate the other samples,” he explains. As an example, he points out that Thermo Fisher Scientific’s ART (aerosol resistant tips) “come with a special barrier that traps even the aerosols and prevents them from contaminating the pipettes.”
Artimo points out that various options can be considered. “Currently, it is common to choose filter pipette tips that are discarded after every use, but for some pipettes like Sartorius’ we offer safe-cone filters,” he says. “These are inserted into the pipette’s tip cone, and they are really effective in protecting the pipette.”
The tip can even contribute to contamination in possibly unexpected ways, including when a scientist ejects it. “In order to avoid spreading the droplets around the bench, one should choose a pipette with soft tip ejection like Sartorius Tacta or an electronic pipette with electronic tip ejection,” Artimo says. In addition, he mentions that an electronic pipette “helps to reduce droplet and aerosol generation.”
Added precautions
Even with the best tools and techniques, something unwanted can end up in a pipette. This often happens without a scientist even knowing it. Here, the best defense comes from regular cleaning.
Bui recommends that scientists “clean or disinfect the pipette periodically, and the best option is to choose pipettes that are autoclavable.” He notes that fully autoclavable pipettes reduce the risk of contamination noticeably.” When a pipette can go in an autoclave, that “ensures that the microbes that may get inside the cone of the pipette are killed—not only the microbes from the outer surface of the pipette,” Bui emphasizes.
For the outside of a pipette, scientists often wipe the device with alcohol. That does some good, but it’s not enough over the life of a pipette. “Wiping the outer surface of the pipette with 70% ethanol is nowhere near as effective as autoclaving,” Bui says.
For any pipette and even after taking every precaution, take one more: professional cleaning on a regular schedule. At least once a year, depending on use, schedule a pipette for a complete cleaning, inside and out. That takes a lab a long way toward keeping contamination out of pipetting, which also helps to keep samples clean.