Prior to fully integrating new labels into your workflow, it’s imperative to test them first to ensure that they do not fail at any point during the required protocol(s). As many basic experimental protocols in the lab require harsh chemicals, it can be helpful to make a quick list of those used in each protocol, along with the concentrations and possible exposure times for all labels. Doing so ensures that any accidental spills, as well as planned exposures (such as microscope labels used in histology), do not result in label failure or smudging/fading of the printout, thus keeping your samples accurately identified in the short and long term.

SDS-PAGE/Western blot

A variety of solutions are used for protein separation and identification:

Protein isolation and purification: Harvesting proteins utilizes a number of solvents, the main ones being solubilizing detergents. These include:

• Triton-X (non-ionic)
• SDS (anionic)
• NP-40 (non-ionic)
• Tween 20 or 80 (non-ionic)
• CHAPS (zwitterionic)
• Cholate (non-ionic)

Lysis buffers may also include other chemicals like EDTA and DTT to eliminate contaminating divalent cations, inhibit protease activity, and reduce disulfide bridges. If containers are exposed to these chemicals, it is likely by accident and for short periods. However, water can also be included in this list as heating samples at -100°C is often a necessary step for denaturation. While this can be performed using a heat block, many still rely on boiled water to perform this step.

SDS-PAGE/Western blot: SDS is included throughout denaturing SDS-PAGE, in both sample buffers, running buffers, and when preparing the gel. Again, exposure is like to be short. However, if spilled, containers may become fully immersed in SDS buffers, which may be difficult to remove thoroughly. Tris base and glycine are also used in the running buffers, while glycerol is found in the sample buffer, which makes it sticky.

Histochemistry

The main culprit for label failure in histochemistry is xylene. Used as a clearing agent for histochemistry, xylene is one of the strongest organic solvents used in the lab that can cause your label to fall off or the printout to smudge. Xylene-resistant labels are required for their resistance to xylene, which can withstand immersion in the solvent, some for more than 24 hours, but testing them prior to use is still recommended. Testing is also recommended if using xylene substitutes for clearing, as they may also affect your labels and/or printout, depending on the chemical used as well as its concentration and exposure time.

Two other frequently used classes of chemicals applied during histochemistry that can cause your labels to fail include:

• Staining agents, such as hematoxylin and eosin Y
• Tissue fixation agents, including acetone, formaldehyde, and methanol

Cell culture

The main chemical used for cell culture is 70% ethanol. Because it is only used for sterilization purposes, labels likely only need to be tested for short-term exposure. DMSO at a concentration of 7%-10% is also frequently used during cell preservation, and if spilled, it can readily stick to the surface of tubes and vials and ruin the labels. Cryo preservation is typically done inside liquid nitrogen Dewars, which requires labels that withstand long-term storage under cryogenic conditions and immersion in liquid nitrogen. Therefore, cryogenic labels are recommended for this application.

Lipid Extraction

Various lipid extraction methods exist, including the Folch method and the methanol/tert-butyl methyl ether method (MTBE). Chemicals like acetonitrile, butanol, methanol, hexane, chloroform, and ammonium formate are frequently utilized among these methods. Though exposure to labels on the outside of tubes is likely to be short, performing a quick test using these volatile chemicals is recommended. This is especially important for the printout, as these chemicals may be prone to causing labels to smudge, especially those not generated with a thermal-transfer printer.

Drug Screening

The drug discovery process involves many different stages, one of which is the drug screening phase, where multiple drugs are tested to determine their effectiveness. The creation of chemical libraries is utilized to test large numbers of drugs; to that end, each drug in the library must be solubilized in a common solvent for long-term storage. DMSO at a concentration of 100% is often used for this purpose due to the fact most drugs will dissolve in concentrated DMSO, while also providing resistance to bacterial growth. Therefore, any labels used to identify chemical library plates must confer resistance to concentrated DMSO exposure without smearing or failing.

LabTAG by GA International is a leading manufacturer of high-performance specialty labels and a supplier of identification solutions used in research and medical labs as well as healthcare institutions.