by George Vaniotis, Ph.D., Medical Writer, LabTAG by GA International
Anyone who has worked in a research lab, clinical lab, biobank, biorepository, or any industry that stores samples, specimens, and other material in low temperature conditions knows the importance of using cryo labels to identify containers. Storage in ultra-low temperature freezers or liquid nitrogen poses a risk to accurate sample identification, as lab labels without an adhesive designed for cryogenic environments can detach and facestock can smudge or smear due to the high humidity and fade over time. The result of this type of label failure can be devastating, requiring valuable samples to be discarded and entire experiments redone. This guide will review how to choose appropriate cryogenic labels for your lab, ensuring you enjoy efficient, accurate, and error-free sample identification.
Types of Labeled Containers
The first thing to consider is the type of container you intend to label. The container’s material (polypropylene, metal, glass), curvature (round, flat), and overall dimensions (height, width, length) may impact the type, size, adhesive, and configuration of the cryo labels you need. When choosing the correct label size, also consider what information you will print on it, and ensure you have ample room to include all the necessary data, including barcodes and alphanumeric data. Here is a breakdown of some of the most common containers encountered in the lab and the type of cryogenic label that will best meet their requirements.
Cryogenic Tubes & Vials
Cryo tubes and vials can be identified with cryo dots on their caps and rectangle labels on their side. These tubes can vary significantly in size, from 0.2 ml tubes used in PCR to 50 ml Falcon tubes used to store specimens or experimental reagents. The cryogenic label must fit securely on the tube, with the flexibility to firmly adhere to the curved surface of the vial. Cryo vials are often stored in liquid nitrogen tanks, so the label should withstand temperatures as low as -196°C. Unique formats may also require specially designed laboratory labels, as is the case with 2D-barcoded tubes. The unique shape of these tubes requires a label that will identify the side of the tube, with a connected dot label at the bottom, for printing a 2D barcode.
Storage Boxes & Plates
Storage boxes typically come in cardboard or plastic and have a wide flat surface for labeling, while microplates provide a smaller surface area for applying labels. In both cases, the label should always be applied to the container’s body, not the lid, as this can lead to mix-ups and misidentified containers. Plates and dishes need a thin lab label and typically only need to withstand temperatures as low as -80°C. If cryo boxes need to be relabeled regularly, removable laboratory labels are advised.
Metal Racks & Canes
Metal racks are often used to store and organize cryo boxes in freezers and liquid nitrogen tanks. Cryogenic labels used to identify these racks need an adhesive designed to adhere to metal surfaces in low temperature conditions. Cryo labels for metal surfaces can also be used to identify aluminum cassettes, X-ray film cassettes, film cans, aluminum vials, aluminum and stainless-steel boxes, sleeves, and canes.
Vitrification Devices
Cryogenic straws and vitrification devices are storage containers used in assisted reproductive technology clinics as well as animal breeding and biotechnology companies to preserve oocytes, sperm, and fertilized embryos. They are designed to withstand the vitrification process, an ultra-rapid freezing of oocytes and embryos used to avoid ice crystal formation. These containers require cryo labels that can wrap around their small diameter and remain firmly attached during snap-freezing and long-term cryogenic storage in liquid nitrogen tanks (-196°C).
Cryo straws require specialized labels that are both cryogenic and low emitters of volatile organic compounds (VOCs), particularly for in vitro fertilization (IVF) clinics. Wrap-around labels are recommended, with a strong cryo-adhesive that easily conforms to the small diameter of standard and high-security cryo straws as well as other vitrification devices and remains permanently attached during snap-freezing and long-term cryogenic storage (-196°C/-321°F).
Storage & Experimental Conditions
Once the container is chosen, the next step is determining the environment in which the label must perform. Your primary concern must be that it withstands the particular cryogenic storage conditions it will be subjected to, including ultra-low temperature freezers (-80°C), liquid nitrogen dewars (-196°C), or transportation on dry ice. However, many lab labels may also require resistance to additional environmental conditions, such as adhering to wet or frozen surfaces, resisting chemical exposure, or high-heat sterilization.
Labels intended for cryogenic storage are typically also water-resistant. However, this does not mean that they can be applied to wet surfaces. They usually must be applied to a dry surface before being transferred to cryo storage. If you need to label wet containers, such as containers freshly removed from water baths or other solutions, ensure the label adhesive is up to the task. Ideally, they should attach firmly to the wet containers and allow for immediate transfer to cryogenic storage, requiring zero cure time. Frozen containers present another challenge, as thawing them would potentially compromise the integrity of their contents. This requires a label that will firmly adhere to the container, despite the presence of frost and its extremely cold surface. When labeling already frozen vials and tubes, cryogenic labels that can be applied at -80°C are a must, thus eliminating unnecessary freeze-thaw cycles.
Your lab labels may also encounter conditions beyond cryo storage. This may include short-term exposure to chemicals, such as alcohols and disinfecting solutions. Cryo vials used to freeze cells for cell culture are often exposed to isopropanol during the freezing process and may be sprayed with ethanol or wiped down using alcohol wipes to ensure they remain contamination-free. Some cryo labels can resist short-term exposure to alcohols; however, if your labels are expected to endure longer periods of exposure, wrap-around labels are recommended. These labels self-laminate when wrapped around a tube, providing the printout with an extra layer of protection against harsh solvents as well as abrasion. Wrap-around cryo labels can even provide added protection against elevated temperatures if required.
Laboratory Label Special Features
Now that you’ve chosen the container and experimental conditions, we can consider any special label features that may help optimize sample identification for your application. These unique material features are more related to convenience or preference and may add an extra layer of functionality to your labeling choice.
Label Adhesive
Labels with either a permanent or removable adhesive are available. If the container will be reused and regularly relabeled, a removable label is suggested, which can be lifted from the container without leaving a mark.
Blackout/Cover-up Labels
Blackout labels have a unique opaque design. They can be placed over an existing label to efficiently cover-up any pre-existing information. They are generally used to relabel or over-label containers and can also be employed to block-out sensitive information.
Clear Labels
Transparent labels ensure the contents of labeled containers remain visible. Perfect for identifying aliquot tubes as well as containers where the volume needs to be readily evident.
Tamper-Evident/Destructible Labels
Tamper-evident labels will tear or destruct upon any attempt to remove them from their container, clearly indicating that the container’s contents have been tampered with. Ideal for sealing sensitive samples during storage or transport.
Wrap-Around Labels
As mentioned above, these self-laminating labels come with a transparent laminate that provides additional protection against extreme temperatures, exposure to harsh chemicals, as well as abrasion and physical damage.
Piggyback Labels
Piggyback labels have a unique label-on-label multi-layer design. Composed of multiple smaller labels nestled within a larger adhesive label, they are perfect for record-keeping and enhancing sample traceability.
Printing Method & Software Integration
Partnering with a label manufacturer, like LabTAG by GA International, that can supply both labels and printing solutions in one order will help simplify printer and software selection, as the printing method may directly depend on the labels you choose
Thermal-Transfer
This method utilizes ink ribbons and label rolls to provide the greatest versatility in material choice and associated resistance. Printing on rolls also gives the user the flexibility to use only the number of labels required, without wasting additional labels. Conversely, these printers can only print in one color (typically black).
Direct Thermal
Direct thermal, similar to thermal-transfer, uses rolls of labels to print. However, they do not apply ink to the label; instead, labels are coated with a leuco dye, a chemical that changes color when heat from the print head is applied. While this method is suitable for short-term cryo storage, these laboratory labels can fade over time and are not well suited to chemical exposure. DYMO printers are a popular brand of direct thermal printers due to their low cost and portability.
Laser
Most labs already have a desktop laser printer that can also be used to print adhesive labels. Provided in sheet format, lab labels printed with a laser printer can be printed in color with a smudge proof, waterproof, UV-resistant, and cryogenic-resistant printout. However, cryogenic laser labels are not recommended for chemical exposure unless a laminate is applied over the printout.
Inkjet
Inkjet labels are available in sheet and roll formats and allow for printing with full-color inkjet printers. They provide some resistance to spraying and wiping with alcohols, though they offer little versatility in material choice.
About the Author: George Vaniotis, Ph.D., is a medical writer and product development coordinator at GA International. He earned his Ph.D. in biochemistry at the University of Montreal and has published scientific articles investigating the signaling in cardiac hypertension and colon cancer, as well as on drug development.