Question: How can I prevent tissue sections from freeze-drying during cryostat sectioning?
Answer: Freeze-drying can occur if tissue sections placed on the Visium slide are exposed to the cryostat environment for long periods. Freeze-drying will impact tissue morphology and data quality.
Affected tissue sections will remain opaque instead of turning transparent during the 1 min 37°C incubation (step 2.1c in the H&E Staining or the Immunofluorescence Staining Demonstrated Protocols). The left two tissue sections in Figure 1 provide examples of the freeze-drying phenotype.
Figure 1. Post-37°C 1 min incubation. From left to right, tissue sections were exposed in the cryostat for one hour, 30 min, 15 min, and 0 min (immediately processed) after section placement.
Figure 2. Post-H&E staining. Blue boxes mark over-dried tissue regions.
To prevent tissue from freeze-drying during sectioning, the Visium slide can be placed inside a pre-chilled slide mailer or a 50ml centrifuge tube and kept sealed in the cryostat between placing of sections on the slide. If working with multiple tissue blocks, prepare each tissue block ahead of time for sectioning (e.g., equilibration and mounting of tissue onto specimen chuck) so that blocks can be interchanged quickly. We don’t recommend placing tissue sections across multiple days on a single Visium slide to avoid tissue damage due to temperature fluctuations.
Visium slides with placed tissue sections can be stored in a sealed container at -80°C for up to 4 weeks. Failure in using a sealed container will also lead to freeze-drying. Additional details regarding storage post tissue placement can be found here: How should I store Visium Slides once tissue sections have been placed?
Product: Visium for fresh-frozen