How to Correctly Thaw, Store, and Aliquot Fetal Bovine Serum? A Must-Read for Lab Beginners

Thawing: Slower Is Actually Safer

Fetal bovine serum is generally recommended to be thawed slowly at 2°C to 8°C, rather than directly heated with hot water or a microwave. Rapid warming can easily lead to protein precipitation or uneven distribution of nutrients. The serum can be transferred from the freezer to the refrigerator in advance and left overnight. If time is tight, it can also be thawed at room temperature with the aid of room-temperature water, but vigorous shaking should be avoided. After thawing, it needs to be gently swirled to mix the contents evenly.

Aliquoting: Avoid Repeated Freeze-Thaw Cycles

Repeated freeze-thaw cycles can damage proteins and growth factors in the serum and reduce its ability to support cell growth. A common practice is to aliquot the serum into small volumes according to daily usage, such as 50 mL or 100 mL per tube. Aliquoting should be performed in a clean environment or a biosafety cabinet, using sterile centrifuge tubes with proper labeling. Take one tube at a time to avoid repeatedly thawing the entire bottle. This can reduce waste and also help maintain consistent quality within a batch.

Storage: Temperature Must Be Stable

For long-term storage, fetal bovine serum is usually recommended to be kept at -20°C or lower, avoiding frequent temperature fluctuations. Refrigerators should be checked regularly to prevent temperature rises caused by defrosting or power outages. For short-term use, it can be stored at 2°C to 8°C, but it should not be kept for extended periods; generally, it is recommended to use it as soon as possible. Be careful not to place the serum near the refrigerator door or in other locations with large temperature variations.

What to Do If Precipitate Appears

After thawing, a small amount of flocculent or granular precipitate may appear in the serum, which does not necessarily mean the product has deteriorated. In many cases, it is proteins, lipids, or calcium phosphate precipitating at low temperatures. If the amount of precipitate is small, it can be gently swirled and used; if there is a large amount of precipitate or abnormal color or odor, use should be suspended and the supplier contacted. It is not recommended to forcibly dissolve the precipitate with high heat, as this may damage the active components.

"Small Steps" in Daily Operations

Wipe the bottle opening with 75% alcohol before taking serum, and wait until dry before opening the cap.

Avoid leaving it open for extended periods to reduce the risk of microbial contamination.

Label aliquot tubes clearly with name, lot number, and date.

Record each thawing time for easy troubleshooting.

Proper storage and use can help fetal bovine serum function more stably. A little more patience in daily operations can often reduce experimental variability and also make experimental results more reliable.