Fetal bovine serum is a biological raw material. Despite careful sourcing and testing, it can carry bovine viruses or mycoplasma. Gamma irradiation is the most widely used method for adding a validated inactivation step to FBS, and it is commonly expected for FBS used in the manufacture of biologics, vaccines and cell-based products.
This article explains the process step by step. Gamma irradiation is an industrial process carried out at specialised, validated irradiation facilities, not in a cell culture lab. Ready-to-use FBS Gamma Irradiated is available from SeamlessBio, and other sera can be irradiated on request through our serum processing service.
How gamma irradiation inactivates viruses and mycoplasma
Gamma rays, typically from a cobalt-60 source, penetrate the frozen serum completely. They damage nucleic acids directly and through free radicals, so viruses and mycoplasma lose their ability to replicate.
- Larger genomes are more sensitive. The bigger the genome, the more likely it is hit at a given dose.
- Enveloped viruses such as BVDV are inactivated efficiently at the usual doses.
- Small, non-enveloped viruses such as parvoviruses are more resistant. Irradiation reduces them, but complete inactivation is not guaranteed.
- Mycoplasma are reliably inactivated at the usual doses.
- Prions (TSE agents) are not inactivated at these doses. TSE safety comes from herd origin and documentation (e.g. TSE/BSE certificates), not from irradiation.
Why serum is irradiated frozen
Free radicals formed during irradiation also attack proteins. In frozen serum, these radicals can move far less, so damage to growth factors and other proteins is greatly reduced. For this reason, FBS is irradiated frozen, on dry ice, in its final bottles.
The process step by step
1. Select and test the lot
The serum lot is tested before irradiation: sterility, mycoplasma, viruses, endotoxin, haemoglobin and biochemical parameters. Irradiation adds safety but does not replace this testing.
2. Freeze the bottles
The filled and closed bottles are frozen completely at −20 °C or colder.
3. Pack in a validated configuration
The bottles are packed on dry ice in a defined arrangement (number of bottles, box size, dry ice quantity). The dose distribution has been validated for exactly this configuration.
4. Dose mapping
During validation, dosimeters are placed at many positions in the package to determine where the lowest dose (Dmin) and highest dose (Dmax) occur. The process is set up so that Dmin reaches the specified minimum dose and Dmax does not exceed the specified maximum.
5. Irradiation
The packages pass the radiation source until the target dose is reached. Typical doses for serum are 25–45 kGy. The dose window is defined per order.
6. Dosimetry and certificate
Routine dosimeters travel with each run and are read out afterwards. The facility issues an irradiation certificate with the minimum and maximum dose achieved.
7. Frozen return transport
The serum is returned on dry ice and stored at −20 °C or colder.
8. Post-irradiation QC and release
After irradiation, the lot is retested, at least for sterility and growth or cell culture performance, and released with a CoA. The CoA states that the lot has been gamma irradiated and refers to the irradiation certificate.
Effect on cell culture performance
At the usual doses and in the frozen state, most cell lines show no relevant difference from non-irradiated FBS. Very sensitive applications, such as some stem cell or primary cell cultures, may respond to small changes. As with any new lot, test it with your own cells first.
Regulatory context
For FBS used in the manufacture of medicinal products, regulators expect a risk-based approach to viral safety:
– EU: the EMA guideline on the use of bovine serum in the manufacture of human biological medicinal products
– USA: the requirements of 9 CFR for ingredients of animal origin
Gamma irradiation is an accepted and well-established inactivation step within that approach. Documentation (irradiation certificate, dose report, facility validation) is part of the batch record.
Gamma irradiation is also the standard sterilisation method for single-use systems such as 2D bioprocessing bags and 3D bioprocessing bags, see What is gamma sterilisation in bioprocessing?
FAQ
What dose is used to gamma-irradiate FBS?
Typically 25–45 kGy. The exact dose window (minimum and maximum) is defined per order and documented on the irradiation certificate.
Does gamma irradiation make FBS sterile?
FBS is already sterile-filtered before irradiation. Irradiation adds an inactivation step against viruses and mycoplasma that may pass filtration.
Does gamma irradiation inactivate all viruses?
No. Enveloped viruses are inactivated efficiently. Small, non-enveloped viruses such as parvoviruses are more resistant. Irradiation therefore complements donor-herd selection and virus testing; it does not replace them.
Does irradiation affect cell growth?
In the frozen state and at the usual doses, the effect is small for most cell lines. Test sensitive cells with the specific lot.
Can I irradiate serum myself?
No. Gamma irradiation requires a licensed, validated irradiation facility with dosimetry. SeamlessBio organises irradiation at an external ISO 11137-compliant facility.
What is the difference between gamma irradiation and heat inactivation?
Heat inactivation (56 °C, 30 min) destroys complement activity but is not a reliable virus inactivation. Gamma irradiation targets viruses and mycoplasma; it is not a substitute for heat inactivation if your assay requires complement-free serum. See the heat inactivation protocol.
Is gamma-irradiated FBS also available heat-inactivated?
Ask us about combinations of processing steps – request a quote.
Gamma-irradiated FBS from SeamlessBio
FBS Gamma Irradiated comes with CoA, certificate of origin, TSE/BSE statement and irradiation certificate. Batch reservation is available. Prices and availability on request – request a quote.
Related: What is Gamma Irradiated FBS? · FBS Gamma Irradiated · Serum Processing Services · FBS for Pharma · Batch Reservation
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