Does fetal bovine serum used for antibody detection necessarily require heat inactivation?

For the same batch of 500 ml serum, pH usually changes slightly after inactivation, mainly affected by the buffer system and CO2 escape after opening, generally around 0.1-0.3. Before use, it is best to adjust to 7.2-7.4 with sterile Hepes. During inactivation, keep the bottle cap loose and do not seal it tightly to prevent pressure changes inside the bottle. In terms of procurement, 500 ml in-stock sizes are common, but if only a small amount is used after opening, it is recommended to aliquot into 50 ml or 100 ml portions in a biosafety cabinet and freeze them to avoid repeated opening and closing of the whole bottle. Ask the supplier whether this lot number already has an inactivated version. Sometimes directly purchasing the inactivated finished product is more stable than processing it yourself, but after arrival, endotoxin and cell growth still need to be tested.

When preparing ELISA blocking buffer or antibody dilution buffer, if conventional fetal bovine serum is used and subsequent washing is sufficient, complement interference is usually limited, and heat inactivation is not necessarily required. A more reliable approach is to replace it with complement-free BSA, casein, or a commercial blocking buffer. Especially when detecting low-abundance proteins, nonspecific serum protein background may be of greater concern than complement. If serum must be used, it is recommended to first perform a small-scale comparison between inactivated and non-inactivated serum, observing changes in the OD values of blank wells and the slope of the standard curve. Heat inactivation has little effect on the binding activity of some antibodies, but if the antibody concentration is very low, functional recovery validation is recommended.

In most cases, Western blot blocking solution can be used directly with non-inactivated serum, but if an HRP-conjugated secondary antibody is used, endogenous IgG or complement in the serum may cause background, and inactivation cannot completely solve this. For detection of low-abundance proteins, it is more advisable to switch to 5% BSA or an animal-origin-free blocking solution, because serum proteins have complex components, and after inactivation, flocculent precipitates and denatured proteins may block part of the membrane surface, increasing nonspecific signals. If you insist on using fetal bovine serum, it is recommended to first inactivate at 56°C for 30 minutes, then centrifuge at high speed, collect the supernatant, filter through 0.22 μm, aliquot, and store at -20°C to avoid background fluctuations caused by repeated freeze-thaw cycles.