There are two things that you are trying to stabilize here - the antibody and the functional group on the linker. Without knowledge of the linker and details of when you intend to complete the conjugation process, it is hard to give a single recommendation.

Two scenarios:

If you have completely stable linker/functional group, I would be inclined to store at 4 degrees to avoid a free-thaw cycle on the antibody, and complete the conjugation process as soon as possible.

If your linker is unstable or if you face a significant delay before continuing I would store at a colder temperature. The safest option is -70, but it is important how you get to that temperature. I would snap freeze in liquid nitrogen and then transfer to -70 (or potentially to -20 if you do not have a -70).

Hello Nick Gee,

Thank you so much for your response.

I am working on

antibody - Trastuzumab(Humanized(from mouse)Anti-HER2 IgG1

Linker - SMCC (N-succinimidyl -4-(N-maleimidomethyl)-Cyclohexane-1- Carboxylate) ( Non-cleavable linker)

Okay thanks. SMCC has two elements, the linker part (completely stable) and maleimide functional group (fairly stable). Now that I know the functional group, the pH of the buffer that your antibody-SMCC derivative is being stored in becomes a critical parameter. Maleimide is increasingly unstable as the pH rises. What is your current pH? You need to be below pH 7.5 for storage, preferably significantly lower. If not, you should complete the conjugation process as fast as possible! If your buffer is slightly acidic, you have a bit more time to play with. Good luck.

Thank you so much Sir

Currently I am using a buffer of pH 6.5.

So sir can I store it at 4 degree Celsius for 1 week?

It is impossible to be certain because I have not tried that particular pH and for that time period, but the pH is favorable at least. If possible, I would try to couple the two parts of the process more tightly in the future, on the same day, or across two days.

There is great reagent for checking that your maleimides are still reactive - SAMSA-fluorescein. Essentially its fluorescein with a protected thiol which you can release very easily with NaOH. You then add Fluorescein-SH to a portion of the maleimide derivative (in your case an Ab) and then after the reaction you desalt the sample. If the maleimides are active you will get a fluorescent Ab. If not, you know you have lost your maleimide groups.