How should the remaining wells of an ELISA kit microplate be stored after stripping the strips? Is the inter-batch variation large?

Whether there is significant variation between different batches depends on the manufacturer's process and cannot be generalized. You can ask the supplier to provide inter-batch CV and COA. Preferably, after the new batch arrives, retain the remaining strips from the old batch and run a parallel test with the same batch of samples using the new batch to see whether the readout shift for the same sample exceeds the acceptable range. The preservation issue after removing strips is essentially about preventing moisture and contamination. If the aluminum foil bag is well sealed and the desiccant is effective, storage at 2-8°C is not a major problem, but each opening increases the risk. It is recommended to plan the experiments well, remove enough strips at one time, and reduce the number of times the package is opened.

For the remaining strips after breaking apart the plate, I generally put the ELISA plate strips back into the original foil bag, keep the original desiccant, expel the air, seal it, and store at 2-8°C. Do not store at -20°C; the strips are prone to problems if they absorb moisture or undergo repeated freeze-thaw cycles. When breaking apart strips, work quickly in a dry environment, and seal the bag immediately after taking what is needed. You can mark the date of first opening on the outside of the bag. Most manufacturers will state the recommended time to use up the contents after opening, ranging from as short as one to two weeks to as long as one month, but the safer practice is to try to use them within two weeks, and to check whether the desiccant has changed color before each use.

Even when using boxes from the same lot split into two separate runs, I prepare a fresh standard curve each time. Do not reuse the standard curve from the previous plate, even if it is the same lot and incubated on the same day; differences in plate washing conditions, color development time, and room temperature can all cause plate-to-plate variation. Quality control samples must also be run on the same plate. Lot-to-lot variation does exist; changes in the coating antibody between lots can cause the overall OD values to drift. Therefore, for large-scale experiments, try to lock in the same lot number. When changing lots, the standard curve and quality controls must be re-validated, and it is best to use pooled samples from the same lot for bridging.

If you often cannot use up a whole plate, consider single-strip coated or pre-coated breakable strip versions. However, pricing and shelf life need to be confirmed in advance. When storing the remaining wells after breaking the strips, I place a humidity indicator card inside; if the color changes, replace the desiccant. The manufacturer says storage at 4°C is sufficient, but do not place it in the frequently opened and closed refrigerator door area. Regarding timing, I generally control use within 2-4 weeks after opening; for wells exceeding one month, I would rather run a preliminary test than use them directly for critical samples.

The strip-well design is suitable for small sample volumes, but splitting the strips themselves introduces the risk of exposure after opening. Before splitting, it is recommended to equilibrate at room temperature for 20-30 minutes to prevent condensation. After removing the required number of strips, do not touch the wells of the remaining strips with your hands, and immediately place them back into the aluminum foil bag containing desiccant, expel all air, and seal. Do not stack the strip plates; store them flat at 4°C. It is difficult to give you an absolute answer on storage time, as it depends on laboratory humidity; if you notice elevated OD in negative wells or deterioration of the standard curve, stop using them.