Has anyone noted any problems with regenerating Cytiva Series S NTA chips? There have been a couple of examples in our laboratory, where after an experiment we have stored the chip in buffer, then after a period of a few weeks attempted to strip the surface (with 350 mM EDTA), recharge with Nickel and then re-capture a his-tagged ligand. In these instances, the nickel recharging appears different to when a fresh chip is used and the capture of the protein has failed. Initially we wrote it off as dodgy protein or an inadvertent mistake, but we are now wondering if there is some sort of issue with storing the NTA chips in buffer for a period of time before regenerating. The only common component in the buffers is ~ 1 % DMSO, which Cytiva say is tolerated in the manual (though they do not state for how long).
From my experience, the capacity of the NTA sensor surface declines the first cycles more rapidly than the following. I did store the NTA sensor after full regeneration and Nickel recharging to make sure no previous ligand was left behind. Storage was in HBS 7.4 at 4°C. From what I read in your question you left the ligand on the sensor surface. I would not recommend that.