Increasing sensorgram in dissociation phase

I am working on a project determining binding kinetic of an antigen (TNF) to
an antibody (Etanercept). The sensorgram became increasing in the dissociation
phase, I have attached the results. Does anybody have any idea about
the probable reason that may be related to this problem?
It is noteworthy to mention that I have desorbed, sanitized and
supercleaned my instrument before.

Hi ramin,

Cleaning the instrument may give some extra drift. This will become extra visible when having long dissociation times (as with the curves you show).
Normally I let the system on standby overnight after the cleaning procedure to minimize drift.

It is also a good idea to have multiple dummy runs before your experiment and have some blanks in between the analyte injection to perform some double referencing. If drift is persistent, double referencing can possibly compensate.

You may want to read the experimental strategy page ( www.sprpages.nl/experiments/strategy ) for other experimental set-ups. Since you have long dissociation times it can be beneficial to use an other strategy.

Kind regards

Arnoud

Question; did you run the higher concentration analyte injections before the lower concentrations? You could have drift due to the fact that the surface has not been completely regenerated.

The experiment started with lower analyte concentrations. The regeneration condition is ok.