Negative RU - big dip after injection

Hi, I am trying to see if my protein of interest (ligand) binds the ds RNA (analyte). My base3lines seem ok but my sample curve has a huge dip right after the injection(green curve in the picture. What does that indicate? Is there any indication of binding for this analyte sample or is it just a negative curve due to non specific binding?

It is difficult to say where this kind of dips come from. Generally there is a buffer mismatch or sample carry-over from the previous injection. In rare cases the refractive index near the surface is changed by a compound but in general proteins should give a positive binding curve upon interaction.

See for instance www.sprpages.nl/experiments/troubleshooting

Kind regards
Arnoud