Here's a plot. The BSA binding should be much less

I deal with a regular SPR, not with LSPR but I guess the differences should not be principal in this case.

What makes you think that signal from BSA is too high? It is comparable to the signal from the thiols layers. And as you already pointed , -OH surfaces really give only some level of protection against BSA. So it might be actually within expected range.

And where is the rest of the curve? I mean the flashing again with MES. The signal in solution with BSA should be somewhat higher just because of the change of solutions bulk RI, whether it is bound or not you can say only after flashing the sensor with buffer again.

Thank you Shavkat,

I believe the BSA signal is too high based on a few things. First, based on free-solution AuNP-BSA binding, which we've seen to be at least 10 times less adsorptive on coated AuNPs. By comparison, this is only about 50% the binding of what we get on bare AuNPs. This is also confirmed in a few papers, about a 10-fold increase, on AuNP-coated surfaces. Secondly, we have some old data (although of course it's questionable) that suggests this was the case when the experiment was originally attempted last may. Again, since I did that experiment, who is to say it is the correct one.

The rest of curve is just flat; we flushed with MES and had no response, indicating permanent binding. This was true in all the runs we performed.

Probably, you have also to try passivate the fiber surface itself. e.g. with some hydroxy or peg functionalised silane compounds. A short treatment in plasma oxygen might also do the trick. I mean that proteins are not directly binding to the NP's, but rather to the substrate surface around them.

I would also expect that some molecules are physically adsorbed in the cavities (consider the space between the planar surface and sperical particle lying on it). Then you first have to fill these cavities and then try again with albumin. But these are, well, just my speculations.

Thanks, these are good speculations.

I had not considered the ozone treatment; I will look into it, thanks. In princple, the sensor should not be very sensitive to regions away from the AuNPs, but as you say, the very close regions of the substrate likely are going to influence the AuNPs.

I've never seen people do this with AuNP-sensors; that is, to fill cavities, so I imagine it's hard. Like, how does one fill the cavity without coating the AuNP. Anyway, I will delve into it a bit, thanks for the suggestion.

Hi Adam Hughes I was looking for the stability of MHDA: MUD in solution and I ran into your question. So, in your experience, is it necessary to prepare the new solutions every time or how long can the solutions be stored?

Thanks in advance.