You could try making your own ELISA plate by coating it with Abcam's ab126388 antibody or any other (you may have one of your own?). If you have a source of pure 43RF amide you'll need to make a dilution series of this to quantify your results. You may find that you need to dilute your CSF in order to fit it on your standard curve.These "home-made" ELISAs work just as well as the commercial ones which are also vastly expensive. I'd give it a try; it's really good fun and so rewarding when it works!

Good luck

Simon 

thanks Simon, this is a very good idea about which I forget =] I need definitely to try it.