Sean Lauber:ELISA Development
First you need to determine what reagents you will use for your ELISA. The protocol I use is based off of a generic R&D ELISA. The primary antibody binds to the plate (this should be monoclonal), the sample binds to the primary, then the secondary binds to the sample (this should be be biotinylated), then strep-HRP binds to biotin and the HRP is used for color development (see any R&D ELISA for the complete protocol).
Next you need to determine what concentration of primary and secondary will work best for giving good color development for a range of sample concentrations. I choose the range 0.25 - 8 μg/mL for the primary, 50 - 400 ng/ml for the secondary, and 0, 10, 100, 1000 pg/ml for sample detection. Set up the plate as follows (checkerboard ELISA):
Then you want to determine what concentrations of primary/secondary give the highest change between sample concentrations (so 10 - 0, then 100 - 10, then 1000 - 100), this is the concentration you want to use. Usually the highest concentration of both primary/secondary works best but if reagents are expensive you might want to reconsider.
At this point it's a good idea to repeat the optimal concentration with a tighter sample size (so instead of 0, 10, 100, 1000, try 0, 10, 25, 50, 100, 250, 500, 1000 or something), do these samples in duplicate/triplicate. You want to make sure this works before putting precious sample on it. It would even be a good idea to repeat it AGAIN and make sure you get the same numbers. You don't want to have to think about redoing this because at some point the whole thing decides to not work. This happened to me. Keep all your reagents under the same condition (primary, secondary and standard should be at -80*C).
If your standard is not detectable at 10 pg/ml then you may not be able to detect this low. You can play around with things like buffers and washes and incubation times and %FBS but that's information you can find elsewhere. If you're looking to detect protein in serum I believe %FBS is an important contributor.
Also a good idea at this point to do a test for specificity. Test varying concentrations of different proteins that show some similarity or proteins you suspect may cross-react with the antibody. Show that the antibody pair you're using is specific. Use a high concentration (10 ng/ml) to really show you're not picking it up.