For ELISAs to show binding we used an HRP-conjugated protein that we conjugated with a kit (3 hour process, very easy to do) and it worked great. Plenty of labs conjugate the "primary" sensor (antibody or protein) and forgo secondary. There are disadvantages of course but sometimes you don't have a choice and it works fine with enough concentration.

That's not Newton's gravity, that's Einstein's relativity. Newton's simply posited that massive objects pulled things to them, not that they warped space-time.