Medtronic R&D Engineering Intern interview questions

I forget the specifics but the general gist: There is a protein in the blood that undergoes a reaction with oxygen that has a 1-1 ratio with insulin. The protein reacts with oxygen to make a biproduct that can be detected by our device. The issue is, there is approximately 100 times more mols of the protein than there is oxygen, so we aren't detecting all of it. How would you go about detecting all of the proteins in this case?