Figure 17. (a) SPR sensorgrams showing the injection of 50-μl aliquots of 10^–3 mg ml^–1 CRP standard (FC2) and tenfold diluted human plasma (FC1) across anti-CRP antibody-derivatized flow cells. The affinity capture of the CRP standard leads to an SPR response of 564 RUs of CRP. This corresponds to 564 pg (1 RU = 1 pg of protein), or about 25 fmoles of CRP (MW_CRP = 20,030). Injection of the plasma sample leads to a binding response of 276 RUs. (b) Mass spectra taken from the surfaces of FC1 and FC2, showing the presence of multiply charged CRP ions (MW_CRP = 20,030). Both mass spectra contain multiply charged CRP signals, at expected m/z values. The signals from FC2 where the standard CRP was captured are stronger than the signal obtained from FC1 where CRP from plasma was captured, which was expected because of the higher SPR-binding response observed in FC2. However, nonspecific binding of other plasma components might also contribute to the SPR response in FC1, further diluting the contribution of CRP binding to the overall SPR response.