**3.3 Influence of the grafting process**

If probe release occurs, this may be related to the nature of the link between the probe and the chip surface, i.e. to the grafting process. To evaluate this hypothesis, C131 peptide was immobilized using either electropolymerization of pyrrole-peptide conjugates or electrodeposition, as a monolayer, of diazonium-peptide adducts and the signals obtained upon successive anti-C131 serum injections were recorded in both cases.

As shown in Fig. 3, the stability of the SPR signal was much better when C131 was immobilized via diazonium, but the change in reflectivity is much lower (likely due to lower probe density on the surface), impairing the sensitivity of the system. At first sight, this observation fits with a probe release in the case of pyrrole electropolymerization protocol, but this eventuality will be discussed later on in light of the other results (§ 4).

Stability of Peptide in Microarrays: A Challenge for High-Throughput Screening 205

Fig. 4. Efficiency of the regeneration process. C131 peptide was immobilized in triplicate on the gold chip surface via pyrrole electropolymerization. Successive injections of NIS (1/50) with periodical injections of anti-C131 serum (1/200) were performed, followed by HCl-Glycine regeneration. SPR signal was quantified after anti-C131 injection and after the

Fig. 5. Influence of the saturation process and of the peptide sequence on SPR signal loss. C131, C20 and Ova75 peptides were immobilized in triplicate on the gold chip surface via pyrrole electropolymerization. Saturation of the chip surface was ensured using either NIS or PLL-PEG or PVP. Successive injections of anti-C131, anti-C20 and anti-Ova75 serums (1/50) were performed, followed by HCl-Glycine regeneration. SPR signal loss after 74 injections.

regeneration step.

Fig. 3. Influence of the grafting process on the evolution of SPR signal (change in reflectivity = R). C131 peptide was immobilized in triplicate on the gold chip surface via either pyrrole electropolymerization or diazonium electrodeposition. Successive injections of NIS (1/50) with periodical injections of anti-C131 serum (1/200) were performed, followed by HCl-Glycine regeneration.
