Drug Affinity and Functionalization of Gold Nanoparticles: AFM–SEIRA and SERS Study

This study presents the first investigation of the adsorption behaviour of Afatinib on gold nanoparticle (AuNP) monolayers, employing a combination of AFM–SEIRA and SERS techniques. Two types of AuNPs with distinct sizes, synthesized using different reagents, were employed to elucidate the influence of surface type on drug adsorption. The first type of AuNPs was synthesized using sodium borohydride (SB), whereas the second type was obtained using hydroxylamine hydrochloride (HH) as the reducing agent.

AFM–SEIRA revealed that Afatinib interacts to the AuNPs primarily through the quinazoline ring, amide group, and amino moiety, with adsorption geometry strongly dependent on nanoparticle type. Contributions from CH3 and CH2 moieties were also identified, indicating their role in stabilizing the molecule/metal interface. Time–resolved SERS studies demonstrated that the adsorption process is dynamic and involves molecular reorientation, followed by gradual desorption, which is accelerated at physiological temperature (37 °C). Competitive adsorption experiments with phenylboronic acid (PBA) showed that Afatinib exhibits higher affinity toward AuNPs, however, co–adsorption leads to reduced stability of both species on the surface. The results reveal molecular insights into drug/nanoparticle interactions and emphasize the role of surface functionalization in efficient nanocarrier design. This work deepens understanding of adsorption at plasmonic interfaces for biomedical use.