Plasma polymer films and gold nanoparticles: coupling of properties to design a biosensor

The present investigation deals with the functionalization of gold nanoparticles (Au NPs) with primary amine-based plasma polymer films (NH2-PPF), to improve their properties for bioanalytical applications. Cyclopropylamine (CPA) plasma polymerization, in pulsed and continuous wave radio frequency discharges, was employed to growth CPA amino-based PPFs coatings (18 nm) onto Au NPs of 12 nm of diameter deposited on glass and silicon substrates. A multi-technique investigation, based on FT-IR and XPS spectroscopies, AFM and SEM microscopies and Tof-SIMS spectrometry, revealed peculiar features of the CPA PPFs. In particular, by FT-IR it was possible to obtain an overview about the rich chemistry of such PPFs, and by XPS, combined with chemical derivatization by using the reagent TFBA, it was possible to quantify unambiguously the surface –NH2 amount. For testing the response in a biological environment, the behavior of the PPFs in phosphate buffer saline solution was studied upon 24 hours of immersion. The decrease of thickness occurred, related to a restructuring of the PPF structure induced by the diffusion of the solvent in the polymeric network. Such an effect of diffusion strongly depends on the cross-linking density of the PPF, characterized in the present study by ToF-SIMS. Despite such structural rearrangements, SEM does not show any evidence of delamination or damage caused after 24 hours of ageing in PBS. Results are therefore very promising for biosensor applications, as demonstrated by proof-of-work experiments with proteins and peptides.