The goal of this internship was to use plasma deposition of functional siloxane-based films to cre-ate vertical gradients and examine their adsorption characteristics with optical sensors. Several conditions of deposition were used (presence or not of oxygen in the plasma, different deposition times) in order to have hydrophilic or hydrophobic conditions or a hydrophobic-to-hydrophilic vertical gradient on the surface of the substrates. These characteristics were controlled by contact angle measurements.
These three types of surfaces had specific adsorption behavior in presence of Bovine Serum Al-bumin (BSA), a model protein. Indeed, thanks to Transmission Interferometric Adsorption Sensor (TInAS), the optical thickness of the BSA adsorption (from 0.9 nm to 1.9 nm, depending on the characteristics), and therefore, the adsorbed mass, was detected.
Then, I studied the effect of the concentration of the BSA solution and whether it was possible to reuse it without contamination and without changing the adsorption kinetics.
Knowing that it was better to have a freshly prepared 5 mg/mL BSA solution, the study of the ad-dition of BSA antibody adsorption on the different surfaces was carried out with the aim to identi-fy the actual BSA conformation. The presence of antibodies, however, did not affect the TInAS signal, which is why the BSA solution concentration was later set at 0.2 mg/mL to reduce potential reactions with BSA in solution. Indeed, the low concentration of the BSA antibodies comparing to the 5 mg/mL BSA solution could explain the absence of any significant signal change.
Moreover I analyzed dry, hydrated and dehydrated plasma coatings. The dry and the dehydrated ones had the same behavior than a hydrophobic surface; whereas the hydrated gradient films ex-hibited a lower adsorption of BSA than the reference coatings.
Finally, the interesting result of these experiments is that water plays a major role in the reduced BSA adsorption of hydrated coatings: confined water in the vertical gradient structure allows to alter the way proteins adsorb to surfaces, while dehydration proceeds within minutes in air sus-pending the effect of reduced BSA adsorbed.