ИСТИНА

It is known that, in contact with biological fluids, synthetic materials get coated with proteins. Depending on their affinity for the surface, these biomolecules bind strongly, forming a hard corona, or weakly, forming a soft corona. Here we use cubic silver nanoparticles (Ag NPs) as a model system with high surface area to quantitatively study the time-dependent binding of serum proteins. Metal nanoparticles exhibit localised surface plasmon resonances (LSPRs) due to the oscillations of their surface electrons. The position of LSPR peaks is sensitive to refractive index changes in the vicinity of the nanoparticle, caused by events such as protein binding. We incubated polymer-coated cubic Ag NPs in serum-supplemented media and observed a progressive binding of both strongly-attached and weakly-attached proteins over a time range from 1 to 24 h, resulting in increasing red-shifts of the plasmon peak position. Finite-difference time-domain simulations of a model Ag NP surrounded by 7 nm thick protein layers of various densities were correlated with the experimentally observed UV–vis absorption spectra, resulting in a method to calculate the amounts of both strongly and weakly bound proteins. We showed the formation of a monolayer hard corona with conserved protein-composition over time, but increasing protein density up to limits imposed by the random sequential absorption model. Furthermore, we used Time of Flight Secondary Ion Mass Spectrometry to study the binding of biomolecules vs. the polymer replacement and found that, while proteins exhibit a rapid strong attachment to the NP surface, polymer detachment is a slow process, spanning over 1 h. We showed that LSPRs of metal NPs can be used as a powerful tool to quantitatively study both strong and weak protein interactions with synthetic surfaces, including in the presence of polymer coatings. This analysis model could presumably also be employed to analyse the complement protein binding.