The adsorption of proteins at biomaterial surfaces depends on the properties of the substrate and can cause changes in protein conformation. Time-of-flight secondary ion mass spectroscopy (ToF-SIMS) was used in this study to characterize human serum albumin (HSA) adsorption on two different polycarbonate surfaces:  a native membrane and a hydrophilic treated one. The amount adsorbed as a function of HSA concentration in solution was compared for the two substrates. The treated membrane was found to have a lower affinity for albumin than the native one. Principal component analysis was used to reveal changes in albumin conformation as a function of albumin concentration in solution and to compare the conformations adopted on the two substrates. The albumin conformation was different on the two substrates, and in every case, the protein lost its native structure. A correlation was found between the amount adsorbed on the hydrophilic surface and the albumin conformation on this surface.

The structure and the composition of adsorbed protein films containing human serum albumin (HSA) and/or human insulin were studied with time-of-flight secondary ion mass spectrometry (ToF-SIMS). The proteins were adsorbed either on native polycarbonate (PC) membranes or on PC membranes treated with poly(N-vinylpyrrolidone) (PVP/PC). These membranes have been developed for their use as encapsulation membranes in a bioartificial pancreas. Principal component analysis (PCA) of the ToF-SIMS results allowed the determination of the main factors affecting the surface structure and composition of the protein layer. The substrate surface properties were found to be the most influencing factor. The amount and type of the adsorbed protein also influence the adsorbed protein layer surface composition and structure. A partial least squares (PLS) regression model allowed confirmation of the correlation between the adsorbed amount of protein and the surface composition of the protein layer.

The enhancement of the vibrational sum-frequency generation (SFG) signal from molecules adsorbed on metallic nanopillars excited at a resonance frequency matching their localized surface plasmons is reported. The nanopillars stand vertically on a metal surface and possess two plasmon modes that can be selectively excited by either the incident visible laser beam, or the generated SFG beam itself. This nanostructured platform increases the molecular SFG signal of a monolayer by two orders of magnitude. The localization and the geometry of the two plasmon modes enables to probe the molecules adsorbed onto the vertical nanopillar wall, or on the top of it, or on the fl at surface between the pillars, selectively. In practice, this spatial selectivity is set by switching the polarization of the visible and SFG beams at resonance. Owing to the largely improved sensitivity combined with a specifi c spatial selectivity, plasmon-enhanced SFG boosts the versatility of second-order vibrational SFG spectroscopy or microscopy. This makes them promising platforms in the development of analytical molecular devices. 245SFG measurement alignment procedure and the data reproducibility are discussed. Complementary SFG spectra at different wavelengths are also provided.

Characterisation of the protein films has been a subject of long-standing interest in biomaterials research. With the advent of polyatomic ion beams such as C 60 , Time-of-Flight-SIMS (ToF-SIMS) depth profiling analysis is now able to provide information about the protein-substrate interface chemistry. To investigate this effect, two types of films, bovine serum albumin (BSA) onto hydrophilic silicon wafer, and BSA onto hydrophobic silanized silicon were fabricated using the dried-droplet procedure. Depth profiling experiments were conducted in a ToF-SIMS instrument equipped with C 60 + and Ga + ion sources (sputtering ion, 15 keV C 60 + ; analysis ion, 12 keV Ga + ). The molecular information is kept during the protein film depth profiling for both films. Principal component analysis (PCA) was used to determine the relative changes in the spectra recorded during the depth profiling. Spectral differences identified using PCA were correlated to conformational changes of the protein that occurred during drying according to the substrate properties.

No abstract