Characterization of Poly(l-lysine)-graft-Poly(ethylene glycol) Assembled Monolayers on Niobium Pentoxide Substrates Using Time-of-Flight Secondary Ion Mass Spectrometry and Multivariate Analysis

Abstract

Control of protein adsorption onto solid surfaces is a critical area of biomaterials and biosensors research. Application of high performance surface analysis techniques to these problems can improve the rational design and understanding of coatings that control protein adsorption. We have used static time-of-flight secondary ion mass spectrometry (TOF-SIMS) to investigate several poly(L-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG) adlayers adsorbed electrostatically onto negatively charged niobium pentoxide (Nb(2)O(5)) substrates. By varying the PEG graft ratio (i.e., the number of lysine monomers per grafted PEG chain) and the molecular weights of the PLL and PEG polymers, the amount of protein adsorption can be tailored between 1 and 300 ng/cm(2). Detailed multivariate analysis using principal component analysis (PCA) of the positive and negative ion TOF-SIMS spectra showed changes in the outermost surface of the polymer films that were related to the density and molecular weight of the PEG chains on the surface. However, no significant differences were noted due to PLL molecular weight, despite observed differences in the serum adsorption characteristics for adlayers of PLL-g-PEG polymers with different PLL molecular weights. From the PCA results, multivariate peak intensity ratios were developed that correlated with the thickness of the adlayer and the enrichment of the PEG chains and the methoxy terminus of the PEG chains at the outermost surface of the adlayer. Furthermore, partial least squares regression was used to correlate the TOF-SIMS spectra with the amount of protein adsorption, resulting in a predictive model for determining the amount of protein adsorption on the basis of the TOF-SIMS spectra. The accuracy of the prediction of the amount of serum adsorption depended on the molecular weight of the PLL and PEG polymers and the PEG graft ratio. The combination of multivariate analysis and static TOF-SIMS provides detailed information on the surface chemistry and insight into the mechanism for protein resistance of the coatings.

Immobilized Antibody Orientation Analysis Using Secondary Ion Mass Spectrometry and Fluorescence Imaging of Affinity-Generated Patterns

“…ToF-SIMS has been used to characterize proteins and other biological molecules on various substrates by collecting and identifying characteristic ion fragments originating from constituent amino acids 57, 58. However, since the overall amino acid composition of most proteins is generally restricted to the natural amino acid library, with only small differences in amino acid composition often observed between proteins, similar amino acid fragments are frequently detected from different protein ensembles on surfaces 58.…”

The Influence of Anchoring-Group Structure on the Lubricating Properties of Brush-Forming Graft Copolymers in an Aqueous Medium

“…This has been assumed to be a consequence of the persistence length, since the 300 kDa backbones are more prone to loop away from the surface rather than adsorb flat, which is more likely for the 20 kD backbones [24,29]. From ToF-SIMS analysis and neutron scattering studies of PLL(300)-g-PEG, it is known that such molecules tend to adsorb only partially, looping away from the surface rather than lying flat [24,28,38]. It is very likely that PAAm(70)-g[3.5]-PEG(5) molecules also adsorb with loops or ends curling away from the surface, allowing the molecules to pack more closely and increasing the total adsorbed mass.…”

Poly(l-lysine)-grafted-poly(ethylene glycol)-based surface-chemical gradients. Preparation, characterization, and first applications

“…24, 35 The architecture of the a͒ Author to whom correspondence should be addressed; electronic mail: spencer@mat.ethz.ch graft copolymer ͑molecular weight of the PEG chains and grafting ratio͒ and the adsorbed mass determine the ethylene glycol density on the surface. 34,36,37 Serum adsorption was found to decrease below the detection limit of optical waveguide lightmode spectroscopy ͑OWLS͒ measurements for ethylene glycol densities ജ20 nm −2 . 34 Specific ͑bio͒func-tional groups can be attached at the position of the PEG side chains, e.g., biotin, 38 nitrilotriacetic acid, 39 or bioadhesive peptides such as Arg-Gly-Asp ͑RGD͒, 40,41 resulting in a surface that exposes a specific functionality in a proteinresistant background.…”