Surfaces such as Ni(100) and Si(100) have been extensively studied and each has been found to be more complicated than simple geometric models would suggest. In this context, consider more mobile surfaces than these precisely defined crystal surfaces that are comprised of 20 amino acids integrated into hundreds of different proteins. Also, these surfaces may contain lipids and complex saccharide structures. It should be apparent that these surfaces can be staggeringly complex, and yet, as with surfaces in general, they efficiently catalyze complex reactions. But they do this at room temperature and atmospheric pressure in a way that makes life possible. For these reasons, the ability to characterize such surfaces will certainly lead to advances in surface design and surface functionality. Tools taken from the “surface science tool chest” can be applied in special ways to complement the tools developed by biologists for molecularly characterizing such surfaces. This talk, primarily focused on electron spectroscopy for chemical analysis (ESCA) and secondary ion mass spectrometry (SIMS), will start with analysis of amino acids and peptides, move to adsorbed protein films and finally consider complex surfaces such as decellularized extracellular matrices and cell monolayers.

Films of cells on solid substrates are encountered in a variety of biological and biomedical environments, including cells in biofilms that spontaneously colonize medical devices and multilayers of cells filtered from suspensions for analysis. Understanding the chemical properties of cells in such films is important for providing clues about the behavior of the cells or about the effects of treatments that had been applied to the cells. Similarly to other types of surface-based systems, the characterization of cells on solid substrates poses several analytical challenges. In particular, the small number of cells on each sample, the interference from surface interactions, and the absorbance of the substrate material prevent the characterization of cells on surfaces by the standard optical methods that are used in solution. We show that protocols similar to those used for preparing samples for electron microscopy can be adapted to prepare biofilm samples for characterization by X-ray photoelectron spectroscopy (XPS). Modern XPS instruments also provide the functionality required for characterization of these complex samples, for example, sample charging on insulating substrates can be efficiently and consistently compensated. Finally, the Ar cluster ion beam technology that recently became available on XPS instruments provides additional capabilities for a more detailed characterization of cells in biofilms, which typically have thicknesses larger than the sampling depth of XPS. We characterized several types of fixed and dried cell samples, including biofilms and cells filtered from suspensions, to compare different preparation protocols and to identify qualitative and quantitative parameters that can be reliably obtained from XPS analysis of such films of cells. We will present the results of our comparative analysis and possible applications of our methodology for characterization of cells in biological and biomedical experiments.

Bacterial biofilms are structured communities of microbes encapsulated within a self-developed polymeric matrix which adhere to surfaces and display genetic expression distinct from freely floating bacteria. Biofilms are frequently found to populate medical devices, leading to significant problems of infection in the first few days after implantation. Polyelectrolyte multilayers are developed for the delayed delivery of antibiotics to inhibit biofilm growth on biomedical devices [1]. Ten layers each of chitosan and alginate are prepared on a gold substrate, then infused with a novel antibiotic compound. This antibiotic-infused multilayer is found to inhibit the growth of Enterococcus faecalis bacterial biofilms on membranes over an 18 hour exposure. Laser desorption postionization mass spectrometry (LDPI-MS) is used to characterize the antibiotic after synthesis [2]. LDPI-MS analysis shows that the antibiotic survives sterilization of the multilayer surface, but <1% of the antibiotic remains after exposure to the biofilm.

[1] M. Blaze M.T., L.K. Takahashi, J. Zhou, M. Ahmed, G.L. Gasper, F.D. Pleticha, and L. Hanley, Anal. Chem. 83(2011) 4962.

[2] A. Akhmetov, J.F. Moore, G.L. Gasper, P.J. Koin, L. Hanley, J. Mass Spectrom. 45 (2010) 137.

The interaction between an ethylene oxide-block-butylene oxide (EOBO) copolymer surfactant and the surfaces of four silicone hydrogel (SH) contact lenses—PureVision® (PV), O₂OPTIX® (O₂), ACUVUE® Oasys ® (AO), and Biofinity® (BF)—was investigated using angle-resolved X-ray photoelectron spectroscopy (AR-XPS) following treatment in test solutions containing various concentrations of EOBO. The nature of this interaction was further understood by quantifying the amount of eluted EOBO from each lens following the same treatment using ultra performance liquid chromatography (UPLC). The elution study revealed a large disparity in the amount of EOBO uptake by the different samples following each solution treatment. The XPS results, however, suggested that the amount of EOBO retained on the surface of the lenses demonstrated a largely different trend. For example, AO and BF displayed little evidence of signal at binding energies characteristic of the EO blocks, whereas O₂ and PV exhibited a clear EO signature. The correlation between the elution and XPS results highlights the difference in the interaction mechanism of the EOBO copolymer with different lenses. For lenses such as O₂OPTIX®, this interaction is predominantly bound to the surface; for ACUVUE® OASYS®, however, EOBO was uniformly distributed through the lens structure.

Microfluidic devices promise to have a significant impact on human health, particularly in diagnostics and drug development. We have developed a suite of microfluidic devices for high-throughput protein biochemistry and applied them to a wide range of applications spanning from protein biophysics to diagnostics, drug development, and vaccine development. Here I will discuss a novel approach to obtaining hundreds of kinetic rate measurements of bimolecular interactions on a single microfluidic device. In a second example I will present a generic microfluidic platform capable of quantitating biomarkers from a wide variety of samples in high-throughput and ultra-low cost, which could ultimately supersede the classical ELISA assay. We applied this platform to vaccine development by quantitating the activation of dendritic cells in response to a large panel of binary adjuvant combinations.