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Biomedical applications, including functional biomaterials, carbohydrate-arrays, and glycan-based biosensors.
The chemistry of glycan immobilization plays an essential role in the bioavailability and function of surface bound carbohydrate moieties. For biomedical applications the stability over time (shelf life) of glycan arrays is a crucial factor. Herein we report on approaches for surface and interface characterization relevant to the needs of production of glycan microarrays which were tested using model carbohydrate surfaces. For detailed characterization of glycan model surfaces we used a combination of X-ray photoelectron spectroscopy (XPS), near edge X-ray absorption fine structure spectroscopy (NEXAFS) and ToF SIMS which are complementary techniques of surface chemical analysis. Links to fluorescence spectroscopy often used for characterization in the microarray community were established as well. In detail, amine-reactive silicon oxide and glass surfaces were used for anchoring oligosaccharides with an amino linker. The amount of surface bound carbohydrates was estimated by X-ray photoelectron spectroscopy (XPS). Glycan immobilization was investigated using lectins, which are glycan-binding molecules. A shelf life study of model glycan microarrays on epoxy-coated glass surfaces was done over a period of 160 days under different storage conditions utilizing fluorescence, ToF-SIMS and XPS analysis. It was shown that glycan activity of the models used can be maintained at least for half a year of storage at 4 °C.
In this study, epoxy-terminated silicon oxide surfaces were chemically derivatized with trifluoroacetic anhydride (TFAA) and 4-(trifluoromethyl)-benzylamine (TFMBA) and analyzed by X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy and water contact angle measurements. TFAA was used for quantitative derivatization to determine the amount of reactive epoxy groups on these surfaces. Furthermore, epoxy-terminated surfaces were derivatized with TFMBA (a model compound for biomolecules with an amino linker) yielding secondary amines because of formation of covalent C–N bonds between TFMBA and the epoxy films. Fluorine being part of TFAA and TFMBA composition was used to follow the progress of the chemical derivatization reaction. Both derivatization agents – TFAA and TFMBA – gave comparable reaction yields of ~60% on epoxy silicon surfaces, whereas on epoxy glass slides, the derivatization yields were considerably lower (30–40%).The protocol for attachment of TFMBA (model compound) on epoxy-modified surfaces was adapted to (bio)molecules with an amino linker, e.g. carbohydrates to prepare carbohydrate-functionalized biointerfaces.
Methods for characterization of epoxy-functionalized substrates used for microarray applications, prepared by silanization with 3-glycidoxypropyltrimethoxysilane, have been developed. Contact angle measurements, X-ray photoelectron spectroscopy, time of flight secondary ion mass spectrometry and fluorescence based methods have been applied to investigate these epoxy-functionalized microarray substrates. The surface density of epoxy-functionalized glass slides was investigated by fluorescence labeling of surface species utilizing Rhodamine 110 as fluorescence probe.