Invited Paper BI+VT-MoA1
Self-Assembled Monolayers of Carboxy-Terminated Poly(ethylene glycol): Protein Resistance, Biospecific Functionalization and Application to Immunodiagnostics
The high specifity of antigen/antibody reactions has been widely exploited to develop accurate detection methods for biomolecules. Heterogeneous immunoassays, where proteins are selectively bound by immobilized antibodies and detected by the use of labeled secondary antibodies are a standard diagnostic technique. Also, a considerable amount of research has been focused on immunosensor development. A general problem in immunodiagnostics is non-specific protein adsorption: Macromolecules are not only bound to the substrate by specific antigen/antibody recognition, but also adhere due to non-specific interaction forces. Hereby, the accurate determination of antigen concentration may be significantly deteriorated. Moreover, non-specifically adsorbed proteins may even block and deactivate the immobilized receptors. The integration of specific receptors into a protein resistant matrix would, therefore, significantly improve quantitative analysis. Self-assembled monolayers (SAMs) of poly- and oligo(ethylene glycol) have proven to effectively prevent protein adsorption. We, therefore, synthesized a carboxy-terminated poly(ethylene glycol) alkanethiol (HOOC-CH@sub 2@-(OCH@sub 2@-CH@sub 2@)@sub n@-O-(CH@sub 2@)@sub 11@-SH, n = 22-45) which facilitates covalent coupling of antibodies. In contrast to most other previous studies, where receptors have been coupled to SAMs formed from a binary mixture of differently functionalized molecules, only a single chemical functionality is involved. After characterizing the films by infrared absorption (FTIR) and X-ray photoelectron spectroscopy, ellipsometry and contact angle measurements, their performance as bioselective coatings with reduced non-specific adsorption has been tested in both FTIR and acoustic wave sensor experiments. The protein resistant properties of the films are put in context with previous results on oligo(ethylene glycol) alkanethiolate SAMs including neutron reflectivity studies on protein/surface interactions.