The use of self-assembled monolayers (SAMs) in various fields of research is rapidly growing. In particular, many biomedical fields apply SAMs as an interface-layer between a metal surface and a solution or vapour. This review summarises methods for the formation of SAMs upon the most commonly used materials and techniques used for monolayer characterisation. Emphasis will lie on uniform, mixed and functionalised monolayers applied for immobilisation of biological components including (oligo-)nucleotides, proteins, antibodies and receptors as well as polymers. The application of SAMs in today's research, together with some applications will be discussed.
A recently developed liposome sandwich immunoassay for interferon-gamma (IFN-gamma), to be applied in microtiter plates, is tailored for surface plasmon resonance (SPR) spectrometry. The assay is performed on a thin (approximately 20 nm) polystyrene layer that covers a gold surface. This way, analytical data obtained from microtiter plate technology can directly be extrapolated toward SPR. For assaying the antigen IFN-gamma, a 16-kDa cytokine, a capture monoclonal antibody is physically adsorbed onto the polystyrene surface. After addition of the sample containing IFN-gamma, a biotinylated detecting antibody is added. Avidin is used as a bridging molecule between the biotinylated antibody and the biotinylated liposomes. All solutions are prepared with PBS buffer (10 mM, pH 7.4). This avoids additional changes in index of refraction caused by the use of various buffer solutions in immunoassays on microtiter plates for coating, binding, and washing procedures. It is shown that, when liposomes are used, a substantial enhancement of the detection limit is achieved. The "liposome" strategy improves the sensitivity for the IFN-gamma assay approximately 4 x 10(4) times and the detection limit to low picomolar. The method is generally applicable to other sandwich immunoassays.
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