Surface coating, protein biochips

Another important application field comprises biochips, such as DNA or protein chips. A DNA chip (Fig. 9) is a collection of microscopic DNA spots arrayed on a solid surface by covalent attachment to a chemical matrix, which utilize the selective nature of DNA-DNA or DNA-RNA hybridization and fluorophore-based detection for expression profiling, i.e. monitoring expression levels of thousands of genes simultaneously. Plasma polymerization techniques have been applied to achieve larger densities of the DNA probes attached, e.g. HMDS or allylamine coatings. ... 

SELDI-TOF is a proteomic technology that aims at the quantitative analysis of protein mixtures. This technique relies on the use of trapping surfaces that allow differential capture of proteins based on intrinsic properties of the proteins themselves to identify proteins from crude samples without the need for an initial separation step. A small amount of sample can be directly applied to a biochip coated with specific chemical matrices (hydrophobic, cationic, or anionic) or specific biochemical materials, including DNA fragments or purified proteins. Bound proteins can then be analyzed by MS to obtain either the protein fingerprints or the amino acid sequence when interfaced with a tandem MS. 

Similar to biochip technology a poly-L-lysine monolayer can be bound via adsorption onto a gold cluster coated with a self-assembled monolayer of a carboxylated thiol e.g. mercapto-succinic acid. Using a biotinylated lysine-polymer proteins are immobilized via avidin conjugation. The poly-L-Iysine monolayer including all the proteins can be rinsed from the surface with a low or high pH buffer. 

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