Aldehyde microarray surfaces

Seong (2002) compared silylated (aldehyde) and silanated (amine and epoxy) compounds from several commercial sources to the performance of an antigen (IgG) microarray. In addition, the efficiency of phosphate-buffered saline (PBS) (pH 7.4) and carbonate (pH 9.6) printing buffers were compared. While the various slides and surface chemistries showed differences in their binding isotherms, they ultimately reached similar levels of saturation. Silylated (aldehyde) slides showed comparable loading in both buffer systems. Apparently, tethering of antibody to the surface by Schiff s base formation of the surface aldehyde and lysine residues on the protein was applicable over a broad pH. However, carbonate buffer increased binding of proteins on silanated surfaces. 

Most immobilizahon chemistries for microarrays currently rely upon derivatization of the substrate with amine-reactive functional groups such as aldehydes, epoxides, or NHS esters. While we can choose from many available surface-reactive chemistries, it is important to keep in mind that they must be compatible with a printing process. Ideally, the biomolecule should react completely and rapidly with the substrate in order to achieve good spot formation. It is also critical that the probe remain or be recoverable in its active state following printing. If too reactive a chemistry is employed there is the possibility for excessive crosslinking that can hinder performance by reducing the number of rotatable bonds in the probe. 

Slides specifically selected for microarray applications should be used. They are available as ultracleaned (an important consideration) and untreated for those who wish to prepare their own surfaces or they can be purchased with a variety of precoated surface chemistries (e.g., lysine, aldehyde, or epoxide). The densities of reactive groups and surface coating uniformity are difficult to control. Thus, if lot-to-lot slide consistency is most important factor, consider using commercially available slides that are quality controlled. 

In protein microarrays, capture molecules need to be immobilized in a functional state on a solid support. In principle, the format of the assay system does not limit the choice of appropriate surface chemistry. The same immobilization procedure can be applied for both planar and bead-based systems. Proteins can be immobilized on various surfaces (Fig. 1) (12). Two-dimensional polystyrene, polylysine, aminosilane, or aldehyde, epoxy- or thiol group-coated surfaces can be used to immobilize proteins via noncovalent or covalent attachment (13,14). Three-dimensional supports like nitrocellulose or hydrogel-coated surfaces enable the immobilization of the proteins in a network structure. Larger quantities of proteins can be immobilized and kept in a functional state. Affinity binding reagents such as protein A, G, and L can be used to immobilize antibodies (15), streptavidin is used for biotinylated proteins (16), chelate for His-tagged proteins (17, 18), anti-GST antibodies for GST fusion proteins (19), and oligonucleotides for cDNA or mRNA-protein hybrids (20). 

Shdes for microarrays have become commercially available with a variety of fimctionalized surfaces for oligonucleotide, protein, and small molecule immobihzation. Aminopropylsilane with different surface properties are available from Asper, Corning, and Schott amine-reacting NHS shdes are available from GE Healthcare and Schott epoxide-functionalized sUdes are available from Corning and Schott aldehyde-fimctionalized smface for im-... 

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