Photolithographic spatially peptide synthesis

A special case of parallel synthesis is the spatially addressable synthesis pioneered by Fodor et al. [17,18] in 1991. Here, each member of the library is synthesized at a specific location on a functionalized silica wafer rather than on resin beads in separate reaction vessels. This approach, based initially upon solid-phase peptide synthesis and semiconductor photolithographic techniques by using photolabile amino protecting groups, allows the synthesis of combinatorial libraries containing about 50000 compounds localized to a 50 pm square site on a silica wafer ( library on a chip ). 

With the same number of chemical steps, the diversity and number of peptides synthesized using light-directed, spatially addressable chemical synthesis depends, among other factors, on the patterns of photolithographic masks used for each photodeprotection. Different masking strategies can be used. 

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