Figure 1

Phosphoramidite synthesis cycle in maskless, light-directed synthesis of microarrays. The cycle is similar to that used in solid-phase synthesis of nucleic acids with some key differences: UV light from the I-line of mercury, in the presence of an organic base, is used to deprotect the 5'-OH; the array surface is dried with helium before photodeprotection; oxidation of the phosphites is not required in the cycle because they are not exposed to acid; the final chemical deprotection must not cleave the nucleic acids from the surface. The duration of each step in the synthesis cycle depends on experimental conditions and objectives, but typical values are given.