Abstract
Fabrication of high density oligonucleotide arrays using metal on glass photolithographic masks is inflexible and expensive. Maskless methods using computer-controlled projection have been proposed and implemented, but associated stray light effects on photodirected oligonucleotide synthesis and their analysis have not been reported. We have developed a theoretical approach: it predicts that the stray light content of the output of digital micromirror devices and other spatial light modulators of similar performance (contrast ratio approximately 400) will cause extensive random base insertions. For example, use of a digital micromirror device for synthesis of a 20mer array will result in the majority of oligonucleotide chains being 21mers or 22mers. This chain lengthening effect of stray light would not be preventable when synthesis involves a directly photosensitive 5'-blocking group. If the 5'-blocking group is acid labile and released with photogenerated acid, the presence of low concentrations of weak base will prevent the effect of stray light. We have demonstrated experimentally the anticipated chain lengthening effect of stray light on photoacid-dependent synthesis of oligonucleotides and prevention of the effect by low concentrations of n-octylamine. The application of these findings should facilitate the development of maskless fabrication and availability of high density and high fidelity user-designed arrays for research applications.