Maskless fabrication of light-directed oligonucleotide microarrays using adigital micromirror array

Oligonucleotide microarrays, also called "DNA chips," are currently made by a light-directed chemistry that requires a large number of photolithograph ic masks for each chip. Here we describe a maskless array synthesizer (MAS) that replaces the chrome masks with virtual masks generated on a computer, which are relayed to a digital micromirror array. A 1:1 reflective imaging system forms an ultraviolet image of the virtual mask on the active surfac e of the glass substrate, which is mounted in a flow cell reaction chamber connected to a DNA synthesizer. Programmed chemical coupling cycles follow light exposure, and these steps are repeated with different virtual masks t o grow desired oligonucleotides in a selected pattern. This instrument has been used to synthesize oligonucleotide microarrays containing more than 76 ,000 features measuring 16 mu m(2). The oligonucleotides were synthesized a t high repetitive yield and, after hybridization, could readily discriminat e single-base pair mismatches. The MAS is adaptable to the fabrication of D NA chips containing probes for thousands of genes, as well as any other sol id-phase combinatorial chemistry to be performed in high-density microarray s.