A color-corrected, high-contrast catadioptric relay for high-resolution biological photolithography

Large-scale synthesis of DNA and RNA is a crucial technology for modern biological research ranging from genomics to nucleic acid therapeutics and for technological research ranging from nanofabrication of materials to molecular-level writing of digital data. Maskless Array Synthesis (MAS) is a versatile and efficient approach for creating the required complex microarrays and libraries of DNA and other nucleic acids for these applications and, more generally, for the synthesis of sequence-defined engineered and biological oligomers. MAS uses digital photomasks displayed by a digital micromirror device (DMD) illuminated by an appropriate light source and imaged into a photochemical reaction chamber with an optical relay system. Previously, Offner relay systems were used for imaging, but modern DMD formats with more and smaller micromirrors favor a different solution. We present a desktop MAS optical system with the larger numerical aperture and larger field of view required by 1080p and other large-format DMDs. The resulting catadioptric relay is well suited to modern DMDs in this application, and is corrected for first order axial and lateral color, enabling the use of high-power LEDs as inexpensive and long-lasting light sources spanning the ultraviolet-to-violet to perform the required photochemistry. Additional characteristics of the system, including high contrast and low scatter, make it ideal for reducing the error rates in photochemical synthesis of biomolecules.