In this "maskless" approach, the chrome photomasks were replaced with virtual masks generated by a computer and displayed on the DMD in the form of patterns of ON and OFF mirrors. Ultraviolet light is imaged onto the DMD, and reflections from the ON mirrors are further imaged onto a glass substrate mounted in a flow cell connected to a standard solid phase synthesizer, as shown schematically in Figure . Each light exposure is then followed by a coupling reaction that results in a sequence-defined synthesis of oligonucleotides, with one sequence per mirror as illustrated in Figure . This approach, termed Maskless Array Synthesis (MAS) was implemented as a lowmaintenance tabletop device with almost no moving parts and which is suitable for routine laboratory use .