Abstract
Ultraviolet light emitting diodes (UV LEDs) have become widespread in chemical research as highly efficient light sources for photochemistry and photopolymerization. However, in more complex experimental setups requiring highly concentrated light and highly spatially resolved patterning of the light, high-pressure mercury arc lamps are still widely used because they emit intense UV light from a compact arc volume that can be efficiently coupled into optical systems. Advances in the deposition and p-type doping of gallium nitride have recently permitted the manufacture of UV LEDs capable of replacing mercury arc lamps also in these applications. These UV LEDs exceed the spectral radiance of mercury lamps even at the intense I-line at 365 nm. Here we present the successful exchange of a high-pressure mercury arc lamp for a new generation UV LED as a light source in photolithographic chemistry and its use in the fabrication of high-density DNA microarrays. We show that the improved light radiance and efficiency of these LEDs offer substantial practical, economic and ecological advantages, including faster synthesis, lower hardware costs, very long lifetime, an >85-fold reduction in electricity consumption and the elimination of mercury waste and contamination.
Highlights
Light is a highly versatile energy source for triggering and controlling chemical reactions.[1]
We have constructed and evaluated such an LED source for maskless array synthesis (MAS), a chemical photolithographic application that uses an optical imaging system centered around a digital micromirror device (DMD) to direct the chemical synthesis of complex microarrays of biomolecules, such as nucleic acids and peptides, via the selective removal of photolabile protecting groups.[8−10,26−28] In this type of imaging system, the complexity of the optics and the requirements for a very small numerical aperture (NA) result in very low light throughput.[29]
ultraviolet light emitting diodes (UV LEDs) with useful outputs have been available for several years and have been used in photolithography[37,38] and photochemistry, primarily as arrays of LEDs, to expose and cure inks, adhesives, and coatings
Summary
Light is a highly versatile energy source for triggering and controlling chemical reactions.[1]. We have constructed and evaluated such an LED source for maskless array synthesis (MAS), a chemical photolithographic application that uses an optical imaging system centered around a digital micromirror device (DMD) to direct the chemical synthesis of complex microarrays of biomolecules, such as nucleic acids and peptides, via the selective removal of photolabile protecting groups.[8−10,26−28] In this type of imaging system, the complexity of the optics and the requirements for a very small numerical aperture (NA) result in very low light throughput.[29] When a 350 W ultrahighpressure Hg arc source is used, which generates ∼20 W of 365 nm photons,[30] the system transmits to the target only about ∼0.6% of the total lamp emissions of this spectral line. Data was normalized and fit with the four parameter sigmoidal function in Sigmaplot
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