Triplet‐Sensitized Photodeprotection of Oligonucleotides in Solution and on Microarray Chips

Conditions and kinetics of triplet sensitization as a method for increasing the light sensitivity of photolabile protecting groups used for the photolithographic synthesis of oligonucleotide microarrays were quantitatively studied with the photolabile 2‐(2‐nitrophenyl)propyl protecting group in homogeneous solutions and on glass substrates by using laser flash photolysis, continuous illumination with HPLC analysis, fluorescence dye labelling, and hybridization. In terms of efficiency and avoidance of chemical side reactions, 9H‐thioxanthen‐9‐one was the most‐suitable sensitizer. Both in solution and on a glass substrate, the photostationary kinetics were quantitatively modelled and the relevant kinetic parameters determined. While the sensitization kinetics was diffusion‐controlled both in solution and on the chip, the photostationary kinetics was essentially of zero order only on the chip because here the triplet‐quenching effect of the released photoproduct 2‐(2‐nitrophenyl)propene was suppressed as a consequence of the inhomogeneous reaction that took place in a narrow diffusion zone above the surface from where the photoproducts could quickly escape. The kinetic simulation allowed quantitative estimate of the density of reactive groups on the surface. It was further demonstrated that, with 9H‐thioxanthen‐9‐one as a sensitizer, high‐density oligonucleotide microarrays of high quality can be produced with one‐third of the normal exposure time.