The decomposition of DNA oligonucleotides with the sequences G(6)T(3)G(6) and G(6)(BrU)(3)G(6) (BrU = 5-bromouracil) by electrons with energy lower than the electronic excitation energy was studied by a fluorescence method. The single stranded oligonucleotides were immobilized on a gold surface in a microarray format. After the electron irradiation they were hybridized with the complementary C(6)A(3)C(6) strand marked with a dye. The fluorescence signal in positive and negative tests showed clearly the decomposition of the BrU and T oligonucleotides by low energy electrons. (C) 2004 Published by Elsevier B.V.