Surface plasmon resonance (SPR) imaging is a promising label free method that can be used in an array format for the detection of biomolecular interactions. In this work the DNA–DNA interaction was investigated. A DNA SH-oligonucleotide sequence was immobilized onto suitable photolithography patterned gold substrates and the hybridization reaction with the complementary strand was monitored by means of changes in the optical properties of the surface. The DNA probe used in this work was specific for the 35S promoter, a marker of the presence of genetically modified organisms (GMOs).