Enhancement of Surface Plasmon Resonance Signals by Gold Nanoparticles on High-Density DNA Microarrays

We have developed a new methodology to fabricate high-resolution DNA microarrays (2500 dots/cm 2 ) in combination with microcontact printing (μCP) and surface plasmon resonance (SPR) imaging. A novel COOH-terminated PEG-disulfide with para -carborane ( p -carborane) was synthesized as an initiator chemically bound to a gold substrate for surface coupling reactions with NH 2 -terminated DNA. The hybridization between target DNA immobilized on gold nanoparticles and probe DNA arrayed on flat gold substrates was successfully demonstrated by SPR imaging, where nonspecific adsorption was not observed at the array background. The gold nanoparticles on the array give quite high contrast even at low surface coverage with gold nanoparticles (∼10%) by the enhancement effect of optical signals based on nanoscale phenomena. This enhancement effect can be well described by the simulation based on the Maxwell-Garnett theory for the effective dielectric constants and Fresnel's equation.