Hitoshi Tabata

Dye-DNA complex film was prepared by modifying DNA with acridine orange (AO) and depositing it on goldelectrodes having a gap in the order of micrometers. Measurement of the electrical characteristics of the dye-DNA film was performed in a vacuum and in various humidities. A photoinduced conductivity change, which we suggest is caused by band or hopping conduction, was observed at relatively low humidity (20%) and in a vacuum. As the humidity rises to 70% and above, the current jumps from picoampere to milliampere levels. This dramatic resistance change corresponds to a dominant conductor mechanism change from hopping or band conductivity to ion conductivity. These reproducible characteristics of photoinduced and humidity-dependent conductivity suggest that the AO-DNA setup could be used as a photosensitive semiconducting device and as a humidity sensor chip.

DNA molecules [poly(dG-dC).poly(dG-dC)] were modified with acridine orange (AO). Direct measurement of the electrical characteristics of the AO-DNA network were performed using a conducting atomic-force microscope (AFM) with a gold coated tip, a second gold electrode being electrically contacted to the dye-DNA/mica surface. Enhancement of electrical conductivity was observed while irradiating the sample with visible light. The results indicated that excited AO obtains an electron from the G site and eventually a hole is generated.