Photoconductivity of DNA-Porphyrin Complexes*

DNA has attracted attention for potential use in nanocircuitry largely due to its pattern-recognition and self-assembly characteristics, but low electrical conductivity limits its potential usefulness for these applications. We attempt to address these issues by modifying DNA with meso-tetrakis(N-methyl-4-pyridiniumyl)porphyrin (TMPyP) intercalated between the base pairs. By measuring the electrical characteristics of these DNA-porphyring complexes deposited on a SiO2 under nitrogen gas, we show that this alteration increases the DNA strand conductivity and leads to significant photoconductive behavior at 445 nm, a wavelength strongly absorbed by the TMPyP-DNA complex. We also find a strong dependence on humidity, as photoconductive effects were only observed above 30% relative humidity, and increased both with the humidity in the chamber and with the length of exposure to the humid environment. A significant hysteresis is also observed, as the increased conductivity observed at higher humidity persists even after the humidity is lowered.