Photoemission study of poly(dA)-poly(dT) DNA : Experimental and   theoretical approach to the electronic density of states
  We present results of an ultraviolet photoemission spectroscopy study of artificially synthesized poly(dA)-poly(dT) DNA molecules on $p$-type Si substrates. For comparison, we also present the electronic density of states (DOS) calculated using an \emph{ab initio} tight-binding method based on density-functional theory (DFT). Good agreement was obtained between experiment and theory. The spectra of DNA networks on the Si substrate showed that the Fermi level of the substrate is located in the middle of the band gap of DNA. The spectra of thick ($\sim 70$ nm) DNA films showed a downward shift of $\sim 2$ eV compared to the network samples. 
Hiroki Wadati, Kozo Okazaki, Yasuhiro Niimi, Atsushi Fujimori, Hitoshi   Tabata, Jared Pikus, James P. Lewis