Interactions of THz vibrational modes with charge carriers in DNA: Polaron-phonon interactions

This paper presents models and experimental measurements that shed light on THz-phonon mediated transport of polarons in biomolecules. Polaron transport in DNA has been considered recently in view of the expected derealization of charge carriers on a one-dimensional wire as well as the highly charged nature of DNA.^1,2 An understanding of the electrical transport properties and THz-phonon interactions of biomolecules is important in view of DNA's potential applications both as electrically conductive wires and as structures that facilitate the chemically-directed assembly of massively integrated ensembles of nanoscale semiconducting elements into terascale integrated networks. Moreover, understanding these interactions provides information of the THz spectrum of vibrational modes in DNA. A primary focus of this paper is on charge transport in biomolecules using indirect-bandgap colloidal nanocrystals linked with biomolecules.³ Through a combination of theoretical and experimental approaches,^4-7 this paper focuses on understanding the electrical properties and THz-frequency interactions of DNA. Moreover, this paper presents observed charge transport phenomena in DNA and discusses how these measurements are related to carrier scattering from the THz vibrational modes in DNA. Indeed, carrier transport in DNA is analyzed in light of theoretical calculations of the effects of THz-frequency phonon emission by propagating carriers, THz-frequency phonon absorption by propagating and trapped carriers, and effective mass calculations for specific sequences of the DNA bases.^1-7 These studies focus on THz-phononmediated processes since an extra carrier on a one-dimensional chain minimizes its energy by forming an extended polaron, and since many biomolecules, including DNA, exhibit THz vibrational spectra.⁸ Accordingly, these calculations focus on THz-phonon-mediated processes. These results are discussed in terms of the role of THz-phonon-mediated charge trapping and detrapping effects near guanine-rich regions of the DNA as well as on the understanding and identification of DNA with specific base sequences that promote charge transport. As in previous studies, optical excitation is used to inject carriers into DNA wires. Moreover, this paper reports on the use of gel electrophoresis to study chargeinduced cleavage of DNA and the related transport of charge in DNA. Phonon absorption and emission from polarons in DNA,⁹ is analyzed using parameters from the well-known Su-Schrieffer-Heeger Hamiltonian.