Functional conducting polymers for DNA sensing

Conducting polymers (CPs) are polyconjugated polymers with electronic properties similar to metals, but retain the properties of conventional organic polymers. Compared to saturated polymers, CPs have different electronic structures which result in the unique properties, such as electrical conductivity, low ionization potentials and high electron affinity. For CPs in ground state (insulating or semiconducting state), Π-bonds (Π- Π*) are partially localized that are a consequence of a phenomena called the Peierls distortion. During the doping process, the excitation across the Π- Π* band gap creates self-localised excitations of conjugated polymers with localized electronic states in the gap region. Such electronic structure of CPs is highly susceptible to changes in the polymeric chain environment and other perturbations of chain conformation caused by a biological recognition event, such as DNA hybridization. The changes in delocalized electronic structure or other CPs properties are manifested in altered electrical and optical properties of the CPs, and, when measured, can provide a signal for the presence of the corresponding target molecule. These advantages of CPs make them a good material for chemical sensors and biosensors. In this chapter, we provide an overview of functional CPs for DNA sensing. In the Introduction section, we briefly introduce the history of CPs and the advantages of functional CPs as sensing element for DNA detection. In the section of Electronic Structure and Synthesis of CPs, some fundamental physical principles needed to understand the properties of CPs and the methods to prepare functional CPs are addressed. In the section of Functional CPs for DNA Sensing Based on Electrochemical Methods, we discuss the DNA probe immobilization methods and transduction mechanism including amperometry, conductometry, impedimetry and photocurrent spectroscopy, and then summarize the functional CPs reported in the literatures for DNA sensing. In the section of Functional CPs for DNA Sensing Based on Optical Methods, the detection of DNA by using cationic CPs in the solution and on solid substrate is presented. The probable future trends are presented in the last section of Summary and Future Outlook.