Electrostatic denaturation of double-stranded DNA (dsDNA), i.e. electrochemical melting, can be used to interrogate duplex stability, allowing discrimination of dsDNA based on the presence of mismatches, deletions, and other mutations (1). More recently, electrochemical melting has allowed examination of DNA-small molecule interactions, e.g. DNA-cisplatin adducts (2). Denaturation of dsDNA in self-assembled monolayers (SAMs) occurs when a sufficiently negative potential is applied to the DNA-modified working electrode, presumably due to strong electrostatic repulsion of the phosphate background in the presence of the high electric field in the electrical double-layer (109 V/m). In our work, we use a purely electrochemical approach for monitoring the electric field-induced melting of dsDNA SAMs. Application of moderate negative potentials (-500 mV vs. Ag/AgCl) is sufficient to melt DNA without substantial thiol reduction (1). Here we present the dependence of electrochemical melting on the temperature of the buffer and the frequency of applied potential in an effort to better understand the complex interplay of DNA stability, backbone charge screening, and double-layer structure. Previous studies have shown that electrochemical melting depends on temperature in the range 10 – 18 °C while no effect of temperature was found above this 18 °C (3). Here, we explore the temperature dependence in more detail to better understand how temperature effects the electric field effects. In particular, we examine the kinetics of the melting process at different temperatures. Additionally, the formation of the high electric fields necessary for melting depends on the screening of electrode charge by counterions from solution. Rant et al. reported that the responsiveness of the immobilized DNA is directly related to the formation of the electrical double-layer (4). By applying fast potentials pulses to melt the DNA, we determine the frequency at which the rate of melting drastically decreases due to insufficient time for the strong field to develop. Together, the temperature and frequency dependence of electrochemical melting shines new light on the role of electrical fields on DNA stability.
References
1. S. Mahajan, J. Richardson, T. Brown and P. N. Bartlett, Journal of the American Chemical Society, 130, 15589 (2008).
2. E. Madrigal, G. Raghu, J. Taylor and R. M. West, Cross-linking of DNA Monolayers by Cisplatin Examined Using Electrochemical Melting Analysis, The Journal of Electroanalytical Chemistry, Submitted (2019).
3. E. Papadopoulou, M. Meneghello, P. Marafini, R. P. Johnson, T. Brown and P. N. Bartlett, Bioelectrochemistry, 106, 353 (2015).
4. C. Sendner, Y. W. Kim, U. Rant, K. Arinaga, M. Tornow and R. Netz, physica status solidi (a), 203, 3476 (2006).
