Paper BI-ThP10
Electrochemical Behavior of Electroactive Species in Nucleic Acid Monolayers of Different Chain Length

Thursday, October 18, 2007, 5:30 pm, Room 4C

Monolayers of immobilized nucleic acids (DNA) are promising experimental models for investigating fundamental properties of charged polymers at solid-liquid interfaces. We have investigated the charging behavior of single-stranded DNA polyelectrolyte brushes. In this study, voltammetric behavior of hexaamineruthenium(III) chloride (RuHex) in end-tethered single-stranded DNA monolayers of different strand lengths is investigated. The surface coverage of non-labeled DNA chains was determined independently with X-ray photoelectron spectroscopy (XPS). Our results show that, for DNA chains varying from 5 to 100 thymine nucleotides, the reduction potential of RuHex³⁺ counterions associated with the DNA monolayer is predominantly a function of chain surface coverage and is rather insensitive to the chain length. However, the total charge passed to reduce the counterions to the 2+ oxidation state is predominantly a function of the total nucleotide number, given by the product of chain surface coverage and chain degree of polymerization. A model is proposed to explain the observed behavior. The dynamic evolution of the reduction peak area and potential are also investigated, providing a picture of the time dependence of the adsorption of RuHex³⁺ into the monolayers. The research provides a method to estimate the chain coverage of non-labeled, end-tethered DNA chains with various chain lengths.