Electrochemical Quantitation of DNA Immobilized on Gold

Adam B. Steel (presenting), Tonya M. Herne, and Michael J. Tarlov

Process Measurements Division
Chemical Science and Technology Laboratory

Eletrochemical quantitation of the surface density of DNA immobilized on gold has been achieved using electrostatic trapping of cationic, electrochemically-active redox molecules. The surface density of DNA, more specifically the number of nucleotide phosphate residues, is calculated from the number of redox molecules measured at the gold surface. DNA was immobilized on gold by forming mixed monolayers of thiol-derivatized, single-stranded oligonucleotide and 6-mercapto-1-hexanol. Cationic redox molecules associate with the anionic phosphate backbone of DNA providing charge compensation. The number of redox molecules at the gold surface is measured using chronocoulometry. At saturation of the redox molecule in the DNA monolayer on gold, the number of redox molecules measured at the surface is directly proportional to the phosphate residues and thereby the surface density of DNA. This electrochemical method permits quantitative determination of both single- and double-stranded DNA with remarkable ease, in contrast to alternative quantitation methods.