Electrochemical Quantitation of DNA Immobilized on Gold

TLDR

The method enables quantitative determination of both single‑ and double‑stranded DNA at gold electrodes. DNA surface density is measured by chronocoulometry of a cationic redox marker proportional to phosphate residues, after immobilizing oligonucleotides in mixed thiol‑derivatized monolayers with 6‑mercapto‑1‑hexanol. The electrochemical technique accurately quantifies DNA surface density on gold, allows precise tuning of single‑stranded DNA densities from 1–10×10¹² molecules cm⁻², and shows that hybridization efficiency peaks at an optimal density.

Abstract

We have developed an electrochemical method to quantify the surface density of DNA immobilized on gold. The surface density of DNA, more specifically the number of nucleotide phosphate residues, is calculated from the amount of cationic redox marker measured at the electrode surface. DNA was immobilized on gold by forming mixed monolayers of thiol-derivitized, single-stranded oligonucleotide and 6-mercapto-1-hexanol. The saturated amount of charge-compensating redox marker in the DNA monolayer, determined using chronocoulometry, is directly proportional to the number of phosphate residues and thereby the surface density of DNA. This method permits quantitative determination of both single- and double-stranded DNA at electrodes. Surface densities of single-stranded DNA were precisely varied in the range of (1−10) × 1012 molecules/cm2, as determined by the electrochemical method, using mixed monolayers. We measured the hybridization efficiency of immobilized single-stranded DNA to complementary strands as a function of the immobilized DNA surface density and found that it exhibits a maximum with increasing surface density.