Electrochemistry of methylene blue bound to a DNA-modified electrode.
Gold surfaces have been derivatized with 15-base-pair double-stranded DNA oligonucleotides containing a pendant 5' hexanethiol linker. The electrochemistry of intercalated methylene blue has been investigated at these modified electrodes. Chronocoulometry, cyclic voltammetry, ellipsometry, and quantitation via 32P labeling are all consistent with a surface coverage of > or = 75% with the DNA helices stacked at an angle from the electrode surface. Cyclic voltammetry at low methylene blue/ duplex stoichiometries yields well-behaved surface waves with E degrees = -0.25 V (vs SCE), a value 0.03 V negative of that in aqueous solution. A binding isotherm for methylene blue at an electrode derivatized with the double-stranded sequence 5' SH-(CH2)6-p-AGTACAGTCATCGCG 3' was obtained from coulometric titrations and gave an affinity constant equal to 3.8(5) x 10(6) M-1 with a saturation value of 1.4(2) methylene blue intercalators per DNA duplex. Taken together, these experiments support a model for the surface morphology in which DNA duplexes are densely packed; methylene blue therefore reversibly binds to sites in the DNA that are close to the bulk solution. Electrochemistry at DNA-derivatized electrodes provides a valuable methodology to examine DNA-bound redox reactions and may offer new insight into DNA-mediated electron transfers.
Kelley
S O
SO
Beckman Institute, Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena 91125, USA.
Barton
J K
JK
Jackson
N M
NM
Hill
M G
MG
D004247:DNA; D004563:Electrochemistry; D004566:Electrodes; D008751:Methylene Blue / Q000378:metabolism; D010084:Oxidation-Reduction; D013816:Thermodynamics
D004247:DNA; D008751:Methylene Blue