DNA Electrochemistry with Tethered Methylene Blue
Methylene blue (MB′), covalently attached to DNA through a flexible C_12 alkyl linker, provides a sensitive redox reporter in DNA electrochemistry measurements. Tethered, intercalated MB′ is reduced through DNA-mediated charge transport; the incorporation of a single base mismatch at position 3, 10, or 14 of a 17-mer causes an attenuation of the signal to 62 ± 3% of the well-matched DNA, irrespective of position in the duplex. The redox signal intensity for MB′–DNA is found to be least 3-fold larger than that of Nile blue (NB)–DNA, indicating that MB′ is even more strongly coupled to the π-stack. The signal attenuation due to an intervening mismatch does, however, depend on DNA film density and the backfilling agent used to passivate the surface. These results highlight two mechanisms for reduction of MB′ on the DNA-modified electrode: reduction mediated by the DNA base pair stack and direct surface reduction of MB′ at the electrode. These two mechanisms are distinguished by their rates of electron transfer that differ by 20-fold. The extent of direct reduction at the surface can be controlled by assembly and buffer conditions.
© 2012 American Chemical Society. Published In Issue May 01, 2012; Article ASAP April 18, 2012; Received: February 07, 2012; Revised: April 03, 2012. This research was supported by the National Institute of Health (GM61077). The authors thank N. Muren for discussions and her contributions in fabricating the multiplexed chips. This work was completed in part in the Caltech Micro Nano Fabrication Laboratory.
Accepted Version - nihms385190.pdf