Chain Dynamics Limit Electron Transfer from Electrode-Bound, Single-Stranded Oligonucleotides

A wide range of new devices aimed at in vivo molecular detection and point-of-care diagnostics rely on binding-induced changes in electron-transfer kinetics from an electrode-attached, redox-reporter-modified oligonucleotide as their signaling mechanism. In an effort to better characterize the mechanisms underlying these sensors, we have measured the electron-transfer kinetics associated with surface-attached, single-stranded DNAs modified with a methylene blue redox reporter either at the chain’s distal end or at an internal chain position. We find that although the rate of electron transfer from a reporter placed either terminally or internally is independent of chain length for chains shorter than the length scale of methylene blue (and its linker), for longer chains it follows a power-law dependence on length of exponent approximately −2.2. Such behavior is consistent with a diffusion-controlled mechanism in which the diffusion of the DNA-bound reporter to the surface controls the rate of electron tra...