Comparative Study on Electron Transfer of Methylene Blue Modified Stem-Loop and Linear DNA Self-Assembled Monolayers on Gold Electrodes

Understanding the electron transfer performance of DNA self-assembled monolayers (SAMs) on a transducer substrate was important for constructing DNA electrochemical sensors with high sensitivity. Here we immersed the gold electrodes in mixed solutions comprising thiol-modified stem-loop DNA (SL-DNA) or linear DNA (L-DNA) terminally bound with methylene blue (MB), and aliphatic thiols (HOC 6 SH, C 6 SH, HOOCC 5 SH, H 2 NC 6 SH, HOC 11 SH, C 12 SH, or HOOCC 10 SH) to obtain DNA/thiols mixed self-assembled monolayers (SAMs). MB electron transfer performances through SL-DNA/thiols and L-DNA/thiols mixed SAMs were investigated by cyclic voltammetry (CV). Our results showed that the mixed assembly of thiols with DNA was conducive to MB electron transfer. The electron transfer rate ( k s ) values of MB through L-DNA SAMs were bigger than those through SL-DNA SAMs, indicating that the flexibility of DNA chains was important to MB electron transfer. Thiols chain length or terminal groups influenced k s of MB significantly, that increasing NaCl or MgCl 2 concentrations in solution around DNA availed MB electron transfer, and Mg 2+ advanced MB electron transfer more than Na + , and that the stability of L-DNA/thiols SAMs was much better than SL-DNA/thiols SAMs. These conclusions might provide a reference for studying DNA electron transfer mechanisms or designing DNA or RNA electrochemical sensors with optimal performance.