In this article we investigated the effect of surface pretreatment procedures on electron transfer of methylene blue (MB) covalently labeled double-stranded DNA (ds-DNA)/mercaptohexanol (MCH) mixed self-assembled monolayers (SAMs) on gold by cyclic voltammetry (CV) and chronocoulometry (CC). The pretreatment procedures included M+E, M + C (piranha), M + C (dilute aqua regia), M + C + E (piranha), M + C + E (dilute aqua regia) and RM + C + E (piranha). The M was mechanical polishing, C was

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... a or dilute aqua regia dipping, E was electrochemical polishing and RM was roughly mechanical polishing. Results indicated electron transfer reaction of MB was mainly adsorption controlled. The electron transfer rate (k s ) values of MB labeled ds-DNA/MCH mixed SAMs on gold pretreated by M+C(piranha) and M+C(dilute aqua regia) were 0.84 ± 0.15 and 0.82 ± 0.17 s −1 , smaller than those (2.76 ± 0.28, 4.76 ± 2.68, 3.89 ± 2.06, 2.26 ~ 7.79 s −1 ) by M+E, M+C+E(piranha), M+C+E(dilute aqua regia) and RM+C+E(piranha) respectively. Thus, electrochemical polishing was an important pretreatment step, which might influence the k s of MB. Furthermore, the k s values of MB did not change monotonically with increasing gold surface roughness R f , indicating that R f was not the key factor to make the difference of k s . We considered that the difference of elemental composition on gold surface possibly led to different k s of MB. These conclusions provided the important reference for electrochemically studying DNA electron transfer mechanism.