Exploration of the specific structural characteristics of thiol-modified single-stranded DNA self-assembled monolayers on gold by a simple model

This paper proposed a simple hexagonal model to explore the specific structural characteristics of thiol-modified single-stranded DNA (ss-DNA) self-assembled monolayers (SAMs) on gold substrate. The calibrated gyration diameter d′gd′g (d′g=rdgd′g=rdg) was used to quantify the size of ss-DNA molecules on gold by introducing a calibrating factor r, where dg was ss-DNA gyration diameter in solution. Based on the model, the interfacial parameters of ss-DNA-SAMs on gold assembled under different ionic strength were obtained theoretically. The ss-DNA-SAMs were assembled on gold under different concentrations of CNaCl and six important electrochemical parameters were used to validate the model experimentally, which include surface coverage (Γm), interfacial capacitance (C), phase angle (Ф1 Hz), ions transfer resistance (Rit*), current density difference (Δj) and charge transfer resistance (Rct) from chronocoulometry (CC), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Three main aspects were included in this paper: (1) construction of a simple hexagonal model to describe the specific structural characteristics of ss-DNA-SAMs on gold; (2) calculation of the calibrating factor r by CC experiments and several important conclusions from the simple model; and (3) confirmation of the simple model by our experimental results and literature reports. The simple model may provide an important reference for optimizing the design of DNA sensor.