Effect of mixed thiols on the adsorption, capacitive and hybridization performance of DNA self-assembled monolayers on gold

Abstract

In this article, we investigated the effect of mixed thiols (HS(CH2)5CH3, HS(CH2)6OH and HS(CH2)2NH2) on the adsorption, capacitive and hybridization performance of thiol-modified probe DNA self-assembled monolayers on gold by chronocoulometry (CC) and cyclic voltammetry (CV). Co-assembly of HS(CH2)5CH3 with probe DNA availed DNA surface adsorption on gold more than HS(CH2)6OH and HS(CH2)2NH2. With the increase of the assembly concentration ratio of probe DNA and mixed thiols (C DNA/C thiols), DNA surface coverage (Γ m) was almost constant for DNA/HS(CH2)5CH3 mixed SAMs and increased gradually for DNA/HS(CH2)6OH or DNA/HS(CH2)2NH2 mixed SAMs. Interfacial capacitance (C d) value of DNA/thiol-mixed SAMs on gold mainly depended on the capacitance of thiols SAMs. DNA hybridization almost did not change the capacitance value of DNA/thiol-mixed SAMs on gold. Hybridization experiments indicated that the maximal DNA hybridization density (H D) was 1.2 × 10−11 and 1.1 × 10−11 mol cm−2 with HS(CH2)5CH3 or HS(CH2)6OH as mixed thiols respectively, much bigger than that with short-chain thiols (HS(CH2)2NH2). The size fitting coefficient d c/d t values for the optimal hybridization of DNA/HS(CH2)5CH3 and DNA/HS(CH2)6OH mixed SAMs were 0.70 and 0.93, respectively. This indicated that probe DNA with much bigger Γ m should be co-assembled with HS(CH2)5CH3 on gold to obtain the biggest H D than with HS(CH2)6OH. These conclusions provided the important reference for optimally designing DNA sensor.