Chronocoulometric Quantification of DNA Surface Coverage on Electrochemically Functionalized MoS2 Interfaces

Abstract Quantitative control of the surface coverage of nucleic acid is critical for the development of reproducible and sensitive biosensing platforms. However, establishing covalently defined biointerfaces on molybdenum disulfide (MoS2) remains challenging due to the chemical inertness of its basal planes. Here, we present a rapid, environmentally benign solid-state electrografting strategy to functionalize MoS2 surface that enables rapid immobilization and direct quantification of DNA constructs. Liquid-exfoliated MoS2 nanosheets deposited on indium tin oxide (ITO) substrates were modified via electroreduction of halogenated carboxylic acids to activate the MoS2 surface with carboxylate groups, followed by conjugation of amine-terminated DNA and surface passivation with aminohexanol. The covalently linked DNA/MoS2 interface was characterized using surface probe and electrochemical techniques. Chronocoulometry was employed for the direct quantification of single- and double-stranded constructs with matched and mismatched base pairs. Single-stranded DNA exhibits Langmuir adsorption with a maximum surface density Γmax = 23 ± 3 × 1013 molecules cm–2 and a dissociation constant Kd = 1.1 nM, indicating high-affinity and reproducible probe immobilization. The electrografted iodobenzoic linker promotes slightly higher surface density (26 ± 6 × 1013 molecules•cm–2) of the probe DNA relative to aliphatic analogues. In contrast, double-stranded constructs, including matched and mismatched sequences, show less than half the surface coverage of the probe DNA due to a larger footprint and, in some cases, due to structural distortion. Overall, structurally rigid electrografted linkers show better probe coverage and may be considered a reliable tool for designing biosensors on MoS2 surface.