Chronocoulometric Quantification of DNA Surface Coverage on Electrochemically Functionalized MoS₂ Interfaces

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 Γ_max = 23 ± 3 × 10¹³ molecules cm^-2 and a dissociation constant K_d = 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.