Self-assembled monolayers of sulfonate-terminated alkanethiols investigated by frequency modulation atomic force microscopy in liquid

Abstract

A molecular-scale understanding of self-assembled monolayers (SAMs) of sulfonate-terminated alkanethiols is crucial for interfacial studies of functionalized SAMs and their various applications. However, such an understanding has been difficult to achieve because of the lack of direct information on these molecular-scale structures in real space. In this study, we investigated the structures of sulfonate SAMs of sodium 11-mercapto-1-undecanesulfonate (MUS) by frequency modulation atomic force microscopy (FM-AFM) in liquid. The subnanometer-resolution FM-AFM images showed that the single-component MUS SAM prepared in pure water had random surface structures. In contrast, the MUS SAM prepared in a water-ethanol mixed solvent showed periodic striped structures with a flat-lying conformation. The results suggest a significant solvent effect on molecular-scale structures of long-chain sulfonate SAMs. In addition, we investigated the molecular-scale structures of mixed SAMs of MUS and 11-mercapto-1-undecanol (MUO) with alkane chains of the same length. The FM-AFM images of the mixed SAMs showed clear phase separation between MUS SAM and MUO SAM domains. In the MUO SAM domains, the incorporated MUS molecules appeared as protrusions. The results obtained in this study provide direct structural information on long-chain sulfonate and mixed SAMs.

Interstitially Mixed Self-Assembled Monolayers Enhance Electrical Stability of Molecular Junctions

“…34,35 The surface coverage (Γ, mol/cm 2 ) for the ReSEMprocessed mixed SAM was higher (by up to three times) than that of the pure SAM, and the mixed SAM of the two cycles was revealed to be the most densely packed (Figure 2f). Unlike for traditional mixed SAMs, 36,37 a single reductive desorption peak (inset in Figure 2f) was observed in the cyclic voltammogram of the ReSEM mixed SAM, which evidenced the homogeneity in surface structure and strong lateral interaction between the reinforcement and matrix molecules. 33 Finally, all the surface analysis data in Figure 2 explicitly indicate that the ReSEM yielded imSAMs with more ordered and densely packed structures than the pure SAM and that the imSAM 2nd resulted in the best system, accounting for the V BD data.…”

Toward a Quantitative Relationship between Nanoscale Spatial Organization and Hybridization Kinetics of Surface Immobilized Hairpin DNA Probes

“…Therefore, both target-induced crowding effect and inaccurate identification of tether points can potentially be responsible for the discrepancy between experiment and simulation. The development of noncontact AFM that can potentially achieve subnanometer resolution will help us to understand hybridization on more crowded biosensor surfaces. − …”

Dynamic Light Scattering Measurements for Soft Materials on Solid Substrates: Employing Evanescent-wave Illumination and Dark-field Collection with a High Numerical Aperture Microscope Objective

“…[8][9][10][11][12] The static properties of soft materials supported on solid substrates, such as domain structure, thickness, and molecular conformations, have been widely investigated using atomic force microscope, sum frequency generation spectroscopy, and X-ray or neutron scattering methods. [13][14][15] On the other hand, the dynamic properties of soft materials supported on substrates, such as diffusion behavior and collective fluctuation, are also important for the expression of their functions, such as re-construction of self-assembling structures according to environmental changes, transport of matter both in lateral and normal directions, and interactive and repulsive interactions in molecular recognitions. These dynamic properties and resultant functions are expected to be applied to various devices such as biosensors.…”

“…In addition, in the supported soft materials, inhomogeneous domains are expected to be formed on substrates depending on the compositions and concentrations of material components. 15,19 Thus, measurements on the dynamical properties of the supported soft materials at arbitrary points are also desired.…”