Single Molecule Dynamics on Hydrophobic Self-Assembled Monolayers

详细信息    查看全文

• 作者：Nathaniel Nelson ; Robert Walder ; Daniel K. Schwartz
• 刊名：Langmuir
• 出版年：2012
• 出版时间：August 21, 2012
• 年：2012
• 卷：28
• 期：33
• 页码：12108-12113
• 全文大小：292K
• 年卷期：v.28,no.33(August 21, 2012)
• ISSN：1520-5827

文摘

The interactions between adsorbate molecules and hydrophobic surfaces are of significant interest due to their importance in a variety of biological and separation processes. However, it is challenging to extrapolate macroscopic ensemble-averaged force measurements to molecular-level phenomena. Using total internal reflection fluorescence microscopy to image individual molecules at hydrophobic solid鈥揳queous interfaces, we directly observed dynamic behavior associated with the interactions between fluorescently labeled dodecanoic acid (our probe molecules) and self-assembled monolayers (SAM) comprising n-alkyltriethoxysilanes with systematically increasing chain length (from n = 4鈥?8). In all cases, we observed at least two characteristic surface residence times and two diffusive modes, suggesting the presence of multiple distinct adsorbed populations. In general, the mean surface residence time increased and the mobility decreased with increasing SAM chain length, consistent with stronger probe鈥搒urface interactions. However, these trends were not primarily due to changes in characteristic residence times or diffusion coefficients associated with the individual populations but rather to a dramatic increase in the fraction associated with the long-lived slow-moving population(s) on long-chain SAMs. In particular, on longer (16鈥?8 carbon) alkylsilane monolayers, the probe molecule exhibited far fewer desorption-mediated 鈥渇lights鈥?than on short (4鈥? carbon) monolayers. Additionally, probes on the longer chain surfaces were much more likely to exhibit extended surface residence times as opposed to short transient surface visits.