Xiong Kun, Nagayama Masaharu, Ijiro Kuniharu, Mitomo Hideyuki
Graduate School of Life Science, Hokkaido University Sapporo 060-0810 Japan.
Research Institute for Electronic Science, Hokkaido University Sapporo 001-0021 Japan
Nanoscale Adv. 2024 Jul 16;6(18):4583-4590. doi: 10.1039/d4na00270a. eCollection 2024 Sep 10.
Surface modification with functional molecules is essential for introducing various surface properties. As gold nanoparticles (AuNPs) have extraordinary chemical, physical, and optical properties, control of their surface, mainly through modification with mixed alkanethiols Au-S interactions, has attracted much attention. However, surface modification of AuNPs with mixed alkanethiols to provide a strictly regulated composition remains challenging. Further, there are very few methods that can easily establish the nature of ligands and their replacement with similar molecules at nanoparticle surfaces, limiting precise analyses. Herein, we demonstrate an unfair ligand exchange between oligo(ethylene glycol) (OEG)-attached alkanethiols as a source of unfair surface modification utilizing programable thermo-responsive properties of OEG-alkanethiols-modified AuNPs and fair surface modification with mixed OEG-alkanethiols by minimizing this effect. OEG-alkanethiols-modified AuNPs show an assembly/disassembly behavior in response to the solution temperature. Assembly temperature ( ) changes in the presence of other OEG-alkanethiols, confirming the ligand exchange between alkanethiols in an aqueous solution. Kinetic analyses indicate that the competitive exchange reaction of these two alkanethiols results in an unfair ligand exchange, which leads to gradual changes in surface composition. As this ligand exchange between alkanethiols takes a longer time compared to that from citric acid, which initially covered the AuNPs, exact surface modification of AuNPs with OEG-alkanethiols is performed by moderate reaction conditions (25 °C, several to 24 hours). This insight regarding "more prolonged reaction is not always better" could be widely applied for surface modifications with various thiol-ligands.
用功能分子进行表面修饰对于引入各种表面性质至关重要。由于金纳米颗粒（AuNPs）具有非凡的化学、物理和光学性质，主要通过混合烷硫醇的修饰来控制其表面的Au-S相互作用，已引起了广泛关注。然而，用混合烷硫醇对AuNPs进行表面修饰以提供严格调控的组成仍然具有挑战性。此外，很少有方法能够轻松确定纳米颗粒表面配体的性质及其被类似分子取代的情况，这限制了精确分析。在此，我们展示了作为不公平表面修饰来源的、连接有寡聚（乙二醇）（OEG）的烷硫醇之间的不公平配体交换，利用OEG-烷硫醇修饰的AuNPs的可编程热响应特性，以及通过最小化这种效应来实现用混合OEG-烷硫醇进行的公平表面修饰。OEG-烷硫醇修饰的AuNPs在溶液温度变化时表现出组装/拆卸行为。在存在其他OEG-烷硫醇的情况下，组装温度（ ）会发生变化，这证实了水溶液中烷硫醇之间的配体交换。动力学分析表明，这两种烷硫醇的竞争性交换反应导致不公平的配体交换，从而导致表面组成逐渐变化。由于与最初覆盖AuNPs的柠檬酸相比，烷硫醇之间的这种配体交换需要更长时间，因此通过适度的反应条件（25°C，几小时至24小时）对AuNPs进行精确的OEG-烷硫醇表面修饰。这种关于“反应时间延长并不总是更好”的见解可广泛应用于各种硫醇配体的表面修饰。
