Department of Physics, The George Washington University, Washington, DC 20052, USA.
Langmuir. 2013 Jun 25;29(25):7661-73. doi: 10.1021/la400582v. Epub 2013 Jun 12.
To understand which organic molecules are capable of binding to gold nanoparticles and/or inducing nanoparticle aggregation, we investigate the interaction of gold nanoparticles with small molecules and amino acids at variable pH. Dynamic Light Scattering (DLS) and ultraviolet-visible (UV-vis) spectra were measured on mixtures of colloidal gold with small molecules to track the progression of the aggregation of gold nanoparticles. We introduce the 522 to 435 nm UV-vis absorbance ratio as a sensitive method for the detection of colloidal gold aggregation, whereby we delineate the ability of thiol, amine, and carboxylic acid functional groups to bind to the surfaces of gold nanoparticles and investigate how combinations of these functional groups affect colloidal stability. We present models for mechanisms of aggregation of colloidal gold, including surface charge reduction and bridging linkers. For all molecules whose addition leads to the aggregation of gold nanoparticles, the aggregation kinetics were accelerated at acidic pH values. Colloidal gold is maintained only in the presence of anionic carboxyl groups, which are neutralized by protonation at lower pH. The overall reduced charge on the stabilizing carboxyl groups accounts for the accelerated aggregation at lower pH values.
为了了解哪些有机分子能够与金纳米粒子结合和/或诱导纳米粒子聚集，我们研究了金纳米粒子与小分子和氨基酸在不同 pH 值下的相互作用。通过动态光散射（DLS）和紫外-可见（UV-vis）光谱测量胶体金与小分子的混合物，跟踪金纳米粒子聚集的进展。我们引入了 522 至 435nm UV-vis 吸光度比作为检测胶体金聚集的灵敏方法，由此我们描绘了巯基、氨基和羧酸官能团结合到金纳米粒子表面的能力，并研究了这些官能团的组合如何影响胶体稳定性。我们提出了胶体金聚集的机制模型，包括表面电荷减少和桥接连接体。对于所有导致金纳米粒子聚集的分子，在酸性 pH 值下，聚集动力学得到了加速。只有在带负电荷的羧基存在的情况下，胶体金才得以维持，而在较低的 pH 值下，羧基会被质子化而中和。稳定的羧基的总电荷量减少解释了在较低 pH 值下加速聚集的原因。
