Department of Materials Science and Engineering, Seoul National University, Seoul, South Korea.
Department of Chemical Engineering, Pohang University of Science and Technology (POSTECH), Pohang, South Korea.
Nature. 2018 Apr;556(7701):360-365. doi: 10.1038/s41586-018-0034-1. Epub 2018 Apr 18.
Understanding chirality, or handedness, in molecules is important because of the enantioselectivity that is observed in many biochemical reactions , and because of the recent development of chiral metamaterials with exceptional light-manipulating capabilities, such as polarization control, a negative refractive index and chiral sensing . Chiral nanostructures have been produced using nanofabrication techniques such as lithography and molecular self-assembly, but large-scale and simple fabrication methods for three-dimensional chiral structures remain a challenge. In this regard, chirality transfer represents a simpler and more efficient method for controlling chiral morphology. Although a few studies have described the transfer of molecular chirality into micrometre-sized helical ceramic crystals, this technique has yet to be implemented for metal nanoparticles with sizes of hundreds of nanometres. Here we develop a strategy for synthesizing chiral gold nanoparticles that involves using amino acids and peptides to control the optical activity, handedness and chiral plasmonic resonance of the nanoparticles. The key requirement for achieving such chiral structures is the formation of high-Miller-index surfaces ({hkl}, h ≠ k ≠ l ≠ 0) that are intrinsically chiral, owing to the presence of 'kink' sites in the nanoparticles during growth. The presence of chiral components at the inorganic surface of the nanoparticles and in the amino acids and peptides results in enantioselective interactions at the interface between these elements; these interactions lead to asymmetric evolution of the nanoparticles and the formation of helicoid morphologies that consist of highly twisted chiral elements. The gold nanoparticles that we grow display strong chiral plasmonic optical activity (a dis-symmetry factor of 0.2), even when dispersed randomly in solution; this observation is supported by theoretical calculations and direct visualizations of macroscopic colour transformations. We anticipate that our strategy will aid in the rational design and fabrication of three-dimensional chiral nanostructures for use in plasmonic metamaterial applications.
理解分子的手性或对映手性很重要，因为在许多生化反应中都观察到了对映选择性，而且最近还开发出了具有特殊光操控能力的手性超材料，例如偏振控制、负折射率和手性传感。使用纳米光刻和分子自组装等纳米制造技术已经制造出了手性纳米结构，但用于三维手性结构的大规模和简单制造方法仍然是一个挑战。在这方面，手性传递代表了一种更简单、更有效的控制手性形态的方法。尽管有几项研究描述了将分子手性转移到微米级螺旋陶瓷晶体中，但这项技术尚未应用于尺寸为数百纳米的金属纳米粒子。在这里，我们开发了一种合成手性金纳米粒子的策略，该策略涉及使用氨基酸和肽来控制纳米粒子的光活性、手性和手性等离子体共振。实现这种手性结构的关键要求是形成高米勒指数表面（{hkl}，h ≠ k ≠ l ≠ 0），由于纳米粒子在生长过程中存在“扭结”位点，这些表面具有内在的手性。纳米粒子无机表面以及氨基酸和肽中的手性成分导致这些元素之间的界面处发生对映选择性相互作用；这些相互作用导致纳米粒子的不对称演化和螺旋形态的形成，这些形态由高度扭曲的手性元素组成。我们生长的金纳米粒子表现出很强的手性等离子体光学活性（不对称因子为 0.2），即使在分散在溶液中时也是如此；这一观察结果得到了理论计算和宏观颜色转变的直接可视化的支持。我们预计，我们的策略将有助于合理设计和制造用于等离子体超材料应用的三维手性纳米结构。
