A giant chiroptical effect caused by the electric quadrupole.
A giant chiroptical effect caused by the electric quadrupole.
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DOI：
10.1039/c6nr09419h
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发表时间：
2017-04
期刊：
影响因子：
6.7
通讯作者：
Tong Wu;Weixuan Zhang;Rong-Yao Wang;Xiangdong Zhang
中科院分区：
文献类型：
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作者：
Tong Wu;Weixuan Zhang;Rong-Yao Wang;Xiangdong Zhang
近年来，等离子体粒子对生物分子的超灵敏检测和表征引起了人们的极大兴趣，因为它们在生物医学科学和药剂学中具有相当重要的意义。到目前为止，所有关于等离子体激元诱导的圆二色(CD)的理论都是建立在偶极近似的基础上的，电四极效应通常被认为是相对较小的，被忽略了。在这里，我们证明了电四极的贡献不仅不能被忽略，而且在许多情况下它也起着关键作用。特别是，对于具有择优分子取向且位于等离子体纳米结构热点的手性介质，分子电四极(EQs)贡献的等离子体CD强度可以比分子电偶极子/磁偶极子贡献的等离子体CD强度高两个数量级。与偶极近似不同的是，与分子方程相关的等离子体CD活动主要出现在等离子体共振吸收处，该吸收有利于电场梯度陡峭的光学增强近场，并且与分子方程的增强发射率相关。基于这样的物理理解，我们可以根据需要设计纳米结构，利用EQ的贡献来实现巨大的手性效应，为超灵敏的分子手性检测和量化提供了一种新的策略。
Recently, there has been great interest in studying ultrasensitive detection and characterization of biomolecules using plasmonic particles, because they are of considerable importance in biomedical science and pharmaceutics. So far, all the theories on plasmon-induced circular dichroism (CD) have been based on the dipole approximation; the electric quadrupolar contribution is generally considered to be relatively small and neglected. Here we demonstrate that the electric quadrupolar contribution not only cannot be ignored, but it also plays a key role in many cases. Particularly, for the chiral medium that possesses preferential molecular orientations and is located at the hotspot of plasmonic nanostructures, the plasmonic CD strength contributed by molecular electric quadrupoles (EQs) can be two orders of magnitude higher than that contributed by molecular electric/magnetic dipoles. Unlike the case of the dipole approximation, molecular EQ associated plasmonic CD activity appears mainly at the plasmonic resonance absorptions that facilitate the optically enhanced near-field with steep electric field gradients, and is correlated with the boosted emission rate of a molecular EQ. Based on such physical understandings, we can design nanostructures to realize a giant chiroptical effect using the EQ contribution according to the requirements, which provide a new strategy for ultrasensitive detection and quantification of molecular chirality.