Unexpected Chirality of Nanoparticle Dimers and Ultrasensitive Chiroplasmonic Bioanalysis

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• 作者：Xiaoling Wu ; Liguang Xu ; Liqiang Liu ; Wei Ma ; Honghong Yin ; Hua Kuang ; Libing Wang ; Chuanlai Xu ; Nicholas A. Kotov
• 刊名：Journal of the American Chemical Society
• 出版年：2013
• 出版时间：December 11, 2013
• 年：2013
• 卷：135
• 期：49
• 页码：18629-18636
• 全文大小：459K
• 年卷期：v.135,no.49(December 11, 2013)
• ISSN：1520-5126

文摘

Chiral assemblies of nanoparticles (NPs) are typically constructed with helical or tetrahedral geometries. Simple pairs of NPs are not expected to display chirality due to basic symmetry considerations made under the assumption of their spherical geometry. In this study we demonstrate that assemblies consisting of two metallic NPs do possess chirality and strongly rotate polarization of light. Their chiroplasmonic properties are attributed to the prolate geometry of individual colloidal particles. When bridged by biomolecules, the NP pairs acquire scissor-like geometry, with the long axes of NPs forming an angle of 9掳. This small dihedral angle results in chirality of the NP pair, while the consistency of its sign due to the specific conformation of the bridging biomacromolecules breaks the enantiomeric equivalence of the NP pairs. Strong polarization rotation in these nanoassemblies makes possible their utilization in biological analysis. Heterodimers of gold and silver NPs were made using antibody鈥揳ntigen bridges. Taking advantage of their chiroplasmonic properties, we investigated their bioanalitical potential for detection of an environmental toxin, microcystin-LR, and a cancer biomarker, prostate-specific antigen. The order-of-magnitude improvements in limits of detection compared to all other analytical techniques are attributed to plasmonic enhancement of intrinsic chirality of biological compounds, strong optical coupling of photons with NP assemblies with twisted geometries, and signal amplification due to the bisignate nature of circular dichroism bands.