环糊精与表面活性剂主客体作用诱导的金纳米棒可控自组装

Controllable Self-Assembly of Gold Nanorods via Host–Guest Interaction between Cyclodextrins and Surfactants

纳米结构基元的可控自组装是自下而上构筑功能材料及纳米器件的有效途径。各向异性的金纳米棒具有独特的等离激元特性,而如何通过简单有效的方法实现其可控自组装仍具有较大的挑战性。本文利用环糊精(CD)与吸附于金纳米棒表面的十六烷基三甲基溴化铵(CTAB)的主客体作用,实现了金纳米棒(GNR)在水溶液中的可控自组装。通过调节α-CD的浓度可以分别实现金纳米棒肩并肩组装或头对头组装,初步揭示α-CD与CTAB的超分子作用是金纳米棒组装的主要诱因。根据实验结果推测α-CD诱导金纳米棒组装的机理如下:在α-CD浓度较低时,GNR表面的CTAB吸附层部分被α-CD/CTAB超分子复合物取代,从而发生缓慢的肩并肩组装;在α-CD浓度较高时,GNR表面的CTAB吸附层大量被α-CD/CTAB复合物取代,并且GNR两端的CTAB几乎完全被取代,因而发生快速的头对头组装。借助于α-淀粉酶对α-CD的水解作用,可以利用该组装体系实现对溶液中微量淀粉酶的检测。这种基于主客体作用的自组装策略为非球形纳米基元的可控自组装提供了新的思路。

The self-assembly of colloidal nanocrystals has emerged as a powerful strategy for the bottom-up fabrication of functional materials and nanodevices.Recently,the self-assembly of gold nanorods(GNRs)has attracted significant attention because of their unique plasmonic properties,but the realization of their adjustable self-assembly of GNRs through facile and effective approaches remains challenging.In this work,the controllable selfassembly of GNRs in aqueous solution was realized through the host-guest interactions of cyclodextrins(CDs)and the cetyltrimethylammonium bromide(CTAB)molecules adsorbed on the surface of the GNRs.The self-assembly of GNRs was readily achieved by the addition of aqueous α-CD solutions with varied concentrations into aqueous dispersions of CTAB-stabilized GNRs.At a relatively lowα-CD concentration,slow aggregation of the GNRs occurred,resulting in their side-by-side assembly.This was revealed by the blue shift of the longitudinal surface plasmon resonance(LSPR)band in the absorption spectra and confirmed by transmission electron microscopy(TEM)observations.On the other hand,when a higher concentration of α-CD was added,fast aggregation of the GNRs occurred,resulting in their end-to-end assembly.This was revealed by the red shift in the LSPR band together with the TEM observations.If β-CD was employed instead ofα-CD,the self-assembly of GNRs could also be induced,although a relatively higher concentration of β-CD was required to achieve the extent of aggregation similar to that induced byα-CD,indicating that the supramolecular host–guest interaction between CDs and the surfactant CTAB was crucial to the directed self-assembly of GNRs.Furthermore,the α-CD-induced assembly was inhibited on addition of excess CTAB,confirming that the supramolecular interaction of α-CD and CTAB played a key role in directing the self-assembly of the GNRs.Based on these experimental results,a possible mechanism for the α-CD-induced self-assembly of GNRs was proposed as follows:at a lower α-CD concentration,the gradual formation of the host-guest inclusion complex α-CD/CTAB led to the partial replacement of the highly charged CTAB bilayers adsorbed on the GNRs by the less charged complex,which resulted in a slow side-by-side assembly of the GNRs;at a higherα-CD concentration,the CTAB bilayers were quickly replaced by the α-CD/CTAB complex,and the CTAB molecules adsorbed at both ends of the GNRs were almost completely replaced,resulting in a fast end-to-end assembly of the GNRs.Additionally,on the basis of the hydrolysis ofα-cyclodextrin catalyzed by α-amylase,the selfassembly of GNRs directed by the host-guest interaction could be used to realize the feasible detection ofα-amylase in solutions.This self-assembly strategy mediated by the host-guest interaction may be extendable to other colloidal systems involving surfactants adsorbed on the surface of nanoparticles,and may open new avenues for the controllable selfassembly of non-spherical nanoparticles.