Assembling single gold nanorods into large-scale highly aligned nanoarrays via vacuum-enhanced capillarity
© Wang et al.; licensee Springer. 2014
Received: 31 August 2014
Accepted: 22 September 2014
Published: 7 October 2014
We report a simple, straightforward, and efficient approach to assemble single gold nanorods (AuNRs) into highly aligned arrays, via a unique vacuum-enhanced capillarity. The assembled AuNR arrays demonstrate both an excellently unidirectional ordering and a wonderful single-rod resolution. The key role of vacuum in this approach enables high-aspect-ratio (10 to 22) AuNR alignment and efficiently facilitates large-area alignment. Further investigation of one- and two-dimensional AuNR arrays would undoubtedly be beneficial to their potential applications.
Controlled assembly and alignment of one-dimensional (1D) nanostructures such as nanorods, nanotubes, and nanowires are essential for their integration and applications in many macroscopic devices for nanoelectronics,  sensing, [2–4], and plasmonics [5, 6]. Although 1D nanostructures such as gold nanoarrays can be fabricated by conventional top-down lithography (e.g., electron beam lithography), the process is time-consuming and the gold involved is polycrystalline, which may ultimately degrade the performance of devices. Recent wet chemical approaches have made it possible to synthesize various anisotropic gold nanostructures including dimeric gold nanorod (AuNR) junctions [4, 5, 7]. Meanwhile, several novel bottom-up strategies, such as capillary-driven assembly, [8–10] chemically template-directed assembly [11–13], spontaneous self-assembly , surface amidation assembly , and polymer-based assembly [16–18], have been developed to assemble spherical gold colloid nanoparticles  and anisotropic pentahedrally twinned AuNRs into ordered gold nanostructures [11, 15, 19]. However, the manipulation of anisotropic AuNRs to form highly aligned and ordered nanoarrays still remains significantly challenging. Herein, we employ a strong capillarity enhanced by a vacuum created from a syringe to assemble AuNRs into nanoarray structures. The assembled linear nanoarrays are not only single-rod resolved but also extremely well aligned. Compared with the spontaneous capillary assembly, this approach is simple, quick, and clean (does not involve any other chemicals such as polymers) and can be highly efficient in large-area assembly of AuNRs with high aspect ratios (ARs) (approximately 10 to 22). The vacuum-enhanced capillary force effectively promotes the formation of highly aligned AuNR arrays. This work is an extended study of our previous work on gold nanorods .
Results and discussion
We have developed a simple, inexpensive, and efficient procedure that is based on a vacuum-enhanced capillary force for assembling anisotropic AuNRs into AuNR arrays. The AuNR arrays generated are not only single-rod resolved but also highly aligned and ordered. The created vacuum enables fast alignment of high-AR AuNRs on a large scale. Further work is needed to investigate the impact of various parameters on assemblies and to refine the process of forming two-dimensional AuNR nanoarrays as demonstrated in the proof-of-concept example. The approach presented here could be extended to assemble other anisotropic nanostructures including other nanorods/nanowires, carbon nanotubes, and DNA, and the nanoarrays fabricated could find potential applications in nanoelectronics, nanoplasmonics [5, 6], SERS sensing , and chemical detection .
This work was supported by the 100 Talents Program of the Chinese Academy of Sciences (Y1291720S3) and the National Basic Research Program of the Ministry of Science and Technology of China (2011CB933101).
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