Highly Pure Gold Nanotriangles with almost 100% Yield for Surface-Enhanced Raman Scattering

Abstract

Gold nanotriangle (Au NT), a unique anisotropicshaped plasmonic nanostructure with distinctive optical, electrical, and catalytic characteristics, has been utilized in a variety of hightechnological applications. However, the basic and practical applications of Au NTs are often hindered by size and yield (less than 60%) and engineering a facile and manageable approach to acquire Au NTs with high yields is still challenging. Herein, a simple and rapid seed-mediated method to prepare high-purity Au NTs (up to 97.4%) is proposed by precisely controlling the reaction kinetics. Importantly, there are two key factors to achieve high-yield Au NTs (70%) during the two-growth synthesis: (1) the high concentration of hexadecyltrimethylammonium chloride (CTAC) that can provide a greater binding force on the ⟨111⟩ facet of Au seed and (2) the selective adsorption of potassium iodide (KI) on the ⟨111⟩ facet. Additionally, Au NTs with a wide range of sizes from 58 to 137 nm with a high uniformity can be tailored by a small window parameter regulation. Additionally, it is found that the addition of optimized salts can induce the rapid precipitation of Au NTs to form self-assembled microfibers and the efficient purification of Au NTs with a yield of about 97.4%. Furthermore, the finite difference time domain (FDTD) simulation shows that anisotropic electromagnetic field enhancements and hot spot excitation modes can be generated in different assembling models of Au NTs. Finally, we construct macroscopic two-dimensional (2D) ordered monolayer films of Au NTs through volatilizing self-assembly. As a proof of concept, the ordered Au NT arrays exhibit both high surface-enhanced Raman spectroscopy (SERS) sensitivity and detecting stability compared to random assembling structures and Au NPs. Therefore, we believe that our proposed rapid synthesis and high-yield purification approach of Au NTs would pave a way to prepare designed nanomaterials for a variety of basic and high-technological practical applications.

Large‐Area Periodic Arrays of Atomically Flat Single‐Crystal Gold Nanotriangles Formed Directly on Substrate Surfaces

“…The NT synthesis, therefore, is in need of further refinements in terms of yield along with improvements in size and shape uniformity if it is to be competitive with leading‐edge colloidal NT growth modes that are subjected to purification procedures. [ 30,32 ] It is, however, of significance that the NT synthesis forwarded in this study realizes structures, which after a mere rinse in solvents, present (111) surfaces that are atomically flat, as exemplified by the close‐packed arrangement of Au atoms observable in AFM measurements. This is in contrast to other NT syntheses where surfaces are compromised by capping agents that can decisively influence physicochemical properties.…”

“…The colloidal approach is, however, currently able to achieve thinner nanoplates than those accessible to the new approach. Even though the yield of seeds with the required stacking fault defects is quite high when compared to colloidal methods, [30][31][32] the requirement placed on yield is far more demanding since substrate-immobilized NTs are not amenable to standard postsynthesis purification schemes. The NT synthesis, therefore, is in need of further refinements in terms of yield along with improvements in size and shape uniformity if it is to be competitive with leading-edge colloidal NT growth modes that are subjected to purification procedures.…”

“…[28,29] Even though such shape-directing agents have proven highly effective, the reaction product is compromised by structures having a 3D character because it has proven difficult to produce uniformly-sized defect-laden seeds in high yield. This has necessitated the need for shape-purification procedures, with depletion flocculation [30,31] and centrifugation in the presence of a NaCl additive [32] both giving rise to exceptionally high yields. Current methods for the preparation of seeds are also deficient in that they allow for limited variability in their diameter.…”

“…Advances are, however, occurring for selfassembly techniques yielding substrate-based Au NTs in closepacked configurations. [28,32,[37][38][39] In contrast, only two reports by Mirkin and co-workers [40,41] have been responsive to the challenge of forming periodic arrays of Au NTs in which they use lithographically-defined trapping sites to capture and orient structures from a colloidal suspension. These demonstrations, while undeniably impressive, have only yielded sub-squaremillimeter arrays, require the use of the technically demanding e-beam lithography method, and can only be practiced on substrate materials amenable to these techniques (e.g., Si, PDMS, AuCr layers).…”

Plasmon Coupling and Efficient Charge Transfer in Rough-Surfaced Au Nanotriangles/MXene Hybrids as an Ultrasensitive Surface-Enhanced Raman Scattering Platform

“…When the Raman scattering is strongly coupled with the plasmonic hotspot, the scattering signal is greatly enhanced to be proportional to the fourth power of the near-field enhancement. , Additionally, the metal nanostructure can contribute to CT between the SERS substrate and Raman probe. Both the direct electron transfer between the Femi level of metal, the highest occupied molecular orbital (HOMO) and unoccupied molecular orbital (LUMO) levels of molecules, and the plasmon-induced hot electron injection from metal to analytes play an important role in amplifying Raman signals. − Various plasmonic metal nanostructures have been developed for efficient SERS, such as films, cubes, nanostars, nanotriangles (NTs), nanorods, and so on. − Thereinto, Au NTs have in-plane and out-of-plane plasmon resonances, strong hotspots, and high-concentration hot electrons under plasmon excitation, which have been widely applied in plasmon-enhanced SERS. − However, Au NTs also have shortcomings that limit their SERS performances. The EM hotspot is sparse, the plasmon hotspots are highly concentrated at the three tips, and the planes that take up most of the superficial areas have very weak near-field enhancement.…”