Synthesis of Ag Nanorods with Highly Tunable Plasmonics toward Optimal Surface‐Enhanced Raman Scattering Substrates Self‐Assembled at Interfaces

Abstract

Plasmonic nanoparticles, such as Au, Ag, and Cu nanoparticles, can support the collective oscillation of free electrons in the metals excited by electromagnetic radiation, generating resonant extinction peaks and significantly enhanced electric near-fields as well as hot carriers. [1] The plasmonic properties of nanoparticles have enabled a vast range of applications, Ag nanorods receive intensive attention due to the excellent plasmonic properties. However, the difficulty in synthesis of monodisperse Ag nanorods with broad aspect ratios has limited their in-depth applications. Here, a seed-mediated method is reported for the synthesis of Ag nanorods with lengths from 65 to 5000 nm, corresponding to aspect ratios from 2 to 156. The plasmonic resonance is tuned from visible to mid-infrared wavelength. The synthesis protocol relies on robust Au seeds synthesized in N,N-dimethylformamide (DMF), which induces the one-dimensional (1D) growth of Ag atoms. To maintain symmetry breaking initiated by the Au seeds, the reduction rate of Ag + is decreased by adding hexadecyltrimethylammonium chloride (CTAC) to form AgCl particles. The optimized conditions to prevent the homogeneous nucleation of Ag nanoparticles and residue of AgCl particles in products are identified, under which the conversion efficiency of Ag ions to Ag nanorods is evaluated about 48%. More importantly, the anisotropic Ag nanorods are selfassembled into monolayers at interfaces with the long axis of Ag nanorods perpendicular or parallel to the interfaces, respectively. The as-fabricated monolayers exhibit uniform and reproducible surface-enhanced Raman scattering (SERS) activities. The optimal SERS performance is achieved from Ag nanorod monolayer with vertical orientation and the longest rod length.

Advances in Plasmonic Sensing at the NIR—A Review

“…Wang et al [ 63 ], with incredibly high aspect ratios up to 85.5, could be used to place the longitudinal LSPR mode from 1500 nm to 4450 nm. Finally, a mention to the work done by Tian et al [ 161 ] must be made, due to the authors description on the synthesis of mono-disperse and high aspect ratios of Ag NRs, reporting lengths from 65 nm to 5 μm, corresponding to astonishing aspect ratio from 2 to 156.…”

Facile and robust fabrication of hierarchical Au nanorods/Ag nanowire SERS substrates for the sensitive detection of dyes and pesticides

“…Besides using surface patterns to generate enhanced EM fields, the assembly of Au or Ag nanostructures, such as nanospheres, 27,28 nanorods, 29–31 nanowires, 32 nanotriangles, 33 nanotubes 34,35 and nanostars, 36–39 could also be adopted to improve the EM fields and be fabricated as SERS substrates. These nanoparticles could be synthesized via relatively simpler chemical methods, 28,40–44 compared to the sophisticated physical methods mentioned above.…”

Signature of Plasmonic Nanostructures Synthesised by Electrical Exploding Wire Technique on Surface-Enhanced Raman Scattering

“…Compared to other noble metal nanomaterials, silver nanostructures are more widely utilized as an active SERS substrate through exploiting their wide range of plasmon resonance influences in the visible region, strong signal enhancement, and reliable synthesis technique [10]. So far, silver nanostructures with varied morphologies, such as nanospheres [11], nanorods [12], nanowires [13], and nanosheets [14], have been described as active SERS substrates that attain very sensitive molecular detection. Among the nanostructures mentioned above, the metal nanostructures with rougher surfaces (e.g.…”