Controlling the Aspect Ratios of Au Nanocrystals with Ag⁺ Addition Time in Seed-Mediated Synthesis: Implications for Surface-Enhanced Raman Scattering

Abstract

Among various factors playing pivotal roles in the typical seed-mediated growth of Au nanocrystals (NCs), the role of Ag (AgNO3) has remained debatable over time and seminal research efforts have helped us in reaching a consensus, albeit from the standpoint of [Ag+] concentration. This study aims to provide an understanding of the role of Ag+ from the perspective of time. Here, we show that different Au NCs with tunable aspect ratios (ARs) can be generated in one system in high yield simply by varying the time of addition of Ag+ in the growth solution. The generality of the method has been demonstrated in tuning the ARs of anisotropic Au NCs like concave cuboid (CCB, AR = 2) and elongated tetrahexahedra (AR = 2.5), where the delayed addition of Ag+ leads to the formation of their isotropic counterpart concave cube (CC, AR = 1) and tetrahexahedra (AR = 1), respectively. This work, apart from establishing timed addition of Ag+ as a crucial parameter in controlling the AR, may also help in the realization of a universal growth mechanism of Au NCs. The Au NCs with varying ARs (CCB, AR = 2 and CC, AR = 1) have been further explored as potential substrates for surface-enhanced Raman scattering (SERS) due to the presence of their high-index facets and sharp tips.

Cooperative Design of the Ag3PO4/NH2-MIL-88B (Fe/Co) Heterojunction Integrated with Conductive Polypyrrole for Advanced Photocatalytic Water Purification

“…56 For Ag/PPy/ MIL@f, new peaks for the reduced form of Ag metal (Ag 0 ) appeared at 372.4 and 374.4 eV, which may result from the enhanced charge transfer ability by the heterojunction. 55 These Ag 0 and Ag + would act as cocatalysts in the heterojunction system, enhancing the photocatalytic activity of Ag/PPy/ MIL@f. 57 From Figure 2c of N 1s spectra, a peak appeared at ∼398.0 eV for MIL@f, Ag/MIL@f, and Ag/PPy/MIL@f, which correspond to −NH 2 groups in BDC−NH 2 (aminoterephthalic acid) of MIL. In comparison to MIL@f, Ag/MIL@f displayed a higher intensity of C−N peak (399.8 eV), due to the electron density change attributable to interactions between MIL and Ag 3 PO 4 .…”

“… 56 For Ag/PPy/MIL@f, new peaks for the reduced form of Ag metal (Ag 0 ) appeared at 372.4 and 374.4 eV, which may result from the enhanced charge transfer ability by the heterojunction. 55 These Ag 0 and Ag + would act as cocatalysts in the heterojunction system, enhancing the photocatalytic activity of Ag/PPy/MIL@f. 57 …”

Cysteine-assisted overgrowth of gold nanorods to prepare highly branched gold nanoantennas with tunable morphological and plasmonic properties

“…This phenomenon is likely due to the underpotential deposition of Ag + ions on the surface of AuNRs. 51,52 These results suggest that when the overgrowth of AuNRs was performed under standard Ag-assisted conditions, a spherical core was exhibited rather than the original rod-like structure in the center of the resulting AuNPs.…”

Single Molecule Surface Enhanced Raman Scattering in a Single Gold Nanoparticle-Driven Thermoplasmonic Tweezer

“…Generally, fluorescence is sensitive enough to detect single molecules in a fluid, but Raman scattering remains a weak process due to low optical cross sections . An important way to overcome this problem is to use SERS, − a spectroscopic method that is sensitive enough to detect single molecules in a fluid phase. ,− An important prerequisite for single molecule SERS (SM-SERS) detection is the enhanced electromagnetic fields. − Plasmonic structures have been extensively designed and utilized for near-field interaction with the molecules, − and thereby influencing their optical emission not only in terms of their intensity − but also in terms of their directivity. , …”