Mini Gold Nanorods with Tunable Plasmonic Peaks beyond 1000 nm

Abstract

Gold nanorods of small sizes have larger absorption cross sections and higher photothermal efficiency compared to larger ones. However, tuning the surface plasmon resonance of small gold nanorods remains a challenge because increasing an aspect ratio usually results from increasing dimensions. We demonstrate the synthesis of mini gold nanorods with tunable longitudinal surface plasmon resonance from ~600 to >1300 nm accompanied by precise control over widths <10 nm. Two weak reducing agents, ascorbic acid and even milder hydroquinone, were applied to a seed-mediated growth method to tune the aspect ratios of mini gold nanorods from 2.2 to 10.8 corresponding to average dimensions 19.3 × 9.0 nm through 93.1 × 8.7 nm, respectively. This seed-mediated growth of mini gold nanorods results in an average 96% of rods and yields of at least 79% based on gold ion reduction. The extinction coefficients of mini gold nanorods were established based on the gold content from inductively coupled plasma mass spectrometry. The longitudinal extinction coefficients range from 1.6 × 108 to 1.4 × 109 M−1 cm−1 depending on aspect ratio. We show that liter-scale mini gold nanorod syntheses are reproducible, and the dimensions, aspect ratios, and shape percent yields are comparable to those of a small-scale synthesis.

Synthesis of Gold Nanorods Using Poly(vinylpyrrolidone) of Different Molecular Weights as an Additive

“…For the AuNRs control, ϵ is 1.3 x 10 9 M −1 cm −1 and the value decreases to 1.0 x 10 9 ‐2.9 x 10 8 M −1 cm −1 as the molecular weight of PVP increases. The values of extinction coefficient obtained are in agreement with the previous reported values of 1.9 x 10 8 M −1 cm −1 for small AuNRs synthesized by the seedless approach and 2–3 x 10 8 M −1 cm −1 for mini AuNRs prepared by the seed‐mediated method …”

“…Recently, Chang et al. extended the range of LSPR band beyond 1000 nm by utilizing ascorbic acid and hydroquinone to synthesize mini AuNRs with lengths from 19 to 93 nm and width of less than 10 nm …”

Disconnecting Symmetry Breaking from Seeded Growth for the Reproducible Synthesis of High Quality Gold Nanorods

“…10 3 nm 3 ), their preparation in high yield has remained elusive. [27][28][29] Several issues are encountered, most of them related to the shape yield (usually below 90%) and overall size dispersity. Still, reproducibility remains the main obstacle toward the synthesis of small anisotropic nanocrystals with low size dispersity.…”

“…within the state-of-the-art values of typical syntheses of short rods ( Figure 6B, Figure S24, Tables S8 and S9). Although selected approaches for the preparation of AuNRs with LSPR wavelengths either above 1150 nm 29,46,47 or below 650 nm 48 have been reported, the dispersity and/or shape purity of the products was generally poor. In our case, Figure 6A,F).…”

Photochemical Formation of Tunable Gold Nanostructures Using Versatile Water‐Soluble Thiolate Au(I) Precursor

“…Several approaches to AuNP preparation have been developed . One of the most successful shape‐selected preparations of AuNPs is the rod synthesis . In this approach, cetyltrimethylammonium bromide (CTAB) is used in larger amounts, which helps with the reactivity and stabilization of Au(I) in shape‐selective synthesis.…”