Synthesis and Characterization of Gold Nanorods

Gold nanorods are anisotropic colloidal particles whose elongated geometry confers dual plasmonic resonances, enabling precise control of optical absorption in the visible and near-infrared regions. The predominant fabrication route employs seed-mediated growth, wherein small gold seeds are introduced into a growth solution containing a gold precursor, surfactant and mild reducing agent. Surfactants such as cetyltrimethylammonium bromide (CTAB) direct anisotropic deposition by preferential adsorption on specific crystal facets, while additives (silver ions, halides, binary surfactant mixtures or Hofmeister salts) fine-tune aspect ratio and monodispersity. Ligand exchange protocols further modify surface chemistry for compatibility with biological media or conductive inks. Characterisation typically combines transmission electron microscopy, dynamic light scattering and UV–vis–near-infrared spectroscopy, the latter revealing shifts in longitudinal surface plasmon resonance that correlate directly with aspect ratio and local refractive index. Advances in automated spectral deconvolution and computational modelling have enhanced throughput and mechanistic insight. Gold nanorods now underpin applications ranging from photoacoustic imaging and photothermal therapy to catalysis and printed electronics, with ongoing efforts directed towards scalable synthesis, reproducible shape control and minimal cytotoxicity.

Research from Nature Portfolio

Recent studies have unveiled that the predominant species in conventional seed solutions are atomically precise gold nanoclusters rather than simple small particles. A 32-atom core cluster bearing mixed halide and quaternary ammonium ligands has been identified, with rapid dynamic ligand exchange enabling the formation of a family of distinct clusters. Enrichment of this uniform cluster precursor yields nanorods with significantly narrowed size distributions and reduced shape impurities, clarifying a longstanding mechanistic gap in anisotropic growth. In parallel, a novel algorithm based on optimality principles has been devised to determine aspect-ratio distributions directly from UV–vis extinction spectra. By relating peak position and full-width half-maximum to nanoparticle geometry, this approach bypasses labour-intensive image analysis and offers a rapid, cost-effective alternative to electron microscopy and scattering techniques for quality control of colloidal gold nanorods.

Synthesis and Characterization of Gold Nanorods publication trend

The graph below shows the total number of articles in synthesis and characterization of gold nanorods across all publications each year (not limited to Nature Index journals).

Technical terms

Aspect ratio (AR): The ratio of nanorod length to diameter, directly influencing plasmon resonance wavelengths.

Localized surface plasmon resonance (LSPR): Collective oscillation of conduction electrons confined to the nanoparticle surface, responsible for sharp optical absorption bands.

Seed-mediated synthesis: A two-step process in which pre-formed nanoparticles (seeds) nucleate anisotropic growth in a subsequent growth solution.

Ligand exchange: Replacement of initial stabilising molecules on the nanoparticle surface with alternative ligands to modify colloidal stability or functionality.

Surfactant-directed growth: Use of amphiphilic molecules (e.g., CTAB, sodium oleate) that selectively adsorb on specific crystal facets to promote anisotropic deposition.

References

1. Atomically precise nanoclusters predominantly seed gold nanoparticle syntheses. Nature Communications (2023).
2. Fine-tuning of gold nanorod dimensions and plasmonic properties using the Hofmeister effects. Journal of Materials Chemistry C (2016).
3. Anisotropic Gold Nanoparticles in Biomedical Applications. International Journal of Molecular Sciences (2018).
4. Gold nanorods with conjugated polymer ligands: sintering-free conductive inks for printed electronics. Chemical Science (2016).
5. Seed-Mediated Synthesis of Tunable-Aspect-Ratio Gold Nanorods for Near-Infrared Photoacoustic Imaging. Discover Nano (2018).
6. Fast characterization of gold nanorods ensemble by correlating its structure with optical extinction spectral features. AIP Advances (2014).
7. Determination of the Aspect-ratio Distribution of Gold Nanorods in a Colloidal Solution using UV-visible absorption spectroscopy. Scientific Reports (2019).
8. Effect of reducing agents on the synthesis of anisotropic gold nanoparticles. Nano Convergence (2022).
9. Morphological control of seedlessly-synthesized gold nanorods using binary surfactants. Nanotechnology (2018).
10. Understanding blue shift of the longitudinal surface plasmon resonance during growth of gold nanorods. Nano Express (2021).