nanorod

Nanorods are nanoscale, rod-shaped particles with a high aspect ratio, a form of one-dimensional nanostructures. They typically measure tens of nanometers in length and a few nanometers in diameter, corresponding to aspect ratios from about 3:1 to well over 100:1. Materials include noble metal, semiconductor, and oxide systems, with gold and silver nanorods among the most studied for optical applications.

Most common synthesis is seed-mediated growth, especially for gold nanorods, where a small spherical seed catalyzes elongated growth in the presence of a surfactant such as cetyltrimethylammonium bromide (CTAB) and additives like silver ions or halides. Reaction conditions, including temperature, seed size, and reagent ratios, determine the final aspect ratio and optical properties. Other approaches include hydrothermal or solvothermal synthesis for oxide and semiconductor nanorods, polyol methods, and template-assisted electrodeposition.

Nanorods exhibit anisotropic properties, notably plasmonic resonances along their long axis that shift with aspect ratio. In gold nanorods, the longitudinal plasmon peak can be tuned across the visible to near-infrared region, enabling enhanced light absorption and photothermal effects. In semiconductor nanorods, exciton confinement can influence electronic and optical behavior, with potential quantum-confined emission.

Applications span bioimaging and sensing, photothermal therapy, surface-enhanced spectroscopy, catalysis, and components in photovoltaic and optoelectronic devices. Their elongated shape can facilitate alignment in ordered films and influence charge transport in nanoscale networks.

Characterization typically uses transmission electron microscopy and scanning electron microscopy to assess shape and size, and UV–visible spectroscopy to monitor plasmon bands. Challenges include stability in solution, cytotoxicity for some materials, purification from surfactants, and reproducible large-scale synthesis.