Gold nanorods with localized surface plasmon resonance (LSPR) can be chemically synthesized. We systematically investigated the effects of reaction parameters and centrifugation on the fine tuning of the rod dimension in scale-up production (80–100？mL). Nanorods of absorption bands from 600–1050？nm were fabricated with precise control of the aspect ratio (AR) from 1.5 to 8.9. Although all chemicals are important in directing the nanostructure, silver ion concentration and seed/Au3+ ratio were the most effective variations to adjust the absorption wavelength. With a single surfactant under the influence of silver nitrate, short nanorods up to AR of 5 were synthesized with corresponding maximum absorption wavelength at 902？nm. To achieve higher aspect ratio with absorption band beyond 1,000？nm, two-surfactant growth solution was sought to further elongate the rod length. Centrifugation speed and times were found to exert significant influences on the final rod dimension, which is important during the purification process. In a relatively large quantity nanorod synthesis, even distribution and sufficient mixing of chemical ingredients play an essential role in determining the yield, uniformity, and stability of the final nanorod formation. 1. Introduction Nanoparticles provide unique physical and optical properties to serve as building blocks for a wide-ranging applications in nanoelectronics, nanophotonics, nanodevices, and nanomedicine [1–5]. Particularly, nanoscale gold exhibits properties which are fundamentally different from other nanoparticles [6–8]. The small size comparable to biological molecules, intense photophysical properties, and high efficiency of heat conversion from light absorption have made gold nanoparticle a huge popular nanomaterial for biomedical diagnostic (e.g., bioanalysis, nanophotonics) and therapeutic (e.g., drug delivery, hyperthermia) applications. Gold nanoparticles of varying morphologies and sizes can be fabricated by photolithography techniques and biosynthetic organisms. Nevertheless, chemical synthesis may be one of the favored and cost-effective routes. Nowadays, nanomaterials of various shapes can be precisely synthesized with seemingly limitless chemical functional groups. A variety of gold nanoparticles including nanospheres, nanorods, nanocages, nanoshells, nanoprisms, nanocubes, and nanorings have been chemically fabricated with high yield [7–12]. Among these geometries, nanorod is particularly interesting to us, because it provides an excellent platform with well-defined absorption spectrum for a label-free
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