Facile, fine post-tuning of the longitudinal absorption wavelengths of pre-synthesized gold nanorods by introducing sulfide additives

Because the specific surface plasmon resonance (SPR) wavelength of gold nanorods (GNRs) is required in most photothermal bio-applications to enhance therapeutic efficacy, the precise expectation of the SPR wavelength of GNRs in the synthesis is required. Here, we present a facile, fine post-tuning of the longitudinal absorption spectrum of pre-synthesized gold nanorods by introducing controlled amounts of sulfide additives. The longitudinal SPR wavelength was controlled to a longer wavelength (red-shifted) by increasing the concentration of sulfide. In addition, the SPR wavelength determined after sulfide treatment was not shifted and was fixed for a long period of time. This allows a powerful second chance to adjust the SPR wavelength of given GNRs by a simple post-treatment, which can circumvent the risk of experimental failure in a GNR synthesis with a specific wavelength. This method may be beneficial in the efficient preparation of GNRs for various applications requiring specific SPR wavelengths with high stability.