Abstract

The paper presents the study of light-induced spectral redshift observed for a single gold nanorod immersed in hydroquinone solution. Two lasers emitting at 532 nm and 633 nm were used to excite the nanorods to perform a wavelength-dependent study and thereby investigate the mechanism behind the spectral redshift. Gold nanorods with longitudinal surface plasmon resonance (LSPR) at ~650 nm was chemically synthesized by the seed mediated growth method [1]. The nanorods were then deposited on glass substrate for the single particle study. A home-built confocal microscopy setup that utilized the photoluminescence property of the gold nanorods was used to obtain single-particle images and spectra. A gradual redshift (~60 nm on average) of the LSPR of the single gold nanorods was observed on continuous illumination by a 532 nm laser in the presence of hydroquinone solution. This was surprising because hydroquinone does not react with the gold nanorods in a solution and is therefore usually used as a mild reducing agent during the synthesis of gold nanorods. Also, single gold nanorods immersed in hydroquinone solution and kept in the dark did not show any shift of the LSPR. This observation proved that the red shift of the LSPR is driven by light. The mechanism behind the spectral shift can be either due to reshaping of the nanorods causing a change in its aspect ratio, or due to the change in the local refractive index. In a follow up experiment, the LSPR of the gold nanorods was restored to its initial position on washing with cetrimonium bromide (CTAB) solution without laser excitation.

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