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Short Gold Nanorod Growth Revisited: The Critical Role of the Bromide Counterion

Authors

  • Dr. Satyabrata Si,

    1. Laboratoire Photonique Numérique et Nanosciences, Université de Bordeaux, Institut d'Optique Graduate School & CNRS, 351 cours de la libération, Talence (France)
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  • Dr. Cecile Leduc,

    1. Laboratoire Photonique Numérique et Nanosciences, Université de Bordeaux, Institut d'Optique Graduate School & CNRS, 351 cours de la libération, Talence (France)
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  • Dr. Marie-Hélène Delville,

    1. Institut de Chimie de la Matière Condensée de Bordeaux, UPR 9048, CNRS, Université de Bordeaux, 87 Avenue du Dr. A. Schweitzer, 33608 Pessac Cedex (France)
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  • Prof. Brahim Lounis

    Corresponding author
    1. Laboratoire Photonique Numérique et Nanosciences, Université de Bordeaux, Institut d'Optique Graduate School & CNRS, 351 cours de la libération, Talence (France)
    • Laboratoire Photonique Numérique et Nanosciences, Université de Bordeaux, Institut d'Optique Graduate School & CNRS, 351 cours de la libération, Talence (France)
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Abstract

A one-step, surfactant-assisted, seed-mediated method has been utilized for the growth of short gold nanorods with reasonable yield by modifying an established synthesis protocol. Among the various parameters that influence nanorod growth, the impact of the bromide counterion has been closely scrutinized. During this study it has been shown that, irrespective of its origin, the bromide counterion [cetyltrimethylammonium bromide (CTAB) or NaBr] plays a crucial role in the formation of nanorods in the sense that there is a critical [Br]/[Au3+] ratio (around 200) to achieve nanorods with a maximum aspect ratio. Beyond this value, bromide can be considered as a poisoning agent unless shorter nanorods are required. The use of AgNO3 helps in symmetry breaking for gold nanorod growth, whereas the bromide counterion controls the growth kinetics by selective adsorption on the facets of the growth direction. Thus, a proper balance between bromide ions and gold cations is also one of the necessary parameters for controlling the size of the gold nanorods; this has been discussed thoroughly. The results have been discussed based on their absorption spectra and finally shape evolution has been confirmed by TEM. Due to their efficient absorption in the near-IR region, these short nanorods were used in photothermal imaging of living COS-7 cells with improved signal-to-background ratios.

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