Iodide Impurities in Hexadecyltrimethylammonium Bromide (CTAB) Products: Lot−Lot Variations and Influence on Gold Nanorod Synthesis

Abstract

Recent reports [Smith and Korgel Langmuir 2008, 24, 644-649 and Smith et al. Langmuir 2009, 25, 9518-9524] have implicated certain hexadecyltrimethylammonium bromide (CTAB) products with iodide impurities, in the failure of a seed-mediated, silver and surfactant-assisted growth protocol, to produce gold nanorods. We used two of the three "suspect" CTAB products and a "good" CTAB product in the protocol, varying silver nitrate solutions in the growth solutions. We obtained excellent gold nanorod samples as witnessed in signature longitudinal plasmon peaks in optical extinction spectra, which we substantiated using electron microscopy. Analysis of these samples using inductively coupled plasma mass spectroscopy (ICP-MS) failed to detect iodide. We subsequently learnt from discussions with Smith et al. that different lot numbers within the same product had been analyzed by our respective laboratories. We can conclude that iodide impurities can vary significantly from lot to lot within a product, to such an extent that there is no guarantee that gold nanorods can be synthesized with one or other CTAB product. Conversely, labeling a CTAB product, identified by a product number or supplier name, as one whose use precludes the formation of nanorods, is also hasty.

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

“…[28] Later Manohar et al reported variation in this iodide impurity in CTAB from lot-to-lot, which hindered nanorod growth. [29] Recent work by Jin et al demonstrated that Br À indeed acts as a crucial shape-directing agent for gold nanorod formation in the seed-mediated process. [30] It has also been found that addition of electrolytes has a great impact in controlling the nanocrystal shapes.…”

Microspectroscopic characterisation of gold nanorods for cancer detection

“…[14][15][16][17][18]37,38,40,44,45,50,53,54,67 Gold nanorod sizes can be tuned by altering the ratios of chemicals involved. 14,[16][17][18]20,22,23,[67][68][69] …”

“…14,69 Cetyl trimethylammonium bromide (CTAB) is crucial as a shape-directing component in this method, 14,69,144 and gold nanorod particles have therefore been subjected to surface modification with methoxy-(polyethylene glycol)-thiol (mPEG-SH) before administration to cells in biomedical applications. Such PEGylated GNR (PEG-GNR) have been shown to be non-toxic for various cell lines.…”

“…It has therefore been proposed that gold fluorescence is related to the shape of gold nanoparticles, since surface plasmon bands are dependent on the particle shape. 14,21,69,194 Therefore, the geometry of nanoparticles may give rise to dependence in the emission properties. …”

“…bromide anions, cetyl trimethylammonium ions and Ag + -ions) on the ICG-gold interaction. Such investigations are more complex on GNR because of their more involved synthesis 17,23,68,69,271 and high susceptibility to aggregation and reshaping upon surface reactions. 16,50,53 GNR of different size and aspect ratios are grown from seed gold nanospheres in the presence of CTA + Br − (CTAB), which acts as surface directing agent.…”