Effective removal of surface-bound cetyltrimethylammonium ions from thiol-monolayer-protected Au nanorods by treatment with dimethyl sulfoxide/citric acid

Abstract

Cetyltrimethylammonium bromide (CTAB)-based surfactants are typically used as morphology-directing/ stabilising agents for gold nanorods (AuNRs), forming bilayers on their surface. However, the biological applications of AuNRs require the removal of surface-bound CTAB due its high toxicity and the poor colloidal stability of CTAB-covered AuNRs in biological media. Herein, we report a simple and effective strategy for removing surface-bound cetyltrimethylammonium (CTA) cations from poly(ethylene glycol)thiolate-protected AuNRs (PEG-AuNRs) by treatment with dimethyl sulfoxide/citric acid (DMSO/Cit), achieving residual CTA ion levels that cannot be detected by highly sensitive mass spectrometry or X-ray photoelectron spectroscopy (XPS) techniques. The DMSO/Cit treatment is thought to destabilise the Ag-Br-CTA complex on AuNRs, since citric acid forms strongly bound chelate complexes with CTA cations.

Cholesterol-coated gold nanorods as an efficient nano-carrier for chemotherapeutic delivery and potential treatment of breast cancer: in vitro studies using the MCF-7 cell line

“…The prepared GNRs has a low concentration of CTAB which has a welldocumented cytotoxicity. 30,31 The concentration of CTAB that bound to the surface of GNRs was further reduced by effective surface modication with a cholesterol moiety that was linked to a thiolated PEG. PEG has a pivotal role in enhancing the colloidal stability of the nanoparticles upon cellular exposure since it retards the non-specic adsorption of biomacromolecules by steric repulsion in addition to enhancing the aqueous dispersibility of Chol-PEG-SH in water.…”

Symmetry Breaking in Seed-Mediated Silver Nanorod Growth Induced by Dimethyl Sulfoxide

“…Although DMSO-water mixture have been studied extensively, DMSO has seldom been used in colloidal chemistry. [34][35][36] For instance, it was used as a solvent and shapedirecting agent in order to stabilize the {311} facets of Au bipyramids with an octagonal cross section. 35 In another example, coordination of DMSO to the surface of gold nanorods favored the formation of Au@Ag octahedra.…”

Plasmon Resonant Two-Photon Luminescence Inducing Photosensitization and Nonlinear Optical Microscopy In Vivo by Near-Infrared Excitation of Au Nanopeanuts

“…Many other works that have also employed TBO conjugation have similar issues [36,37]. Thin-layer polyelectrolyte deposition could mitigate this problem [37]. Following this surface modification strategy, we could improve the two-photon fluorescence yields of TBO-PEGylated nanopeanuts in the future.…”

“…The reason TBO fluorescence was not completely quenched by gold nanopeanuts could be due to the residual CTAB surfactant on the surface of gold [35]. Many other works that have also employed TBO conjugation have similar issues [36,37]. Thin-layer polyelectrolyte deposition could mitigate this problem [37].…”