A Fast and Efficient Replacement of CTAB with MUA on the Surface of Gold Nanorods Assisted by a Water‐Immiscible Ionic Liquid

Abstract

The synthesis and surface modification of gold nanorods (GNRs) is one of the most important and basic issues in nanoscience. Most of the widely investigated GNRs are coated with a cetyltrimethylammonium bromide(CTAB) bilayer. Here, a highly efficient method is proposed to replace CTAB from the surface of GNRs with a bifunctional 11-mercaptoundecanoic acid in order to decrease the possible toxicity caused by CTAB. This ligand exchange is achieved in a biphasic mixture of an aqueous solution and a water-immiscible ionic liquid (IL), [BMIM][Tf N]. That is, by mixing IL, mercaptoundecanoic acid (MUA)/IL (200 × 10 m) and a concentrated aqueous solution of GNRs together, followed by vortex stirring for 90 s, CTAB-capped GNRs with varying aspect ratios can be turned into corresponding MUA-capped GNRs with the same aspect ratio. Furthermore, the formed MUA-capped GNRs can be obtained in a large quantity and stored as powders for easy use. The MUA-capped GNRs with improved biocompatibility and colloidal stability are well suited for further biological functionalization and potential applications. This IL-assisted ligand exchange can reverse the surface charge, enhance the stability of GNRs, and suppress its cytotoxicity.

Tailoring the ORR and HER electrocatalytic performances of gold nanoparticles through metal–ligand interfaces

“…The Au 4f signal for AuNPs@Citrate did not require deconvolution, where the peaks at 83.1 eV and 86.7 eV were assigned to Au 4f7/2 and Au 4f5/2, respectively, belonging both photoemissions to Au(0). 41,42 Intriguingly, the Au4f7/2 binding energy (83.1 eV) was clearly shifted to lower value energy compared with the same signature reported for a pure metallic Au, which was attributed to the negatively surface charged AuNPs@Citrate. 43 The Au-CTAB interaction also provided the appearance of two doublets, where two contributions of Au 4f7/2 appear at 82.4 eV (17 %) and 84.1 eV (83 %), respectively (Fig.…”

“…S1) and the appearance of a C-S stretch at ≈580 cm -1 confirmed both the presence of MUA and the formation of Au-S bonds. 40,41 XPS measurements not only assisted in further confirming the ligand-exchange procedure, but also offered insights on the oxidation state of Au-surface. Fig.…”

“…On the other hand, S 2p and S 2s were only detected in AuNPs@PSS and AuNPs@MUA samples displaying significant differences between both signals, while N 1s, Br 3p (180 eV) and Br 3d (68 eV) were only detected in AuNPs@CTAB. 41 Fig. 2A compares in greater detail the high-resolution N 1s core level spectrum of AuNPs@Citrate and AuNPs@CTAB, showing a single contribution at 402 eV typical of an alkylammonium cation.…”

“…2D). 41 Additional contributions with comparatively much lower relative intensity were assigned to sulfide groups at low binding.…”

Strategies for the functionalisation of gold nanorods to reduce toxicity and aid clinical translation

“… Schematic representation of (a) partially PEG-functionalised GNRs, (b) one-step surface functionalisation of GNRs with Tween 20, BSPP, PEG-SH and NaCl and (c) the preparation of MUA-GNR using an IL via the phase transfer method. Images adapted with permission from reference 27 , copyright 2015 American Chemical Society and from reference 34 , copyright 2017 John Wiley & Sons. …”