Gold Nanorods Synthesized without CTAB

Table of Contents

Introduction
Specifications of CTAB-free Gold Gemini Nanorods Kit
Procedure for Re-dispersing Surfactants
Additional Product Details

Introduction

The production of SONA gold nanorods (Figure 1) (GNRs) with unique surfactant technology has many benefits over GNRs produced with the cetyltrimethylammonium bromide (CTAB) synthesis technique. CTAB is a surfactant exclusively used in the synthesis of GNRs on a large scale. Highly stable gold nanorods will be produced using these surfactant technologies, but in certain cases the precipitated surfactant may be observed in the GNR sample stored under temperatures below room temperature for prolonged periods, which would be their typical recommended storage conditions. This will not affect the quantity of GNRs dispersed in the solution, nor is it an indication of an irreversible aggregation process that causes the destruction of GNRs, which is often observed in other CTAB prepared GNRs.

Figure 1. Gold Gemini nanorods, CTAB-free (wavelength 800nm)

Specifications of CTAB-free Gold Gemini Nanorods Kit

The specifications of the CTAB- free Gold Gemini Nanorods Kit are listed below:

Storage conditions Store at 4°C - 8°C. Do not freeze.
Concentration > 30 µg/ml
pH 5.5 - 7.5
Stabilizer Amphiphilic agents
Solvent Stabilized with amphiphilic agents in conductivity grade water (18.0MΩ cm-1)
Optical density 1.0 - 1.2
Shelf life 12 months

Each kit consists of the following:

79-7010 Gold Gemini Nanorods, CTAB Free (Wavelength 650 nm) 5 ml
79-7015 Gold Gemini Nanorods, CTAB Free (Wavelength 700 nm) 5 ml
79-7020 Gold Gemini Nanorods, CTAB Free (Wavelength 750 nm) 5 ml
79-7025 Gold Gemini Nanorods, CTAB Free (Wavelength 800 nm) 5 ml
79-7030 Gold Gemini Nanorods, CTAB Free (Wavelength 850 nm) 5 ml

Additional sizes can be obtained upon request.

Product Number LPSR Maximum (nm) Length (nm) Width (nm) Aspect Ratio Color & Form
79-7010 640 – 670 25 – 31 13 – 18 1.7 - 1.9 Violet liquid
79-7015 685 – 715 37 – 43 13 – 18 2.4 - 2.8 Blue liquid
79-7020 735 – 765 37 – 44 10 – 13 3.4 - 3.7 Red-purple liquid
79-7025 785 – 815 40 – 50 10 – 13 3.8 - 4.1 Red-orange liquid
79-7030 835 – 865 48 – 55 9 – 12 4.6 - 5.3 Maroon-purple liquid

Procedure for Re-dispersing Surfactants

It is recommended to apply the following procedures for homogenization of the solutions:

650, 700, and 750 nm wavelengths – The vial containing the GNR sample is placed in a warm water bath at 30-35°C for roughly 15 minutes. The vial is removed from the bath and the solution inside the vial is swirled gently. Following this, the contents of the remaining precipitated surfactant are examined visually. The process is repeated until a clear solution is obtained, if the precipitated surfactant is still seen.

800 and 850 nm wavelengths – The surfactants employed for the production of these GNRs have longer nonpolar chains, so they​ require more warming to homogenize the solution. The temperature and the duration of the water bath where the vial containing the GNR is placed are roughly 45°C and 20-25 minutes, respectively. The vial is removed from the bath and the solution (which now looks like a thick gel) is gently swirled, the constituents of the precipitated surfactant are then visually examined. Additional warming may be required for approximately 15 minutes at 45°C to obtain a clear solution, due to the presence of the high rheology surfactant. The solution may appear to be in the clear condition at different times during heating. However the surfactant will be precipitated out upon shaking the solution. The solution will appear homogenized when shaking the solution leads to air bubbles being entrapped within the viscoelastic gel, rather than precipitating out.

Additional Product Details

GNRs are small particles and it is possible to alter their surface plasmon resonance frequencies as a function of aspect ratio, providing them with optical properties that make them a potential candidate in a number of applications; ranging from the visible region to the near-infrared region in the electromagnetic spectrum. These anisotropic particles are utilized in a number of biomedical applications for their hyperthermal effects and as contrast agents for optical biomedical imaging.

The efficient exchange and removal of CTAB, a cationic surfactant with a very low critical micelle concentration, is a major barrier when applying GNR-based materials for in-vivo applications, such as hyperthermal cancer treatment. The function of the cytotoxic surfactant in the production of the GNRs is still a subject of discussion, but the general belief is that there is aformation of a strongly adsorbed bilayer by the CTAB around the surface of evolving GNRs. The most often used concentration of CTAB in their synthesis is 0.10 M or 100 times its critical micelle concentration. This means a considerable amount of CTAB is available in the bulk of the solution after the formation of the GNRs, which helps to stable them that they will be prevented from self-aggregating in solution.

The use of CTAB surfactant, a critical component for the GNR synthesis, is a major barrier for in-vivo applications. The CTAB is removed or partially exchanged using a number of methods, including frequent washing with solvents and treatments with surface active materials like PEGylated thiols or other polymers. Nevertheless, CTAB-coated GNR dispersions are always destabilized upon surfactant exchange, leading to particle aggregation and low GNR recovery yields. These surface modified GNRs often have residual CTAB as contaminants.

This information has been sourced, reviewed and adapted from materials provided by Strem Chemicals.

For more information on this source, please visit Strem Chemicals.

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