Gold Nanostar Synthesis with a Silver Seed Mediated Growth Method

Summary

We synthesized star shaped gold nanostars using a silver seed mediated growth method. The diameter of the nanostars ranges from 200 to 300 nm and the number of tips vary from 7 to 10. The nanoparticles have a broad surface plasmon resonance mode centered in the near infrared.

Abstract

The physical, chemical and optical properties of nano-scale colloids depend on their material composition, size and shape ^1-5. There is a great interest in using nano-colloids for photo-thermal ablation, drug delivery and many other biomedical applications ⁶. Gold is particularly used because of its low toxicity ^7-9. A property of metal nano-colloids is that they can have a strong surface plasmon resonance ¹⁰. The peak of the surface plasmon resonance mode depends on the structure and composition of the metal nano-colloids. Since the surface plasmon resonance mode is stimulated with light there is a need to have the peak absorbance in the near infrared where biological tissue transmissivity is maximal ^{11, 12}.

We present a method to synthesize star shaped colloidal gold, also known as star shaped nanoparticles ^13-15 or nanostars ¹⁶. This method is based on a solution containing silver seeds that are used as the nucleating agent for anisotropic growth of gold colloids ^17-22. Scanning electron microscopy (SEM) analysis of the resulting gold colloid showed that 70 % of the nanostructures were nanostars. The other 30 % of the particles were amorphous clusters of decahedra and rhomboids. The absorbance peak of the nanostars was detected to be in the near infrared (840 nm). Thus, our method produces gold nanostars suitable for biomedical applications, particularly for photo-thermal ablation.

Protocol

1. Silver seed preparation

1. Prepare a stock solution of silver nitrate (AgNO₃) by taking an arbitrary mass and mixing it with 10 mL of deionized (DI) water. Calculate molarity of the solution. Keep the solution in a dark place to isolate it from light.
2. Add 14.7 mg of sodium citrate tribasic (Na₃C₆H₅O₇) to 10 mL of DI water to make a 5 mM solution. Shake the vial until the powder is dissolved.
3. Add 15.1 mg of sodium borohydride (NaBH₄) to another vial with 10 mL of DI water to make a 40 mM solution. Close the vial immediately. Gently shake the solution by hand and place it i....

Discussion

In this work we have presented a method to synthesize gold nanostars using silver seeds. We found that silver seeds resulted in a yield of 70 % production of nanostars. The nanostars have a near infrared absorption peak, corresponding to their surface plasmon resonance mode, centered between 800 nm and 850 nm ^{7, 23}. These properties properties allow our gold nanostars to be of use for biomedical applications ^24-26, such as photo-thermal ablation.

A major difference betwe.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Sodium citrate tribasic dehydrate	Sigma-Aldrich	S4641	99.0 %
Silver nitrate	Aldrich	204390	99.9999 %
Sodium borohydride	Aldrich	213462	99 %
L-Ascorbic acid	Sigma-Aldrich	255564	99+ %
Gold chloride trihydrate	Aldrich	520918	99.9+ %
Hexadecyltrimethylammonium bromide (CTAB)	Sigma-Aldrich	H6269
JEOL 2010-F	JEOL		Transmission electron microscope
Hitachi S-5500	Hitachi		Used in scanning electron microscope mode
Olis Cary-14 spectrophotometer	Olis		Spectrophotometer