Synthesis of gold nanorods

AIM :  Synthesis of gold nanorods using seed mediated method.

Publication referred : “Azide-Derivatized Gold Nanorods : Functional Materials for “Click” Chemistry.” Anand Gole and Catherin J Murphy (ACS 2008,24,266-72)

Abstract : Seed mediated gold nanorods synthesis is a two step procedure. Firstly, we need to synthesis gold seeds and then make growth solution.

PART 1 – Let us start by first learning how to make seed solution.

Materials and Equipment Required for Seed Solution:

Chemicals :

1. 0.6 ml, 10mM, NaBH4(Sodium borohydride; mol. wt. 37.83 da or g/mol; 1 dalton = 1 gram/mol)

2. 10 ml, 0.1 M, Gold Solution ( prepared from Gold (III) chloride trihydrate)

3. 10 ml, 0.1 M, CTAB solution ( Centrimonium bromide; mol. wt. 364.45 da)

4. Other equipment : 50 ml conical flask (1), magnetic stirrer, 10 ml standard flask (1), 25 ml beaker (1), crushed ice, magnetic bead, micro-pipette, lots of DI water. 

Procedure :

Step 1 : Wash all the utensils first with chromic acid followed by soap water, followed by DI water. Wash again by DI water. [this is the first and foremost step and very important too as we dont want any impurities because a dust particle of even 10nm radius can hinder the growth and create toxicity which we can not afford as these gold rods will be used in biological applications.]

Step 2 : Take 10 ml DI water in 50 ml conical flask. Now take CTAB; weigh it for 364.45 mg, and mix it with water in conical flask. Sonicate if it doesn’t disperse completely. Put the flask on stirrer with magnetic bead inside. [CTAB is a surfactant here.] 

Step 3 :  Take 3.7 mg NaBH4 in 10 ml DI water in 10 ml standard flask. [If small bubbles are observed then that’s the confirmation of NaBH4 dissolving in water.]

Step 4 : Now, pick 25 µl (microlitre) of gold solution from micro-pipette and pour it in the CTAB solution kept on stirrer. [the color of the solution should change to gold; if not, do over.]

Step 5 : Now, pick 600 µl of NaBh4 solution and add drop by drop to the golden colored (CTAB+Gold) solution kept on stirrer. [the color should become light brown after neutralizing golden color. Brown color confirms the formation of gold seeds.]

Step 6 : Stir for another 10 minutes and keep this beautiful seed solution aside for later use. 

Step 7 : Proceed to synthesis of growth solution by acquiring and  washing chemicals and equipment mentioned in the next part.