Nanoparticle Synthesis

Table of Contents

What is a Nanoparticle?

A nanoparticle is a particle of matter that ranges between 1 to 100 nanometres in size. Compared to its bulk counterparts, nanoparticles hold unique physical, optical, and chemical properties due to quantum electronic effects observed at the nanoscale. Gold nanoparticles (AuNPs) in particular, have drawn attention in the field of bionanotechnology for their stability, versatility, and biocompatibility [1]. This page will be focusing on the use of gold nanoparticles in biosensing applications. 

What is Nanoparticle Synthesis? 

The synthesis of nanoparticles holds significance as it is what determines the properties of the resulting nanoparticles. The properties of nanoparticles are largely dependent on their shape, size, chemical surroundings and functional groups and the method used to synthesize nanoparticles will directly influence these elements. This page will explore the synthesis of gold nanoparticles via chemical reduction of gold salts, using a stabilizing agent.

How are Gold Nanoparticles Synthesized? 

Gold nanoparticles can be synthesized either by the chemical reduction of gold salts or by the physical treatment of bulk gold. The gold nanoparticles discussed in this page will be synthesized by chemical reduction methods so the exact shape, size, stability, and solubility can be controlled [1].  

The synthesis of gold nanoparticles by chemical reduction requires the use of an appropriate reducing agent and stabilizing agent [1]. The reducing agent is responsible for providing electrons to transform gold ions into elemental gold, which then combine to form gold nanoparticles. The capping agent, on the other hand, is responsible for stabilizing the gold nanoparticles by preventing its uncontrollable growth. The size and shape of the nanoparticles can be tuned based on different applications.

Nanoparticle Synthesis Methods

There are various well established methods used to synthesize nanoparticles that fit into the following two categories: bottom-up and top-down. The top-down approach involves milling, lithography and quenching and overall does not result in good control over the nanoparticle properties [3]. Bottom-up methods typically involve the chemical reduction of a salt.

The Frens Method is an example of a chemical reduction synthesis method and it produces gold nanoparticles with diameters of approximately 20nm. In this method, tetrachloroauric acid is reduced by sodium citrate dihydrate. In this reaction, the citrate also acts as a capping agent in order to increase the stability of the nanoparticles and maintain their size. 

Applications of Gold Nanoparticles 

The unique properties of gold nanoparticles allow for them to be used in high technology applications such as biosensing, drug delivery, bioimaging, water treatment, nanomanufacturing, electronics, catalysis, organic photovoltaics, and much more.

Specific information about applications of gold nanoparticles can be found here:

• Biosensing (Colorimetric Glucose Detection)
• Fuel Cells
• Water Purification 
• Solar Cells