The colloidal features suspension of a gold nanoparticle of submicrometre sized used within a fluid like water is colloidal gold. This liquid colors rich red for nanoparticles which are less than 100 nm. For particles more than 100 nm, this liquid turns blue or purple color. For centuries artists has been used them due to their reflectivity in light.
In recent times extensive research has proved the eligibility of the particle to be used for various advanced technical applications like sensory probes, drug delivery, organic photovoltaics, and theurapetic purposes in various medical and biological uses. One can tune the optical and electrical properties of gold nanoparticles.
Method of Gold Nanoparticle Synthesis
There are many ways to synthesize and produce gold. Gold nanoparticle synthesis can occur using –Turkevich method, Brust method, Perrault method, Martin method, Navarro method, Sonolysis, Block copolymer method and green chemistry techniques.
Generally this nanoparticle can be produced by some liquid chemical technique by reducing chlorauric acid. The solution after dissolving it is stirred at a fast pace. This colloidal nanoparticle gold is then added with a reducing agent.Au3+ ions are reduced to Au + ions. A disproportionate response occurs. Here Au3+ and 2Au+ ions get produced. A stabilizing agent helps the nanoparticles to be stable. The nucleation centre in this case surrounds around the Au0 atoms.
Properties of gold nanoparticles – optical and electrical
The optical interactions in between light source and gold nanoparticles are really strong. Various applications of the particle are made due to the gold nanoparticle synthesis and optical properties. It is also dictated by the particles size, physical properties, dimensions and environment.
The electric field of any light source which is oscillating close by colloidal nanoparticle gold reacts with the free natured electrons. Thus an accumulation of electron oscillation occurs which can also be termed as resonance of the frequency of the light source visible. These oscillations resonant in nature are also termed as surface plasmas.
If large amount of salt is added into a solution of gold nanoparticles the same phenomenon can be observed. The surface area charged because neutral in nature. Hence the gold nanoparticles accumulate. The solution changes its color from red to blue here. Polymer coating is added to minimize this aggregation.
They are also coated with small amount of molecules and molecules of various biological recognitions. The modifications made on their surface made these nanoparticles of gold to be of great use in engineering, biological, medical and chemical sector.
