We specialise in the manufacture of Traditional Amber Colloidal Silver, which contains silver nanoparticles. These nanoparticles absorb and scatter light with extraordinary efficiency and the yellow colour is caused by surface plasmon resonance (SPR). By controlling the particle size, shape, and the local refractive index near the particle surface, nanoparticle absorption and scattering properties can be finely tuned.
Smaller nanospheres primarily absorb light and have peaks near 400 nm, while larger spheres exhibit increased scattering and have peaks that broaden and shift towards longer wavelengths (known as red-shifting), so the yellow colour indicates the smaller particle sizes.
Please note that the colour only appears with concentrations over 5 PPM. It is easy to see this colour in large vessels but is less obvious in small quantities.
The yellow colour of the solution relates to unaggregated silver nanoparticles. Unaggregated silver nanoparticles will have a yellow colour in solution. If the particles aggregate, the solution with appears grey. The Yellow colour also relates to the stability of the solution, as it achieves a desired zeta potential and pH. Nanoparticles are either charge stabilized or sterically stabilized. For charge stabilized particles, the zeta potential is a measure of the particle’s stability. Typically, nanoparticles with zeta potentials greater than 20 mV or less than -20mV have sufficient electrostatic repulsion to remain stable in solution.”
Extinction (the sum of scattering and absorption) spectra of NanoXact silver nanoparticles with diameters ranging from 10 – 100 nm at mass concentrations of 0.02 mg/mL. BioPure nanoparticles have optical densities that are 50-times larger.)
Dried nanoparticles are aggregated and in nearly all cases cannot be re-dispersed as individual particles.
Most clear Colloidal Silver solutions do not contain any or a very small percentage of silver particles and tend to be ionic silver water solutions only.
This picture shows the amber colour in the large 3-litre reaction vessels. The colour is subtle in smaller amounts indicating the correct particle size range. The stronger the colour, the larger the particles which is NOT desirable.