Proprietary Surfactant as stabilizer
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12 - Non Combustible Liquids
The storage conditions that a Sigma-Aldrich catalog and label recommend for products are deliberately conservative. For many products, long-term storage at low temperatures will increase the time during which they are expected to remain in specification and therefore are labeled accordingly. Where short-term storage, shipping time frame, or exposure to conditions other than those recommended for long-term storage will not affect product quality, Sigma-Aldrich will ship at ambient temperature. The products sensitive to short-term exposure to conditions other than their recommended long-term storage are shipped on wet or dry ice. Ambient temperature shipping helps to control shipping costs for our customers. At any time, our customers can request wet- or dry-ice shipment, but the special handling is at customer expense if our product history indicates that the product is stable for regular shipment. See Shipping and Storage for more information.
If available for a given product, the recommended re-test date or the expiration date can be found on the Certificate of Analysis.
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The majority (>95%) of the gold nanoparticles are spherical.
No, the Gold nanoparticles should not be frozen. If frozen, the gold nanoparticles will irreversibly aggregate, turning the solution clear.
The size of gold nanoparticle to use is very depandent upon the intended application. Generally, smaller particles offer better sensitivity in applications such as immunogold labeling due to less steric hindrance and the ability to bind more gold nanoparticles to the desired target. Small gold nanoparticles are less visible than larger particles, however, which must also be taken into account.As an application example, particles with a size between 30-50nm are particularly useful for the development of rapid tests such as lateral flow assays.
Settling of gold nanoparticles on the bottom of the storage flask is completely normal and is especially common for larger sized particles, which settles at greater speed. Settling does not affect the performance of the particles. Prior to use, simply swirl the solution to properly disperse your gold nanoparticles and obtain a homogenous solution.
Due to repulsive forces arising from the surface charge of gold nanoparticles, an energy barrier must be overcome for individual particles to interact. When no (or small) amounts of electrolytes such as NaCl is present, this energy barrier is too strong for interaction to occur between particles. However, upon addition of NaCl this energy barrier is reduced allowing the gold nanoparticles to interact and aggregate. This aggregation causes a phenomenon called surface-plasmon coupling which changes the adsorption maximum of light to a higher wavelength resulting in a change in color of the solution.