Gold Nanoparticle Handling and Storage

Storage

Store product away from direct sunlight at 4-25°C. Lower temperature prolongs the shelf life of the product. Do NOT freeze. If frozen, standard gold nanoparticles will irreversibly aggregate. This is indicated by a change in color of the solution, see figure below. When stored as specified the colloidal gold is stable for at least 1 year.

Handling

When stored for a long period of time the gold nanoparticles might sediment at the bottom of the flask, which is especially true for larger particle sizes. Prior to use, re-suspend the sedimented particles by swirling until a homogenous solution is obtained.
To maintain optimal performance, and stability of the colloidal gold, care should be taken to use clean storage containers if using other than supplied with the product.

Characterization of Gold Nanoparticles

Please read our “Introduction to Gold Nanoparticle Characterization” tech note for information on how to analyze gold nanoparticles and their properties.

Washing of Gold Nanoparticles

Although it is not always necessary to wash the gold nanoparticles prior to use, some applications might require additional washing procedures. The easiest way to remove possible contaminants in the nanoparticles solution is by centrifugation. Centrifugation force is dependant on size of the gold nanoparticles and should be adjusted according to table I for optimal performance.
Note:
Since non-functionalized gold nanoparticles are sensitive to salt containing buffers, re-suspension should always be performed in ultra-pure water to prevent irreversible aggregation. Irreversible aggregation is characterized by a clear to bluish solution upon the addition of salt.

Procedure

1. Place aliquot of colloidal gold in appropriate centrifuge tube.*
2. Centrifuge the gold nanoparticles for 30 minutes using the appropriate G force depending on size of the gold nanoparticles, see Table I.
3. Remove supernatant and re-suspend in appropriate volume of ultra-pure water.
4. Vortex to re-disperse particles.

*Note: Addition of Tween 20 to a final concentration of 0.025% (w/v) at this step improves performance during centrifugation and can prevent the formation of aggregates. However, Tween 20 binds to the gold surface and can slightly affect the adsorption of other molecules to the gold surface.

Table I. Appropriate G forces for centrifugation of gold nanoparticles. Note that recommended conditions are for a volume of 1ml and centrifugation using a microcentrifuge, except for 5nm gold nanoparticles that requires an ultracentrifuge.