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, our non-functionalized spherical gold nanoparticles and non-functionalized gold nanourchins will irreversibly aggregate. This is indicated by a change in colour of the solution as seen for 15nm standard gold nanoparticles in the image 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 gold nanoparticle solution 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 below.
3. Remove supernatant and re-suspend in appropriate volume of ultra-pure water.
4. Vortex (sonication in an ultra-sonication bath can also help ) to re-disperse the pelleted gold nanoparticles.

*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. A centrifugation time of 30 minutes is generally sufficient for a 1mL sample in a 1.5mL microcentrifuge tube.

Gold Nanoparticle Diameter	Centrifugation Force	MWWCO Spin Column
5nm	N/A	Required
10nm	22,000 x g**	Highly recommended
15nm	17,000 x g	Recommended
20nm	10,000 x g	Optional
30nm	2,500 x g	Optional
40nm	1,400 x g	Optional
50nm	1,100 x g	Optional
60nm	900 x g	Optional
70nm	700 x g	Optional
80nm	600 x g	Optional
90nm	500 x g	Optional
100nm	400 x g	Optional

**For 10nm gold nanoparticles the recovery is estimated to be approximately 50% at this particular speed. For better recovery, 1) use an ultracentrifuge to achieve higher speeds or 2) use MWCO Spin Columns (any MWCO size is suitable for gold nanoparticles that are not being functionalized). While not required for sizes above 10nm, the use of MWCO Spin Columns will still improve product recovery. For centrifugation speeds and time for MWCO Spin Columns, please refer to Table II below.

Table II. Recommended centrifugation speeds and time for MWCO Spin Columns.

Spin Column Size	Centrifugation Force	Centrifugation Time
0.5 mL	10,000 x g	10 min.
4 mL	1,700 x g	10 min.
15 mL	1,700 x g	10 min.