Gold nanoparticles, 40nm, supplied in 0.1 mg/ml sodium citrate with stabilizer, OD1, 530nm absorption

Irreversible aggregation is characterized by a clear to bluish solution upon the addition of salt. 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.

Although it is not generally necessary to wash the gold nanoparticles prior to use, some applications may require additional washing procedures. The easiest way to remove possible contaminants in the nanoparticles solution is by centrifugation. Centrifugation force is dependent on size of the gold nanoparticles. We recommend the following to wash gold nanoparticles:
1. Place 1 mL aliquot of colloidal gold in a 1.5 mL microcentrifuge tube.
2. Centrifuge the gold nanoparticles for 30 minutes using the recommended G force based on particle size (see below).
3. Remove the supernatant and re-suspend in an appropriate volume of ultra-pure water.
4. Vortex to re-disperse the particles.

Centrifugation speed guide for nanoparticle size:
size - G force
5 nm - 100,000 g
10 nm - 17,000 g
15 nm - 17,000 g
20 nm - 6,500 g
30 nm - 4,500 g
40 nm - 2,500 g
50 nm - 2,000 g
60 nm - 1,125 g
80 nm - 600 g
100 nm - 400 g

Although it is not generally necessary to wash the gold nanoparticles prior to use, some applications may require additional washing procedures. The easiest way to remove possible contaminants in the nanoparticles solution is by centrifugation. Centrifugation force is dependent on size of the gold nanoparticles. We recommend the following to wash gold nanoparticles:
1. Place 1 mL aliquot of colloidal gold in a 1.5 mL microcentrifuge tube.
2. Centrifuge the gold nanoparticles for 30 minutes using the recommended G force based on particle size (see below).
3. Remove the supernatant and re-suspend in an appropriate volume of ultra-pure water.
4. Vortex to re-disperse the particles.

Centrifugation speed guide for nanoparticle size:
size - G force
5 nm - 100,000 g
10 nm - 17,000 g
15 nm - 17,000 g
20 nm - 6,500 g
30 nm - 4,500 g
40 nm - 2,500 g
50 nm - 2,000 g
60 nm - 1,125 g
80 nm - 600 g
100 nm - 400 g

We recommend 4°C storage for our Gold nanoparticles that are supplied in 0.1 mg/ml sodium citrate with stabilizer. Do not freeze the particles because this causes irreversible aggregation. When stored for a long period of time, gold nanoparticles may 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.