Store silver nanoparticles at 2-8°C and protected from light. Do NOT freeze. If frozen, the silver nanoparticles will irreversibly aggregate. Aggregation of silver nanoparticles is indicated by change in color of the solution and an increase in the absorption of light in the red part of the visible spectrum, as detailed in our Silver Nanoparticle Properties Tech Note.
When stored as specified, the colloidal silver is stable for at least one year.
Large silver nanoparticles, i.e., above 60 nm in size, might sediment over time but will not affect the performance of the silver nanoparticles. Prior to use, re-suspend the sedimented particles by swirling the container until a homogenous solution is obtained.
For optimal performance and stability of the product, silver nanoparticles should not be stored diluted from the original concentration or in a bottle or flask other than that the product is supplied in. Care should be taken to use clean storage containers if other than supplied with the product.
Although it is not always necessary, washing of silver nanoparticles might be required for certain applications. Silver ions released from the silver nanoparticle surface may affect some applications. The easiest way to remove such possible contaminants from the silver nanoparticle solution is by centrifugation. Centrifugal force is dependent on the size of silver nanoparticles, as listed Table I.
Table I. Appropriate G force for the centrifugation of silver nanoparticles. The conditions are based on centrifuging 1 mL of silver nanoparticles in a 1.5 ml microcentrifuge tubes using a standard microcentrifuge.
|Size (nm)||Speed (g)||Time (min)|
*For 10nm silver nanoparticles, recovery was about 50% at the specified condition. For better recovery, 1) use an ultracentrifuge to achieve higher G force; 2) use a Centricon Spin Column.