Silver nanoparticle dissolution and ion release are important considerations in nanotoxicology and environmental studies. Dissolved and ionic silver can contribute substantially to the biological effects associated with silver nanoparticles, although toxicity also depends on particle properties, exposure conditions, and the biological or environmental system being studied.
The rate and extent of silver release depend on factors including nanoparticle size, surface area, surface chemistry, temperature, dissolved oxygen, light exposure, and the composition of the surrounding medium. Understanding these variables can help researchers distinguish effects associated with intact nanoparticles from those associated with dissolved silver species.
Need to quantify silver or other metals in your samples?
Our ICP-MS analytical service provides sensitive elemental concentration measurements for nanoparticle formulations, biological samples, and other materials.
How Particle Size Affects Silver Ion Release
At a fixed silver mass concentration, smaller nanoparticles provide more total surface area in contact with the surrounding solution. This greater specific surface area can increase the potential for oxidative dissolution and release of dissolved silver.
Particle curvature can also influence dissolution. At very small particle sizes, atoms at highly curved surfaces have higher surface energy and may be more susceptible to dissolution than atoms on larger, less curved particles. Surface coatings and the surrounding solution can either promote or inhibit this process.
The surface area-to-volume ratio of a sphere is inversely proportional to its diameter, as shown below.
| Nanosphere Diameter (nm) | Surface Area (nm2) | Volume (nm3) | Surface Area / Volume |
|---|---|---|---|
| 2 | 13 | 4 | 3.0 |
| 5 | 79 | 65 | 1.2 |
| 10 | 310 | 520 | 0.6 |
| 20 | 1,300 | 4,200 | 0.3 |
| 50 | 7,900 | 65,000 | 0.12 |
| 100 | 31,000 | 520,000 | 0.06 |
| 200 | 130,000 | 4,200,000 | 0.03 |
Surface area, volume, and surface area-to-volume ratio for spherical particles of different diameters. Values are rounded.
What Controls Silver Nanoparticle Dissolution?
Particle size is only one factor that determines silver release. Dissolution can also depend on:
- Surface chemistry: Ligands and coatings can change access to the silver surface and alter oxidation or dissolution rates.
- Dissolved oxygen: Oxidative dissolution of metallic silver requires an oxidizing environment, making oxygen availability an important variable.
- Temperature: Changes in temperature can affect the kinetics of dissolution and subsequent chemical reactions.
- Solution composition: Chloride, sulfide, pH, ionic strength, and other components can alter silver speciation, precipitation, and the concentration of dissolved silver.
- Light exposure: Silver nanoparticles and dissolved silver species can undergo light-dependent transformations, making consistent storage and exposure conditions important.
Because these variables interact, silver release measurements should be performed under conditions that closely match the intended experiment whenever possible.
Measuring Dissolved Silver with ICP-MS
To evaluate silver released from nanoparticles, the nanoparticle fraction must first be separated from the surrounding solution. Centrifugation, centrifugal filtration, ultrafiltration, dialysis, or other separation approaches may be appropriate depending on particle size and the experimental system.
After particle removal, inductively coupled plasma mass spectrometry (ICP-MS) can quantify the silver remaining in the particle-depleted fraction. This measurement is often described as dissolved silver concentration.
It is important to distinguish dissolved silver from free Ag+. ICP-MS measures the total amount of elemental silver in the analyzed fraction and does not independently identify its chemical form. Depending on the solution, measured silver may include free ions, soluble complexes, or other silver-containing species that remain after particle separation.
ICP-MS can also determine the total silver concentration of a nanoparticle suspension. In this case, the complete sample is digested before analysis so that both nanoparticulate and dissolved silver are included in the measurement.
Separating Silver Nanoparticles Before ICP-MS
The centrifugation conditions below have been used as starting points to separate aqueous silver nanospheres from their supernatant prior to silver analysis. Required conditions can vary with particle size, concentration, surface coating, dispersion medium, aggregation state, rotor geometry, and centrifugation path length.
Researchers should confirm that nanoparticles have been adequately removed before interpreting the silver concentration of the supernatant as a dissolved fraction.
| Nanosphere Diameter (nm) | Relative Centrifugal Force (×g) | Duration (min) |
|---|---|---|
| 10 | 40,000 | 120 |
| 20 | 25,000 | 90 |
| 30 | 20,000 | 60 |
| 40 | 16,000 | 45 |
| 50 | 15,000 | 30 |
| 60 | 14,000 | 30 |
| 80 | 12,000 | 30 |
| 100 | 9,000 | 30 |
Starting centrifugation conditions developed for aqueous silver nanosphere formulations. Verify adequate particle separation for the specific formulation and experimental conditions before analysis.
Comparing the dissolved silver fraction with the total silver concentration can provide useful information about nanoparticle dissolution and help researchers evaluate the relative contribution of intact particles and released silver species in nanotoxicology studies.
Planning a nanoparticle dissolution or metal analysis study?
Talk with our technical team about nanoparticle separation, ICP-MS analysis, sample preparation, or characterization strategies for your experimental system.
Related nanoparticle resources