Proper nanoparticle storage and handling are important for maintaining particle size, dispersion state, surface chemistry, and other properties that can affect experimental results. Nanoparticles may respond to changes in temperature, light exposure, ionic strength, pH, contaminants, or the composition of the surrounding medium.
For biological and nanotoxicology studies, researchers should also consider what happens after nanoparticles enter the experimental system. Agglomeration, settling, surface interactions, and dissolution can change the effective dose and properties of the material during an experiment.
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Nanoparticle Storage and Handling
Storage requirements vary with nanoparticle material, surface chemistry, concentration, and solvent. Always follow the storage and handling instructions provided for the specific product. In general, careful handling can help prevent changes in particle dispersion or surface properties.
- Follow the recommended storage temperature. Avoid freezing aqueous nanoparticle suspensions unless the product documentation specifically permits it.
- Limit unnecessary light and air exposure. Light-sensitive materials, including many silver nanoparticle formulations, should remain protected from light when not in use.
- Prevent contamination. Use clean labware and pipette tips when transferring nanoparticles. Trace contaminants can alter surface chemistry or destabilize sensitive colloidal formulations.
- Recap containers promptly. Limiting exposure to the surrounding environment reduces the potential for contamination, evaporation, or chemical changes.
- Redisperse settled particles before sampling. Some nanoparticles may settle during storage. Mix according to the product-specific handling instructions to obtain a representative sample. Avoid unnecessary sonication unless recommended for the formulation.
For nanoComposix products, consult the storage and handling document associated with the individual product before use.
How to Verify Nanoparticle Stability
Monitoring nanoparticle properties before and during a study can help distinguish a biological or environmental response from changes in the particle formulation itself. Establishing a baseline when the material is received also provides a useful reference for later measurements.
Several characterization methods can help assess nanoparticle stability:
- Visual inspection: Plasmonic nanoparticles such as gold and silver have characteristic colors that depend on their optical properties and dispersion state. Visible color changes, sediment, or particulates can indicate a change in the formulation, although visual inspection alone cannot confirm stability.
- UV-Visible spectroscopy: UV-Vis spectroscopy is particularly useful for monitoring plasmonic nanoparticles. Changes in peak position, width, or long-wavelength extinction can indicate aggregation or other changes in the particle system. Comparing measurements with an initial baseline can help track stability over time.
- Dynamic light scattering (DLS): DLS measures hydrodynamic particle size in suspension and is highly sensitive to the presence of larger aggregates. Comparing hydrodynamic diameter and size distribution over time can help identify changes in colloidal stability.
- Transmission electron microscopy (TEM): TEM directly evaluates particle size, morphology, and size distribution. It can help determine whether changes observed by other methods reflect changes to the primary particle size rather than reversible agglomeration in solution.
No single characterization technique describes every aspect of nanoparticle stability. Combining complementary methods such as UV-Vis, DLS, and TEM can provide a more complete understanding of changes to the particle system. Learn more about nanoparticle characterization techniques.
Nanoparticle Agglomeration in Biological Media
Introducing nanoparticles into salts, buffers, cell culture media, or other complex solutions can change their colloidal stability. Increased ionic strength can screen electrostatic repulsion between particle surfaces, while proteins and other biomolecules can adsorb to the nanoparticle surface and alter interparticle interactions.
The extent and rate of agglomeration depend on nanoparticle material, size, surface chemistry, concentration, and the composition of the surrounding medium. Once particles agglomerate, their effective hydrodynamic size and settling behavior change, which can alter the dose delivered to cells or other components of the experimental system.
Whenever possible, evaluate nanoparticle stability under conditions that closely approximate the intended experiment. A particle-free version of the relevant medium can provide a useful starting point when cells, tissues, or environmental particulates would otherwise interfere with characterization.
Monitoring UV-Vis spectra or DLS hydrodynamic diameter over time can help determine whether agglomeration occurs immediately or develops gradually. If particle properties change rapidly after preparation, consistent timing between sample preparation and dosing becomes especially important for experimental reproducibility.
Surface chemistry can strongly influence this behavior. Sterically stabilized surfaces such as PEG may tolerate substantially higher ionic strength than small, charge-stabilizing ligands such as citrate. For additional examples, see Salt Stability of Nanoparticles.
Nanoparticle Dissolution During Experiments
Some nanomaterials can partially dissolve during an experiment, producing soluble species that contribute to the observed biological or environmental response. Silver nanoparticles are an important example because dissolved silver species can contribute to effects attributed to the nanoparticle formulation.
Dissolution depends on multiple variables, including particle size, surface chemistry, temperature, dissolved oxygen, pH, and surrounding solution chemistry. Smaller nanoparticles generally provide greater surface area per unit mass and may therefore exhibit greater dissolution potential under equivalent conditions.
Researchers can evaluate dissolved material by separating nanoparticles from the surrounding solution using an appropriate filtration, centrifugation, or other separation method and analyzing the particle-depleted fraction. ICP-MS can quantify elemental silver or other metals in this fraction, although the measurement represents total elemental concentration and does not by itself distinguish free ions from soluble complexes.
When dissolution may affect an experiment, measuring both nanoparticle stability and the dissolved fraction can help distinguish changes in the intact particle population from effects associated with released species. See Silver Nanoparticle Dissolution and Ion Release for additional guidance.
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