Nanoparticle Frequently Asked Questions

I can’t find the material or size I need. Can nanoComposix make it?

Yes. We develop custom metal, metal oxide, silica, and polymeric nanoparticles with tailored size, composition, morphology, surface chemistry, and formulation. Learn more about Custom Nanoparticle Development.

Can you modify the surface or conjugate a biomolecule to my nanoparticles?

Yes. We support custom surface modification and conjugation of antibodies, proteins, nucleic acids, peptides, and other biomolecules. Explore Custom Conjugate Development & Manufacturing.

What manufacturing scale can nanoComposix support?

We support projects from research-scale material through bulk supply and scaled manufacturing. Available scale depends on the particle composition, formulation, and process. Contact our team to discuss your volume and manufacturing requirements.

My nanoparticles settle during storage. Is this normal?

Larger or denser nanoparticles can gradually settle during storage without necessarily indicating irreversible aggregation. Redisperse the material before use according to the handling instructions provided with the product. If the particles do not readily redisperse or their appearance has changed substantially, contact our technical team.

Do you offer “bare” or uncapped gold nanoparticles?

Colloidal nanoparticles require surface stabilization to remain dispersed, so a truly bare gold nanoparticle would rapidly aggregate. Weakly bound stabilizers such as citrate can provide colloidal stability while allowing subsequent ligand exchange, passive adsorption, or other surface modification.

Learn more about citrate surface chemistry and other nanoparticle surfaces in our Knowledge Base.

Why isn’t the peak wavelength of my gold nanorods or nanoshells exactly at the nominal wavelength?

Gold nanorods and nanoshells have relatively broad optical resonances. For wavelength-specified materials, nanoComposix uses an optical specification based on the extinction at the advertised wavelength relative to the peak extinction. A small shift in the exact peak wavelength can therefore occur while the material remains within specification and retains strong absorption and scattering near the target wavelength.

Do silver nanoparticles oxidize?

Yes. Silver nanoparticles can undergo oxidation and reactions with sulfur-containing species. The extent and rate depend on particle size, surface chemistry, formulation, and environmental conditions. These processes can influence silver-ion release and particle properties over time.

Are silver nanospheres amorphous or crystalline?

Silver nanospheres are generally polycrystalline. Individual particles can contain multiple crystal domains while maintaining an overall spherical morphology. These domains may appear as lines or regions of varying contrast in TEM images.

Do silver nanoparticles have antimicrobial activity?

Yes. Silver nanoparticles are widely studied for antimicrobial applications. Their activity is influenced in part by silver-ion release, which depends on particle size, shape, surface chemistry, concentration, and environmental conditions.

Learn more about Antimicrobial Silver Nanoparticles.

How can I tell if my silver nanoparticle dispersion has destabilized?

Changes in solution color or the UV-Visible spectrum can indicate aggregation or other changes in particle state. Aggregation commonly broadens or shifts the plasmon resonance. Comparing a current UV-Vis spectrum with the original product spectrum or Certificate of Analysis can help identify significant changes.

Are silica nanospheres amorphous or crystalline?

Colloidal silica nanoparticles are amorphous rather than crystalline. Their atomic structure lacks the long-range order found in a crystalline material and is more similar to bulk glass.

What are silica nanoparticles used for?

Silica nanoparticles support a broad range of applications because their particle size, porosity, and surface chemistry can be tailored. Applications include drug delivery, biosensing, catalysis, optical systems, coatings, and other engineered materials.

See Silica Nanoparticle Applications for more detail.

How many amines are on the surface of aminated silica nanoparticles?

Based on the reagent loading used during surface functionalization and the available particle surface area, we calculate a theoretical maximum of approximately 2.5 amine groups/nm². The number of amines accessible for conjugation can be lower because of ligand orientation, packing density, and incorporation of some amines below the accessible particle surface.

Do you offer membranes, pads, and backing materials for lateral flow development?

Yes. nanoComposix offers lateral flow development materials including nitrocellulose membrane, conjugate pads, sample pads, absorbent pads, and backing materials. See our Lateral Flow Material Starter Kit or contact us for application-specific needs.

Which nanoparticle should I start with for a lateral flow assay?

40 nm gold nanospheres are a common starting point for visual lateral flow assays. If greater visual signal is needed, larger gold nanospheres or 150 nm gold nanoshells can provide stronger optical response per particle. The best reporter depends on assay format, target sensitivity, conjugation strategy, and flow behavior.

See our Reporter Nanoparticle Selection Guide.

When should I consider gold nanoshells for lateral flow?

Gold nanoshells can be useful when conventional gold nanospheres do not generate enough visual contrast at the required cutoff. Their larger optical cross section can produce stronger signal per particle, although assay-level sensitivity still depends on conjugation, membrane behavior, target concentration, and overall assay design.

Learn more about Increasing Lateral Flow Assay Sensitivity.

What is the difference between carboxyl and NHS-activated particles?

Carboxyl-functionalized particles use EDC/Sulfo-NHS chemistry to activate surface carboxyl groups before coupling to primary amines on a protein or other biomolecule.

For current catalog products, NHS activation is available as a 150 nm gold nanoshell conjugation format. The activated NHS ester can react directly with primary amines, reducing the number of conjugation steps compared with starting from a carboxyl surface.

What conjugation kits and protocols are available?

nanoComposix offers conjugation kits and protocols for passive adsorption, covalent conjugation, streptavidin-based binding, NHS-activated gold nanoshells, magnetic particles, and other common workflows.

Explore BioReady Conjugation Kits and our Conjugation Protocols.

How are nanoComposix materials characterized?

nanoComposix materials include batch-specific characterization appropriate to the product. Depending on the material, documentation may include TEM, UV-Visible spectroscopy, DLS, zeta potential, concentration, pH, and other product-specific tests.

See Nanoparticle Characterization Techniques for an overview of the major methods.

How do you calculate nanoparticle size and coefficient of variation by TEM?

Mean particle size is calculated from individual nanoparticle measurements in TEM images. The coefficient of variation (CV) describes the width of the size distribution relative to the mean:

CV (%) = standard deviation ÷ mean particle size × 100

For example, a 50 nm particle population with a 3 nm standard deviation has a CV of 6%.

Can I request the raw characterization data associated with my Certificate of Analysis?

Yes. Individual characterization files or a more complete data package can be provided by request. Please include the relevant lot number when contacting us.

Characterization Data Purchase Options

Available data include:

• TEM images: original full-size image files
• TEM sizing data: individual particle-size measurements
• UV-Vis: spectrophotometer measurement data and dilution information
• DLS: summary data table; Malvern software PDF report available for an additional $15
• Zeta potential: summary data table; Malvern software PDF report available for an additional $15
• ICP-MS report: contact us for details

Contact us to request characterization data and include the lot number of the material in your request.

Why does my specification sheet list DLS or zeta potential as N/A?

DLS and zeta potential depend on detecting light scattered by particles in suspension. Very small particles, dilute samples, or materials with low scattering intensity may not generate enough signal for a reliable measurement. In these cases, TEM or another sizing method may provide more useful information.

See our measurement guidelines for additional guidance on DLS, zeta potential, TEM, UV-Vis, and other characterization methods.

Why might I see a second population of very small particles when imaging silver nanoparticles by TEM?

In some cases, functionalized TEM grids can create an imaging artifact. Amine-, thiol-, or carboxyl-functionalized surfaces may act as nucleation sites for dissolved silver ions, producing small particles on the grid that were not present as a second nanoparticle population in the original dispersion.

Carbon-coated Formvar grids are generally preferred for imaging silver nanoparticles when this artifact is a concern. This phenomenon has also been described in the literature: Glover et al., ACS Nano ↗.

What types of nanoparticles can be imaged by TEM?

TEM works best when the particles have sufficient electron-density contrast relative to the supporting film. Metals such as gold and silver, many metal oxides, silica, magnetic nanoparticles, and other inorganic materials are generally well suited to TEM imaging.

Low-density polymers, biomolecules, and some organic materials can provide lower contrast and may require specialized preparation or staining.

How should I prepare a sample for TEM analysis?

Clean, well-dispersed samples generally produce the clearest TEM images. Residual salts, polymers, biomolecules, surfactants, or other solution components can dry onto the TEM grid and obscure the nanoparticles.

Provide as much information as possible about particle composition, expected size and shape, concentration, solvent, and residual formulation components. This information helps determine an appropriate preparation approach.

What if my TEM images do not look as expected?

Unexpected images can result from particle concentration, sample preparation, residual solution components, low material contrast, or the selected imaging conditions. Depending on the sample, next steps may include re-imaging at another dilution, modifying grid preparation, or processing the sample before imaging.

Contact our team to discuss the sample and possible next steps.

How does the surrounding environment affect nanoparticle optical properties?

The localized surface plasmon resonance of gold and silver nanoparticles depends on the refractive index of the surrounding environment. Moving a particle into a higher-refractive-index medium generally shifts the resonance toward longer wavelengths.

Adding a silica shell also changes the local optical environment. The magnitude of the spectral shift depends on factors such as particle size, core composition, shell thickness, and surrounding refractive index.

Use our Mie Theory Calculator to explore how these variables influence calculated extinction, absorption, and scattering.

How do I choose a nanoparticle for a specific optical response?

Particle composition, size, shape, shell structure, and surrounding refractive index all influence nanoparticle absorption and scattering. Start by defining the wavelength range and whether your application requires stronger absorption, scattering, field enhancement, or refractive-index sensitivity.

Our Mie Theory Calculator can help compare spherical and core-shell structures, while Nanomaterials for Optical Engineering provides application-focused guidance. For additional background, see The Science of Plasmonics.