Nanotoxicology Research Guide

Reliable nanotoxicology studies require more than selecting a nanoparticle and measuring a biological response. Particle size, surface chemistry, aggregation state, dissolution, formulation components, exposure conditions, and assay interference can all affect the observed result.

This guide outlines practical controls and characterization strategies for designing reproducible nanoparticle toxicology studies. It focuses on understanding the material that enters the experiment, how it changes in the exposure environment, and which factors may contribute to the measured biological response.

On this page

• Nanotoxicology Experimental Design
• Characterize the Starting Material
• Characterize Nanoparticles in Exposure Media
• Dose and Dosimetry
• Dissolved Species and Formulation Controls
• Endotoxin as an Experimental Confounder
• Nanoparticle Assay Interference
• Sample Preparation and Handling
• What to Report

Nanotoxicology Experimental Design

Nanoparticle properties can change between the stock container and the biological or environmental system being studied. Experimental design should therefore consider both the properties of the starting material and its behavior under the actual exposure conditions.

A useful nanotoxicology study should address several questions:

Question	Recommended Control or Measurement
What material is entering the experiment?	Characterize relevant properties such as primary size, morphology, hydrodynamic size, surface chemistry, concentration, and composition.
Does the material remain dispersed in the exposure medium?	Evaluate aggregation, agglomeration, settling, or other changes under relevant media and incubation conditions.
Does the nanoparticle dissolve or transform?	Measure dissolved elemental species or other transformation products when relevant to the material.
Could formulation components contribute to the response?	Include appropriate vehicle, dispersant, excipient, or particle-depleted formulation controls.
Could endotoxin influence the biological endpoint?	Measure endotoxin using a method demonstrated to work with the nanoparticle formulation.
Could the nanoparticle interfere with the biological assay?	Use particle-only, recovery, and other cell-free controls and consider an orthogonal assay when appropriate.
What dose actually reaches the biological target?	Consider sedimentation, diffusion, aggregation state, exposure time, and the most relevant dose metric.

Not every study requires every measurement. Select controls based on the nanoparticle composition, exposure system, biological endpoint, and research question.

Characterize the Starting Material

Begin with a well-characterized nanoparticle preparation. Differences in particle size, morphology, surface chemistry, purity, or concentration can produce differences in biological response even when materials share the same nominal composition.

Useful starting-material measurements may include:

• Primary particle size and morphology: TEM or another appropriate imaging method
• Hydrodynamic size: DLS or another solution-state sizing technique
• Surface properties: surface chemistry and, where relevant, zeta potential
• Elemental or mass concentration: ICP-MS, gravimetric analysis, or another appropriate quantitative method
• Optical properties: UV-Vis for plasmonic or optically active nanoparticles
• Purity and residual formulation components: based on synthesis and formulation chemistry
• Endotoxin: particularly for studies involving immune, inflammatory, or other endotoxin-sensitive endpoints

The Nanoparticle Characterization Techniques overview can help identify appropriate methods. More detailed measurement guidance is also available in our DLS, zeta potential, UV-Vis, TEM, and ICP-MS guides.

Use the Same Material Throughout Comparative Studies

Record the nanoparticle lot or batch used in the experiment. When comparing particle sizes, surfaces, or compositions, minimize unrelated formulation differences that could complicate interpretation.

For guidance on selecting materials for controlled comparisons, see Nanoparticle Selection for Nanotoxicology Studies.

Characterize Nanoparticles in the Exposure Medium

A nanoparticle characterized in water or its original storage medium may behave very differently after dilution into cell culture medium, serum, simulated biological fluid, environmental water, or another exposure matrix.

Changes in ionic strength, pH, proteins, dissolved organic matter, salts, and other components can alter particle-particle and particle-medium interactions. These changes may affect:

• Agglomeration and aggregation
• Hydrodynamic size
• Sedimentation rate
• Surface charge
• Surface chemistry
• Dissolution or degradation
• Cellular exposure and uptake

Monitor Stability Under Relevant Conditions

Where colloidal stability may influence the biological result, characterize the particles after preparation in the exposure medium and over an experimentally relevant time period.

For example, measurements may be collected immediately after dispersion and after selected incubation periods that correspond to the biological study. Use the same nanoparticle concentration, temperature, medium composition, and preparation procedure whenever possible.

DLS can monitor changes in hydrodynamic size, while UV-Vis spectroscopy can provide a sensitive measure of aggregation for plasmonic nanoparticles such as gold and silver. TEM provides valuable information about primary particle morphology but should not serve as the sole measure of aggregation in liquid because drying can bring particles together on the grid.

See Nanoparticle Storage, Handling, and Stability for additional guidance.

Biological Media Can Change the Nanoparticle Surface

Proteins and other biomolecules can adsorb to nanoparticle surfaces when particles enter biological fluids or protein-containing media. The resulting biomolecular or protein corona can alter the particle's effective surface properties, colloidal behavior, cellular interactions, and biological identity.

The exact corona depends on the nanoparticle surface and the biological environment. Protein adsorption may increase dispersion stability in one system and contribute to different interactions in another.

When biological media are part of the study:

• Record the medium composition and protein or serum concentration.
• Use consistent serum or protein conditions across comparison groups.
• Keep pre-incubation conditions and exposure timing consistent.
• Evaluate dispersion stability after the nanoparticle enters the relevant medium when stability may affect the study.

Order of Addition Can Matter

The sequence used to combine nanoparticles, salts, proteins, buffers, and other media components can affect the final dispersion state. A particle exposed abruptly to a high-ionic-strength environment may behave differently from the same particle introduced under different preparation conditions.

A single order of addition is not universally optimal. Establish a preparation sequence that produces the intended exposure condition, use it consistently, and document it. Characterizing the resulting dispersion provides stronger evidence than assuming a particular mixing sequence preserves stability.

Consider Dose and Dosimetry

Nanoparticle concentration in the exposure medium does not necessarily equal the dose delivered to cells or another biological target.

In static in vitro systems, particle transport depends on factors that include:

• Particle and agglomerate size
• Particle density
• Diffusion
• Sedimentation
• Exposure-medium height
• Aggregation state
• Exposure duration

Large or dense particles and agglomerates may settle onto adherent cells more rapidly than smaller or lower-density particles. Two materials tested at the same nominal mass concentration can therefore produce different delivered doses over the same exposure period.

Choose a Meaningful Dose Metric

Mass concentration such as µg/mL remains useful and should usually be reported, but other dose metrics may provide additional insight depending on the hypothesis:

• Mass concentration
• Particle number concentration
• Particle surface area
• Elemental concentration
• Administered dose per cell or culture area
• Measured or modeled delivered dose

The appropriate metric depends on the mechanism being investigated. Reporting more than one metric can make comparisons across particle sizes or materials easier to interpret.

For studies where delivered dose is especially important, direct measurement or an appropriate particle-transport model can help account for sedimentation and diffusion.

Separate Particle Effects from Dissolved Species and Formulation Components

A biological response observed after nanoparticle exposure may result from the particle itself, dissolved material released from the particle, soluble formulation components, or a combination of these factors.

Appropriate controls help distinguish these contributions.

Useful Formulation Controls

Control	Purpose
Medium or vehicle control	Establishes the baseline response of the exposure medium without nanoparticles.
Formulation/excipient control	Tests surfactants, stabilizers, buffers, or other known non-particle formulation components when they can be matched independently.
Particle-depleted fraction	Can evaluate soluble material remaining after validated particle separation.
Dissolved-species control	Tests an appropriate soluble form of a component, such as a metal salt, at a concentration relevant to the measured dissolved fraction.
Particle control	Provides the complete nanoparticle formulation for comparison with the component controls.

Particle Separation Requires Validation

Centrifugation, ultrafiltration, dialysis, or another separation method can be used to isolate a particle-depleted fraction, but no method should be assumed to provide complete particle removal or complete recovery of dissolved species.

Small nanoparticles may remain in a centrifuged supernatant or pass through some filters. Dissolved analytes can also adsorb to membranes, tubes, or particle surfaces. Validate the separation approach for the specific particle, medium, and analyte when quantitative interpretation depends on it.

Silver Nanoparticle Dissolution

Silver nanoparticles provide an important example because dissolved silver can contribute substantially to biological responses. The relative roles of particulate and dissolved silver depend on particle properties and the exposure environment.

Dissolution can change with factors such as:

• Particle size and available surface area
• Surface coating
• Temperature
• pH
• Dissolved oxygen
• Ionic strength
• Chloride, sulfide, proteins, and other ligands
• Exposure time

When ICP-MS is used to analyze a particle-depleted fraction, the result represents the elemental silver present in that operationally defined fraction. Conventional ICP-MS does not distinguish free Ag⁺ from soluble silver complexes or other dissolved silver species.

See Silver Nanoparticle Dissolution and Ion Release for detailed guidance.

Control for Endotoxin

Endotoxin contamination can produce inflammatory and immune responses that may be incorrectly attributed to the nanoparticle. This is particularly important when studying cytokine production, immune-cell activation, inflammatory signaling, or related biological endpoints.

Nanoparticles can also interfere with endotoxin assays through optical extinction, aggregation, adsorption, or interactions with assay reagents. A numerical endotoxin result should therefore be supported by appropriate assay-suitability controls.

For detailed guidance on sample dilution, optical interference, inhibition/enhancement controls, and interpretation, see the Endotoxin Measurement and Analysis Guide.

Evaluate Nanoparticle Assay Interference

Nanoparticles can interfere with biological assays independently of their effect on cells. Their optical, surface, catalytic, and adsorptive properties can alter assay signals and produce apparent increases or decreases in biological response.

Potential mechanisms include:

• Absorption or scattering at the assay detection wavelength
• Intrinsic fluorescence or fluorescence quenching
• Adsorption of dyes, proteins, enzymes, cytokines, or other analytes
• Direct oxidation or reduction of assay reagents
• Catalytic reactions with indicator molecules
• Interactions with assay enzymes or substrates
• Particle sedimentation into the measurement region

Common cytotoxicity, oxidative stress, fluorescence, and immunoassay formats can all be affected depending on the nanoparticle and experimental conditions.

Include Cell-Free Interference Controls

Useful controls may include:

• Nanoparticle + assay reagent without cells: tests whether the nanoparticle directly generates or suppresses the analytical signal.
• Nanoparticle + known analyte or assay standard: tests whether the nanoparticle affects recovery of the measured analyte.
• Nanoparticle + medium blank: establishes particle-related optical or fluorescent background.
• Orthogonal biological endpoint: confirms an important result using a detection principle that is affected differently by the nanoparticle.

Perform interference controls at nanoparticle concentrations relevant to the biological experiment. Assay interference is often concentration dependent.

When a strong biological conclusion depends on one analytical assay, confirmation with an independent method can substantially strengthen interpretation.

Standardize Sample Preparation and Handling

Nanoparticle exposure preparation should be reproducible across experiments. Small differences in dilution, mixing, sonication, incubation, or order of addition can change the final dispersion.

Start with Product-Specific Handling Guidance

Storage and handling requirements vary with nanoparticle material, surface chemistry, solvent, and concentration. Follow the specifications and handling guidance for the individual formulation rather than applying one storage condition to every nanomaterial.

Before withdrawing an aliquot, confirm that settled material has been appropriately redispersed without introducing a treatment that changes the particle population.

Document Dilution and Dispersion Procedures

Record:

• Stock concentration
• Dilution sequence
• Dilution medium
• Order of component addition
• Mixing or vortexing conditions
• Sonication method, if used
• Pre-incubation time and temperature
• Time between preparation and dosing

If sonication is required, document the method rather than simply reporting that the sample was sonicated. Sonication intensity, duration, equipment, sample volume, and temperature can influence dispersion and may affect particle coatings or other material properties.

Use Dispersing Agents Carefully

Surfactants, solvents, proteins, and other dispersing agents can improve colloidal stability but may also alter nanoparticle surface properties or affect the biological system.

Avoid adding unnecessary dispersants. When a dispersing agent is required, use an appropriate matched vehicle control and keep its concentration consistent across comparison groups.

Monitor Time-Dependent Changes

Particles may remain stable immediately after preparation and change during the exposure period. Where this behavior matters, monitor the dispersion over a time course that reflects the actual experiment.

Time-dependent characterization is particularly important when:

• Particles visibly settle
• DLS size changes after dilution
• UV-Vis spectra change over time
• The exposure medium contains high salt or protein concentrations
• The material can dissolve or degrade
• Different experimental groups receive particles at different times after preparation

What to Report in a Nanotoxicology Study

Transparent reporting makes nanotoxicology results easier to interpret, compare, and reproduce. Include the parameters that materially affect the exposure and biological endpoint.

Nanoparticle identity and characterization

• Material and composition
• Manufacturer or synthesis method
• Lot or batch identifier
• Primary particle size and morphology
• Relevant surface chemistry
• Nanoparticle concentration and measurement method
• Hydrodynamic size or dispersion state when relevant
• Zeta potential or other surface-property measurements when relevant

Exposure preparation

• Stock and final nanoparticle concentrations
• Exposure medium composition
• Protein or serum concentration
• pH and other relevant solution conditions
• Mixing, sonication, or dispersion procedure
• Order of addition
• Pre-incubation conditions
• Exposure duration

Behavior under exposure conditions

• Aggregation or agglomeration state when relevant
• Time-dependent stability
• Sedimentation observations
• Dissolution or degradation where applicable
• Relevant dissolved-species concentration

Experimental controls

• Vehicle and formulation controls
• Dissolved-species controls where relevant
• Endotoxin measurement where appropriate
• Nanoparticle assay-interference controls
• Positive and negative biological controls

Dose information

• Nominal concentration and dose units
• Additional mass, particle-number, or surface-area metrics when useful
• Culture geometry and medium height when relevant to dosimetry
• Delivered-dose measurement or modeling when performed

A nanotoxicology result becomes substantially more informative when the experimental design can distinguish the biological effect of the nanoparticle from changes in dispersion state, dissolved components, formulation chemistry, contamination, and analytical artifacts.

Selected References

1. Guidance on Sample Preparation and Dosimetry for Manufactured Nanomaterials, 2025 Edition. OECD Series on the Safety of Manufactured Nanomaterials and other Advanced Materials. 2025.
2. Clogston, J.D. Parameters, Methods and Considerations for the Physicochemical Characterization of Colloidal Metal Nanoparticles. National Cancer Institute Nanotechnology Characterization Laboratory Assay Cascade Protocols. Version 2. 2024.
3. Guidance Document for the Testing of Dissolution and Dispersion Stability of Nanomaterials, and the Use of the Data for Further Environmental Testing and Assessment. OECD Series on Testing and Assessment No. 318. 2020.
4. Hinderliter, P.M., Minard, K.R., Orr, G., et al. ISDD: A computational model of particle sedimentation, diffusion and target cell dosimetry for in vitro toxicity studies. Particle and Fibre Toxicology. 2010;7:36.
5. MacCormack, T.J., Meli, M.-V., Ede, J.D., et al. Revisiting nanoparticle-assay interference: There's plenty of room at the bottom for misinterpretation. Comparative Biochemistry and Physiology Part B. 2021;252:110601.
6. Hajipour, M.J., Safavi-Sohi, R., Sharifi, S., et al. An Overview of Nanoparticle Protein Corona Literature. Small. 2023;19(36):e2301838.
7. Ahmed, K.B.R., Nagy, A.M., Brown, R.P., et al. Silver nanoparticles: Significance of physicochemical properties and assay interference on the interpretation of in vitro cytotoxicity studies. Toxicology in Vitro. 2017;38:179-192.

---

Related nanotoxicology resources

• Nanotoxicology Overview
• Nanoparticle Selection for Nanotoxicology Studies
• Nanoparticle Storage, Handling, and Stability
• Silver Nanoparticle Dissolution and Ion Release
• Endotoxin Measurement and Analysis Guide
• Gold Nanoparticle Safety
• Silver Nanoparticle Safety