Reporter nanoparticle selection is one of the most important decisions in lateral flow assay development. The reporter can affect achievable sensitivity, stability in the sample matrix, assay cost, development time, and whether a reader is required for signal detection. Starting with high-quality, well-characterized particles also helps support reproducible assay performance.
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Not sure which gold reporter to start with?
Use our interactive Particle Selection Guide to compare gold nanoparticle options based on your diagnostic assay needs.
Choosing a Gold Reporter Nanoparticle
Gold nanoparticles are widely used as visual reporters in lateral flow assays because their optical properties generate a visible signal without requiring specialized instrumentation. The appropriate particle depends primarily on the sensitivity required, the assay format, and how the recognition molecule will be attached to the particle surface. For a broader overview of nanoparticle options across diagnostic applications, see Nanoparticles for Precision Diagnostics.
| Reporter | When to Consider It | Explore |
|---|---|---|
| 40 nm Gold Nanospheres | Established starting point for many visual lateral flow assays when conventional gold provides sufficient signal. | 40 nm Gold |
| 80 nm Gold Nanospheres | Consider when greater visual signal is needed while retaining a spherical gold reporter format. | 80 nm Gold |
| 150 nm Gold Nanoshells | Consider when conventional gold nanospheres cannot generate sufficient contrast at the required cutoff. | Gold Nanoshells |
While 40 nm gold has historically been a common reporter for lateral flow assays, increasing particle size can increase the optical signal generated by each binding event. Gold nanoshells provide an additional option when conventional gold nanospheres cannot generate sufficient contrast at the required cutoff. For more information, see Gold Nanoshells for Maximizing Visual Detection Sensitivity.
Choosing a Conjugation Strategy
Once you select the reporter size and structure, the next decision is how to attach the antibody, protein, or other recognition molecule to the particle surface. Passive adsorption, covalent conjugation, and streptavidin-biotin binding each offer different advantages depending on the assay and biomolecule.
Passive Adsorption
Passive adsorption is the traditional method for attaching proteins to gold nanoparticle reporters. Antibodies spontaneously associate with a citrate-stabilized gold surface through intermolecular forces. The process is relatively straightforward, but conjugation conditions are antibody-dependent and typically require optimization of pH and antibody loading. Because the protein is not covalently attached to the particle, conjugate stability can also depend on the sample and buffer conditions.
Covalent Conjugation
Covalent conjugation permanently attaches antibodies or other amine-containing molecules to carboxyl-functionalized nanoparticles. BioReady carboxyl nanoparticles use EDC/sulfo-NHS chemistry to form an amide bond between the particle surface and accessible primary amines on the protein. Covalent conjugates can provide increased stability in challenging sample matrices and allow greater control over antibody-to-particle loading.
Streptavidin-Biotin Binding
If the antibody, protein, or oligonucleotide is available in biotinylated form, a streptavidin-functionalized reporter can provide a convenient alternative to performing the conjugation chemistry directly.
Explore BioReady™ nanoparticles and conjugates for diagnostics to compare available particle sizes, surfaces, and conjugation formats.
Other Reporter Particles for Lateral Flow
Gold is not the only reporter material used in lateral flow assays. Dyed polystyrene particles and cellulose beads can provide visible signals, while fluorescent reporters such as europium beads and up-converting nanoparticles can support higher-sensitivity reader-based assays. Fluorescent reporters require specialized instrumentation for signal detection and quantification, and particle surface chemistry and lot-to-lot consistency should also be considered when selecting these materials.
The best reporter ultimately depends on the assay format, required sensitivity, target concentration range, conjugation strategy, cost requirements, and available reader technology. Because subsequent conjugation and assay-development steps depend on the particle selected, it is useful to establish the reporter strategy early in development.
For additional guidance on choosing nanoparticles for diagnostic applications, explore our Nanoparticles for Precision Diagnostics resource or contact our technical team for help selecting a reporter particle.
Next: Choose your conjugation method