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80 nm Gold Nanospheres for Covalent Conjugation

Product Number


  • All BioReady products are specially formulated for lateral flow and biodiagnostics
  • Mean diameter: 80 ± 5 nm
  • Size distribution (CV) < 15%
  • Carboxyl (–COOH), provided at 20 OD in DI water
  • Looking for greater sensitivity?

Which Surface Should I Choose?

Surface Binding type Pros Cons
NHS Learn more + Covalent
  • Simplest covalent conjugation procedure
  • Lyophilized powder format
  • Best for rapidly fabricating and testing conjugates
  • Must be used immediately after reconstitution with water
  • More expensive than Carboxylic Acid at larger scales

BioReady NHS gold can be covalently conjugated to primary amines (–NH2) of proteins in a simplified procedure. Covalent coupling of proteins (e.g. antibodies) to a gold nanoparticle surface yields robust and reliable gold particle conjugates. The BioReady NHS gold nanoparticles are surface functionalized with an active NHS ester to generate gold nanoparticle-antibody amide bonds, eliminating the need for the user to perform the intermediary EDC/Sulfo-NHS chemistry steps. The particles are supplied as a lyophilized powder that can be resuspended with a buffer to covalently bind to an added antibody. This coupling reaction is rapid, simple, robust and requires little optimization.

The following is included in every NHS reaction kit:

  • Antibody Purification Buffer (10 mM potassium phosphate, pH 7.4)
  • Reaction Buffer (5 mM potassium phosphate, 0.5% 20K MW PEG at pH 7.4)
  • Quencher (5% (w/v) hydroxylamine)
  • Conjugate Diluent (0.1× PBS, 0.5% BSA)

Antibody purification spin filters (Amicon® Ultra 0.5 mL Filters 10 kDa) may also be purchased with your nanoparticles.

Carboxyl Learn more + Covalent
  • Maximizes sensitivity
  • More cost effective at large production scales
  • Requires additional EDC/Sulfo-NHS activation step

BioReady carboxyl (–COOH) gold is an effective and economical nanoparticle for covalent conjugations to proteins through carbodiimide crosslinker chemistry. Covalent coupling of proteins (e.g. antibodies) to a gold nanoparticle surface yields robust and stable gold particle conjugates. The nanoparticles are surface functionalized with a tightly bound monolayer that contains terminal carboxylic acid functional groups which can be activated through EDC/Sulfo-NHS chemistry to generate gold nanoparticle-antibody amide bonds. The EDC/Sulfo-NHS chemistry requires an extra step to activate the carboxyl group but can be performed at scale at reasonable cost, making carboxyl gold the most cost-effective method of covalently binding antibodies to gold.

Certificate of Analysis Examples

Please note that these are representative Certificates of Analyses (CoAs) provided as examples for this product. We provide a unique batch-specific CoA with each product during shipment; only the CoA that arrives with your product should be referred to for actual characterization and measurement data. If you would like an electronic copy of the CoA for the product you received or the material(s) we currently have in stock, please contact us.

Product Line Surface Example Certificate of Analysis Product # Price
BioReady Carboxyl, 20 OD AUXR80-5M $125+
BioReady Carboxyl, 20 OD AUXR80-30M $535+
BioReady Carboxyl, 20 OD AUXR80-100M $1,495+

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Gold Nanoparticle Applications

Diagnostic Applications

Gold nanopaticles are readily conjugated to antibodies and other proteins due to the affinity of sulfhydyl (-SH) groups for the gold surface, and gold-biomolecule conjugates have been widely incorporated into diagnostic applications, where their bright red color is used in home and point-of-care tests such as lateral flow assays.  

Biomedical Applications

Gold nanomaterials can be conjugated to biomolecules to specifically target cancer cells, and used for photothermal cancer therapy, where their tunable optical properties cause them to convert laser light into heat and selectively kill cancerous cells.   


Gold nanoparticles have unique optical properties because they support surface plasmons. At specific wavelengths of light the surface plasmons are driven into resonance and strongly absorb or scatter incident light. This effect is so strong that it allows for individual nanoparticles as small as 30 nm in diameter to be imaged using a conventional dark field microscope.  This strong coupling of metal nanostructures with light is the basis for the new field of plasmonics.  Applications of plasmonic gold nanoparticles include biomedical labels, sensors, and detectors. The gold plasmon resonance is also the basis for enhanced spectroscopy techniques such as Surface Enhanced Raman Spectroscopy (SERS) and Surface Enhanced Fluoressence Spectroscopy which can be used to detect analytes with ultrahigh sensitivity. 

Ultra Uniform Gold Nanospheres

Our standard Au nanospheres have a variety of useful surface chemistries and narrow size distributions (CV < 15%), appropriate for a variety of applications ranging from lateral flow assays to optical coatings. Some applications, however, such as multiplexed dark field labeling or standards for nanoparticle size and shape, require even tighter tolerances on shape and size dispersity. For these applications, nanoComposix has successfully manufactured ultra-uniform, monodisperse gold nanospheres with sizes tunable from 10 nm up to 200 nm. As shown below, these gold nanoparticles have a nearly perfect spherical shape, smooth surfaces, and impressively narrow size distributions (CV < 6%, and for many sizes CV < 4%).

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Optical and Scattering Properties

Due to their high uniformity in size and shape, these Au nanospheres scatter a single color of light under dark field microscope imaging (shown below). The high purity of their light scattering signatures makes these nanospheres perfect scattering labels for imaging and building blocks for plasmonic nanostructures and devices.

Surface Chemistry

The gold nanospheres are stabilized with citrate in an aqueous solution. With their stable, easily displaceable surface chemistry, the gold nanospheres can be readily functionalized with a wide variety of molecules, including polymers and small molecules with desired functional groups, inorganic coatings such as silica, and biomolecules including DNA and antibodies for your application.

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