Created by Digital Micrograph, Gatan Inc.

Passive versus covalent conjugation of antibodies to gold nanoparticles

Antibodies can be attached to gold nanoparticles by a variety of methods. These include passive adsorption, covalent attachment to surface-functionalized nanoparticles, and attachment to nanoparticles which have been pre-coated with a binding reagent such as streptavidin, biotin or Protein A/G.

Passive adsorption

Passive adsorption relies primarily on hydrophobic attractions and electrostatic interactions between the antibody and the nanoparticle. It is a traditional approach that requires specialist knowledge and often involves a lengthy optimization process. Optimization steps include antibody titration to ensure full coverage of the surface of the particle, as well as identification of an appropriate conjugation buffer at a suitable pH.

Covalent attachment to surface-functionalized nanoparticles

Covalent attachment provides greatly increased conjugate stability over passive adsorption, since the antibody becomes permanently bound to the nanoparticle and is unable to detach from it. This provides tighter control over assay variability and, in some instances, can use considerably less antibody than passive adsorption, thereby saving precious reagent.

Attachment to pre-coated nanoparticles

Rather than attaching the antibody to the gold nanoparticle via passive adsorption or covalent conjugation, a biomolecular interaction can instead be exploited. For example, a streptavidin coated gold nanoparticle can be used as a secondary reagent to visualize a biotinylated detection antibody.

The performance of an antibody-gold nanoparticle conjugate will vary from one antibody to another, since every antibody is unique. Although the same antibody can be used to produce both a passively adsorbed conjugate and a covalent conjugate, these reagents may often show very different levels of performance in the downstream application. One antibody might produce a higher signal when passively adsorbed to gold nanoparticles, while another may demonstrate a superior signal when covalently conjugated.

Comparison of the performance of antibody conjugates following passive adsorption and covalent conjugation to gold nanoparticles

Comparison of the performance of antibody conjugates following passive adsorption and covalent conjugation to gold nanoparticles. Three different anti-CRP antibodies were attached via passive adsorption to 40nm colloidal gold nanoparticles, or via covalent binding to 40nm InnovaCoat® GOLD. Each antibody was incubated with 50ng/ml CRP in buffer, and the solution was then run on a lateral flow test strip with an anti-CRP antibody immobilized at the Test line. Strips were read with a lateral flow strip reader. The no CRP control samples gave no signal (data not shown).

Colloidal gold

We use specialized techniques to produce our colloidal gold, enabling the production of extremely uniform spherical particles with a narrow size distribution. These methods provide excellent batch to batch consistency, minimizing variability in the downstream application. Our colloidal gold can be produced in large volumes without compromising on quality, and is available in a range of particle sizes and concentrations for maximum flexibility.

Colloidal gold from Expedeon

Colloidal gold from Expedeon. We use proprietary techniques to produce extremely uniform spherical particles. Our colloidal gold is available in a range of particle sizes and concentrations, with bulk purchasing available on request.

Our colloidal gold undergoes stringent QC, and every batch is supplied with a certificate of analysis which details the various test parameters. These include the wavelength at which the peak maximum is reached, and the optical density of the product, as well as the mean particle diameter, with standard deviation and % CV.

InnovaCoat® GOLD

Our InnovaCoat® GOLD nanoparticles have a proprietary surface coating which covalently binds the antibody to form highly stable conjugates. Like our colloidal gold, our coated nanoparticles have a uniform spherical shape and a narrow size distribution, ensuring a robust and consistent downstream assay. InnovaCoat® GOLD nanoparticles are available as conjugation kits in a variety of particle sizes and different chemistries, or separately as carboxylated 40nm gold nanoparticles.

Conjugation kits 10nm 20nm 40nm 60nm 80nm Target Chemistries
InnovaCoat® GOLD Amine groups
InnovaCoat® GOLD Maleimide Thiol groups (Fab’, oligo)


InnovaCoat® GOLD Hydrazide Aldehyde groups (IgG, IgM)


The InnovaCoat® GOLD product range. Our InnovaCoat® GOLD conjugation kits are available as different nanoparticle sizes, in a variety of pack sizes, and as different conjugation chemistries, providing excellent flexibility. Furthermore, the products are fully scalable, allowing easy transfer from R&D to manufacturing.

The use of InnovaCoat® GOLD has been referenced in a range of publications, including multiple citations in Nature.

Pre-coated gold nanoparticles

Our range of pre-coated gold nanoparticles includes streptavidin, biotin, goat anti-mouse antibody, goat anti-rabbit antibody, Protein A and Protein G conjugates. These are manufactured using our InnovaCoat® GOLD technology; the proprietary surface coating of the gold nanoparticles covalently binds the detection protein to form highly stable conjugates.

 Conjugation Kits 10nm 20nm 40nm 80nm Target Group
InnovaCoat® GOLD Streptavidin  ● Biotin
InnovaCoat® GOLD Biotin Streptavidin
InnovaCoat® GOLD Goat Anti-Mouse Mouse IgG
InnovaCoat® GOLD Goat Anti-Rabbit Rabbit IgG
InnovaCoat® GOLD Protein A IgG
InnovaCoat® GOLD Protein G IgG

Pre-conjugated gold nanoparticles. Our gold nanoparticle conjugates are manufactured using our InnovaCoat® GOLD technology. These reagents are available in a range of particle sizes, and include many popular specificity moieties.

We offer high quality products for both passive and covalent conjugation of antibodies to gold nanoparticles. For more information about these, please contact us.