Passive versus covalent conjugation of antibodies to gold nanoparticles
July 3rd, 2017
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 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.
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.
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.
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.