Gold, Silver, Gold NanoUrchins Conjugates Technical Information

One of the greatest attributes of noble metal nanoparticles are their ability to create high avidity bio-recognition conjugates through the attachment of multiple antibodies (or other proteins) to their surfaces. This can either be achieved through passive non-specific adsorption of an antibody (protein) to the nanoparticle surface, or through a more controllable approach, covalent conjugation.

Regardless if you are using passive adsorption or covalent conjugation the factor limiting the amount of antibody (protein) that can be bound to the nanoparticles is the available surface area of the nanoparticles themselves. For example, a 100nm gold nanoparticle has a surface area of 31,400 nm2 and can accommodate far more proteins than a 10nm particle having only a surface area of 314 nm2. For a standard rabbit derived antibody (IgG) with an approximate molecular weight of 150 kDa and an approximate docking area of 33.4 nm2 a 100nm particles can theoretically bind a maximal 936 IgGs per particle and 12 IgGs per 10nm, a 78 fold difference.

Table I below list the theoretical number of IgG, Streptavidin, and Protein A molecules that can bind a nanoparticle of a given size. As mentioned above the theoretical surface density is based upon the docking area of each protein and the available surface area on each nanoparticle that can accommodate the protein. 

Due to their similar surface properties this table is valid for our gold, silver, and gold nanourchin conjugates.

Table I. Estimated protein density per noble-metal nanoparticle (gold nanoparticle, silver nanoparticles or gold nanourchins).