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Gold, Silver, and Gold NanoUrchin Conjugate 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 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. 
Gold Nanoparticle Size Conjugated Protein Maximum Number of Proteins Per Particle Molar Protein Concentration (@ OD=10) Mass Protein Concentration (@ OD=10)
5nm IgG 3 2.7 uM 405 ug/ml
Streptavidin 5 4.5 uM 238 ug/ml
Protein A 4 3.6 uM 151 ug/ml
10nm IgG 12 1.2 uM 180 ug/ml
Streptavidin 20 2.0 uM 106 ug/ml
Protein A 16 1.6 uM 67 ug/ml
15nm IgG 27 0.73 uM 110 ug/ml
Streptavidin 45 1.2 uM 63 ug/ml
Protein A 36 0.97 uM 41 ug/ml
20nm IgG 48 0.52 uM 78 ug/ml
Streptavidin 80 0.87 uM 46 ug/ml
Protein A 64 0.69 uM 29 ug/ml
30nm IgG 86 0.26 uM 39 ug/ml
Streptavidin 180 0.43 uM 23 ug/ml
Protein A 144 0.34 uM 14 ug/ml
40nm IgG 150 0.18 uM 27 ug/ml
Streptavidin 320 0.30 uM 16 ug/ml
Protein A 256 0.24 uM 10 ug/ml
50nm IgG 234 0.14 uM 21 ug/ml
Streptavidin 500 0.23 uM 12 ug/ml
Protein A 400 0.18 uM 7.6 ug/ml
60nm IgG 337 0.11 uM 17 ug/ml
Streptavidin 719 0.18 uM 9.5 ug/ml
Protein A 575 0.15 uM 6.3 ug/ml
80nm IgG 599 78 nM 12 ug/ml
Streptavidin 1280 130 nM 6.9 ug/ml
Protein A 1024 100 nM 4.2 ug/ml
90nm IgG 757 68 nM 10 ug/ml
Streptavidin 1617 110 nM 5.8 ug/ml
Protein A 1294 90 nM 3.8 ug/ml
100nm IgG 936 60 nM 9.0 ug/ml
Streptavidin 2000 100 nM 5.3 ug/ml
Protein A 1600 79 nM 3.3 ug/ml