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 goldsilver, 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/Particles Molar Protein Concentration (@ OD=10) Mass Protein Concentration (@ OD=10)
5nm IgG 3 2.7uM 405 ug/ml
Streptavidin 5 4.5uM 238 ug/ml
Protein A 4 3.6uM 151 ug/ml
10nm IgG 12 1.2uM 180 ug/ml
Streptavidin 20 2.0uM 106 ug/ml
Protein A 16 1.6uM 67 ug/ml
15nm IgG 27 0.73uM 110 ug/ml
Streptavidin 45 1.2uM 63 ug/ml
Protein A 36 0.97uM 41 ug/ml
20nm IgG 48 0.52uM 78 ug/ml
Streptavidin 80 0.87uM 46 ug/ml
Protein A
64 0.69uM 29 ug/ml
30nm IgG 86 0.26uM 39 ug/ml
180 0.43uM 23 ug/ml
Protein A
144 0.34uM 14 ug/ml
40nm IgG 150 0.18uM 27 ug/ml
320 0.30uM 16 ug/ml
Protein A
256 0.24uM 10 ug/ml
50nm IgG 234 0.14uM 21 ug/ml
500 0.23uM 12 ug/ml

Protein A
400 0.18uM 7.6 ug/ml
60nm IgG 337 0.11uM 17 ug/ml
719 0.18uM 9.5 ug/ml
Protein A
575 0.15uM 6.3 ug/ml
80nm IgG 599 78nM 12 ug/ml
1280 130nM 6.9 ug/ml
Protein A
1024 100nM 4.2 ug/ml
90nm IgG 757 68nM 10 ug/ml
1617 110nM 5.8 ug/ml
Protein A
1294 90nM 3.8 ug/ml
100nm IgG 936 60nM 9.0 ug/ml
2000 100nM 5.3 ug/ml
Protein A
1600 79nM 3.3 ug/ml