All nanoComposix carboxyl products contain a carboxyl ligand that’s covalently bound to the metal nanoparticle with a dithiol which forms a strong, stable bond to the metal surface. The acid group provides a highly negatively charged surface.
Carboxyl surfaces can be used to covalently bind molecules with free amines (e.g. antibodies) to the surface of the particles. An amide bond between the acid surface and the free amine is formed using EDC / NHS chemistry. Our BioReady materials are provided with a detailed protocol to use EDC/NHS chemistry to covalently link molecules containing free amines to the carboxy surfaced nanoparticles.
At nanoComposix we use two different molecules to provide a surface with chemically accessible carboxylic acids. One is lipoic acid and the other is the lipoic acid derivative, lipoic-dPEG12-acid, which is similar to lipoic acid but contains a PEG spacer between the thiol and carboxylic acid functional groups.
For BioReady gold nanoparticles with diameters less than 100 nm, the lipoic-dPEG12-acid is used. For larger diameter BioReady nanoparticles (e.g. 150 nm gold nanoshells), lipoic acid is used because it provides better bioconjugation results for these particle sizes.
For more details on which one of these two types of carboxyl surfaces is used on your nanoparticle of choice, visit that product’s web page or see the certificate of analysis for that specific product.
- Provides a stable particle surface in a variety of different solvents. Due to the strong binding of the lipoic acid to the surface of the particles, this ligand is not displaceable
- Allows for covalent linkages to molecules with primary amines
- Negative Zeta potential
Representative Source: Lipoic m-PEG (Quanta Biodesign, 10808), Lipoic acid (Alfa Aesar, L04711)
Molecular Weight: 806.03 for m-PEG, 206.3 MW for lipoic acid
Comparison to Alternatives
Displaceable: Not displaceable
Negatively charged (Zeta -20 mV at pH 7.4)
Salt stability: stable in many salt solutions
Toxicity: Generally regarded as safe, low toxicity
Solvent compatibility: Water, ethanol, chloroform, many other polar solvents