Bare gold nanoparticles, non-functionalized.
Carboxylate functionalized gold nanoparticles carry negative charge in buffer with pH greater than 4.They can covalently bind to the primary amine groups after EDC/NHS activation.
Amine functionalized gold nanoparticles carry positive charge in buffer with pH less than 10.
Maleimide functionalized gold nanoparticles permanently bind to covalently bind to thiol groups (-SH). This reaction is very specific and fast.
Disulfide functionalized gold nanoparticles permanently bind to covalently bind to thiol groups (-SH) through thio-disulfide exchange. After binding, the new formed disulfide bond can be broken by another thiol compound.
Ni chelated gold nanoparticles bind to his-tagged proteins.
Protein A modified gold nanoparticles bind to immunoglobulins, especially IgG.
Streptavidin immobilized gold nanoparticles bind to biotin-labeled biomolecules.