Catalase-coupled gold nanoparticles: Comparison between the carbodiimide and biotin–streptavidin methods

The use of proteins for therapeutic applications requires the protein to maintain sufficient activity for the period of in vivo treatment. Many proteins exhibit a short half-life in vivo and, thus, require delivery systems for them to be applied as therapeutics. The relative biocompatibility and the ability to form functionalized bioconjugates via simple chemistry make gold nanoparticles excellent candidates as protein delivery systems. Herein, two protocols for coupling proteins to gold nanoparticles have been compared. In the first, strong biomolecular binding between biotin and streptavidin was used to couple catalase to the surface of gold nanoparticles. In the second protocol the formation of an amide bond between carboxylic acid-coated gold nanoparticles and free surface amines of catalase using carbodiimide chemistry was performed. The stability and kinetics of the different steps involved in these protocols were studied using UV–visible spectroscopy, dynamic light scattering, and transmission electron microscopy. The addition of mercapto-undecanoic acid in conjugation with (N-(6-(biotinamido)hexyl)-3′-(2′-pyridyldithio)-propionamide increased the stability of biotinylated gold nanoparticles. Although the carbodiimide chemistry-based bioconjugation approach exhibited a decrease in catalase activity, the carbodiimide chemistry-based bioconjugation approach resulted in more active catalase per gold nanoparticle compared with that of mercapto-undecanoic acid-stabilized biotinylated gold nanoparticles. Both coupling protocols resulted in gold nanoparticles loaded with active catalase. Thus, these gold nanoparticle systems and coupling protocols represent promising methods for the application of gold nanoparticles for protein delivery.