Protein immobilization on carbon nanotubes via a two-step process of diimide-activated amidation

Ferritin and bovine serum albumin (BSA) proteins are chemically bonded to nitrogen-doped multi-walled carbon nanotubes (CNx MWNTs) through a two-step process of diimide-activated amidation. First, carboxylated CNx MWNTs were activated by N-ethyl-N'-(3-dimethylaminopropyl) carbodiimide hydrochloride ( EDAC), forming a stable active ester in the presence of N-hydroxysuccinimide ( NHS). Second, the active ester was reacted with the amine groups on the proteins of ferritin or BSA, forming an amide bond between the CNx MWNTs and proteins. This two-step process avoids the intermolecular conjugation of proteins, and guarantees the uniform attachment of proteins on carbon nanotubes. TEM and AFM measurements clearly confirmed the successful attachment. This approach provides a universal and efficient method to attach biomolecules to carbon nanotubes at ambient conditions.