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

Abstract

Ferritin and bovine serum albumin (BSA) proteins are chemically bonded to nitrogen-doped multi-walled carbon nanotubes (CN_x MWNTs) through a two-step process of diimide-activated amidation. First, carboxylated CN_x 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 CN_x 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.