Adsorption of Bovine Serum Albumin and Lysozyme on Functionalized Carbon Nanotubes

In this work, we examined adsorption of bovine serum albumin (BSA) and lysozyme (LYZ) on carboxylated (CM), hydroxylated (HM), and graphitized (GM) multiwall carbon nanotubes (CNTs). All adsorption isotherms were fitted well with the Langmuir model. The maximum adsorption capacities (mg/g) followed the order HM > CM > GM for both BSA and LYZ, which positively related to the surface areas of the three CNTs. However, after surface area normalization, adsorption capacities (mg/m²) followed the order HM > GM > CM for BSA and GM > CM > HM for LYZ, indicating that functional groups and hydrophobicity of CNTs also contributed to protein adsorption. In addition, adsorption of LYZ (81 800–90 700 mg/g) was at least 300 times higher than that of BSA (132–266 mg/g) for all the three CNTs. BSA molecules on CNTs surface mainly showed a monolayer adsorption while LYZ adsorption was through multilayers. Moreover, BSA at the tested concentrations was able to disperse the three CNTs. However, no significant dispersion was observed for all the three CNTs in the presence of LYZ at the same concentrations. The results revealed that α-helix structure of both the proteins diminished after interacting with the three CNTs. This research will be helpful to clarify the mechanism of protein adsorption on functionalized CNTs and would be of importance for using CNTs in biomedical and pharmaceutical fields.