Role of oxidant in surface modification of carbon nanotubes for tyrosinase immobilization

Abstract

Studies on the development of interface between biological molecules and novel nanomaterials have attracted research worldwide. Carbon nanotubes (CNTs) have become an important matrix for the fabrication of biomaterials due to its unique properties. Surface properties of the CNTs and the medium of immobilization are critical in the immobilization of biological molecules such as enzymes. In this study surface modification of multi-walled carbon nanotubes (MWCNTs) for carboxylic moieties attachment was accomplished by acid treatment and reaction with potassium permanganate. The effect of these two oxidants on the surface modification of MWCNTs for the purpose Tyrosinase immobilization was studied. Commercial MWCNTs were treated with either concentrated sulfuric acid and nitric acid mixture with ratio 3:1 or with 0.1 M potassium permanganate via reflux, stirring and ultrasonication. The resulting surface modified MWCNTs were characterized with FT-IR spectrophotometer, FESEM, and TGA analyzer. The immobilized Tyrosinase was tested for leaching assay. The FTIR spectra of functionalized MWCNTs showed a significant peak in the range of 1700 cm- 1 to 1729 cm-1 indicating the presence of carboxyl double bond, which confirmed the successful functionalization of MWCNTs by chemical oxidation. The carboxylic peak of MWCNTs treated with KMnO4- showed higher intensity as compared to acid-treated MWCNTs. The acid-treated MWCNTs displayed a sparkling crystalline-like particles while the KMnO4-modified MWCNTs consists of smooth powdery particles. Both treated MWCNTs also showed good dispersion in aqueous solution with different amount of acidic and basic site present.