Hydration properties of carbon nanotubes and their effects on electrical and biosensor applications

As-grown carbon nanotubes grown by thermal chemical vapor deposition are hydrophobic, i.e., more attractive to nonpolar groups than polar substances. The surfaces of hydrophobic carbon nanotubes have been treated by means of electrochemical, thermal, and plasma oxidation processes to convert them to hydrophilic surfaces. Thermal oxidation of carbon nanotubes in ambient air or a brief exposure to a plasma in ambient air had slight effects on electron field emission properties; but, electrochemically treated carbon nanotubes emitted a lower electron field emission current and required higher electric fields to emit the same current compared with the electron field emission characteristics of as-grown carbon nanotubes. The immobilization of antibodies on hydrophilic carbon nanotubes was enhanced significantly compared with that on hydrophobic carbon nanotubes. Binding of Staphylococcus aureus bacteria that were specific to the immobilized antibody, on hydrophilic carbon nanotubes for biosensor applications has been demonstrated.