System optimization for the development of ultrasensitive electronic biosensors using carbon nanotube nanoelectrode arrays.

Vertically aligned multi-walled carbon nanotubes (MWCNTs) have been reported in fabricating nanoelectrode arrays. Further studies on optimizing this system for the development of ultrasensitive DNA sensors are reported here. The mechanical stability of the as-grown MWCNT array can be improved by polymer coating or SiO2 encapsulation. The latter method provides excellent electronic and ionic insulation to the sidewall of MWCNTs and the underlying metal layer, which is investigated with electrochemical impedance spectroscopy. The insulation ensures well-defined nanoelectrode behavior. A method is developed for selectively functionalizing biomolecules at the open end of MWCNTs while keeping the SiO2 surface passivated, using the unique graphitic chemistry. An ultrahigh sensitivity approaching the limit of fluorescence techniques is obtained with this system for DNA detection.