Biochemical Sensors Using Carbon Nanotube Arrays

Vertically aligned carbon nanofibers (CNFs) are fabricated by wafer-scale plasma enhanced chemical vapor deposition (PECVD) on prefabricated microelectrode pads and encapsulated in SiO2 or polymer dielectrics with only the very end exposed at the surface to form an inlaid nanodisk electrode array. As the size of an electrode is reduced, one can obtain: (1) higher sensitivity, i.e., the signal-to-noise ratio, which is inversely proportional to the radius (r) of the electrode, (2) lower detection limit, (3) higher temporal resolution (proportional to 1/r), and (4) miniaturization. Therefore, nanoelectrodes have great properties for electroanalysis. Carbon nanofibers can be fabricated at wafer scale, as high-aspect-ratio metallic wires, down to a few nanometers in diameter on metal microcontact pads to form well-defined nanoelectrode arrays. In addition, CNFs have a wide potential window, well-defined surface functional groups, and good biocompatibility,which are all highly demanded properties for biosensors. CNF arrays have been successfully fabricated on micropatterns. The electrical and electrochemical properties of the embedded CNF nanoelectrode arrays have been thoroughly characterized to show well-defined nanoelectrode behavior. In some schemes, selective covalent functionalization of probe oligonucleotides, antibodies or aptamers have been achieved through the formation of amide bonds at the exposed end of CNFs. Direct electrochemical detection of a target molecules oxidation signal, which is the signal from an electrochemical label, or change in charge transfer resistance, has been demonstrated for DNA, rRNA, proteins, catecholamines, and ions.