Carbon Fiber-based Microelectrodes and Microbiosensors

Abstract

The chemically relatively inert carbon fiber (CF) has outstanding mechanical and electrical properties and provides an excellent base electrode for electrophysiological, electrochemical and biosensor applications on a micrometer or perhaps even on a submicrometer scale. CF microelectrodes have been used to record neuronal action potentials (spikes) since 1979 (Armstrong-James & Millar, 1979). The CFs are graphite monofilaments about 7 μm in diameter. In microelectrodes, they have outstanding extracellular recording qualities similar to those of the best tungsten electrodes. The CF microelectrodes have been demonstrated to be very suitable for in vivo electrochemical detection of catecholamines (Ponchon et al., 1979) and other oxidizable biological species including nitric oxide (NO) (Malinski & Taha, 1992). Since the early times in CF applications for biorecording, a great variety of enzyme-modified CF microbiosensors has been introduced for the in situ determination of glucose, acetylcholine, choline, lactate, glutamate and other important compounds. The immobilization of DNA molecules (Millan & Mikkelsen, 1993) or carbon nanotubes (CNTs) (Zhang et al., 2007) onto CF microelectrodes has opened up new avenues in electrochemical detection of biologically significant species. A basic CF microelectrode is an elementary carbon filament built in a mechanically supportive and electrically insulating borosilicate glass or plastic sheathing. The uninsulated carbon tip protruding from the sheathing by 10 to 100 μm provides a conductive surface for picking up spikes from the near vicinity of neurons and/or surface for electron transfer in microbiosensor applications. In the latter case, the carbon tip is covered with biological sensing elements such as an enzyme, receptor protein, antobody or nucleic acid immobilized in a conducting polymer matrix. This chapter will discuss the fabrication of singleand multibarrel CF microelectrodes, the covalent modifications of the carbon surface as well as the applications of CF microelectrodes in recording spikes from neurons, electrochemical or biosensor signals from the nervous or other tissues. Attention will primarily be focused on microelectrodes containing CFs that have diameters no greater than 30 μm. A novel use of CF microelectrodes as oxigen detectors usable in vitro and in vivo will also be described for the first time.