An in vivo probe based on mechanically strong but structurally small carbon electrodes with an appreciable surface area

Physically small carbon electrodes were fabricated by pyrolyzing acetylene in a nitrogen atmosphere using pulled quartz capillaries as the supporting substrate. A carbon disk geometry was obtained when a parallel flow of acet ylene (50 kPa) and nitrogen (10 mL min(-1)) was introduced into the system. Further, carbon was found to deposit at the tip and on the shank of the qu artz capillaries when the nitrogen flow rate was increased (80 mL min(-1)), yielding an approximately cylindrical geometry. A series of electrochemica l and spectroscopic analyses was carried out to examine the ty. pe of carbo n surface obtained by pyrolysis of acetylene. The results suggested that a surface consisting of an almost defect-free highly oriented pyrolytic graph ite type structure was formed by the pyrolyzed acetylene. However, this con tradicts the kinetically reversible electron transfer observed for dopamine oxidation at these electrodes. Meanwhile, the nonpolar and relatively oxyg en-free characteristics indicate that these electrodes also behave similarl y to a hydrogenated carbon surface. The formation of a hydrogenated carbon- type surface may be plausible as a result of the attack on the carbon surfa ce by a surplus of hydrogen produced by the pyrolysis of acetylene to form graphitic carbon. These characteristics are expected to aid in reducing ele ctrode fouling, which is often encountered in electrochemical detection of neurotransmitters in vivo. In conjunction with a miniature physical dimensi on, their appreciable surface area and enhanced mechanical strength make th ese carbon electrodes well suited to the detection of neurotransmitters in vivo.