Electrochemically etched carbon fiber electrodes

The processes involved in the production of these electrodes involve mounting the carbon fibers, etching them to produce a sharp tip, and subsequent insulation of the tip so that only the very end of the tip is exposed (1, 2). Testing of the electrode is then performed to determine whether there are any pinholes in the insulation. 

AC voltage is then applied between the mounted fiber and a glassy carbon rod auxiliary electrode for a defined period. 

After etching, the fibers are rinsed with water to remove any residual alkaline solution and left to dry prior to the insulation step. 

Cathodic electrophoretic paint is the preferred polymeric material used to insulate the carbon fibers as the negative potentials required for deposition avoid any possibility of further oxidative dissolution of the carbon fiber. The usual approach for electrophoretic deposition is to suspend the article being coated in an appropriate suspension of polymer particles and polarising the iton versus a secondary electrode. 

The final step is to seal the copper-fiber assembly into a glass tube with epoxy resin. Only the insulated carbon fiber should be allowed to protrude from the epoxy sealed glass tube. Electrodes may be re-used and have lifespans of a few weeks. 

---

For example, SWCNTs (Figure 7.2a) were coated on flame-etched carbon fiber nanoelectrodes and used as electrochemical sensors (Figure 7.2b). The (2NT-modified electrode, with tips ranging from 100 to 300 nm, exhibited overall detection capabilities in the nanomolar range, which is an order of magnitude lower than the conventional carbon fiber electrodes of similar geometry. These small electrodes would be well suited for electrochemical applications in ultra-low fluid volumes or biological systems such as tissue or cells. 

When electroactive organic molecules are oxidized on noble metal electrode then often happens that the product of the electrode process stays adsorbed on the surface forming an insulating film. This electrode fouling less frequently happens with carbon electrodes. Carbon fibers are used in industrial scale in composite materials. These fibers are available with diameters of 5-8 and 33 pm. They have been proven excellent material for microelectrode preparation. Buda and coworkers [32, 33] first employed electrochemically pretreated carbon fiber microelectrodes for in vivo measurements. SECM tips with carbon measuring surface can be easily made of carbon fibers embedding them in appropriate pointy bodies. In order to make ultramicro electrode the end of the fiber is chemically etched before embedding. 

Nanosensors for electrochemical detection have been made for years using more traditional fabrication methods, e.g., pulled platinum strings and carbon fibers. Carbon fibers can be purchased with diameters in the low /am range. These can subsequently be etched in an Ar beam until conically shaped tips are produced with tip diameters between 100 and 500 nm [61]. Similarly, a platinum wire can be heated and pulled in order to create tips of similar diameters. Thick film electrodes made by screen printing [62] have also been shown to find application as transducer in microchaimel systems [63]. 

---