Glassy carbons fabrication

At lower ultratrace levels, the less voluminous mercury film electrode has to be used. It consists of a mercury film of only several hundred nm thickness on a glassy carbon electrode as support. The fabrication of this glassy carbon electrode is critical for obtaining an optimal mercury film electrode suitable to perform determinations down I ng/1 or below. 

There are several possible reasons why the overall rate of electron transfer is slow. Occasionally, it is because the electrode is a poor conductor, such as semiconductors like silicon or poor metals such as tungsten (see SAQ 2.6). Fabricating an electrode from metals such as platinum, gold, or from metallic conductors such as graphite or glassy carbon, will circumvent that possibility. 

Optical properties of the material are less critical for microchips hyphenated with MS than for devices with on-chip optical detection where low background absorption or fluorescence is mandatory. Thus, completely opaque polymers like glassy carbon or polyimide " can be used as microfabrication substrates. Furthermore, polymer microchips are of great interest because their potentially low manufacturing costs may allow them to be disposable. Methods used for the fabrication of plastic chips include laser ablation and molding methods. 

Several types of carbon are in common use as electrodes. The most used of these is glassy carbon (GC) [100] it is the most reproducible but very difficult to machine as it is hard and brittle. One thus tends to be confined to the dimensions and shapes which come from the manufacturer. Each manufacturer has his own fabrication method (or more than one). A common problem is that small holes can appear in the middle of the piece of GC if this occurs, there is no option but to machine more away. Additionally, the GC is not always homogeneous. In the authors opinion, the best glassy carbon is Tokai. While it is not always possible to use this because of geometrical considerations, better reproducibility will be obtained with it, especially after electrochemical pretreatment [101]. 

Carbon electrodes. The vitreous carbon electrode usually is fabricated by sealing a plug or disk, but from a thick sheet of glassy carbon, into a glass tube with epoxy cement. The surface of the electrode is then polished until it is bright and smooth. No further treatment is necessary. 

The prospective application of the fabricated porous Ag electrode was tested for the electrochemical reduction of chloroform. The advantageous catalytic effect of the Ag electrode over a glassy carbon electrode is illustrated in Figure 5.6 [35] which shows that while no significant current due to chloroform could be observed... 

Acetylcholineesterase and choline oxidase A glassy carbon electrode (GCE) modified by electrodepositing sub pm Pt-black particles on the surface. ACh and Ch. micro biosensor arrays were fabricated based on immobilization of AChE—ChO or ChO by cross linking with gentar-aldehyde on Pt-black GCE. Significant enhancement in the performance of these biosensors was achieved. The chronoamperometric response of 1 p biosensor array was linear from 29 to 1200 pM with detection limit of 8.7 pM acetylcholine. [109]... 

Probably the most widely used of these is glassy carbon, which is isotropic. However, due to its hardness and fragility, electrode fabrication is difficult, which essentially limits its use to the dimensions and forms that can be acquired commercially. The manufacture of glassy carbon consists in carbonization by heating phenol/formaldehyde polymers or polyacrylonitrile between 1000°C and 3000°C under pressure. Since glassy carbon has some amorphous characteristics, as can be seen from Fig. 7.1, it is not always homogeneous. 

Typically these electrodes are fabricated from an inert and electrically conducting material. Common examples would range from liquid mercury to solid platinum and some forms of carbon (i.e. glassy carbon or graphite). Mercury electrodes (Bond, 1980) are used in the form of dropping electrodes in which the surface is continuously renewed or a hanging mercury drop electrode. Recently diamond film electrodes have been utilized for studies that require wide potential windows (Tenne et al., 1993). Typically, the solid... 

In the AIREs, the nanometer thin film supported on glassy carbon or other conductive substrates was prepared by convenient electrodeposition method of cyclic voltammetery that led to form nanometer-scale thin film of layered structure. The film of island structure is nevertheless fabricated by evaporation method and employed in the SEIRA. 

---