Preparation of the modified electrode

Having decided on what chemical or physical principles the sensor is to operate, a means of electrode preparation must be devised. This section can be divided into several areas choice of substrate, substrate derivatization, and electrode characterization. 

Choice of substrate. If the coating (modifier) to be placed on the electrode is totally impermeable, then the choice of substrate will be governed mainly by the requirements of the preparative stage. If the coating is permeable, then the electrochemical behaviour of the substrate will be a more important consideration. The ideal substrate should be  

Substrate derivatization. This is undoubtedly the aspect of CMEs which has received most attention in the last ten years, and justifiably so. Without the development of convenient, reproducible preparation methods the study of CMEs will remain somewhat academic. Fortunately, it appears this is not to be the case, and feasible, practical electrode preparation methods appear regularly in the literature. As pointed out previously, the electrode should be easily and inexpensively prepared. It should also exhibit the desired chemical and physical properties, have an appropriate capacity and an adequate electron transfer rate constant for the analyte electrode process. 

It is important at this stage to define first-order and second-order derivatization. First-order CMEs are prepared by adding the chemically active group directly to an electrode substrate. There is a limited number of instances where this approach is appropriate. Second-order derivatization, which involves adding the chemically active group to a previously modified substrate, greatly expands the number of different CMEs which can be prepared  

At present not many modified electrodes are derivatized beyond second order, although it is obvious that to do so would again expand the range of electrodes which could be prepared. 

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CHEMICALLY MODIFIED ELECTRODES 5.2.2 Preparation of the modified electrode... 

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