Factors affecting sensor construction

Ion-selective electrodes with a liquid membrane are more reliable than ion-selective electrodes with a solid membrane because of the uniformity of the active material partition in the membrane. For the construction of biosensors the maximum reliability is obtained by using graphite paste as the support. As of the present, for in vivo tests only sensors based on plastic membranes have been used. The main problem associated with using them for in vivo tests is the biocompatibility of the materials.147 149 The membrane biocompatibility, the matrix biocompatibility, and the electroactive material biocompatibility are important factors. The matrix biocompatibility is assured by the biocompatibility of the polymer and by the biocompatibility of the plasticizer. The ratio between the quantity of polymer and quantity of plasticizer affects the response of electrochemical sensors because the matrix of the solid membrane electrodes plays the same role as does the solvent in liquid membrane electrodes. 

Conventional enzyme electrodes employ disorete-maorosoopio membranes to overcome problems associated with interferences, enzyme immobilization, and electrode fouling. While these types of enzyme electrodes have been commercially developed, there are some limitations with this approach. Some sensors use three relatively thick membranes, resulting in a slow smd complex diffusion path for reactants reaching the enzyme and hydrogen peroxide reaching the electrode. Slow diffusion in this type of system adversely affects the response and recovery time, decreasing sampling rate. Each sensor must be individually constructed, and this construction technique is limited to two-dimensional surfaces. In addition, for sensors that have complex and slow diffusion paths, rates of diffusion must remain constant, otherwise calibration of the biosensor, and more important the maintenance of calibration, are difficult. A variety of factors can influence rates of diffusion, and consequently the performance of the enzyme layer and the performance of the sensor. These complicated, and most often uncharacterizable, properties have made the development of roost biosensors difficult. 

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