Tissue electrodes, poisoning

Work with these types of electrodes enables to achieve steady-state current conditions within a short time-period. Primarily proposed for monitoring and control of blood and tissue oxygen tension [10], the electrode systems with selective membranes were manufactured and used in continuous oxygen measurement in a wide variety of aqueous solutions [11]. The sensors of this type, called Clark electrodes, are described in chapter 6 of this volume. Improvements designed for continuous monitoring in industrial bioreactors may be found in section 6 of chapter 3. The most important feature of the membranes used in these sensors is their selectivity which prevents poisoning the electrode system and deteriorating the adherent electrolyte solution. 

Measurement of oxygen availability in tissues or fluids, i.e., the oxygen tension of a system when expressed as pressure of O, is influenced by many factors that render absolute measurements extremely difficult. Attention must be paid to such variables as the diffusion coefficient of oxygen in different tissues, the degree of stirring and the possibility of poisoning the electrode surface by a variety of mechanisms (18). The different designs of these electrodes are all attempts to overcome these limitations, but for this very reason are not universally applicable. 

A major problem with the chronic implantation of electrodes, especially for control of cellular function, is the likelihood that the electrode will poison or cause trauma to the tissue[16]. When large currents are passed through implanted electrodes, the dissolution of ions and the generation of gases can cause lesions. However, the use of transcutaneous stimulation avoids this problem. For example, an area that has received particular attention is the use of electromagnetically induced currents. 

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