of the biological reaction. As illustrated in Fig. 114.5, this detector can consist of an electrical sensor such as used in electrochemical sensors, a thermal sensor, a sensor of changes in capacitance, a sensor of changes in mass,or a sensor of optical propertie An example of a bioanalytical sensor is a glucose sensor. The first portion of the sensor contains the enzyme glucose oxidase. This enzyme promotes the oxidation of glucose to glucuronic acid and consumes oxygen in the process. Thus, by placing an oxygen sensor along with the glucose oxidase in the bioanalytical sensor, one can determine the amount of glucose oxidized by measuring the amount of oxygen consumed. An even better approach is to have two identical sensor structures in the same package. The only difference is that only one of the sensors contains the enzyme. When there is no glucose present, both sensors will measure the same oxygen partial pressure. The presence of glucose, however, will cause the sensor with the glucose oxidase to e a reduced partial pressure of oxygen due to the oxygen consumption of the reaction. By making a differential measurement of oxygen partial pressure with both sensors, other factors that can cause an apparent change in oxygen partial pressure such as temperature will have a much lower effect than if a single sensor was used Stability problems are important for bioanalytical sensors, especially those that are used for long-term measurements. Not only are the stability issues the same as for the physical and chemical sensors, but they are also related to preservation of the biological molecules used in the first stage of the sensor. These molecules can often be degraded or destroyed by heat or exposure to light. Even aging can degrade some of these molecules. Thus, an important issue in dealing with bioanalytical sensors is the preservation of the biochemical components of the sensor. Not all biochemical reactions are entirely reversible, and so the bioanalytical sensors based on them will not be reversible as well. This may be acceptable for some applications but not for others and must be taken into consideration in choosing a bioanalytical sensor 114.5 Applications Biomedical sensors and instrumentation are used in biomedical research and patient care applications. In terms of patient care, sensors are used as a part of instruments that carry out patient screening by making measure ments such as blood pressure using automated apparatus. Specimen analysis is another important application of biomedical sensors in patient care. This can include analyses that can be carried out by the patients themselves in their homes such as is done with home blood glucose analyzers. Instrumentation based upon biomedical ensors can be used carrying out some chemical analyses of patient specimens such as urinalysis or elementary blood chemistries such as serum glucose and electrolytes. Sensors also are a part of large multicomponent automatic blood analyzers used in the central clinical laboratory of major medical centers. Another application for biomedical sensors is in patient monitoring. Sensors represent the front end of critical care monitors used in the intensive care unit and in the operating and recovery rooms. Measurements cover a wide range of biomedical variables such as continuous recordings of blood pressure and transcutaneous measurement of the partial pressure of carbon dioxide in the blood. The performance of these instruments is trongly dependent on biomedical sensors. Patient monitoring can also be carried out in the various clinical units of the hospital. Devices such as ambulatory cardiac monitors that allow patients to be observed while they are free to move around if they desire are becoming important in clinical care in"step-down"units for patients who have completed their stay in the intensive care unit. Patient monitoring has even made its way into the home. Home cardiorespiratory monitors are thought to have some potential value in identifying infants at risk of sudden infant death 114.6 Summary Sensors serve an important function in biomedical instrumentation systems in that they provide the interface between the electronic instrument and the biologic system being measured. Very often the quality of the instrument based upon the quality of the sensor at the instrument's front end. Although electronic signal processing has been developed to a high level, the signals are no better than the quality of the sensors that provide them. Although there ave been many advances in biomedical sensor technology, many problems remain. Biomedical sensors will continue to be an import area for research and development in biomedical engineering e 2000 by CRC Press LLC© 2000 by CRC Press LLC of the biological reaction. As illustrated in Fig. 114.5, this detector can consist of an electrical sensor such as used in electrochemical sensors, a thermal sensor, a sensor of changes in capacitance, a sensor of changes in mass, or a sensor of optical properties. An example of a bioanalytical sensor is a glucose sensor. The first portion of the sensor contains the enzyme glucose oxidase. This enzyme promotes the oxidation of glucose to glucuronic acid and consumes oxygen in the process. Thus, by placing an oxygen sensor along with the glucose oxidase in the bioanalytical sensor, one can determine the amount of glucose oxidized by measuring the amount of oxygen consumed. An even better approach is to have two identical sensor structures in the same package. The only difference is that only one of the sensors contains the enzyme. When there is no glucose present, both sensors will measure the same oxygen partial pressure. The presence of glucose, however, will cause the sensor with the glucose oxidase to have a reduced partial pressure of oxygen due to the oxygen consumption of the reaction. By making a differential measurement of oxygen partial pressure with both sensors, other factors that can cause an apparent change in oxygen partial pressure such as temperature will have a much lower effect than if a single sensor was used. Stability problems are important for bioanalytical sensors, especially those that are used for long-term measurements. Not only are the stability issues the same as for the physical and chemical sensors, but they are also related to preservation of the biological molecules used in the first stage of the sensor. These molecules can often be degraded or destroyed by heat or exposure to light. Even aging can degrade some of these molecules. Thus, an important issue in dealing with bioanalytical sensors is the preservation of the biochemical components of the sensor. Not all biochemical reactions are entirely reversible, and so the bioanalytical sensors based on them will not be reversible as well. This may be acceptable for some applications but not for others and must be taken into consideration in choosing a bioanalytical sensor. 114.5 Applications Biomedical sensors and instrumentation are used in biomedical research and patient care applications. In terms of patient care, sensors are used as a part of instruments that carry out patient screening by making measure￾ments such as blood pressure using automated apparatus. Specimen analysis is another important application of biomedical sensors in patient care. This can include analyses that can be carried out by the patients themselves in their homes such as is done with home blood glucose analyzers. Instrumentation based upon biomedical sensors can be used in the physician’s office for carrying out some chemical analyses of patient specimens such as urinalysis or elementary blood chemistries such as serum glucose and electrolytes. Sensors also are a part of large multicomponent automatic blood analyzers used in the central clinical laboratory of major medical centers. Another application for biomedical sensors is in patient monitoring. Sensors represent the front end of critical care monitors used in the intensive care unit and in the operating and recovery rooms. Measurements cover a wide range of biomedical variables such as continuous recordings of blood pressure and transcutaneous measurement of the partial pressure of carbon dioxide in the blood. The performance of these instruments is strongly dependent on biomedical sensors. Patient monitoring can also be carried out in the various clinical units of the hospital. Devices such as ambulatory cardiac monitors that allow patients to be observed while they are free to move around if they desire are becoming important in clinical care in “step-down” units for patients who have completed their stay in the intensive care unit. Patient monitoring has even made its way into the home. Home cardiorespiratory monitors are thought to have some potential value in identifying infants at risk of sudden infant death. 114.6 Summary Sensors serve an important function in biomedical instrumentation systems in that they provide the interface between the electronic instrument and the biologic system being measured. Very often the quality of the instrument is based upon the quality of the sensor at the instrument’s front end. Although electronic signal processing has been developed to a high level, the signals are no better than the quality of the sensors that provide them. Although there have been many advances in biomedical sensor technology, many problems remain. Biomedical sensors will continue to be an import area for research and development in biomedical engineering