RECOGNITION PROTEINS PhYSICAL TRANSDUCER ELECTRICAL ELECTRODES capacitance THERMAL THERMISTORS MASS SAW DEVICES ELECTRICAL SIGNAL OPTICAL PHOTODETECTORS BIOLOGICAL SENSING REACTION PROTEINS IN SOLUTION FIGURE 114.5 A generalized bioanalytical sensor the theoretical sensitivity of the electrode is approximately 60 mV/pH. It is not practical to measure the potential across the membrane directly and so reference electrodes, sensors that can be used to measure electrical potential of an electrolytic solution, are used to contact the solution on either side of the membrane to measure the potential difference across it. The reference electrodes and the glass membrane are incorporated into the structure shown in Fig. 114.4 known as a glass pH electrode. This is an example of a potentiometric measure- ment made using an ion-selective membrane There are other types of ion-selective membrane potentiometric chemical sensors that are used for biomedical applications. The membranes of these sensors determine the ion being sensed. The membrane can be based upon glass or a polymeric material such as polyvinyl chloride, but the key component is the substance that is added to the membrane that allows it to Important problems in the development of chemical biomedical sensors are similar to those discussed above for the pressure sensor. Issues of long-term stability and packaging are critical to the success of a chemical sensor. The package is even more critical in chemical sensors than it was in pressure sensors in that the package of the sensor that isolation from the solutions being measured while it provides direct contact of the chemically sensitive portions of the sensor to the solution. The maintenance of a window through the package for this contact represents a critical aspect of sensor development. Frequent calibration is lso necessary for chemical sensors. Just about every type of chemical sensor requires some sort of calibration ng a standard solution with known concentration of the analyte being sensed. The best calibration method is a two-point procedure where two standards are used to establish the slope and the intercept of the calibration ine. Some chemical sensors have stable slopes but need to be calibrated in terms of the baseline or intercept. In this case a single-point calibration can be 114.4 Bioanalytical Sensors A special class of sensors of biological molecules has evolved in recent years. These bioanalytical sensors take advantage of one of the following biochemical reactions: (1)enzyme-substrate, (2)antigen-antibody, or(3 ligand-receptor. The advantage of using these reactions in a sensor is that they are highly specific for a particular iological molecule, and sensors with high sensitivity can be developed based upon these reactions. The basic structure of a bioanalytical sensor is shown in Fig. 114.5. There are two principal portions of the sensor. The portion of a bioanalytical sensor is made up of either a physical or chemical sensor that serves as the detector e 2000 by CRC Press LLC© 2000 by CRC Press LLC the theoretical sensitivity of the electrode is approximately 60 mV/pH.It is not practical to measure the potential across the membrane directly and so reference electrodes, sensors that can be used to measure electrical potential of an electrolytic solution, are used to contact the solution on either side of the membrane to measure the potential difference across it. The reference electrodes and the glass membrane are incorporated into the structure shown in Fig. 114.4 known as a glass pH electrode. This is an example of a potentiometric measure￾ment made using an ion-selective membrane. There are other types of ion-selective membrane potentiometric chemical sensors that are used for biomedical applications. The membranes of these sensors determine the ion being sensed. The membrane can be based upon glass or a polymeric material such as polyvinyl chloride, but the key component is the substance that is added to the membrane that allows it to selectively pass a single ion. Important problems in the development of chemical biomedical sensors are similar to those discussed above for the pressure sensor. Issues of long-term stability and packaging are critical to the success of a chemical sensor. The package is even more critical in chemical sensors than it was in pressure sensors in that the package must protect portions of the sensor that require isolation from the solutions being measured while it provides direct contact of the chemically sensitive portions of the sensor to the solution. The maintenance of a window through the package for this contact represents a critical aspect of sensor development. Frequent calibration is also necessary for chemical sensors. Just about every type of chemical sensor requires some sort of calibration using a standard solution with known concentration of the analyte being sensed. The best calibration method is a two-point procedure where two standards are used to establish the slope and the intercept of the calibration line. Some chemical sensors have stable slopes but need to be calibrated in terms of the baseline or intercept. In this case a single-point calibration can be used. 114.4 Bioanalytical Sensors A special class of sensors of biological molecules has evolved in recent years. These bioanalytical sensors take advantage of one of the following biochemical reactions: (1) enzyme-substrate, (2) antigen-antibody, or (3) ligand-receptor. The advantage of using these reactions in a sensor is that they are highly specific for a particular biological molecule, and sensors with high sensitivity can be developed based upon these reactions. The basic structure of a bioanalytical sensor is shown in Fig. 114.5. There are two principal portions of the sensor. The first contains one component of the biological sensing reaction such as the enzyme or the antibody, and the second component involves a means of detecting whether the biological reaction has taken place. This second portion of a bioanalytical sensor is made up of either a physical or chemical sensor that serves as the detector FIGURE 114.5 A generalized bioanalytical sensor