tailieunhanh - Microengineering MEMs and Interfacing - Danny Banks Part 9

Tham khảo tài liệu 'microengineering mems and interfacing - danny banks part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Microsensors 141 this form for long. It interacts with the oxygen entering through the membrane. The products of this interaction are the oxidized form of the enzyme two hydrogen ions and two oxygen ions. When the platinum electrode is biased to the correct potential it will reduce one of the oxygen ions such that the end products are oxygen and water. The resulting electrode current can be measured and will be proportional to the concentration of glucose in the external medium. Note that this is a simplified explanation there are also many other ways to monitor the reaction . One thing to note is that because the various molecules have to physically move through the materials of the sensor such biosensors can be quite slow to respond to changes in the external medium. MICROELECTRODES FOR NEUROPHYSIOLOGY Microelectrodes of fine-wire or electrolyte-filled micropipettes have been used for some time now to study the nervous system on a cellular individual neuron basis. These in particular the metal wire microelectrodes are prime targets for the application of microengineering techniques. The small signal amplitudes involved in the region of 100 pV and high interface impedances 1 to 10 MQ at 1 kHz between the metal and the tissue mean that it is advantageous to place the amplifier as close as possible to the recording site. In addition the characteristics of microfabricated devices can be more reproducible than those of handmade metal wire microelectrodes and their small size enables the accurate insertion of many recording sites into small volumes of tissue to study networks of neurons or for neural prosthesis applications. The microelectrodes operate by detecting the electrical potential generated in the tissue near an active nerve fiber because of action potential currents flowing through the fiber membrane. There are three common types of micromachined microelectrode Figure . Array-type microelectrodes Figure are used to form the floor of cell culture