Neurochip And Its Research For Sensory Mechanisms Of Biological Olfaction

Neuronal electrophysiology is one of the main research fields of the neuroscience. However, recording methods of the electronical signals still depend on the microelectrode or the patch clamp sticking to the membrane of the cells. It is difficult for those techniques to realize long-term monitoring, especially, the multi channels synchronous recording of neuronal networks, due to their unavoidable damage to cells. Therefore, using microelectromechanical systems, researchers have developed neurochips of microelectrode array (MEA) or field effect transistor (FET) array, based on cell-based biosensor, to record the extracellular potentials of neurons. Being an in vitro recording system, neurochip means a technique of culturing neurons on the surface of MEA or FET arrays, where cells can couple with electrodes or gates of FET through a thin layer of electrolyte. The novel biochip allows the communication between chips and cells, as well as monitoring the electrical activities of neurons in vitro in a long-term and non-invasive way. With these merits, neurochip have been applied primarily to biotnedical studies such as drugs screening and environment detection. Furthermore, neurochip allows for investigating the high function of the brain, neuronal prostheses and the reconstruction of damaged sense organs, when used in vivo to the neural system.To settle the key techniques of device design and celluar culture, the paper illustrated a novel neurochip based on light addressable potentiometric sensor (LAPS), using excitable cells cultured from embryonic stem cells, which can be successfully applied to drugs screening. Moreover, the neurochip has also been employed to the research of the biological olfaction in vivo as well as in vitro, which is a new application of the neurochip research. The major contents and contributions of this thesis are given as the following aspects.1. Based on light addressing characters of LAPS, the neurocip realized cell tracking and detection. Both MEA and FET array are restricted to measuring theextracelluar potential only at a limited number of active measuring sites (the tip of each individual microelectrode and the gate-electrode). It is difficult to culture cells just on those sites. LAPS is another commonly used semiconductor chip. When cells produce potential changes, which can be recorded by measuring the photocurrent generated from LAPS. By scanning the light-pointer along LAPS, cells at any desired position can be recorded, hence it can overcome the limitation of other neurochips mentioned before.2. A novel cell source for neurochip was provided, by inducing mouse embryonic stem cells in vitro differentiation culture. Neuronal cell is the bridge of the neurochip and neural system, which can sense the different physical and chemical stimulations of the neural system. Therefore, culture of the neuronal cells is very important to the neurochip. We induced mouse embryonic stem cells in vitro to differentiate into spontaneity beating cardiomyocytes and excited neurons respectively. Using extracellular potentials of the cells recorded by LAPS, a primary application in drugs screening of the stem cell chip was discussed.3. A bionic olfactory neurochip was designed based on a hybrid system of LAPS and olfactory neurons, which is sensitive to odors. Mammalian olfactory system can distinguish thousands of odors even in a minimal concentration level. In order to realize the biomimetic design of electronic nose on the principle of olfactory system, the chip was designed based on the electrophysiology detection of the olfactory cells. Through the simulative response under stimulations of the environment odorants, the results show that the bioelectronic nose of this biomimetic neurochip is sensitive to odorous changes. The technique widened the design idea of the traditional artificial nose.4. Dopamine in rat olfaction monitored in vivo, using a microprobe with microelectrode array. Based on the technique of microelectromechanical systems, a probe chip with 8 channels electrode arrays was fabricated. The sensor area of each electrode is 16 urn* 120 um or 0.3 urn* 120 um. With the very low cross talking noise of each channel, the probe could even detect Dopamine in 50 nM. Catecholamines were also monitored in vivo with the probe settling in rat nasal mucus. Using theanimal model of trigeminal stimulation by CO2, the results demonstrate the chip could monitor the time course of neurotransmitter substances by multiple sensor sites.