Study Of An Inductance-based Sensing Technique And Its Application In Biochemistry

This dissertation is devoted to the fabrication of wireless inductance bio/chemical sensors and their applications in bio/chemical analysis. In response to a time-varying AC magnetic field, an inductive coil of the sensor efficiently couples with the solenoid coil (loop antenna) which generates the AC magnetic field. The mutual inductance between the sensor and the solenoid is changed by the conductivity and permittivity of the liquid media which the sensor immerged, so the inductance of the loop antenna can reflect indirectly the characteristic of the liquid media. The excitation and transmission of signals of inductance sensor are carried out remotely by magnetic field. No direct physical connections between the sensor and the detection system are required, nor is any internal power required. The wireless nature of the inductance sensor makes it a powerful candidate for in situ and in vivo analysis. The details of work are summarized as follows:(1) Research of a wireless remote inductance sensor A wireless remote inductance sensor is reseached for the first time and the inductance is taken as the detection signal. Some factors which affect the inductance are reseached, such as, the number of the loop antenna, the test volume, and the temperature. It plays a critical role to optimize these parameters in the following biological analysis.(2) A wireless remote inductance sensor for research of salinity of different water samples is developed. The mutual inductance was different with different liquid media which the sensor immerged. Five saline solutions (potassium chloride, phosphate buffer solution, sodium sulfate, calcium chloride, magnesium sulfate) are researched. The inductance of the loop antenna is linear between 0 and 0.8 mM of the salinity. To test the the correctness of the experiment, five water samples (distilled water, spring water from Yuelu mountain, rain water, water from Xiangjiang river and tap water) are be chosen to detect the saline concentration. The results are similar to the traditional conductivity menthod, but the inductance menthod has lower limits of detection. The proposed inductance sensor offers a great opportunity for developing a useful measurement technology for the waste water.(3) A wireless remote inductance sensor for rapid detection of bacteria is developed. The wireless remote inductance sensor can control the real-time growth of the E. coli. When bacteria grow in the liquid medium, they produce small molecules, with a corresponding change in conductivity and permittivity of the culture medium. These change rerulted in the inductance changes of the sensor. The inductance starting time (IST) and the inductance ending time (IET) are related to the initiative concentration of the E. coli inoculated into the test tube. Thus, the concentration of the E. coli can be quantified according to it IST and IET. Using the newly developed inductance-based sensor, the pathogenic E. coli was monitored with a limit of detection of 10 cells/mL and a linear semi-logarithmic range of 1.0×101 to 2.5×109 cells/mL. This is a new way to control the microorganism and can avoid contamination.(4) A wireless remote inductance sensor for reseach of glucose is developed. A wireless remote inductance sensor can detect glucose. The inductance can change with the different concentration of the glucose. The GOD-catalyzed oxidation of glucose produces gluconic acid, which can decrease the pH of the solution and decrease the inductance. The glucose detection range can be larger in the ion liquid that is a green solvent, the linear range is 1.5～16 mM and the limit of detection is 1.5 mM. The proposed glucose biosensor can potentially be used as a planted sensor and applied to in vivo and in situ measurement of glucose concentrations in body blood.