Integration Of A Microfluidic Chip Glucose Electrochemical Detection System

Glucose biosensor is widely used for glucose determination. Miniaturization and portability of the detection system is highly demanded in practice. Microfluidic technology offers a good opportunity for the development of smaller biosensor device with less sample and regent consumption. In this thesis, an established microfluidic electrochemical glucose detection system was improved in term of integration of enzyme reactor and sensing electrode. Glucose oxidase was successfully immobilized onto the inner surface of the channel to improve the integration of the system, and the detection system was further simplified by using two-electrode electrochemical detection configuration, and the determination of glucose in human plasma was successfully demonstrated.Glucose oxidase was immobilized onto the inner glass microchannel surface by covalent binding, thus the microchannel was used both as an enzymatic microreactor and electrochemical detection cell. The fluid was driven by a syringe pump, and detection of glucose content was achieved in a flow manner. The Michaelis-Menten constant (Km) of enzyme was10mmol/L, and a linearity coefficient of0.9989was obtained in the range of1.0×10-4-5.0×10-3mol/L with a detection limit of5.0×10-5mol/L(S/N=3) and a relative standard deviation (RSD) of2.7%(n=7) at the potential of+0.5V vs. Ag/AgCl. Stability of the enzymatic microreactor was tested, and no obvious lose of enzyme activity was noticed in three days. The integration of enzymatic microreactor and electrochemical detection cell was achieved in this system, and flowing determination of glucose was successfully demonstrated.Instead of using a macro Ag/AgCl reference electrode outside of the microchip, the electrochemical detection was conducted in two-electrode configuration using the two Pt wires (50μm diameter) positioned in the microchannel, one of the Pt wire electrode was used as the working electrode, and the other as reference as well as auxiliary electrode. The Michaelis-Menten constant (Km) of a capillary enzyme reactor was24mmol/L as measured by the modified system, and a linearity of r=0.9989was obtained in the range of 2.0×10-4～5.0×10-3mol/L with a detection limit of1.0×10-4mol/L (S/N=3) and a relative standard deviation (RSD) of2.9%(n=7) at the potential of+0.7V vs. Pt. The interference to glucose detection due to co-existing electrochemically active species was effectively corrected by measuring the current difference between2states-with and without enzyme reactor, and the interference due to ascorbic acid and uric was decreased from18%to5.4%.