Research On A Microelectrochemical Analysis System Based On Electroosmotically Driven Technology

Miniaturization of a chemical analysis system inevitably requires miniaturization of its fluid driving systems and sensors.A peristaltic pump used in a chemical analysis system is big in size,which is difficult to embed in a microfluidic channel.Moreover,its flow controllability is poor,and further reduction of sample volume is difficult.A light-addressable potentiometric sensor?LAPS?is commonly used in an electrochemical analysis system,which will face a problem of increases noise for reduction of its volume.Thus,an electroosmotic?EO?micropump?EOP?is adopted in this study,which could be easily embed in a microfluidic channel.A microelectrochemical analysis system with lower sample volume consumption and higher integration is developed.Meanwhile,to improve the transfer efficiency of an EOP and the signal-to-noise ratio for LAPS,a bubble-assisted EOP technology and a method of noise suppression based on wavelet transform are proposed,respectively.The dissertation investigated and discussed the relevant questions.The main innovative achievements of this dissertation include:1.A microelectrochemical analysis system based on electroosmotic driving technology is proposed.Due to the limited controllability of flow rate by a peristaltic pump used in combination with LAPS,further reduction of the sample volume is difficult.A microelectrochemical analysis system based on electroosmotic driving technology is proposed.The flow direction of EO flows on the LAPS chip could be controlled by the polarity of the applied DC voltage.The flow rate of EO flows on the LAPS chip could be controlled by the magnitude of the applied DC voltage.The average EO flow rate varies from 48.7 pL·s^-1 at 20 V to 122 pL·s^-1 at 50 V.In addition,the EO flow rate increases linearly with the applied DC voltage.A sample droplet of about 1 nL is generated in the microchannel on a LAPS surface.The EOP could be used as an actuator to drive the sample droplet to the sensing position of a LAPS.The LAPS signal increases at the time when the droplet is passing the sensing position.Photocurrent-time and photocurrent-bias voltage characteristics of different pH droplets are obtained.The bias voltages at the inflection points of photocurrent-bias voltage curves are determined,and the pH sensitivity of LAPS is approximately 50mV/pH,which is closer to the Nernst value.The results show that the designed microelectrochemical analysis system could measure a small volume of sample.To the authors'knowledge,it is the first time that an EOP technology is applied to LAPS.2.A bubble-assisted EOP is proposed.To avoid the problems of electrolysis at high pumping voltages and the complex preparation process of a microfluidic channel with a high surface-to-volume ratio in existing EOPs,a bubble-assisted EOP is proposed.An additional electrode is implanted in a bottleneck region of a microfluidic channel with a dumbbell-shaped structure to generate a bubble.Due to the hydrophilicity of inner walls of the microfluidic channel,a thin water sheet with a high surface-to-volume ratio remains between the bubble and the inner walls.As a result,an efficient EO flow could be generated at relatively low pumping voltages of 20 V to 60V without using a porous material.The results show that the resistance increases linearly with the length of bubble/water sheet,and the EO flow rate decreases with the length of bubble/water sheet increasing.The direction and the flow rate of the EO flow depended on the polarity and the magnitude of the pumping voltage,and the highest flow rate of about±500 pL·s^-1 is obtained at±60 V.A bubble-assisted EOP is combined with a LAPS for measuring the pH value of a droplet with a volume of 1 nL.3.A method of noise suppression for LAPS signal by wavelet transform is proposed.With the miniaturization of the electrochemical analysis system and further reduction of the sample volume,the LAPS signal will become weak resulting in a low signal-to-noise ratio.A method of noise suppression for LAPS signal by wavelet transform is proposed.The LAPS signal is decomposed into three layers by wavelet transform,and the wavelet coefficients and thresholds of each layer are obtained.According to the threshold value and the characteristics of each layer,the new wavelet coefficients are obtained after the original ones processed.Then,the LAPS signal is reconstructed according to the new coefficients.Spectrum analysis shows that wavelet transform is an effective method of LAPS signal denoising.This dissertation is of great significance to the application of microfluidic system combined with LAPS.The microelectrochemical analysis system developed in this study could generate and analyze a sample volume of 1 nL,and it is of great significance for building a new type of Lab-on-a-chip device.