A Microfluidic Analysis System Integrated With Liquid-Liquid Extraction And Liquid-Liquid Waveguide

Integration is one of the main characteristics of microfluidic analysis system. The integrated analysis systems have some advantages, such as simplified operation process, less sample contamination, less consumption of samples and reagents, which contribute to the automation and portability of the analysis devices. In this work, a microfluidic analysis system integrated with liquid-liquid extraction and liquid-liquid waveguide absorbance detection was explored. Ionic liquid-based aqueous two-phase extraction was realized using multiphase laminar-flow in a microchannel. And then the multiphase laminar-flow was introduced into a detection microchannel. Based on the total internal reflection on liquid-liquid interfaces, liquid-liquid waveguide detection was achieved. Sensitivity of the microfluidic absorbance detection was improved greatly owing to the enrichment of the analyte and the long optical path of absorbance detection.In chapter 1, liquid-phase microextraction technology was reviewed, and microfluidic chip-based liquid-liquid extraction techniques were introduced in detail. And then, ionic liquid-based aqueous two-phase systems and their applications were introduced, so were absorbance measurements based on liquid-core waveguides. Finally, purpose and design of this work were proposed.In chapter 2, a microfluidic chip integrated with liquid-liquid extraction and absorbance detection based on liquid-liquid waveguide was designed and fabricated, and an integrated analysis system was established. An ionic liquid aqueous two-phase system (1-butyl-3-propylimidazolium bromide/K3PO4) was used as microextraction system, in which 1-butyl-3-propylimidazolium bromide with higher refractive index was used as liquid core and potassium phosphate solution (containing cresol red sample) with lower refractive index was used as inner liquid cladding. In addition, potassium phosphate solution was introduced as outer cladding to avoid adsorption of cresol red on the microchannel wall. Stable liquid-liquid laminar-flow was formed in a spiral microchannel, where cresol red was extracted continuously into 1-butyl-3-propylimidazolium bromide. Subsequently, three-phase laminar-flow was introduced into a detection microchannel to form a 3 cm-long liquid-liquid waveguide flow cell for absorbance detection. An enrichment factor of 2 and the extraction ratio of more than 90% were achieved in the system. The linear range was 0.1-5 mmol·L-1, and the limit of detection for cresol red was 2.4×10-5 mol·L-1 (3σ). A precision of 3.4% RSD (n=11) was achieved. The absorbance is 3 times than the microfluidic system without liquid waveguide. An absorbance detection system was further established utilizing microfluidic liquid-liquid waveguide based on 3D hydrodynamic flow focusing.In chapter 3, the multiphase laminar-flow-based miniaturized total analysis system integrated with liquid-liquid extraction and liquid-liquid waveguide was summarized, and the system integrated with liquid-liquid extraction and 3D liquid-liquid waveguide was prospected.