Studies On Microfluidic Chip Analysis Systems With Gas Diffusion Separation And Reflected Photometric Detection

The research of microfluidic chip-based sample pretreatment has emerged as an active area in the field of micro total analysis systems (μTAS). Although gas diffusion separation is a powerful and popular method for sample pretreatment in conventional flow injection systems, there were relatively few studies about it applied in gas diffusion separation in microfluidic chip systems. A microfluidic chip based on gas diffusion separation of small size, high diffusion efficiency, simple structure and low cost was developed in this work. Poly(tetrafluoroethylene) (PTFE) membrane was used as gas-permeable membrane. A piece of pH paper covalently bounded acid-base indicator was fixed into the micro acceptor channel. The bounded acid-base indicator demonstrated several advantages, such as repetitive utilization of reagents and reduced reagent dilution. Therefore, a microfluidic chip analysis system integrated with gas diffusion separation and reflected photometric detection was built.In the first chapter, the related techniques of membrane separation in flow injection analysis systems, the types of microfluidic chips based on gas diffusion separation and the techniques of optical detection for micofluidic systems were reviewed. The purpose and design of this work were presented.In the second chapter, a three-layer microfluidic chip analysis system integrated with gas diffusion separation and reflected photometric detection was presented. In this three-layer structure, PTFE membrane was used as the gas-permeable, which was bonded in the middle of poly(dimethylsiloxane) (PDMS) layers—reaction channel and acceptor channel. Reflected photometric detection was achieved by fixing a piece of pH paper bounded acid-base indicator into the micro acceptor channel as the reflected photometric detection module. A micro-syringe pump was used for driving fluids. The slotted-vial array sample introduction system was employed for sampling, and automated sample introduction and change were achieved. NH4+ was used as a model analyte, and the related parameters were optimized. A precision of 1.0% RSD (n=7) was achieved with a detection limit of 0.30 mmol/L NH4+(3a) and sample consumption of 0.67μL for each assay. The system was applied for the detection of ammonium ion in industral wastewater, lake water and urine sample.The microfluidic chip integrated with gas diffusion separation and reflected photometric detection reduced both the bulk of the analysis system and the consumption of the samples and the reagents. The system can be applied for analysing biochemistry samples which are expensive and rare. If the sensitivity can be improved, the system is promisingly adequate to detect ammonium ion in blood with high speed and low consumption.