Research On Fabrication And Application Of Liquid-liquid Extraction Microfluidic Chips

Microfluidic chip has played an extremely important role in the development process of scientific instruments. Miniaturization, integration and portability are the main features of microfluidic chips. Microfluidic chips integrate the sampling, reaction, separation and detection functions together, which have broad application prospects in chemical synthesis, bio-medical, environmental monitoring and other research areas. Along with the development of micro fabrication technology, there are various processing methods for microfluidic chips, not only the conventional photolithography and etching techniques, but also the molding, hot-pressing, soft lithography technology developed in recent years. In this paper, we manufactured the liquid-liquid extraction microfluidic chips based on PDMS by employing the conventional photolithography and etching technology and micro-replication technology of PDMS together, and carried on some research and applications of the microfluidic chips.Microfabrication technology is the primary means for preparing microfluidic chips. In this paper, we manufactured the photoresist mold and silicon mold of microfluidic chips by using the positive photoresist process and negative photoresist process of microfabricaton technology respectively. The microfluidic chips based on PDMS were obtained by the micro-replication process. Combining with an external actuator and detection system components, an integrated microfluidic chip system was completed integrated with the function of sampling, reaction, detection system, et al.One of the critical issues which limit the Lab-on-a-chip applications is the reliable connection between macroscopic world and microfluidic devices. With the development of microfluidic chips, varieties of microfluidic chip interconnection technology are proposed by researchers. In this paper, we presented a novel method of PDMS elastic interconnections, which was reusable and simplifies the manufacturing process by one-molding process. Such PDMS elastic interconnection owns admirable bonding strength and maximum fluid pressure with external tubes, as high as 330kPa. The stress distribution of assembled PDMS elastic interconnections was simulated by the FEM software. By matching the diameter of the auxiliary screws corresponded to the external tubes, the maximum working pressure was probably achieved to a greater value.In the laminar extraction microfluidic chips, extraction efficiency is limited by the slow diffusion coefficient. In this paper, we introduced the auxiliary structure in the microchannel to facilitate the mixture and transport of the laminar flow. The liquid-liquid extraction efficiency is improved. The streamline distribution and velocity vector map were simulated by FEM software, and the principle of extraction efficiency improvement was put forward. The rectangle shape auxiliary structure is considered to be the optimal of the three microchannels. Compared with the conventional blank shape liquid-liquid laminar extraction microfluidic chip, the extraction effiency of cross shape liquid-liquid laminar extraction microfluidic chip is 3.5 times larger by common fluorescence probe, Rhodamine 6G. The enrichment factor of the best liquid-liquid laminar extraction microfluidic chip is 18.6, and the limit of detection is 0.27 ppb.Liquid-liquid extraction separation technology is one of the most common separations in the chemical analysis, but the enrichment factor is limited by the volume ratio of organic phase and aqueous phase. In this paper, we designed a micro-cavity structure to achieve the liquid-liquid microextraction. The microextraction and rinse process in the microfluidic chip were carried out through sampling from different direction. In addition, the relationship between the microextraction efficiency, the duration of microextraction system and sampling rate was also explored. At low sampling rate, the extraction efficiency increases with the flow velocity. High sampling rate shortens the contact of two phases and enhances the dissolution of organic phase. The duration of the microextraction system is shorten and the extraction efficiency is reduced. By the common fluorescence probe, Rhodamine 6G, the enrichment factor of the liquid-liquid microextraction microfluidic chip is 29, and the limit of detection is 0.3 ppb.