Development Of Microfluidic Liquid Chromatographic Systems

Microfluidics is the science and technology that manipulate small (nL～fL scale) amounts of fluids, using channels with dimensions of tens to hundreds of micrometer. Its objective is to integrate all of the units in chemical and biological analysis, including sample preparation, reaction, separation, detection, on a microfluidic chip to build the micro total analysis system. High-resolution microanalytical technique plays a very important role in chemical and biological analysis. Currently, there is a growing demand for the development of liquid chromatography systems for microfluidic systems.In Chapter1, the applications of microfluidic chip-based liquid chromatography systems, as well as sample injection techniques and chromatography columns are reviewed. The recent progress in high-resolution separation approaches for droplet-based microfluidic systems is also reviewed.In Chapter2, a microfluidic chip-based liquid chromatography system with valveless gated sample injection method and monolithic columns was developed. The valveless LC system consisted of a microchip with a separation column and a balance column, two syringe pumps and a laser induced fluorescence detector. Two monolithic columns with the same length were fabricated in the sample and separation channel served as pressure-balance column and LC separation column, respectively. Nanoliter-scale sample injection was achieved by simply switching the ON and OFF states of the syringe pumps under gated injection mode, without the need of any mechanical valve. The balance column facilitated the gated injection process by balancing the back pressure in the sample channel with that in the separation channel. Under the gated injection mode, the sample injection volumes could be varied in the range of0.4-2.4nL. The present system was applied to the fast separation of two fluorescence-labeled amines.The advantages of the present system include simple system structure, ease of operation, convenience for varying injection volume, and high sample loading capacity.In Chapter3, the combination of droplet-based microfluidics with liquid chromatography-mass spectrometry was achieved, for providing a fast separation and high-information-content detection method for analysis of nanoliter-scale droplets with complex compositions. A novel interface method for capillary LC and droplet array chip with significant flexibility in accurate addressing and sampling of interesting droplets on demand was developed. With this method, multistep operations including parallel enzyme inhibition reactions in nanoliter droplets,4-nL sample injection, fast separation with capillary LC, and label-free detection with ESI-MS were successfully realized. The present system was further applied to the screening for inhibitors of cytochrome P450(CYPI A2) and the measurement of IC50value of the inhibitor. The sample consumption for each droplet assay was100nL, which is reduced10to100times compared with conventional384multi-well plate systems usually used in high-throughput drug screening.