Investigation of parameters and porous plug enhanced enrichment with field-Amplified sample stacking in microchip

With the recent great interest in microfluidic devices, a better understanding of preconcentration technology has become increasingly important. Herein, concentration enrichment of charged samples is achieved by using field-Amplified sample stacking (FASS) technology in the microchannel. This paper aims to develop a fundamental understanding of FASS and to propose a method to enhance the enrichment quality of FASS. First, numerical investigations are carried out to systematically study the effects of various parameters including the applied voltage, the charged properties of the sample, the buffer concentration ratio, the injection length, and the microchannel width on FASS enrichment performance. The results show that reducing the width of the microchannel is an effective way to improve the enrichment quality. The maximum enrichment ratio can be improved by 67.35% by reducing the width of the microchannel to less than 10 μm due to the inhibition of background buffer diffusion. Second, to improve traditional FASS performance, a high-conductance gradient boundary is established by photoinitiating fabrication of a porous plug at the enriched interface position. This structure provides a region that reduces the local size of the internal channel to less than 5 μm and has high flow resistance, but allows the electromigration of the charged analyte. Experimental results show that an electropherogram signal increases by a maximum factor of 329 in electrophoretic enrichment of fluorescein-Na with 5 × 10-7 M initial concentrations, and the enrichment quality of traditional FASS is greatly improved.