Voltage-induced concentration enhancement of analyte solutes in microfluidic chips

Abstract

Microfluidic-based enrichment techniques have had a profound impact on chemistry, owing to their ability to improve the sensitivity of detection by increasing the concentration of analytes in minute fluid volumes. Herein, concentration enrichment of analyte solutes is achieved by using voltage assist in a microchip with two reservoirs. A numerical model is developed to describe the complex analyte focusing process, which to date has not been investigated before. Numerical computations are systematically conducted to study the influences of applied voltage, mass transfer coefficient, electrode location, reservoir diameter and number of mass transfer channels on the concentration enrichment in a designed Polydimethylsiloxane (PDMS)/Glass microfluidic electrophoresis chip. The electric fields, concentration distributions, and electrophoretic fluxes are obtained, which can reveal insightful enrichment mechanisms. It is found that the factors that can increase the electrophoretic flux in the mass transfer channel and enhance the electric field strength in the enrichment reservoir, such as moving the electrode back or increasing the number of mass transfer channels, are particularly important to improve the enrichment performance. The final microchip after considering the Joule heating effect has a 335-fold and 2.8-fold maximum and average concentration enrichments, respectively. Furthermore, this method is applied to the experimental enrichment of Rhodamine B and heavy metal cadmium (II) ions to test it performance.