Abstract
On-chip immuno-sensors are a hot topic in the microfluidic community, which is usually limited by slow diffusion-dominated transport of analytes in confined microchannels. Specifically, the antigen-antibody binding reaction at a functionalized area cannot be provided with enough antigen source near the reaction surface, since a small diffusion flux cannot match with the quick rate of surface reaction, which influences the response time and sensitivity of on-chip heterogeneous immunoassay. In this work, we propose a method to enhance the transportation of biomolecules to the surface of an antibody-immobilized electrode with induce charge electroosmotic (ICEO) convection in a low concentration suspension, so as to improve the binding efficiency of microfluidic heterogeneous immunoassays. The circular stirring fluid motion of ICEO on the surface of a floating gate electrode at the channel bottom accelerates the transport of freely suspended antigen towards the wall-immobilized antibodies. We investigate the dependence of binding efficiency on voltage magnitude and field frequency of the applied alternate current (AC) electrical field. The binding rate yields a factor of 5.4 higher binding for an applied voltage of 4 V at 10 Hz when the Damkohler number is 1000. The proposed microfluidic immuno-sensor technology of a simple electrode structure using ICEO convective fluid flow around floating conductors could offer exciting opportunities for diffusion-limited on-chip bio-microfluidic sensors.
Highlights
Immunoassays, which refer to the specific binding interaction between the free antigens in the analytes and the immobilized antibody, have been widely applied in point-of-care detections, biological research, quality control, pharmaceutical research, and environmental diagnostics for their high selectivity and sensitivity
The microfluidic immunoassays are still limited in response time and sensitivity due to the slow diffusion of target molecules/proteins to the detection surface, which limits the overall performance of the immuno-sensors requiring the fast surface reactions
We demonstrate a method to deliver the target antigen to the detection surface under low analyte concentrations and enhance the performance of heterogeneous immunoassays using induce charge electroosmotic (ICEO) convective flow on polarizable
Summary
Immunoassays, which refer to the specific binding interaction between the free antigens in the analytes and the immobilized antibody, have been widely applied in point-of-care detections, biological research, quality control, pharmaceutical research, and environmental diagnostics for their high selectivity and sensitivity. Conventional immunoassays, such as microarrays [1] or enzyme-linked immune sorbent assays (ELISA) [2], require larger sample volume and longer incubation time due to their labor-intensive and sophisticated fluid handling steps at various stages of the assay. The proposed lab-chip immuno-sensor system has the merit of portability, rapid detection, and low energy consumption
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