Poly(dimethylsiloxane) microchip-based immunoassay with multiple reaction zones: Toward on-chip multiplex detection platform

In this work, a poly(dimethylsiloxane) (PDMS) microchip-based immuno-sensing platform with integrated pneumatic micro valves is described. The microchip was fabricated with multiple layer soft lithography technology. By controlling the activation status of corresponding valves, reagent flows in the microchannel network can be well manipulated so that immuno-reactions only take place at designated reaction zones (DRZs). Four DRZs are included in the prototype microchip. Since these DRZs are all isolated from each other by micro valves, cross contamination is prevented. Using the inner surface of the all-PDMS microchannel as immunoassay substrate, on-chip sandwich format solid phase immunoassay was performed to demonstrate the feasibility of this immuno-sensing platform. Mouse IgG and fluorescein isothiocyanate (FITC) were used as the model analyte and the signal reporter respectively. Only 10 μl sample is needed for the assay and low detection limit of 5 ng/ml (≈33 pM) was achieved though low-cost polyclonal antibodies were used in our experiment for feasibility study only. Much lower detection limit may easily be achieved by using high quality monoclonal antibodies. Through a simple yet effective comparison experiment, it was also found that high concentration BSA blocking solution (5% BSA in PBS buffer) can effectively suppress the non-specific binding in the surface of the microfluidic channels. The encouraging results from mouse IgG immunoassay proved the feasibility of our microchip design. With slight modification of the assay protocol, the same chip design can be used for multi-target detection and can provide a simple, cost-effective and integrated microchip solution for multiplex immunoassay applications.