Capillary-driven multiparametric microfluidic chips for one-step immunoassays

Abstract(#br)Here we present a capillary-driven microfluidic chip for “one-step” immunoassays. The chip allows for easy modification of several assay parameters such as the flow rates of sample, the volumes of samples for tests, and the type of reagents and receptors for detecting analytes. We therefore term such a chip a multiparametric chip and illustrate this concept with the integration and release of anti-C-reactive protein (CRP) detection antibodies (dAbs) together with splitting flow of samples containing CRP across lines of anti-CRP capture antibodies (cAbs). The microfluidic chip is fabricated in Si and is sealed with polydimethylsiloxane (PDMS) patterned with cAbs. The microfluidic chip is ∼1.7\u003cce:hsp sp=\"0.25\"/\u003e×\u003cce:hsp sp=\"0.25\"/\u003e3.4\u003cce:hsp sp=\"0.25\"/\u003ecm 2 and is capable of analyzing 20\u003cce:hsp sp=\"0.25\"/\u003eμL of human serum in 6 parallel flow paths with a range of flow rates from 3.3\u003cce:hsp sp=\"0.25\"/\u003enL\u003cce:hsp sp=\"0.25\"/\u003es −1 to 0.46\u003cce:hsp sp=\"0.25\"/\u003enL\u003cce:hsp sp=\"0.25\"/\u003es −1 . An inkjet spotter was used to deposit 10.6\u003cce:hsp sp=\"0.25\"/\u003enL of dAb solution in a structure vicinal to the main flow path of the chip. The consequent asymmetric release of dAbs in a stream of human serum is compensated by a Dean flow mixer having 9 mixing loops and a footprint of 2.8\u003cce:hsp sp=\"0.25\"/\u003emm\u003cce:hsp sp=\"0.25\"/\u003e×\u003cce:hsp sp=\"0.25\"/\u003e0.78\u003cce:hsp sp=\"0.25\"/\u003emm. The quantity of dAb present in the half of the flow path close to the spotting region decreases from 83% at the entrance of the mixer to 52% in the region after the mixer. The sample is then equally split into 6 reaction chambers and proceeds via connecting channels to 2\u003cce:hsp sp=\"0.25\"/\u003eμL capillary pumps. The hydraulic resistance of the connecting channels is designed to vary flow rates, and therefore the kinetics of capture of CRP-dAb complexes, from 10\u003cce:hsp sp=\"0.25\"/\u003emin to 72\u003cce:hsp sp=\"0.25\"/\u003emin. The increased incubation time leads to a fourfold increase in detection signal in the reaction chamber with the longer incubation time. The concept presented here is flexible and suited for implementing various surface fluorescence immunoassays on a capillary-driven microfluidic chip.