Multistory Stairs-based, Fast and Point-of-care Testing for Disease Biomarker Using One-step Capillary Microfluidic Fluoroimmunoassay Chip via Continuous On-chip Labelling

Sufficiently long reaction time and low flow velocity are crucial for capillary microfluidic immunoassay chips, especially for truly “one-step” detection with continuous on-chip labelling and capturing. In this study, a multistory stairs-based new delay valve is used to meet the time and flow requirements for protein testing. The delay strategy is capable of slowing down the flow of liquid into the functional region and delaying the time out of the regions as well, thus extending the labelling and capture time to about 100 and 60 s respectively, and further reducing the flow velocity to below 8 μL/min. Based on the principle of sandwich-like immunocomplex, the designed chip is capable of automatically accomplishing on-chip mixing, labelling and capturing procedures via once sample loading and sensitively detecting human Alpha-Fetoprotein (AFP) in 40 μL serum with a wide dynamic ranging from 10 ng/mL to 10 000 ng/mL within 5 min. It could be foreseeable that this microchip has great potential in biomarkers clinical testing.