Paper-based microfluidic sensing device for label-free immunoassay demonstrated by biotin-avidin binding interaction

Efficient diagnosis is very important for the prevention and treatment of diseases. Rapid disease screening in ambulatory environment is one of the most pressing needs for disease control. Despite there are many methods to detect the results of immunoassays, quantitative measurement for rapid disease screening is still a great challenge for point-of-care applications. In this study, a fabrication method for depositing carbon nanotube bundles has been successfully developed for realization of functional paper-based microfluidic sensing device. Quantitative detection of label-free immunoassay, i.e., biotin-avidin binding interaction, was demonstrated by direct measurement of the current change of the biosensor after single application of the target analyte. Sensitivity of 0.33 μA/ng mL^-1 and minimal detectable analyte concentration of 25 ng/mL were achieved. The time necessary for the detection was 500 s which is a large reduction compared with the conventional immunoassay. Such paper-based biosensor has the benefits of portability, fast response, simple operation, and low cost and has the potential for the development of rapid disease screening devices.