Capillary flow of hybrid mode for enhancement of flow rate on μTADs

Microfluidic paper-based analytical devices (μPADs) and microfluidic thread-based analytical devices (μTADs) have already found many successful applications in biosensing. These devices mainly utilize the autonomous capillary pumping of liquid for sample actuation. Capillary flow control is very interesting and necessary for μPADs and μTADs with point-of-care diagnostic applications. Many attempts have been made on μPADs while few attempts exist for μTADs. Methods for facile flow rate control on μTADs are needed for improving the performance of μTADs on point-of-care diagnostics.

Here, we develop a method for increasing the capillary flow rate on μTADs. By incorporating hollow channels within μTADs that are encapsulated by thermal contraction tubes, we establish a hybrid capillary flow mode, which significantly enhances the flow rates in these devices. We investigate the influence of hollow channel size on the capillary flow rate, and find that the average flow rate increases with the hollow channel size. The average flow rate of the group with hollow channel size as 1200 μm is 12353 % more than that of the control group. Then we choose the group with hollow channel size as 1200 μm for investigation of flow rate enhancement on high viscosity liquid samples (glycerol) and non-Newtonian liquid samples (whole blood). Moreover, we also show that programmed enhancement of capillary flow rate is possible by creating μTADs with a partial hollow channel along the threads.

The simplicity of our method enables it to be used for facile flow rate control on μTADs, and it works well for various and complex liquid samples. We believe that by combination with immunoassays, it has the potential in improving the performance of μTADs for point-of-care diagnostics in the near future.