Bioanalysis Zone

Stacking of paper-based immunoassays for better flow

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Researchers from the A*STAR Institute of Bioengineering and Nanotechnology (Singapore) have developed a more versatile and effective paper-based kit for diagnosing disease from saliva samples. The work, published in Lab on a Chip, sought to improve the control of the flow and the filtering of materials as they move through the device.

Currently, a large number of home diagnostic kits use paper-based immunoassay platforms, usually in the form of lateral flow tests. However, unwanted chemical interactions of the bodily fluids with the paper strips limit the potential applications of this type of device. This can be a particular problem with salivary fluid, in which a high concentration of protein-based substances is believed to cause particle aggregation and adhesion.

To overcome this limitation, Jackie Ying (A*STAR Institute of Bioengineering and Nanotechnology) and his colleagues developed a ‘stacking flow’ system. In this device, the flow streams are stacked on top of each other, and so the saliva sample and detecting reagents initially flow separately. The two streams are kept separate by an impermeable flow regulator until the optimal point. Ying outlined the benefit of this two-stream system: “This allows unnecessary salivary substances to be filtered away before the two streams meet.”

Multi-flow-path devices have been developed previously; however, their input paths merge in the same plan of the paper. Ying explained that while this existing type of system does not allow for uniform flow and mixing, that this would be achievable using the new stacked two-flow-path technology. The A*STAR researchers demonstrated their new device with a dengue virus diagnostic kit, which detects dengue-specific immunoglobulins that are present in salivary fluid.

The team believe that their stacking flow system will have a wider application than just dengue virus detection, and are currently working on employing the device for other infectious diseases.

Sources: Zhang Y, Bai J, Ying JY. A stacking flow immunoassay for the detection of dengue-specific immunoglobulins in salivary fluid. Lab Chip 15(6), 1465­–1471 (2015); Stacking for better flow.

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