Lateral flow assays (LFAs), or rapid tests, such as common pregnancy or drug tests, typically attempt to identify the presence of a substance via a one-time chemical reaction using a paper-based assay, a liquid (e.g., blood, urine, saliva, etc.), and a reagent. However, more complex diagnostic testing, such as COVID-19 detection, can require multi-step, multi-reagent chemical reactions with specific timings. Georgia Tech researchers have developed a technique to control capillary flow on paper-based LFA substrates that leverages a gradual process, thereby allowing for multiplex molecular detection. This technique has led to the development of low-cost, point-of-care (POC) toolkits for the diagnosis of SARS-CoV-2 and influenza A and B viruses, as well as improved pregnancy testing.

Researchers were able to create “timers” by imprinting roadblocks on the flow path with water-insoluble material and utilizing the gradual formation of a void between a wetted paper and a sheath polymer tape (i.e., delamination). Timers are drawn on paper at strategic nodes to hold the capillary flow for a desired period of time, hence multiple liquids can be introduced into the reaction following a programmed sequence. Furthermore, by marking the flow boundaries with a material that remains permanently adhered to the sheath tape, researchers were able to imprint on paper complete LFAs programmed to execute multi-step chemical reactions in an optimized manner. Using this technique, Georgia Tech developed 1) an LFA with built-in signal amplification to detect human chorionic gonadotropin (i.e., a pregnancy test) with an order of magnitude higher sensitivity than the conventional assay and 2) a device to extract and purify DNA from blood, saliva, and urine samples without relying on laboratory instruments for post-processing.

To see more technologies like this by Dr. Sarioglu and his team, please click here.