Revolution in Rapid Testing: A New Generation of Programmable Lateral Flow Assays

Researchers have modified and enhanced the commonly used lateral flow assay method by introducing a technique to control the rate of capillary flow, which enables the test strip to carry out multistep chemical reactions following a programmed sequence.

Lateral flow assays (LFTs) have a wide array of applications and can be used to analyze a variety of samples such as urine, blood, saliva, sweat, serum, and other fluids. They are currently used by clinical laboratories, hospitals, and physicians for quick and accurate tests for specific target molecules and gene expression. Other uses for lateral flow assays are food and environmental safety and veterinary medicine for chemicals, diseases, and toxins. LFTs are also used for disease identification, but the most common LFT is the home pregnancy test.

A weakness of the conventional LFA method is that the physical characteristics of capillary flow prevents them from being able to coordinate complex processes that include the application of multiple reagents in a specific sequence with specific delays in between.

In response to this problem, investigators at the Georgia Institute of Technology (Atlanta, USA) recently described a way to control capillary flow by imprinting roadblocks on the flow path with water-insoluble ink and using the gradual formation of a void between a wetted paper and a sheath polymer tape to create timers. Timers were drawn at strategic nodes to hold the capillary flow for a desired period and thereby enabled multiple liquids to be introduced into multistep chemical reactions following a programmed sequence. By modifying the imprint geometry, the investigators could set the time required for a void to form and effectively created timers that blocked capillary flow for a desired duration.

The investigators employed the new technique to develope (i) an LFA with built-in signal amplification to detect human chorionic gonadotropin with an order of magnitude higher sensitivity than the conventional assay and (ii) a device to extract DNA from bodily fluids without relying on laboratory instruments. The latter device has potential for use as a rapid test for detection of Covid-19 infection.

"These tests have been extremely popular for years, mainly because they are so simple to use. You do not send anything to the lab or clinic because these tests do not require any external equipment to operate. This is an advantage," said senior author Dr. Fatih Sarioglu, assistant professor of electrical and computer engineering at the Georgia Institute of Technology. "But there also is a disadvantage. There are limitations to what they can do. By strategically imprinting these timers, we can program the assays to coordinate different capillary flows. That enables multiple liquids to be introduced, and multistep chemical reactions, with optimal incubation times - so, we can perform complex, automated assays that otherwise would normally have to be performed in laboratories. This takes us beyond the conventional LFA."

"We believe this flow technology research will have widespread impact," said Dr. Sarioglu. "This kind of dipstick test is so commonly used by the public for biomedical testing, and now it can be translated into other applications that we do not traditionally consider to be cut out for these simple tests."

The enhanced LFA technique was described in the October 1, 2021, online edition of the journal Science Advances.

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Georgia Institute of Technology