Paper-based devices demonstrate high accuracy in detecting asymptomatic malaria

Paper-based devices demonstrate high accuracy in detecting asymptomatic malaria

Devices using cheap paper strips have outperformed two other testing methods for detecting malaria infections in asymptomatic people in Ghana - a diagnostic advance that could accelerate efforts to eliminate the disease, researchers say.

Deceptively simple in appearance, the devices facilitate chemical reactions between a drop of blood and molecules embedded in layers of paper and rely on sophisticated but portable instruments to make the diagnosis: a mass spectrometry measurement of the end product—in positive cases, a malaria-specific antigen that triggers the immune system.

Normally you take the sample to the lab, but now we're taking the lab, for example - I'm taking it to Africa, one of the most remote parts of the world, and doing the analysis right there. “

Abraham Badu-Tawiah, lead author of the field study report and professor of chemistry and biochemistry at Ohio State University

"The question was, can we have a sensitive tool that can be delivered to people regardless of where they are. The statistical analysis showed that our method is 90% accurate and comparable to a PCR test. It is very good and we can deliver these results to people who need it most."

The research was recently published inAnalytical chemistry.

Malaria is caused by the bite of mosquitoes that spread infectious parasites. The World Health Organization estimates that 249 million people worldwide had malaria in 2022 and about 608,000 died from the disease. A preventative vaccine is now available to children in Ghana, where over a quarter of the population was infected in 2011, up from 8.6% by 2022.

Badu-Tawiah first reported this invention in 2016, describing a device for at-home or remote location testing using lightweight structures that could keep biological samples stable for months.

Although the technology is already being refined to detect other diseases, malaria was Badu-Tawiah's main concern - particularly as increasing uptake of the vaccine reduces natural immunity in the population, creating the need for widespread surveillance for potential infections in sub-Saharan Africa.

Since 2016, Badu-Tawiah's lab has created a 3D automation process to store antibodies and ions in the device and added a multipripated molecule to amplify the compound signal for detection by mass spectrometry, but the device manufacturing process is still manual. Paper sheets that make up the device's layers—coated with waxy sections that don't penetrate the blood—are individually printed and pressed together with double-sided tape. 25 devices fit on the 8×12 inch sheets.

Once applied, the blood is divided into four chambers - two as positive and negative controls - and induces chemical reactions as it passes through the layers. The chemists designed ionic probes to label antibodies that extract the antigen from the blood and place it permanently on the paper within about 10 minutes. After a buffer wash, the strips are peeled apart and analyzed in front of a handheld mass spectrometer.

"The spectrometer measures the mass of the compound of interest. The molecular weight tells us if we see a certain mass, that means the malaria antigen is in your blood. That's a yes. If it's not there, that's a no," Badu-Tawiah said.

Results are available in approximately 30 minutes, but used devices without refrigeration can also be stored indefinitely for later analysis. The high stability means that after the washing phase, the devices can be transferred in ordinary envelopes - a capability that connects people with asymptomatic infections in the most remote regions of Africa to resource-rich centers elsewhere in the world, without traditional cold chain restrictions.

Over five weeks in 2022 in Ghana, Badu-Tawiah tested the device's effectiveness in 266 asymptomatic volunteers and compared its results with three other most common testing methods for current malaria diagnostic use: microscopic examination of blood cells, commercially available rapid diagnostic tests and PCR (polymerase chain reaction).

A key factor in testing people without symptoms is that Badu-Tawiah found that the density of parasites in their blood is likely to be low when they are infected. This means that a highly sensitive test is required to detect their presence.

The comparison showed that microscopy, the gold standard in African hospitals, had the least accurate results, indicating only 24 positive cases, and rapid diagnostic tests identified 63 infections. PCR identified 142 positive cases and the paper-based devices identified 184 positives.

"Microscopy works well when the person is sick and in the hospital. Here we have been in communities where only 24 were shown positive with microscopy. This test tells us that the majority are negative. This is a big problem," Badu-Tawiah said. "Using a more complex method like PCR, almost 50% of people are sick, and yet microscopy can't tell us. And in people with very low parasite densities, rapid diagnostic tests fail miserably - they can only detect higher parasite densities."

Calculating the sensitivity of each method - the number of true positives divided by true positives plus false negatives - showed that the paper-based devices achieved a sensitivity of 96.5%, compared to 17% for microscopy and 43% for rapid diagnostic tests.

Forty-seven of 266 samples gave a false positive result - and all were confirmed negative by microscopy. PCR, considered the most accurate test, also diagnosed these people as negative.

Badu-Tawiah said the false positive results were caused by different viscosity of the blood samples, which led to redistribution of blood channels during the washing phase. The team modified the device to account for this possibility.

Badu-Tawiah has begun discussions with the government of Ghana about implementing a testing program.

"We told people this was possible in 2016 and we actually went into the field and tested it. It's very promising," he said. “Technology will go hand in hand with vaccination, and you need a sensitive tool to deliver.”

He is also working with Ohio State clinicians to adapt the devices to detect risks for colon cancer and acute pancreatitis.

“I have the hammer now and I could drive different nails,” he said. “We just need to change the antibody to make it applicable to other diseases.”

This work was supported by the National Institute of Allergy and Infectious Diseases. Co-authors include Ayesha Seth, Suji Lee, Girish Muralikrishnan, Edgar Garcia and James Odei from Ohio State and Abdul-Hakim Mutala and Kingsley Badu from the University of Kwame Nkrumah University and Technology in Ghana.

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