For the price of a can of soda, you could be able to quickly and accurately determine whether or not you (or someone you love) has contracted the Zika virus, thanks to a new test developed by a team of chemists and engineers from the University of Pennsylvania.
The new test, which is described in the latest edition of the journal Analytical Chemistry, costs just $2 and does not require any electricity or special technical know-how to use, the Penn team explained in a statement. All it requires is a saliva sample, and when the presence of the virus is detected, color-changing dye turns blue to alert the individual being tested.
Created by Research Assistant Professor Changchun Liu, Professor Haim Bau of the Department of Mechanical Engineering and Applied Mechanics in Penn’s School of Engineering and Applied Science, and their colleagues, the diagnostic is designed to be used in the field to quickly tell if a person has contracted the virus, rather than forcing them to wait for laboratory tests.
“Our work represents a proof of concept at this stage,” Bau explained, noting that before it can be approved for use by patients, the researchers need to ensure that “our assay and system match the performance of the gold standard and operate reproducibly and reliably. We are fortunate to have dedicated colleagues in endemic regions ready to assist us in this task.”
So how exactly does this diagnostic device work?
Ideally, a diagnostic test detects genetic material from the Zika virus itself. Alternatively, a test can look for antibodies produced by the body in response to the virus, the researchers explained, but these can lead to false negatives from infected people who have yet to produce antibodies or false positives from those with antibodies due to a different but similar condition.
Those issues can be avoided by using tests that look for RNA sequences from the virus itself, a type of diagnostic known as reverse transcriptase polymerase chain reaction, or RT-PCR. While these tests are effective, they require the use of laboratories to amplify (repeatedly copy) specific gene sequences in a sample so that they can be detected, making them unfit for field use.
Given that the implication process is the key obstacle preventing portable genetic testing, Lin, Bau and their colleagues set out to study the effectiveness of an alternative technique known as reverse transcription loop-mediated isothermal amplification (RT-LAMP), which requires only that a sample be kept at a specific temperature, not be cycles through multiple precise changes in temperature, as it required in tests that use the RT-PCR technique.
While it uses a simplified amplification process, the authors note that RT-LAMP forces them to use a more specialized set of short gene sequences or “primers” which are designed to match the regions of the virus’ DNA targeted by the diagnostic. Using data mining methods, they identified specific regions of the Zika virus genome that are different than all other known pathogens, then came up with primers through which they would be able to identify this specific sequence.
Using a diagnostic cassette and a processor, the device “isolates, concentrates and purifies” the nucleic acids in saliva, Liu explained. It then “carries out enzymatic amplification” and provides test results by changing the color of a dye – a process which takes about 40 minutes in all. Their diagnostic costs only about $2 to make, and laboratory tests have proven that it is as sensitive as RT-PCR tests, the study authors noted in a statement.
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Image credit: University of Pennsylvania
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