[Image above] A public health officer assesses a sick traveler who had just arrived at the Los Angeles International Airport from another country. Credit: CDC, Unsplash
If we’ve learned one thing in the fight against COVID-19, it’s that frequent testing is crucial to early detection and containment of the disease.
Testing is much more accessible now than it was at the start of the pandemic, especially in many European countries. For people in the United States, however, rapid tests can still be challenging to secure, in part due to regulations that make bringing new tests to market difficult.
Fortunately, barriers to commercialization are not stopping scientists from continuing to develop new and improved methods for rapid testing. In today’s CTT, we look at three recent studies furthering research in this area.
Breathing life into a novel COVID-19 detector
Last June, we published a CTT on the work being done by Pelagia-Irene (Perena) Gouma, Edward Orton, Jr., Chair in Ceramic Engineering and director of the Advanced Ceramics Research Laboratory at the Ohio State University, to develop a breathalyzer capable of detecting COVID-19.
Breathalyzers are devices that can measure various chemical compounds in a person’s breath. Estimating someone’s blood alcohol level is a common application of breathalyzers, but breathalyzers can also be used to detect different diseases.
Gouma, who is an ACerS Fellow, began exploring use of breathalyzers for medical diagnostics in 2003. Her recent work on the COVID-19 breathalyzer is based on research for a breathalyzer that detects the flu virus.
Since the CTT post last year, which saw Gouma’s team just starting human and animal testing, the researchers have now published an open-access paper in PLOS One detailing the results of tests conducted in the Ohio State University hospital system. They compared the breath profiles of patients with and without active COVID-19 respiratory infection, and the breathalyzer detected high exhaled nitric oxide concentration with a distinctive pattern for patients with active COVID-19.
“This is the first work to our knowledge to demonstrate use of a nanosensor breathalyzer system to detect a viral infection from exhaled ‘breathe prints,’” they conclude.
In August, Gouma gave a TEDx Talk on the research, which you can watch below.
Two carbon allotropes lead to sensors that detect SARS-CoV-2 and its proteins
While the breathalyzer described above determines COVID-19 diagnosis based on changes to the chemical makeup of a person’s breath caused by the disease, the other two recently developed sensors instead base diagnosis on direct detection of SARS-CoV-2, the coronavirus that causes COVID-19, and its proteins.
The first study, published in early October, is by researchers at Fudan University in China. They used graphene to develop a field-effect transistor that detects SARS-CoV-2 RNA.
SARS-CoV-2 is an RNA virus, meaning that its genetic material is encoded in ribonucleic acid (RNA). This approach to genetic coding contrasts with humans and other mammals, which rely on deoxyribonucleic acid (DNA) for carrying genetic information.
Among COVID-19 diagnostic methods, reverse transcription polymerase chain reaction (RT-PCR) tests are considered a gold standard. These tests detect the RNA of SARS-CoV-2, even if the virus is present in extremely small amounts. However, these tests normally require extraction and amplification procedures to reach a final diagnosis, which need skilled operators, specialized facilities, dedicated laboratories, and a long reaction time, up to 2–4 hours.
The new transistor developed by the Fudan University researchers detects SARS-CoV-2 RNA as well, through Y-shaped fragments of DNA located on the transistor that target two genes encoded in the RNA genome of SARS-CoV-2. Unlike the RT-PCR tests, however, the transistor does not require extraction or amplification procedures, thus streamlining the diagnosis process.
In a C&EN article, graduate student and first author Derong Kong says, “The detection limit of our method is also very low, detecting about three molecules of SARS-CoV-2 RNA in 100 µL of solution.” That limit of detection makes the test 20 times as sensitive as the standard for quantitative RT-PCR assays set by the U.S. Centers for Disease Control and Prevention, according to the article.
The transistor is not yet optimized for mass production or clinical use, but the researchers are working to improve the device so it can be cleaned and reused without losing sensitivity.
The paper, published in Journal of the American Chemical Society, is “Direct SARS-CoV-2 nucleic acid detection by Y-shaped DNA dual-probe transistor assay” (DOI: 10.1021/jacs.1c06325).
The second study, published in late October, is by researchers at the Massachusetts Institute of Technology. They used carbon nanotubes to develop a sensor that selectively detects certain viral proteins of SARS-CoV-2.
As mentioned above, SARS-CoV-2 encodes its genetic material in RNA. When the virus infects a host cell, it deploys a “translation-ready” RNA molecule that harnesses protein synthesis machinery of the host to express a set of viral proteins crucial for replication.
The MIT researchers chose to use an approach called corona phase molecular recognition (CoPhMoRe) to detect these viral proteins. As explained in the press release, CoPhMoRe takes advantage of a phenomenon that occurs when certain types of polymers bind to a nanoparticle.
“Known as amphiphilic polymers, these molecules have hydrophobic regions that latch onto the tubes like anchors and hydrophilic regions that form a series of loops extending away from the tubes. Those loops form a layer called a corona surrounding the nanotube. Depending on the arrangement of the loops, different types of target molecules can wedge into the spaces between the loops, and this binding of the target alters the intensity or peak wavelength of fluorescence produced by the carbon nanotube,” the press release explains.
The researchers wrapped carbon nanotubes in different polymers that were chosen based on their response to the nucleocapsid and spike proteins of SARS-CoV-2. They then incorporated these sensors into a prototype device with a fiber optic tip that can detect fluorescence changes in the sample in real time, thus eliminating the need to send the sample to a lab.
The sensor produced a result within about 5 minutes and detected concentrations as low as 2.4 picograms of viral protein per milliliter of sample. In addition, the sensor detected the SARS-CoV-2 nucleocapsid protein (but not the spike protein) when it was dissolved in saliva, which is difficult to do because “saliva contains sticky carbohydrate and digestive enzyme molecules that interfere with protein detection,” the press release explains.
The researchers have filed for a patent on the technology.
The paper, published in Analytical Chemistry, is “Antibody-free rapid detection of SARS-CoV-2 proteins using corona phase molecular recognition to accelerate development time” (DOI: 10.1021/acs.analchem.1c02889).