Covid-19 ‘breathalyser’ can detect infection in 5 minutes with PCR accuracy

They could be used to enable rapid screening of people attending large gatherings, such as conferences and weddings. Even those who are asymptomatic can still transmit Covid-19 to others, making it important to identify and isolate them until they are no longer contagious.

The “gold standard” for Covid-19 testing is a technique called reverse transcription-polymerase chain reaction, commonly known as PCR tests. But this technique is typically slow, requires an uncomfortable nasopharyngeal swab for sample collection, and must be performed in a lab.

The rapid antigen test is much quicker but has a higher rate of false negatives and positives. Scientists have also developed breathalyser-type tests for Covid-19, which rely on differences in concentrations of volatile organic compounds exhaled by those infected with the coronavirus, but most require bulky, nonportable instruments for analysis.

Now a team of researchers from Nanyang Technological University in Singapore have developed a “quick, convenient and accurate” breathalyser test that would be suitable for on-site screening of large numbers of people.

They designed a handheld breathalyser that contains a chip with three surface-enhanced Raman scattering (SERS) sensors attached to silver nanocubes.

When a person exhales into the device for 10 seconds, compounds in their breath chemically interact with the sensors. Then, the researchers load the breathalyser into a portable Raman spectrometer that characterises the bound compounds based on changes to the molecular vibrations of the SERS sensors.

The team found that Raman spectra from Covid-positive and -negative people were different in regions responsive to ketones, alcohols and aldehydes, which they used to develop a statistical model for Covid diagnosis.

They tested the breathalyser on 501 people in hospitals and airports in Singapore, who were shown by PCR to be negative (85.2 per cent), positive and symptomatic (8.6 per cent), or positive and asymptomatic (6.2 per cent) for the disease.

The method had a 3.8 per cent false-negative and 0.1 per cent false-positive rate, comparable to PCR tests, but it could be completed on-site in less than 5 minutes. The breathalyser could someday be a new tool to reduce the silent spread of Covid-19 in communities, the researchers said.