Sensor measures virus concentration in the air

Warmth increases reliability

However, it is of course central to this process that only those RNA strands are captured by the DNA receptor on the sensor that fit exactly. This is where a second effect comes into play: the plasmonic photothermal effect (PPT). If the same nanostructure on the sensor is excited with a laser of a certain wavelength, it produces heat.

And how does that help reliability? 

As already mentioned, the genome of the virus consists of only a single strand of RNA. If this strand finds its complementary counterpart, the two combine to form a double strand - a process called hybridization. The opposite - when a double strand splits into single strands - is called melting or denaturation. This happens at a certain temperature, the melting temperature. However, if the ambient temperature is much lower than the melting temperature, strands that are not 100% complementary to each other can also connect. This can lead to false test results. If the ambient temperature is only slightly lower than the melting temperature, only complementary strands can join. And this is precisely the result of the increased ambient temperature caused by the PPT effect.

To demonstrate how reliably the new sensor detects the current COVID-19 virus, the researchers tested it with a very closely related virus: SARS-CoV. This is the virus that triggered the SARS pandemic in 2003. The two viruses - SARS-CoV and SARS-CoV2 - differ only slightly in their RNA, so it is extremely difficult to make a clear distinction. But the experiment was successful: "Our tests showed that the sensor can clearly distinguish between the very similar RNA sequences of the two viruses," explains Jing Wang.

At the moment, the sensor is not yet ready to measure the corona virus concentration in the air at Zurich's main railway station, for example. A number of steps are still needed to do this - for example, a system that sucks in the air, concentrates the aerosols in it and isolates the RNA from the viruses. "This still needs development work," says Wang. But once the sensor has been completed, the principle could be applied to other viruses as well - and help ensure that future epidemics can be detected early and perhaps even stopped.

1. Sensor measures virus concentration in the air
2. Warmth increases reliability