A new device developed at Empa, ETH Zurich and Zurich University Hospital can detect Covid-19.
In future the device could be used to measure the concentration of the virus in the environment – for example in places where there are crowds or in hospital ventilation systems.
Before the COVID-19 outbreak, the team, headed by Jing Wang, was researching sensors that could detect bacteria and viruses in the air.
The sensor will not necessarily replace established laboratory tests, but could be used as an alternative method for clinical diagnosis and to measure virus concentration in the air in real time. For example, it could be used in places like train stations or hospitals.
Most laboratories use a molecular analysis called reverse transcription polymerase chain reaction (RT-PCR) to detect the virus. This can detect even tiny amount of viruses, but it is time consuming and prone to error.
The new device combines two different effects to detect the virus, an optical one and a thermal one.
The key part of the device consists of glass sensor containing tiny gold structures called nanoislands. These nanoislands have artificially produced DNA receptors that match specific RNA sequences of the SARS-CoV-2 virus grafted onto them.
The technology uses localized surface plasmon resonance (LSPR), an optical phenomenon that occurs in metallic nanostructures. When excited, the structures modulate the incident light in a specific wavelength range and create a plasmonic near-field around the nanostructure. When molecules bind to the surface, the local refractive index within the excited plasmonic near-field changes. An optical sensor located on the back of the sensor can be used to measure this change and determine whether the sample contains the RNA strands in question.
The genome of the virus consists of a single strand of RNA. If this strand finds its complementary counterpart in the sensor the two combine to form a double strand, a process called hybridization. This works best at a certain temperature. If the air temperature is too much lower than this specific temperature it can lead to false results, so the second test is to check that the temperature is right.
To test the reliability the new sensor, researchers tested it with SARS-CoV, the closely related virus that caused the SARS outbreak in 2003. “Tests showed that the sensor can clearly distinguish between the very similar RNA sequences of the two viruses,” said Wang.
However, the device is not yet ready for use. A number of developmental steps remain. A system that draws in air, concentrates the aerosols in it, and releases the RNA from the viruses is still required. However, once the sensor is ready, the principle could be applied to other viruses and help to detect and stop epidemics at an early stage.
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