The LFTs are fast, cheap and easy to use, making them ideal for community and home testing. But they are nowhere near as sensitive as the PCR tests – they will only identify people with high viral loads. This means many people who are infected will get a false negative result from such tests.
Ideally, we need a home test that’s as easy to use as the LFTs but as sensitive as the PCR test. An excellent candidate is a method called loop-mediated isothermal amplification (Lamp). This works along very similar principles to PCR, producing multiple copies of the starting genetic material – which you can get from a swab – but has some key advantages.
For example, it can be combined with a handy “colour readout”. When the Lamp reaction occurs, it causes an increase in the acidity of the sample. That means you can add a substance that changes colour according to pH value in the reaction mix, providing a visual indication of a positive or negative result. Another advantage is that Lamp reactions are carried out at a fixed temperature (about 65°C) instead of needing constant cycling through a range of temperatures.
Nevertheless, Lamp still needs fine temperature control. Temperature control systems – be they in a PCR machine, a Lamp instrument or household oven – are usually achieved with electronic thermostats. However, making and shipping new electronic devices specifically designed for home Lamp tests is impractical (especially in the middle of a pandemic). So Saggiomo tried to find a way around this. He hit upon substances called phase change materials that absorb energy (heat) as they melt and so maintain a constant temperature.
After finding a wax made of such a material that melted at exactly the required temperature, Saggiomo set about constructing a device to house the Lamp reaction tubes and chunks of wax. This then needed to be inserted into some other material that could be heated. The perfect housing turned out to be staring him in the face while making his morning coffee: Nespresso coffee machine capsules.
The final step was just finding the right way to heat the capsules. After trying the dishwasher (it worked but samples kept getting lost), the microwave oven (failed, because the tubes overheated and lids popped off) and cups full of hot water (not enough control on the temperature), Saggiomo settled on a simple pan of simmering water on a stovetop. The resulting “CoroNaspresso” device, when tested by other members of the team, with swabs from six people, correctly identified three cases of COVID-19 (these had a different colour to the negative tests).
The test, including the capsules, phase changing wax and vials in which to insert genetic material, would be easy to produce in millions. People could then swab for genetic material at home and heat the capsules to get their results. These devices are also cheap (about €0.20), easy to make, easy to use and largely recyclable. Maybe we’ll see the CoroNespresso tests in our homes soon, just don’t get them confused with your regular coffee pods
This article co-authored by Professor Mark Lorch is republished from The Conversation under a Creative Commons license. Read the original article here. The views or opinions expressed by individuals do not necessarily reflect those of the University.