15-05-2020 | | By Liam Critchey
The world is currently experiencing one of the most significant cases of lockdown since the second world war and has had a profound medical, economic and social impact on the lives of people in all corners of the world. The current situation is one that is likely to proceed for a significant period. Still, a concerted effort is being made by governments, scientists and healthcare professionals to test people with symptoms, to confirm if they have the novel SARS-CoV-2 coronavirus, so that they can either self-isolate or seek appropriate medical treatment if needed.
However, one of the issues around the globe is a lack of testing in some areas, whereas the quality of testing in other areas is coming under fire for producing false results. There are already several tests on the market which are being sold and used by many companies. Still, ways of creating more effective tests to diagnose if people have or had the coronavirus are coming to the fore. These tests will hopefully help to alleviate any issues about the quality of tests on the market soon—this will be especially important in the coming months before (and if) researchers find a vaccine that can contain the spread of the virus.
Ever since the properties of graphene were exploited for electronic applications, sensors have been one of the frontrunning applications. As graphene typically produces a sensor that has a very high sensitivity, while being much smaller than many other types of sensor due to the inherent thinness of graphene. Sensors are one of the most widely exploited electronics areas for nanomaterials in general due to many of the same reasons. Still, graphene as a single material is very versatile when it comes to sensing and diagnostic applications. Even though graphene itself (unless used in a composite) is not typically biocompatible, this does not matter for tests that occur outside of the body.
This is why graphene has received interest during the COVID-19 outbreak for being used in sensors that can detect the SARS-CoV-2 viral strain—from both academia and industry. For example, when the coronavirus started to spread worldwide, several graphene manufacturing companies in Europe like Graphenea and Directa Plus offered free graphene samples to researchers so long as they were building diagnostic devices that could be used in the fight against the coronavirus. Moreover, some companies like Grolltex in the US are already adapting their existing graphene biosensors—which are used to detect flu strains and other viral strains—specifically for detecting COVID-19.
The initiative shown by the industry has also filtered into the academic world where researchers are managing to produce new diagnostic systems that are capable of detecting COVID-19, despite the challenges facing them at this moment in time. One of the most recent examples that has attracted much attention is a graphene field-effect transistor (FET) biosensor that can detect coronavirus at ultra-low concentrations of 1 femtogram/ml, i.e. one-thousandth of a picogram, which is ultra-sensitive.
The new graphene-based sensor is something that has come out of academia (by researchers in Korea). Still, because it shows much promise and is specifically designed to detect for the novel coronavirus strain that is causing the current crisis, it's attracted the interest of the National Graphene Institute (NGI) in Manchester, UK, to see if has commercial potential; and they have been looking to see if the graphene specialists at The University of Manchester can help to develop the technology for use in the real world.
The graphene sensor was created by placing a graphene sheet on a silicon-based surface so that that graphene could act as the active sensing material, and copper was then etched on to the surface to act as the gate, source and drain of the device. To be compatible with the SARS-CoV-2 strain of the virus, the surface of the graphene sheet was functionalised with SARS-CoV-2 spike antibodies. This functionalisation was achieved on the graphene sheet because the research used the chemical 1-pyrenebutyric acid N-hydroxysuccinimide ester, commonly known as PBASE, to act as an interfacial coupling medium. This meant that the protein spikes could be immobilised on the surface of the graphene sheet with relative ease.
The sensor works by the antibody spikes—which protrude off the surface—interacting with the antigen protein on the surface of the virus. One of the most critical aspects of the sensor, besides its extremely high sensitivity, is that, aside from being able to detect cultured SARS-CoV-2, it could sense if the virus was present in both clinical samples and the medium used in nasal swabs. This opens the potential for it to be used on the front line as it requires no sample preparation and could be used in line with many nasal swab tests, making it both a rapid and sensitive diagnostic platform. Moreover, it was found that the sensor could distinguish the SARS-CoV-2 viral strain from other similar viruses such as MERS-CoV.
While it is only at the academic level, it has come from a country, i.e. Korea, that is not under lockdown and still producing tests and research into such devices, so there is the potential to develop this further in the here and now. It's also attracted interest from a leading graphene institute (the NGI) for its potential. There's the chance this graphene biosensor could be one of the frontrunners being used on the frontline of all the COVID-19 tests in development.