Rapid Diagnostic Sensor Detects COVID-19 Directly from Swab Extracts

A team of South Korean researchers has developed a diagnostic tool for the rapid detection of coronavirus from swab samples with no preparation steps.

A novel coronavirus of zoonotic origin, SARS-CoV-2 (2019-nCoV) was first identified in patients with acute respiratory disease (COVID-19). This virus is genetically similar to SARS coronavirus and bat SARS-like coronaviruses. The outbreak was initially detected in Wuhan, a major city of China, but has subsequently exploded into a pandemic, which is raging in most of the countries of the world. At this time more than 2,500,000 cases of the disease have been confirmed worldwide with hundreds of thousands of fatalities. Signs of infection are highly non-specific and these include respiratory symptoms, fever, cough, dyspnea, and viral pneumonia. The elderly and those with chronic diseases seem to suffer a more severe disease than does the younger, healthier population.

One of the characteristics of COVID-19 is that the virus can be spread by individuals who are not symptomatic, having neither fever nor signs of infection. Lacking the ability to screen these asymptomatic patients quickly and effectively, health authorities have no way of predicting the optimum time to reduce the risk of disease transmission by implementing effective quarantine measures or when to ease quarantine restrictions. Thus, tracing unknown COVID-19 sources, fast and accurate screening of potential virus carriers, and diagnosis of asymptomatic patients are crucial steps for intervention and prevention at an early stage.

To meet this challenge, investigators at the Research Center for Bioconvergence Analysis at the Korea Basic Science Institute (Cheongju, Republic of Korea) developed a rapid diagnostic sensor that detects the virus directly in a tube of buffer containing the swab samples, without any preparation steps.

The field-effect transistor (FET)-based biosensing device was produced by coating graphene sheets with a specific antibody against SARS-CoV-2 spike protein. SARS-CoV-2 spike antibody was immobilized onto the fabricated device through 1-pyrenebutyric acid N-hydroxysuccinimide ester (PBASE), an efficient interface coupling agent used as a probe linker.

The performance of the sensor was determined using purified antigen protein, cultured virus particles, and nasopharyngeal swab specimens from COVID-19 patients. Results showed that the FET device could detect the SARS-CoV-2 spike protein at concentrations of one femtogram/millilter in phosphate-buffered saline and 100 femtogram/millilter in clinical transport medium. In addition, the FET sensor successfully detected intact SARS-CoV-2 virus in culture medium and clinical samples.

The clinical potential of the FET device was demonstrated by detecting SARS-CoV-2 antigen protein in transport medium used for nasopharyngeal swabs and cultured SARS-CoV-2 virus, as well as SARS-CoV-2 virus from clinical samples. Furthermore, the sensor could distinguish the SARS-CoV-2 antigen protein from those of the closely related virus MERS-CoV.

The FET device was described in the April 15, 2020, online edition of the journal ACS Nano.

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