Cheap 5-Minute COVID-19 Test Accurately Detects SARS-CoV-2 Antibody in Blood or Saliva

The device developed by researchers at The Hong Kong Polytechnic University (Hong Kong) can detect SARS-CoV-2 IgG with an ultralow detection limit of 1 fM in aqueous solutions and 10 fM in serum and saliva within five minutes.

Currently, COVID-19 antibodies are detected mainly by enzyme-linked immunosorbent assay (ELISA) and colloidal gold lateral flow immunoassays (LFIAs). ELISA is highly accurate, but the technical procedure is complicated, making it difficult to achieve both portable and high-throughput detection. LFIA is easy to operate and portable, but with relatively low sensitivity and prone to misdiagnosis. Therefore, for the detection of COVID-19 antibody, there is a need to develop a highly sensitive and rapid detection method that can be easily operated for point-of-care testing and screening of large populations. In addition to serum-based assays, SARS-CoV-2 IgG can be detected in saliva, with the advantages of a noninvasive process and the possibility of self-collection of samples. Because antibody concentration in human saliva is several orders of magnitude lower than in serum, high analytical sensitivity is needed

Organic electrochemical transistors (OECTs) have been recognized as high-performance transducers and amplifiers that can convert biological signals into electrical signals. OECT-based biosensors have the advantages of high sensitivity, low cost, easy fabrication, and mechanical flexibility and are suitable for high-throughput and multiplexing detections of biomarkers. In recent years, OECTs have been successfully used in the detection of various biomolecules, including nucleic acids, proteins, and metabolite.

In the latest study, the researchers used OECT-based biosensors for the detection of SARS-CoV-2 IgG that is controlled by a portable meter and a mobile phone through Bluetooth. The team developed portable, label-free, and low-cost biosensors based on OECTs for rapid and highly sensitive detections of SARS-CoV-2 IgG. The gate electrodes of the OECTs were modified with SARS-CoV-2 spike proteins that can selectively capture the IgG through the specific antibody-antigen reaction. The positively charged IgG molecules in aqueous solutions form electrical dipoles on gate surfaces and modulate the channel currents of the OECTs. By optimizing the measurement conditions, including electrolyte ion concentration and pH value, high device sensitivity was achieved. The detection limits of the devices can reach 1 fM in aqueous solutions and 10 fM in saliva and serum samples, which are much better than many existing electrochemical methods. Notably, the detectable region can cover the concentrations of the specific antibody in the serum and saliva of patients with COVID-19, promising a high potential for practical applications. Faster detection of IgG has been realized by applying voltage pulses on the gates of OECTs during incubation, and stable signal can be obtained within five minutes. The testing process can be remotely operated with a mobile phone by controlling a portable meter via Bluetooth, which can meet the requirement of fast and point-of-care detections of COVID-19 antibody. In addition to COVID-19 antibody, the biosensor can also be used in the fast detections of many other diseases that may generate antibodies.

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The Hong Kong Polytechnic University