Rapid Direct Detection of SARS-CoV-2 Aerosols in Exhaled Breath at the Point of Care

Abstract

Airborne transmission via virus-laden aerosols is a dominant route for the transmission of respiratory diseases, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Direct, non-invasive screening of respiratory virus aerosols in patients has been a long-standing technical challenge. Here, we introduce a point-of-care testing platform that directly detects SARS-CoV-2 aerosols in as little as two exhaled breaths of patients and provides results in under 60 s. It integrates a hand-held breath aerosol collector and a llama-derived, SARS-CoV-2 spike-protein specific nanobody bound to an ultrasensitive micro-immunoelectrode biosensor, which detects the oxidation of tyrosine amino acids present in SARS-CoV-2 viral particles. Laboratory and clinical trial results were within 20% of those obtained using standard testing methods. Importantly, the electrochemical biosensor directly detects the virus itself, as opposed to a surrogate or signature of the virus, and is sensitive to as little as 10 viral particles in a sample. Our platform holds the potential to be adapted for multiplexed detection of different respiratory viruses. It provides a rapid and non-invasive alternative to conventional viral diagnostics.

Keywords: SARS-CoV-2; aerosol science; biosensors; electrochemistry; virology.

Figure 1

Illustration of SARS-CoV-2 detection using the Breath Aerosol Analyzer: (A) Sampling of the breath aerosols generated from the lower respiratory tract during normal breathing. (B) Schematic of the Breath Aerosol Analyzer system consisting of the aerosol collector, MIE biosensor, and a Potentiostat module. (C) Illustration of the mechanism of virus detection using the MIE biosensor. (D) Picture of the three-dimensional (3D)-printed breath aerosol collection box and the cap with an inlet straw.

Figure 2

MIE Biosensor characteristics and EBC performance for SARS-CoV-2 detection: (A) Specificity of the MIE biosensor tested with SARS-CoV-1 and SARS-CoV-2 spike protein. (B) Biosensor sensitivity (or LoD) was evaluated by serial dilution of different SARS-CoV-2 variants. (C) Normalized oxidation current (I_ox) measured by the MIE biosensor in laboratory experiments. The horizontal dashed line denotes the limit of detection (LoD) of the system. (D) Viral RNA copies/mL determined using RT-qPCR for different aerosolized SARS-CoV-2 variants. The differences between viral RNA copies obtained for the three SARS-CoV-2 variants were statistically insignificant (t-test, p = 0.17) indicating that the strain of viruses did not impact the virus collection efficiency of the breath aerosol collection device. (*Whiskers denote the range of data, and the box represents the inter-quartile range).

Figure 3

Estimating minimum number of exhaled breaths for detection by the MIE biosensor: (A) Number of exhaled breaths are predicted by evaluating the viral copies per breath for assumed range of viral load for COVID-19 patients. (B) Clinical study results demonstrate that SARS-CoV-2 viral particles are detected in as low as two exhaled breaths of patients.