The unprecedented global spread of COVID-19 and its symptomatic heterogeneity have underscored the need for developing accurate yet inexpensive diagnostic and monitoring tools for infectious diseases. Enzyme-Linked Immunosorbent Assays (ELISA), widely used for sensitive measurement of various biomarkers, are currently limited to complex, expensive, and bulky lab-based instruments. We report an inexpensive electronic ELISA (E2LISA) which enables direct electrical detection of molecular biomarkers from a single drop of sample via probe-directed, enzymatically amplified metal nanoparticle deposition on microelectrodes. Capture agents, such as antigens, are coated on interdigitated gold microelectrodes on a glass microchip, and then exposed to sample to selectively bind the analyte to which a horseradish peroxidase (HRP) enzyme-labeled probe solution is then applied. Addition of a substrate results in deposition of silver nanoparticles (Fig. 1A). The conductive layer bridging the electrode gap enables the passage of current upon application of a voltage providing a direct electronic readout. Here we first used a model binding reaction of biotin-labeled bovine serum albumin and streptavidin-HRP to optimize E2LISA performance across various chip design and experimental parameters such as the electrode gap, substrate concentration, reaction time, and impedance measurement frequency. Additionally, we observed that a more uniform metal layer and thus a more robust and repeatable electronic signal could be generated by the addition of probe-labeled gold nanoparticles to the immunoassay. Detection of SARS-CoV-2 spike protein-specific IgG antibodies, which are a biomarker of current or prior infection with the virus, was demonstrated from convalescent COVID19 patient serum (Fig. 1B). All patient samples showed high silver deposition and low measured microelectrode impedance (Fig. 1C). Healthy human serum showed little or no silver deposition and hence a high measured electrode impedance. Further development will include the detection of viral antigens and nucleic acids, which are an early biomarker of infection, using appropriate capture agents and probes.

Electronic enzyme linked immunosorbent assay for detection of COVID19 biomarkers

ACS Fall 2021

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