Utilizing COVID-19 as a Model for Diagnostics Using an Electrochemical Sensor

Abstract

This paper reports a rapid and sensitive sensor for the detection and quantification of the COVID-19 N-protein (N-PROT) via an electrochemical mechanism. Single-frequency electrochemical impedance spectroscopy was used as a transduction method for real-time measurement of the N-PROT in an immunosensor system based on gold-conjugate-modified carbon screen-printed electrodes (Cov-Ag-SPE). The system presents high selectivity attained through an optimal stimulation signal composed of a 0.0 V DC potential and 10 mV RMS^-1 AC signal at 100 Hz over 300 s. The Cov-Ag-SPE showed a log response toward N-PROT detection at concentrations from 1.0 ng mL^-1 to 10.0 μg mL^-1, with a 0.977 correlation coefficient for the phase (θ) variation. An ML-based approach could be created using some aspects observed from the positive and negative samples; hence, it was possible to classify 252 samples, reaching 83.0, 96.2 and 91.3% sensitivity, specificity, and accuracy, respectively, with confidence intervals (CI) ranging from 73.0 to 100.0%. Because impedance spectroscopy measurements can be performed with low-cost portable instruments, the immunosensor proposed here can be applied in point-of-care diagnostics for mass testing, even in places with limited resources, as an alternative to the common diagnostics methods.

Keywords: SARS-CoV-2; electrochemical sensor; nucleocapsid protein; point-of-care test; screen-printed electrodes.

Figure 1

(A) Hilab Volt. (B) COVID-19 sample collection and analysis procedure.

Figure 2

Proposed COVID-19 diagnostics principle for the CovAg-SPE sensor analyzing negative and positive nasopharyngeal swab samples, and the parameters influencing the input and output signals.

Figure 3

(A) Electrochemical calibration curve for N−protein detection in spiked negative nasopharyngeal swab samples (n = 3). (B) Schematic representation of the superficial interactions and capacitors formed by the recognized layer and the analyte layer. t = 300 s; f = 100 Hz; EAC = 0.01 V; EDC = 0 V; electrolyte: 0.01 M 7.4−PB.

Figure 4

Positive and negative sample behavior as a time function for (A) imaginary impedance, and (B) phase. (C) Characteristic behavior used for classification of real samples in validation. (D) Bar graph constructed from the concomitant species study. t = 300 s; f = 100 Hz; EAC = 0.01 V; EDC = 0 V; electrolyte: 0.01M 7.4-PB.