Anti-SARS-CoV-2 IgG ELISA: Replacing the Absorbance Plate Reader by a Regular Scanner with Open-Source Software

Abstract

The COVID-19 global pandemic is still affecting the world, even considering vaccine applications in most countries, especially due to new variant outbreaks and the possibility that they may present immunological escape. Therefore, mass testing is relevant in infection monitoring and restriction policy evaluations, making low-cost and easy-to-use tests essential. Serological tests might also be useful in monitoring immune response after vaccination. The present work proposes a less-expensive ELISA test route, using a scanner instead of a spectrophotometer and using the saturation of the image as a surrogate for the absorbance of each sample. Images from multiple experiments were selected and correlated with their spectrophotometric absorbance. ELISA plate images were digitized by a simple table scanner and, then, preprocessed using Hue, Saturation, Value (HSV) transformation, aiming to determine which correlates best with the obtained absorbance. Saturation correlated better with absorbance, and the experiments presented R2 consistently above 90% between absorbance and the square of saturation. The new methodology showed similar accuracy, sensitivity, and specificity to the original method, all metrics ranging between 90% and 100% in most cases. An open-source software was also designed to analyze the images, perform the diagnosis, and generate reports.