Calibrant-loaded paper-based analytical devices for standard addition quantitative assays

Abstract

This article describes a new approach for performing analytical assays on paper-based analytical devices that relies on the principles of multiple standard additions calibration, and uses calibrant-loaded paper devices. Calibrant-loaded devices have multiple sensing areas pre-loaded with an excess amount of the necessary colorimetric reagents and known amounts (standard solutions) of the tested analyte; thus, a colored product is developed before analysis in each sensing area. After sample addition, the analytical signal from each sensing area corresponds to the total concentration of the analyte, which is the sum of the concentration of the analyte in the tested sample plus the known amount of the analyte pre-stored in the device. The combined signal retrieved from each sensing zone is plotted to form a standard addition calibration curve that is used to calculate the concentration of the analyte in the sample using linear or non-linear models (i.e., first or higher order polynomials). This new approach could reduce the influence of matrix effects, paper inhomogeneity and environmental conditions on the results, and it could simplify the analysis as it may eliminate the steps associated with on-spot calibration that should ideally be performed using standard solutions that are prepared or transported in-situ. The utility and applicability of this approach is demonstrated as proof-of-concept on five assays (i.e., for the determination of iron, protein, hydrogen peroxide, acetic acid and carbonate ions) that use different reactions (i.e. complexation, oxidation and neutralization). This work provides a demonstration of a multiple standard addition methodology applied on calibrant-loaded paper-based analytical devices and illustrate its use as a sample-in result-out tool for point-of-use applications.