Colorimetric sensor for determination of phosphate ions using anti-aggregation of 2-mercaptoethanesulfonate-modified silver nanoplates and europium ions

Abstract

A new, distinctive, and inexpensive colorimetric sensor for the detection of phosphate ions (Pi) performed on paper-based analytical devices (PADs) based on the anti-aggregation of 2-mercaptoethanesulfonate (MS)-modified silver nanoplates is proposed. An aggregation of MS-AgNPls due to the electrostatic interaction between the negatively charged sulfonate group on MS-AgNPls and europium ions (Eu3+) causes a color change. Conversely, the color of MS-AgNPls remains unchanged in the presence of premixed Eu3+ with Pi because of the higher binding affinity that Eu3+ has towards Pi, leaving the AgNPls dispersed. An apparent color change from brown to red with the increasing amount of Pi can be observed by the naked eye on PADs and can be used for quantification by the measurement of color intensity using ImageJ software and determined with the color comparator. The aggregation and anti-aggregation of MS-AgNPls were characterized by TEM, UV–vis spectroscopy, and FT-IR to confirm the mechanism. This method can detect Pi in the range of 1–30 mg L−1, with a detection limit of 0.33 mg L−1 (3SD/slope) and a limit of quantification equal to 1.01 mg L−1 (10SD/slope). The optimum parameters, including pH, MS and Eu3+ concentrations, reaction time, and interference effects, were studied. This method can be applied with the detection of Pi in real samples collected from soils, and the results agree with those of the standard method (UV–vis spectroscopy).