Portable quantitative detection of Fe3+ by integrating a smartphone with colorimetric responses of a rhodamine-functionalized polyacrylamide hydrogel chemosensor

[Display omitted] •A rhodamine-functionalized polyacrylamide hydrogel was synthesized.•The reusable hydrogel displayed good selectivity and sensitivity for Fe3+ sensing.•The hydrogel served as a colorimetric quantitative sensor for Fe3+ by RGB analysis. Recently, the colorimetric quantitative method based on a smartphone and red–green–blue (RGB) analysis is applied to provide rapid on-site monitoring of metal ions. To develop such a fluorescent and colorimetric chemosensor for Fe3+, the functionalized polyacrylamide hydrogel P(AM-co-MBA-co-RhBUEA) was synthesized by free radical polymerization on the basis of a rhodamine-based probe RhBUEA. The physicochemical properties and sensing behavior of the functionalized hydrogel were investigated by FTIR, SEM and fluorescence spectral analysis. And the effects of MBA and RhBUEA amount on gel content and swelling properties were explored. According to the recipe of 1.0 wt.% MBA, 2.0 wt.% RhBUEA to the total monomers, the fabricated hydrogel displayed excellent selectivity, sensitivity and reversibility for Fe3+ sensing in the pH range of 4.95–8.02, with the detection limit of 0.088 μM for the fluorescent quantitative method and the response time less than 20 min, accompanied with a distinct color change. Owing to the integration of RGB analysis with colorimetric responses, the functionalized hydrogel permitted the convenient, simplified and rapid colorimetric quantitative detection of Fe3+ with the detection limit of 1.1 μM, which avoids the need of sophisticated instruments and trained operators.