Smartphone-based visual quantitation of glyphosate in liquid media using effervescent colorimetric tablets...

Although glyphosate is widely applied as a non-selective herbicide in agricultural production, its rapid and on-site monitoring remains challenging. Building upon magnetic effervescent tablets (METs) previously developed by our group, we designed novel METs-based colorimetric tablets (MCTs) using Ru-doped Fe-MOF (Ru₄₀/Fe-MOF) with significantly enhanced peroxidase-mimetic activity. MCTs were integrated with smartphone-based digital-image chromogenesis (SDC) for visual quantitation of glyhosate in surface waters and liquid drinks. Ru-doping not only increased the specific surface area and regulated MOFs' morphology, but also prominently improved the underlying catalytic activity. Upon the addition of H₂O₂, Ru₄₀/Fe-MOF catalyzed the chromogenic substrate ABTS to form a green oxidized product oxABTS, yielding a bright green solution. However, glyphosate could inhibit the aforementioned catalytic activity through coordination and/or H-bonding interactions with the surface groups of Ru₄₀/Fe-MOF (-COOH, -NH₂, Fe-OH, and Ru sites). MCTs enabled rapid auto-dispersion and chromogenic development upon contact with water, thereby eliminating the need for external stirring, shaking or heating. Under optimized conditions, the MCTs-SDC platform exhibited an excellent linearity for glyphosate with a detection limit of 0.006 µg/mL by UV-vis measurement and 0.03 µg/mL by grayscale analysis via a self-developed "Thing Identify" APP. In the lake water and liquid drink samples, the fortified recoveries (94.5-112.2%) by the MCTs-SDC were comparable to those by conventional water-bath-assisted colorimetry and HPLC-DAD analysis. Overall, this work provides a user-friendly, rapid, and on-site smartphone-based visual quantitation scheme for glyphosate in complex liquid media.