A ratiometric fluorescence/colorimetric dual-response sensor based on fluorescent nanozymes and smartphone-assisted readout for the accurate determination of glyphosate residues

Abstract

In this study, a ratiometric fluorescence/colorimetric sensor using copper-based metal–organic framework nanozymes (Cu-BH) was developed for the detection of glyphosate (Gly). The sensor utilized the intrinsic fluorescence properties of the nanozymes in combination with the synergistic effect of o-phenylenediamine (OPD). Cu-BH catalyzed the conversion of OPD into a yellow fluorescent product (oxOPD) and exhibited ultraviolet absorption and fluorescence absorption peaks at 416 nm and 567 nm, respectively. Meanwhile, the oxOPD quenched the fluorescence of Cu-BH at 430 nm via the fluorescence internal filtering effect (IFE), thereby establishing colorimetric (A₄₁₆) and fluorescence (F₅₆₇/F₄₃₀) signals. When Gly is introduced into the system, it interacts with the copper ions of the Cu-BH nanozymes, diminishing the ability of Cu-BH to oxidize OPD, which progressively decreases the absorbance at 416 nm and diminishes the fluorescence intensity at 567 nm. The signal from the dual-mode sensor exhibited a linear relationship with the Gly concentration, and the LOD (3σ/K) for the ratiometric fluorescence and colorimetric modes were 0.103 ng mL⁻¹ and 0.118 ng mL⁻¹, respectively. Moreover, the smartphone-based RGB color digitization provided a quantifiable B/R value with a favorable linear response (1 × 10⁻³ to 1 × 10² µg mL⁻¹). This work not only proposes a straightforward and low-cost approach to pesticide sensing but also contributes to the establishment of food safety pre-warning systems.