Oxidized TMB mediated dual-optical sensing-based paper analytical device for high-throughput visual monitoring of 2,4-dichlorophenoxyacetic acid

High-throughput and accurate monitoring of pesticide residues is extremely crucial, but remains challenging. Herein, oxidized 3,3′,5,5′-tetramethylbenzidine (oxTMB) mediated dual-optical sensing-based paper analytical device (PAD) was unveiled for on-site visual detection of 2,4-dichlorophenoxyacetic acid (2,4-D) in real samples. Colorimetric blue oxTMB (652 nm) can be reduced to colorless TMB by ascorbic acid (AA). Meanwhile, oxTMB was demonstrated for the first time to switch oxidation and condensation reactions between o-phenylenediamine and AA to produce yellow-emission (564 nm) and blue-emission (429 nm) probes. Thus, colorimetric and ratiometric fluorescent dual-mode detection system was developed for 2,4-D detection by combining with alkaline phosphatase (ALP) initiating AA generation (ascorbic acid-2-phosphate as the substrate). Notably, the developed method can correct itself to improve the accuracy due to the dual-response signals. Using the principle, ALP-loaded PAD (array 3 × 10) was designed for efficient and high-performance detection of 2,4-D in turnip and cauliflower with good sensitivity (0.09 μg/mL for colorimetry, 0.06 μg/mL for fluorometry), satisfactory recovery (98.0 %–107.2 %), and high consistency (relative error ≤ 3.1 %). This work demonstrated a promising strategy for high-throughput visual detection of 2,4-D, which may provide a new pathway for the further development of dual-mode sensing platforms to efficiently detect other targets for food safety.