Integrated cloverleaf-like paper-based analytical device for quantitative colorimetric sensing of maleic hydrazide

Paper-based analytical devices (PADs) are becoming pivotal tools in the sensing field; however, the integration of molecularly imprinted polymers (MIPs) on them deserves further exploration to obtain all-in-one selective devices. Herein, a cloverleaf-like PAD integrating a MIP for the smartphone-based selective colorimetric determination of maleic hydrazide (MH), a widely used plant growth regulator, is proposed. The device encompasses the complete MH analysis in a 4-leaved format (4L-μMIP/PAD), where the μMIP is housed at the center and each leaf encloses an analytical step (i.e., sample excess removal, washing, analyte elution, and MH colorimetric detection). The μMIP was synthesized with a UV lamp on fiberglass, while the entire paper device was manufactured via laser plotter and wax printer. The μMIP displays an imprinting factor of 17 and was characterized via FTIR, SEM, and elemental mapping, resulting selective toward MH. The colorimetric sensing, integrated on the sensing leaf, was attempted on 13 different paper types. The final 4L-μMIP/PAD allows the selective MH determination in the range 5–60 mg kg−1 (R2 = 0.995; RSD ≤ 11 %, n = 3) with a LOD of 0.7 mg kg−1, meeting the requirements for MH analysis in samples at Maximal Residual Levels admitted by the law. The device ensures the complete MH analysis in 50 min, with 40 µL of sample, resulting stable and ready-for-use, for 1 month (RSD = 9 %). Eventually, the 4L-μMIP/PAD was successfully tested for MH analysis in garlic, onions, and carrots, obtaining recoveries between 89 % and 110 % and reproducible data (RSD ≤ 15 %, n = 3).