7.

Application of VF-μPADs for environmental monitoring and agriculture. (A) VF-μPAD design with a functional waste reservoir layer, enabling increased sample volume capacity for colorimetric assay of heavy metal ions. Reproduced with permission from ref (). Copyright 2020 Elsevier B.V. (B) Enclosed VF-μPADs for the simultaneous detection of heavy metal ions and a radioactive isotope in water environment. (i) Schematic illustration of enclosed VF-μPADs with four channels for multiplex detection. (ii) (a, b) Multiplex colorimetric response for detection of water samples contaminated with nickel (Ni²⁺), copper (Cu²⁺), mercury (Hg²⁺), and cesium (Cs⁺) ions. Reproduced with permission from ref (). Available under a CC-BY license. Copyright 2023 MDPI. (C) Sensor integrated VF-μPADs for on-site and prompt evaluation of chloride contamination in concrete structures. (i) Design of the vertical flow paper-based sensor. The device is loaded with a few microliters of two solutions having different concentrations of chlorides, drop-cast on the top layer and on the bottom layer. (ii) Photos of the experimental setup applied to concrete. (iii) Chloride evaluation: a portion of the building fundament, a wall from the basement, and the monumental stairs. Reproduced with permission from ref (). Copyright 2021 American Chemical Society. (D) VF-μPADs combined with metal–organic frameworks in a single device for phenolic content assessment in fruits. Reproduced with permission from ref (). Available under a CC-BY license. Copyright 2023 Springer Nature. (E) VF-μPADs for the visual determination of alcohol content in whiskey samples. (i) Layout of the foldable VF-μPADs and the test spots for before and end point of detection (ii) Calibration curve for ethanol and alcoholic content determined for seized samples using a foldable VF-μPADs. Reproduced with permission from ref (). Copyright 2018 Elsevier B.V.