A 3D microfluidic paper-based analytical device with smartphone-assisted colorimetric detection for iodine speciation in seaweed samples

The present work reports on the development of a 3D origami microfluidic paper-based analytical device (3D µPAD) for the determination of iodide and iodate in edible seaweeds by smartphone-based colorimetric detection. In addition, a methacrylate holder was designed and fabricated to enhance interlayer contact in 3D µPADs, obtaining excellent sensitivity and precision, also allowing real-time monitoring in a straightforward and expeditious way. The reported assay, based on the formation of a blue colored triiodide-starch complex at the detection areas of the 3D µPAD, represents an affordable, fast and greener alternative for the simultaneous determination of inorganic iodine species. Under optimal conditions, the proposed method showed limits of detection and quantification of 9.8 and 32.7 µM for I- and 0.6 and 1.8 µM for IO3-, respectively. The repeatability, expressed as relative standard deviation, was 1.7% and 3.3% for I- and IO3-, respectively. The proposed 3D µPAD was applied to the determination of iodine species in extracts of edible seaweeds and related food additives, showing satisfactory recoveries (90–109%).