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[Display omitted] • A smartphone/PAD system was developed for iodate measurement in table salt. • The developed method performed comparably with commercial test kits. • The results of the present method agree well with the reference method. • The proposed method supports the green analytical technique. A digital colorimetric sensor was developed for the on-site measurement of iodate in food-grade salt. It involved a paper-based analytical device (PAD) containing an immobilized iodide/starch reagent and a smartphone as the detection system. Iodate ions produce a blue-black coloration on the PAD, the smartphone captures a digital image of the PAD, and an installed mobile app performs an analysis to generate color values related to the intensity of the color in the PAD. Parameters in the image acquisition and PAD preparation were optimized, and a matrix-matched calibration plot was employed for quantification. The plot exhibited a linear response in the concentration range of 10 to 100 mg iodate kg−1 of salt, and a detection limit of 2.20 mg kg−1 was determined. The present method was applied to analyze real samples, and the results agreed well with those obtained using the reference method at the 95% confidence level. [ABSTRACT FROM AUTHOR]

[Display omitted] • Products of urease catalyzes urea induce color change of Prussian blue nanoparticles. • A paper-based sensor depending on the Prussian blue pH sensitivity is developed. • Smartphone captures color signals of the sensor to achieve rapid detection of urea. Depending on the pH sensitivity of Prussian blue nanoparticles (PB NPs) and the specificity of urease-catalyzed urea, a paper-based colorimetric sensor was developed using urease, PB NPs, and cellulose filter paper. With the assistance of a smartphone, the rapid detection of urea can be realized. Under the optimal conditions, the linear range of the paper-based sensor for detection of urea is 0.5–5.0 mM, and the limit of detection is 0.27 mM. The RSD values of within-batch and between-batch repeatability are 2.5 % and 0.9 %, respectively. The method was successfully applied to the detection of urea in spiked milk samples and artificial urine sample, and the recoveries are in the range of 91.8–107.9%. The developed paper-based colorimetric sensor is a simple, economic, and rapid method that can be used for the determination of urea in real samples, particularly in resource-poor regions. [ABSTRACT FROM AUTHOR]