Paper-based sensor depending on the Prussian blue pH sensitivity: Smartphone-assisted 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.