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[Display omitted] • The accurate measurement of creatinine (Ctn) in human biofluid samples is a challenge. • A stable carboxyl (C=O, COOH) groups were introduced on the electrode surface during electrochemical activation. • ePAD* was applied for the selective non-enzymatic detection of Ctn. • ePAD* detects Ctn in blood serum and urine samples with high reliability. • ePAD* is economic and accurate compared to existing methods for Ctn detection. Selective detection of creatinine (Ctn) is crucial for the clinical diagnosis of early-stage kidney dysfunction. A non-enzymatic electrochemical method for a highly selective and sensitive detection of Ctn in blood serum and urine samples was developed using an electrochemically activated carbon-coated paper-based analytical device (ePAD*). During activation, the growth of stable carboxyl (C = O, COOH) groups on the edge planes of the carbon surface was observed. The prepared ePAD* was characterized using various microscopic, spectroscopic, and electrochemical techniques. The ePAD* was utilized as a medium exchanger, and the voltammetric response of Ctn detection in the linear concentration from 0.03 to 45 mM with a detection limit of 5.41 µM was achieved. In addition, the selective detection of Ctn in the presence of potential interferences (i.e., uric acid, ascorbic acid, ammonia, and urea) was examined. The examination revealed a remarkable selectivity toward Ctn detection. Real-time detection of Ctn in blood serum and urine samples was performed. The results were correlated with the classical Jaffé colorimetric method. Our ePAD* exhibited a better electrochemical response. Thus, it is a highly potential diagnostic method for further development as a rapid and precise detection platform for point-of-care (POC) devices for examining patients with kidney disease. [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]