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Toxic nitrogen, which is formed as a result of the breakdown of proteins, is converted into nontoxic urea by the enzymes in the "urea cycle". While a small part of the produced urea is eliminated with sweat, a large part is removed from the body by the kidneys with urine. Therefore, urea determination in blood and urine provides important information about kidney functions. In this study, a colorimetric paperbased sensor was developed and characterized for use in urea detection. Basically, urea measurement was carried out by immobilization of urease enzyme on pH sensitive papers. The determination of urea was made by observing the changes in pH caused by ammonia with basic properties, which is formed as a result of the destruction of urea by urease. In the presence of different concentrations of urea, the colorimetric changes on the sensor were visualized with a camera and analyzed with the ImageJ program in the computer environment. In the first stage, a calibration curve showing the relationship between urea concentration and color intensity was obtained, and then the detection limit and sensitivity of the system were determined from this curve. Finally, the selectivity of the sensor was demonstrated by testing the different molecules involved.
Şen et al. (Mon,) studied this question.