Sweat urea bioassay based on degradation of Prussian Blue as the sensing architecture

Urea provides pathophysiological information on renal and hepatic disorders. Among the secretion pathways via several bio-fluids, sweat urea represent an important and non-invasive strategy to evaluate kidney and liver pathologies. In this work, a rapid and reliable colorimetric urea bioassay assisted by chemometrics design of experiments has been obtained. The sensing method is based on the hydrolysis of urea to ammonia catalyzed by urease. If urea is present in the sample, the enzymatic reaction leads to an alkaline environment that is capable to ruin the structure of Prussian Blue. For the first time Prussian Blue is adopted as a precision pH sensing element. Alkaline solution destroys the structure of Prussian Blue, leading to a dramatic colorimetric response from blue to colorless. Design of experiments has been adopted to optimize experimental setup by evaluating correlation among variables. The colorimetric method was shown to be able to detect urea down to 0.05 mM, with a linearity up to 2 mM and a relative standard deviation (RSD) lower than 10%. Sweat samples have been satisfactorily analyzed, and the high accuracy of the portable device has been demonstrated with liquid chromatography with tandem mass spectrometry analysis of the same sweat samples.