Electrochemical detection of uric acid in undiluted human saliva using uricase paper integrated electrodes.

In this study, we introduce a uricase-immobilized paper (UOx--paper) integrated electrochemical sensor for detection of uric acid (UA) in saliva. The UOx was immobilized on the detection zone in the wax-patterned paper substrate. This UOx-paper was integrated with a Prussian blue--modified, screen-printed carbon electrode after electropolymerization of o-phenylenediamine to construct an electrochemical cell for small-volume (20 µL) of samples. First, we optimized the fabrication conditions of UOx-paper. Next, the amperometric response of the UOx-paper-based electrochemical UA sensor was analyzed using a known concentration of UA standard solution in artificial saliva at an applied potential of - 0.1 V (versus Ag pseudo-reference electrode). The UOx--paper based electrochemical UA sensor showed a sensitivity of 4.9 µA·mM-1 in a linear range of 50 to 1000 µM (R2 = 0.998), high selectivity and good reproducibility, as well as a limit of detection of 18.7 µM (0.31 mg/dL) UA. Finally, we quantified the UA levels in undiluted saliva samples of healthy controls (n = 20) and gout patients (n = 8). The levels were correlated with those measured with conventional salivary UA enzymatic assays as well as serum UA levels. The UOx-paper-based electrochemical UA sensor is a user-friendly and convenient tool to assess salivary UA levels.

Rapid and simple colorimetric detection of hydrogen sulfide using an etching-resistant effect on silver nanoprisms.

A fast and sensitive colorimetric paper sensor has been developed using silver nanoprisms (Ag NPRs) with an edge length of ~50 nm for the detection of free H2S gas. We prepared two types of Ag NPRs-coated H2S sensing papers: a multi-zone patterned paper for passive (diffusion mode), and a single-zone patterned paper for pumped mode of H2S gas. The change in color intensity was quantitatively analyzed of Ag NPRs-coated paper after KCl treatment depending on the concentration of H2S gas, from yellow to purplish brown. As a result, Ag NPRs-coated H2S sensing paper showed good sensitivity with a linear range of 1.03 to 32.9 µM H2S, high selectivity, and good reproducibility and stability, together with a fast response time of 1 min. The developed H2S sensing paper was applied to detect the free H2S gas released from three types of garlic including crushed, peeled, and fresh garlic. Therefore, it can be utilized as a simple, fast, and reliable tool for on-site colorimetric detection of free H2S gas for quality control of dietary supplements and exhaled breath analysis.Graphical abstract.