Urea is an organic compound that is found everywhere in nature as a result of various processes. In the human body, urea is the end product of nitrogen metabolism, and excessive urea concentration in the human body is the cause of various important diseases such as indigestion, cancer, renal failure, urinary tract obstruction, etc. Among the secretion routes through several biological fluids (blood, urine, sweat), sweat urea is an important and non-invasive strategy for assessing the status of the kidney and liver. In the present study, the aim is to detect urea from sweat, which should be done directly through human skin. In order to make a biocompatible sensor without skin irritation, a silk fibroin nanofibrous film with strong mechanical properties, light weight and low cost is reported, which was made by directly dissolving silk in a formic acid-calcium chloride solution. This solution dissolves silk rapidly at room temperature and, more importantly, decomposes silk into nanofibrils instead of individual molecules. On the other hand, the use of direct band gap molybdenum disulfide semiconductor nanoparticles is a useful and safe choice to improve electrochemical sensing and improve the behavior of polymer-based sensors. In this regard, after the successful fabrication of these two materials, a silk/molybdenum disulfide film was prepared in 9 layers using spin coating and its properties were investigated in two cases where silk or molybdenum disulfide was the top layer. After that, pyrrole as a monomer was electropolymerized in the presence of sodium acetate buffer solution containing urea template to prepare a urea-etched electrode and this process was carried out using cyclic voltammetry (CV) in the range of -0.6-0.8 V and 10 cycles. Then, the formation of molecularly imprinted polymer (MIP) was confirmed by characterization tests including visible-ultraviolet spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and wettability. A non-molecularly imprinted polymer (NIP) electrode was also fabricated by the same MIP process but without urea for a better comparison study, and it was shown that surface printing can overcome the effect of steric hindrance and increase the number of binding sites for a given pattern, thus improving the detection efficiency. The eva‎luation of the sensing properties for the sample with a molybdenum disulfide top layer, whose characterizations were associated with better results, was carried out by differential pulse voltammetry (DPV) in the range of -0.6-0.2 V in potassium ferri/ferrocyanide solution and with an absorption time of 15 min, and the detection limit of the fabricated MIP sensor was obtained to be 0.12 mM. The selectivity of the electrochemical sensor in question was also tested using other substances present in sweat with similar structure or electrochemical activity to urea and eva‎luating their DPV responses, which showed that the current responses at two concentrations with relatively large differences were close to each other, indicating their lack of detection. In this study, the feasibility of developing electrochemical sensors for urea eva‎luation in the form of a multilayer film containing a molecular template was investigated, which offers a promising approach for biological applications, and future research should focus on upgrading the sensor to electronic skin and providing it with self-powered energy through the triboelectric effect.

فتح اله كريم زاده , مهشيد خرازيهاي اصفهاني

عليرضا علافچيان , نرگس جوهري