Unraveling the Potential and Selectivity of MoS2 Quantum Dots for Enzyme-Based Electrochemical Detection of Urea†

In recent years, use of quantum dots (QDs) for sensing urea and glucose has gained significant attention and considerable interest. QDs have great potential for applications in portable kidney devices, water treatment, and food industry. Meanwhile, portable urea sensing devices can be the game changer not only for environmental surveillance but also for improving the life span of kidney patients. There are numerous materials that have been reported for urea sensing, but they are rejected due to various limitations. For example, they are often costly, less durable, toxic, and generally exhibit nonbiocompatibility. Current project has been designed to develop relatively cheaper and more effective material for the urea sensing application. As per purpose, molybdenum disulfide QDs (MoS₂ QDs) and bulk (MoS₂ bulk) have been synthesized via hydrothermal approach followed by their immobilization along with urease in silk fibroin (SF) discs. Aminated glassy carbon electrode (GCE), i.e., NH₂–GCE was used for electrochemical sensing of the urea analyte precursors. By the electrooxidation of carbamic acid, the GCE was tuned with amine groups (−NH₂). SF discs were used to ensure the interaction of urease with MoS₂ QDs and MoS₂ bulk with the surface of NH₂–GCE. Chemical characteristics and structural sensitivity of MoS₂ QDs were assessed via XRD, scanning electron microscopy, transmission electron microscopy, FT–IR, Raman, UV–Vis/DRS, photoluminescence, electron dispersive X-ray, XPS, electrochemical impedance spectroscopy, and AFM approaches and compared with those of bulk MoS₂. Cyclic voltammetry was used to anticipate urea detection of the as-fabricated electrode, i.e., MoS₂ QDs/Urs/SF/NH₂–GCE and MoS₂ bulk/Urs/SF/NH₂–GCE. The MoS₂ QDs-based detection platform exhibited a high sensitivity and detection response of 16.443 μA mM^–1 cm^–2 with a linear correlation among urea concentration and current in range of 0.1−1.9 mM. Limit of quantification and limit of detection were calculated to be 0.831 and 0.274 mM, respectively. Using replaceable SF discs embedded with urease, sensing responses were recorded. As a small volume of electrolyte is employed, MoS₂ QDs are integrated into the miniaturized urea sensing devices. Electrochemical sensing performances of MoS₂ QDs were compared with bulk MOS₂ that is comparatively less sensitive. Based on the sensing performances, it has been concluded that as-prepared MoS₂ QDs hold the potential to be effectively utilized for real-time urea detection.