The quantum yield and fluorescence properties of carbon dots are key issues for environmental detection. In this study, nitrogen–sulfur-doped carbon dots (N,S-CDs) were prepared hydrothermally by adding thiourea to provide the N source. By adjusting the ratio of citric acid (CA) to thiourea (N,S) and adding anhydrous ethanol, blue fluorescent doped carbon dots with a quantum yield of up to 53.80% were obtained. The particle morphology and crystalline organization of the N,S-CDs were analyzed using transmission electron microscopy (TEM) and X-ray diffraction (XRD). Fourier transform infrared (FTIR) spectroscopy was used to illuminate distinct functional units through the recording of typical vibration bands. The luminescence properties of the N,S-CDs were investigated using ultraviolet–visible (UV-vis) absorption spectroscopy and steady-state fluorescence spectroscopy (PL). In addition, the fluorescence stability of the N,S-CDs was studied in detail. The results showed that the functional groups of the N,S-CDs chelate Fe³⁺ ions to quench the fluorescence of carbon dots. This shows that the N,S-CDs exhibit high selectivity for Fe³⁺ ions. With the addition of Fe³⁺ in the concentration of 0–100 µM, the fluorescence intensity of the N,S-CDs exhibited distinct and linear dependence upon the Fe³⁺ concentration (R² = 0.9965), and the detection limit (D = 3ơ/m) was measured as 0.2 µM. The excellent optical properties and Fe³⁺ selectivity of the N,S-CDs provide a huge boost for application in the field of environmental monitoring.

Concurrently achieving high growth rate and high quality in single-crystal diamonds (SCDs) is significantly challenging. The growth rate of SCDs synthesized by microwave plasma chemical vapor deposition (MPCVD) was enhanced by introducing N₂ into the typical CH₄-H₂ gas mixtures. The impact of nitrogen vacancy (NV) center concentration on growth rate, surface morphology, and lattice binding structure was investigated. The SCDs were characterized through Raman spectroscopy, photoluminescence (PL) spectroscopy, and X-ray photoelectron spectroscopy. It was found that the saturation growth rate was increased up to 45 μm/h by incorporating 0.8–1.2% N₂ into the gas atmosphere, which is 4.5 times higher than the case without nitrogen addition. Nitrogen addition altered the growth mode from step–flow to bidimensional nucleation, leading to clustered steps and a rough surface morphology, followed by macroscopically pyramidal hillock formation. The elevation of nitrogen content results in a simultaneous escalation of internal stress and defects. XPS analysis confirmed chemical bonding between nitrogen and carbon, as well as non-diamond carbon phase formation at 0.8% of nitrogen doping. Furthermore, the emission intensity of NV-related defects from PL spectra changed synchronously with N₂ concentrations (0–1.5%) during diamond growth, indicating that the formation of NV centers activated the diamond lattice and facilitated nitrogen incorporation into it, thereby accelerating chemical reaction rates for achieving high-growth-rate SCDs.

Uric acid, a metabolite formed by the oxidation of purines in the human body, plays a crucial role in disease development when its metabolism is altered. Various techniques have been employed for uric acid analysis, with electrochemical sensing emerging as a sensitive, selective, affordable, rapid, and simple approach. In this study, we developed a polymer-based sensor (PPy/α-Fe₂O₃) for the accurate determination of uric acid levels. The PPy/α-Fe₂O₃ hybrids were synthesized using an uncomplicated in situ growth technique. Characterization of the samples was performed using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The electrochemical sensing performance towards uric acid was evaluated through cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The obtained results demonstrated that the sensor exhibited excellent sensitivity towards uric acid detection within a wide range of 5–200 μM with a limit of detection (LOD) as low as 1.349 μM. Furthermore, this work elucidated the underlying sensing mechanism and highlighted the pivotal role played by PPy/α-Fe₂O₃ hybrids in enabling efficient uric acid sensing applications using electrochemical sensors.