Luminescent copper nanoclusters (CuNCs) constitute a very active research topic due to their unique properties and lower cost than gold and silver NCs. In this study, we report a new, facile, and rapid top-down etching method for synthesizing luminescent CuNCs, using Cu nanoparticles (CuNPs) as the precursor and ammonia (NH₃) as the etchant. The etching mechanism is systematically investigated and the optical and structural properties of the obtained CuNCs are carefully studied. The NH₃-triggered etching process is very fast and the newly generated CuNCs can emit strong green fluorescence with a high quantum yield. Moreover, by coupling the urease-catalyzed hydrolysis of urea with the NH₃-induced etching of CuNPs, we developed a novel fluorescence turn-on assay for urea. The linear range for urea detection is from 0.25 to 5 mM, and the limit of detection is 0.01 mM. This novel sensing approach, with good sensitivity and excellent selectivity, is then successfully utilized to detect urea in human serum samples, demonstrating its great potential in clinical diagnosis. In addition, the proposed coupling method can be extended to monitor other analytes that influence the size-focusing etching process, allowing metal NCs to be used to construct diverse chemosensors and biosensors.

Luteolin is a flavonoid reported to occur widely in many medicinal plants. The electrochemical behavior of luteolin was studied in phosphate buffer solution (PBS) of pH 4.0 at a glassy carbon electrode (GCE) by cyclic voltammetry (CV) and differential pulse voltammetric method (DPV). The results indicated the well-defined redox peak of luteolin which was involving two electrons and two protons was observed and the electrode process is adsorption-controlled. The charge transfer coefficient (α) was calculated as 0.66. The relationships between oxidation peak current and the concentration of luteolin are linear in the range of 1.0×10−8—1.0×10−6 M by DPV method. The detection limit had been estimated as 5.0×10−9 M. The facile and rapid method has been successfully applied to the detection of luteolin in tablets.