Herein, a one-pot chemical reduction method was reported to prepare folic acid (FA)-stabilized silver nanoclusters (FA@Ag NCs), in which FA, hydrazine hydrate, and silver nitrate were used as capping agent, reducing agent, and precursor, respectively. Several technologies were employed to investigate the structures and optical properties of FA@Ag NCs, including transmission electron microscopy (TEM), X ray photoelectron spectrometer (XPS), Fourier transform infrared spectrometer (FTIR), X-ray diffractometer (XRD), fluorescence spectrometer, and ultraviolet visible absorption spectrometer. FA@Ag NCs were suggested to be highly dispersed and spherical with a size of around 2.8 nm. Moreover, the maximum excitation and emission wavelengths of FA@Ag NCs were 370 and 447 nm, respectively. Under the optimal detection conditions, FA@Ag NCs could be used to effectively detect malachite green with the linear detection range of 0.5-200 μmol·L^-1. The detection limit was 0.084 μmol·L^-1. The fluorescence-quenching mechanism was ascribed to the static quenching. The detection system based on FA@Ag NCs was successfully used for the detection of malachite green in actual samples with good accuracy and reproducibility.

Herein, ratiometric fluorescence-based carbon dots (N-CDs) with blue emission were prepared by using simple one-step hydrothermal methods from benzimidazole and L-tryptophan as precursors. Dual emission peaks were observed at 356 and 442 nm under the excitation wavelength of 303 nm. Upon addition of sulfide ions (S^2-), the fluorescence intensity at 442 nm decreased significantly, while that at 356 nm increased. The F₄₄₂/F₃₅₆ intensity ratio (where F₃₅₆ and F₄₄₂ refer to the fluorescence intensity at 356 and 442 nm, respectively) exhibited a linear relationship with the concentration of S^2- (0-60.0 μmol·L^-1), and the detection limit was determined to be 0.076 μmol·L^-1. The fluorescence detection mechanism was ascribed to the static quenching effect. Furthermore, this fluorescence probe was successfully used for the determination of S^2- in real samples with satisfactory recoveries. Finally, the analytical greenness metric for sample preparation (AGREEprep) and blue applicability grade index (BAGI) tools indicated the high sustainability of this platform.