In this work, we demonstrated a novel, sensitive and effective fluorescent naringin (NRG) and naringenin (NRGe) detection method using polymethionine nanoparticles (PMNPs) as a fluorescent nanoprobe. The PMNPs were first synthesized by autopolymerization of methionine at 90 °C when trace copper ions existed. The as-prepared PMNPs were thoroughly characterized by transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR), gel permeation chromatograph (GPC), nuclear magnetic resonance spectroscopy (NMR), transient and steady-state fluorescence and UV–Vis absorption spectroscopy. The quenching mechanism was attributed to the inner filter effect (IFE). Moreover, the developed assay was used successfully to detect NRG and NRGe in real samples of citrus fruits, illustrating that this detection method has great potential application in the field of citrus fruits analysis.

Schematic representation of the synthesis and the applications of EGCG–Cu NCs for troxerutin sensing and temperature sensing.

HBEA zeolite modified with highly electronegative cations is a highly efficient and reusable catalyst for the nitration of naphthalene with nitric acid, which has been successfully prepared in this work. Catalytic selective mononitration of naphthalene was investigated. The ratio of 1-nitronaphthalene isomer to 2-nitronaphthalene could reach 19.2, with a moderate yield of 68.2%, when the reaction was carried out in 1,2-dichloroethane, with 1.0 mmol naphthalene, 0.22 mL nitric acid (95%), and 0.10 g HBEA-25 at −15 °C. The effects of reaction temperature and the quantity of zeolites on 1-nitronaphthalene were also studied. The catalyst is readily recyclable, and we believe this to be a major step forward in the area of clean technology for aromatic nitration.