Multi-color fluorescence sensing platform for visual determination of norfloxacin based on a terbium (Ш) functionalized covalent organic framework

Sensitive and visual determination of fluoroquinolone antibiotics (FQs) is of great significance since their abuse and inappropriate handling can be problematic. Herein, we propose a lanthanide covalent organic framework fluorescence sensing system (Tb@COF-Ru) with visualization capability to determine the FQs level, where Tb@COF was employed as the sensing probe, while the red-emitting Ru(bpy)₃²⁺ serves as a constant red fluorescent background. With increasing norfloxacin concentration, the green fluorescence of Tb³⁺ is gradually enhanced, finally realizing the multicolor fluorescence change from red to green. With a smartphone for RGB analysis, visual monitoring and quantitative analysis were realized without any sophisticated instrument. Limits of detection for the fluorescence quantitative and visual mode for norfloxacin were 0.33 nM and 7.3 μM, respectively. This method was rapid (1 min) and visualized, providing a simple analysis of various food matrices (honey, milk, egg and beef) and water samples for trace FQs.

Novel synthesis of orange-red emitting copper nanoclusters stabilized by methionine as a fluorescent probe for norfloxacin sensing

In the present work, we report a novel chemical approach for the synthesis of orange-red emitting copper nanoclusters (Cu NCs) using L-methionine as stabilizing agent at room temperature for the first time. The synthetic route is facile, economical and viable. The methionine stabilized copper nanoclusters (Cu NCs/Met) were thoroughly characterized by TEM, FT-IR, XPS, UV-Vis, steady state and transient fluorescence spectroscopy. The results show the synthesized Cu NCs/Met with a fluorescence quantum yield of 4.37% possessed high stability and excellent optical features such as large Stokes shift and long fluorescence lifetime (8.3 μs). Significantly, the fluorescence intensity of Cu NCs/Met could be efficiently quenched by norfloxacin (NOR) pharmaceutical. A fast and cost-effective NOR sensor was proposed employing Cu NCs/Met as the fluorescent nanoprobe, and the quenching mechanisms were attributed to inner filter effect and agglomeration-induced quenching. The developed sensor exhibited a high sensitivity and selectivity towards NOR in a wide linear range from 0.05 to 250 μM with a detection limit as low as 17 nM. Moreover, the practicability of the developed NOR sensor for real sample assay was validated with satisfactory recoveries, indicating this sensing platform with great potential for label-free pharmaceutical detection in complex systems.