Selective detection of ionic liquid fluorescence probes for visual colorimetry of different metal ions

A smart photosensitive fluorescent probe for sensing Co2+ in extremely alkaline aqueous solution

A novel pH-, viscosity-, and photo-sensitive polymorphic fluorescence probe NHP for sensing Co2+ has been developed. The hydrazone-based NHP can be synthesized by only one step of reflux reaction and purified by washing with poor solvents. Three single crystals of NHP-1, NHP-2, and NHP-3 with different conformations were resolved. As a photo acid generator (PAG), the hydrogen atom on the imino group of the probe NHP can be shed with 365 nm ultraviolet (UV) light illumination or in alkaline conditions. Due to the above two conditions, the negatively charged ligand obtained after dehydrogenation of NHP can accelerate its chelation with Co2+. When irradiated with 365 nm UV light, the product (NHP2-Co2+ (I)) of NHP chelating with Co2+ appears yellowish in aqueous solution. In a strong alkali aqueous solution, the chelate product (NHP2-Co2+ (II)) of NHP and Co2+ showed bright blue-green fluorescence. The formed divalent Co(II) complex NHP2-Co2+ can be oxidized to trivalent Co(III) complex NHP3-Co3+, as confirmed by the resolution of single crystals of NHP3-Co3+.

A quinoline colorimetric ionic liquid probe by electrostatic enhancement for visual detection of Fe3+ in food

Excessive or insufficient iron(Ⅲ) will pose burdens of human body, and its content is the key to control the function of iron-fortified food. In this regard, a functionalized quinoline ionic probe, benefiting from the electrostatic attraction, was designed for the colorimetric detection of Fe3+ in food. This probe formed a 2: 1 complex with Fe3+, altering the UV-vis spectra and solution color. The UV-vis detection limit was 0.2 μM, and visually, the color shifted from light-yellow to dark-green as Fe3+ concentrations increased, with a visual detection limit of 3.4 μM, meeting the maximum acceptable level of 5.4 μM. Noteworthy, ionic liquid-based sensing paper was constructed for rapid, semi-quantitative Fe3+ detection. Furthermore, the satisfying recovery (97.4-102.9 %) was obtained in real samples, showcasing the probe's efficiency. This work demonstrated the potential of ionic liquids for the fast, sensitive, and visual detection of Fe3+, offering a promising direction for metal element sensing platforms.

Fluorescence Detection of Pb2+ in Environmental Water Using Biomass Carbon Quantum Dots Modified with Acetamide-Glycolic Acid Deep Eutectic Solvent

In this study, a novel green fluorescent probe material, nitrogen-doped carbon quantum dots (N-CQDs), was prepared by a one-step hydrothermal synthesis method using walnut green skin as a carbon source and acetamide-glycolic acid deep eutectic solvent (AGADES) as a modifier. By covalent coupling, the amide chromophore in AGADES is designed to cover the surface of walnut green skin carbon quantum dots (W-CQDs), forming a fluorescence energy resonance effect and improving the fluorescence performance of the carbon quantum dots. The prepared N-CQDs have a uniform particle size distribution, and the fluorescence quantum efficiency has increased from 12.5% to 32.5%. Within the concentration range of 0.01~1000 μmol/L of Pb2+, the linear detection limit is 1.55 nmol/L, which can meet the trace detection of Pb2+ in the water environment, and the recycling rate reaches 97%. This method has been successfully applied to the fluorescence detection and reuse of Pb2+ in actual water bodies, providing new ideas and methods for the detection of heavy metal ions in environmental water.