Highly Selective and Scalable Molecular Fluoride Sensor for Naked-Eye Detection

Fluoride is widely present in nature, and human exposure to it is generally regarded as inevitable. High levels of fluoride intake induce acute and chronic illnesses. To reduce potential harm to the general public, it is essential to create selective fluoride detectors capable of providing a colorimetric response for naked-eye detection without the need for sophisticated equipment. Here, we report a one-pot synthesis of four different diaminomaleonitrile-derived Schiff base sensors. The terephthalaldehyde adduct provided a strong color change visible to the naked eye at a F- concentration level as low as 2 ppm. From the evaluation against other anions, such as CN-, I-, Br-, Cl-, NO3-, PO43-, OAc-, and HSO4-, the molecular sensor displayed a visible color change exclusively upon exposure to fluoride, underscoring exceptional selectivity. As a key intermediate for understanding the mechanism, HF2- was confirmed by 19F nuclear magnetic resonance. Theoretical calculations suggested a deprotonation-triggered bathochromic shift brought about by the unique electronic structure of the sensor. Furthermore, the simple synthetic protocol from economically accessible materials allowed for the preparation of the compound on a large scale, rendering it a highly practical visual fluoride sensor.

Surface Ligand Influences the Cu Nanoclusters as a Dual Sensing Optical Probe for Localized pH Environment and Fluoride Ion

Functional metal nanomaterials, especially in the nanocluster (NC) size regime, with strong fluorescence, aqueous colloidal stability, and low toxicity, necessitate their application potential in biology and environmental science. Here, we successfully report a simple cost-effective method for red-/green-color-emitting protein/amino-acid-mediated Cu NCs in an aqueous medium. As-synthesized Cu NCs were characterized through UV-Vis absorption spectroscopy, fluorescence spectroscopy, time-resolved photoluminescence, dynamic light scattering, zeta potential, transmission electron microscopy and X-ray photoelectron spectroscopy. The optical properties of both Cu NCs responded linearly to the variation in pH in the neutral and alkaline ranges, and a robust pH reversible nature (between pH 7 and 11) was observed that could be extended to rapid, localized pH sensor development. However, a contrasting pH response nature between protein-Cu NCs and amino acid-Cu NCs was recorded. The alteration in protein secondary structure and strong binding nature of the surfactants were suggested to explain this behavior. Furthermore, we investigated their use as an efficient optical probe for fluoride ion detection. The limit of detection for protein-Cu NCs is 6.74 µM, whereas the limit of detection for amino acid-Cu NCs is 4.67 µM. Thus, it is anticipated that ultrasmall Cu NCs will exhibit promise in biological and environmental sensing applications.

Rhenium(I)-Based Neutral Coordination Cages with a Spherical Cavity for Selective Recognition of Fluoride

Neutral heteroleptic trinuclear coordination cages containing a preorganized well-defined small spherical endocavity, which is made up of electron-deficient bowl frameworks, three coordination-induced neutral polar C-H donors, and a phenyl motif, were self-assembled via a one-pot approach; the endocavity accommodates fluoride selectively in the presence of other halides.

Ultrasensitive, rapid and selective sensing of hazardous fluoride ion in aqueous solution using a zirconium porphyrinic luminescent metal-organic framework

The development of a rapid and sensitive method for the detection of fluoride ion (F^-) in aqueous systems is of great significance for human health and environmental monitoring. In this study, a zirconium porphyrinic luminescent metal-organic framework (LMOF), PCN-222, was employed as a novel fluorescent probe for the ultrasensitive, rapid and selective detection of F^- in water. The PCN-222 probe was prepared by a facile solvothermal method. It exhibited good fluorescence stability and was highly stable in water. The fluorescence emission of PCN-222 could be effectively and selectively quenched by F^- due to the strong coordination affinity of F^- to the zirconium clusters in PCN-222. The proposed fluorescence method for F^- detection based on PCN-222 probe afforded a linear response range of 1-20 μmol/L and a very low detection limit (0.048-0.065 μmol/L) in reference to many reported F^- fluorescent probes. Moreover, a rapid response time (<10 s) was obtained due to the open and uniform pore structure of PCN-222 that allowed the fast diffusion of F^- to interact with the zirconium recognition sites. Finally, the PCN-222 probe was successfully applied for the fluorescence detection of F^- in real water samples. These results highlight the great application potential of LMOF in the sensing fields.

New Design Strategy Toward NIR I Xanthene-Based Dyes

An effective design strategy with an efficient synthetic route to xanthene-based far-red to near-infrared dyes is reported. The dyes were prepared by the Suzuki cross-coupling of the electron-poor fluorescein ditriflate with the electron-rich boronic acid/ester-functionalized pyrrole (2C/3C) and indole (2D/3D) moieties. Upon treatment with trifluoroacetic acid, the closed nonfluorescent forms of the dyes (2C and 2D) ring-opened to their fluorescent forms (3C and 3D). The absorption maxima were 665 and 704 nm, while the emission maxima were 717 and 719 nm for 3C and 3D, respectively. The closed forms of the dyes were soluble in chloroform and acetonitrile. To test the efficacy of the dyes as probes, a turn-off fluoride ion probe was prepared from 3C, which consisted of a silyl ester receptor. The probe responded strongly to low concentrations of fluoride, carbonate, and acetate ions, weakly to phosphate ions, but not to the other halogens. Moreover, the probe can detect the minimum concentration of F^- in water.

In Vivo Fluoride Ion Detection and Imaging in Mice Using a Designed Near-Infrared Ratiometric Fluorescent Probe Based on IR-780

A ratiometric near-infrared fluorescence probe based on IR-780 is developed and applied to fluoride anion (F^-) detection in potable water and white flour as well as fluorescence imaging in living cells and mice. The proposed probe not only displays a linear ratiometric (F₇₄₀/F₆₉₀ nm) fluorescence response but also possesses near-infrared wavelengths to F^- with a detection limit of 0.2 μM. Moreover, the designed probe displays high selectivity toward F^-, which makes it feasible for F^- detection in potable water and white flour. More importantly, applied to monitor F^- in living HepG2 cells and male BALB/c mice, the probe indicates good biocompatibility and low cytotoxicity. However, no study for F^- detection has been reported by a ratiometric NIR fluorescent probe so far. We expect that this probe with superior properties has great potential for use in F^- detection in biological systems and in vivo studies.

Fabrication of the ternary heterojunction Cd0.5Zn0.5S@UIO-66@g-C3N4 for enhanced visible-light photocatalytic hydrogen evolution and degradation of organic pollutants

This article reports a novel ternary heterojunction Cd_0.5Zn_0.5S@UIO-66@g-C₃N₄ that exhibits enhanced photocatalytic hydrogen production and MO degradation.

Nanomaterials for the optical detection of fluoride

Overexposure to fluoride ions (F^-) causes serious diseases in human beings. Extensive efforts have been made to develop sensitive and selective approaches for F^- detection and a variety of F^- sensors have been constructed recently. The burgeoning nanotechnology has provided novel materials for F^- analysis due to the extraordinary properties of nanomaterials. In this review, we present the recent advances in different nanomaterials-based approaches for the optical F^- detection via colorimetric, fluorescent and chemiluminescent responses. The materials include gold nanomaterials, CeO₂ nanoparticles, semiconductor quantum dots, carbon quantum dots, metal-organic frameworks, upconversion nanoparticles, micellar nanoparticles, polymer dots, SiO₂ nanoparticles and graphene oxide. The recent trends and challenges in the optical detection of F^- with various nanomaterials are also discussed.

Rare earth ions enhanced near infrared fluorescence of Ag2S quantum dots for the detection of fluoride ions in living cells

In this work, a novel phenomenon was discovered that the fluorescence intensity of silver sulfide quantum dots (Ag₂S QDs) could be enhanced in the presence of rare earth ions through aggregation-induced emission (AIE). Based on the strong coordination between rare earth ions and F^-, a facile and label-free strategy was developed for the detection of F^- in living cells. Ag₂S QDs were synthesized using 3-mercaptopropionic acid as sulfur source and stabilizer in aqueous solution. The near infrared (NIR) emitting QDs exhibited excellent photostalilty, high quantum yield and low toxic. Interestingly, the fluorescence intensity of QDs was obviously enhanced upon the addition of various rare earth ions, especially in the presence of Gd³⁺. The AIE mechanism was proved via the TEM, zeta potential and dynamic light scattering analysis. Moreover, the coordination between rare earth ions and F^- could lead to the quenching of fluorescence QDs due to the weakening the AIE. Based on these findings, we developed a highly sensitive and selective method for detection of F^-. The label-free NIR fluorescence probe was successfully used for F^- bioimaging in live cells.