Fluoride Ions In Aqueous Media Research Articles

Water-stable boroxine structure with dynamic covalent bonds

Boroxines are significant structures in the production of covalent organic frameworks, anion receptors, self-healing materials, and others. However, their utilization in aqueous media is a formidable task due to hydrolytic instability. Here we report a water-stable boroxine structure discovered from 2-hydroxyphenylboronic acid. We find that, under ambient environments, 2-hydroxyphenylboronic acid undergoes spontaneous dehydration to form a dimer with dynamic covalent bonds and aggregation-induced enhanced emission activity. Intriguingly, upon exposure to water, the dimer rapidly transforms into a boroxine structure with excellent pH stability and water-compatible dynamic covalent bonds. Building upon these discoveries, we report the strong binding capacity of boroxines toward fluoride ions in aqueous media, and develop a boroxine-based hydrogel with high acid–base stability and reversible gel–sol transition. This discovery of the water-stable boroxine structure breaks the constraint of boroxines not being applicable in aqueous environments, opening a new era of researches in boroxine chemistry.

Fluoride ion detection in aqueous medium: Colorimetric and turn-off fluorescent Schiff base chemosensor

The work described is focused on a newly developed colorimetric Schiff base fluorescent sensor that exhibits a “turn-off” response when detecting fluoride ions (F−) in an aqueous environment. The confirmation of the recognition event is accomplished through fluorescence titration, absorbance titration, and Density Functional Theory (DFT) calculation study. From the results, it is determined that the detection limit of F− is 2.35 × 10−8 M which is much lower than the World Health Organization (WHO) permissible limit for drinking water while the binding constant was obtained to be 0.1 × 106 M−1 indicating a moderate affinity for the fluoride ions. Furthermore, the binding stoichiometry between the Probe L and F− was found to be 1:1 which is evidenced by the Job’s plot and DFT calculation study. Overall, the novel sensor's impressive sensitivity and selectivity make it a promising candidate for the detection of fluoride ions in aqueous media, particularly for monitoring drinking water quality to ensure compliance with WHO guidelines.

Silicon corrole functionalized color catcher strips for fluoride ion detection

Monitoring fluoride ions in drinking water is essential for human health. The ability of (Hydroxy)[5,10,15-tritolylcorrolato]silicon complexes [SiTTC(OH)] to bind fluoride ions with a significant color change is exploited to develop a simple and low-cost device to detect in situ fluoride ions in aqueous media. SiTTC(OH) was deposited on Color Catcher® (CC) strips, representing the first example of this support functionalized with a neutral receptor insoluble in water. The CC-SiTTC(OH) strip preparation protocol was optimized to obtain the best performances. Binding of F−led to a drastic color change in CC-SiTTC (OH), and colorimetric measurements were performed with an inexpensive instrumental setup similar to photo-assisted technique (PT), obtaining a LOD lower than the legal limit of 1.5 mg/L (≈ 80 µM) allowed by WHO. The value of the colorimetric variation, processed in terms of Hue, is able to measure with great accuracy the F−concentration in water samples.

Lowest aqueous picomolar fluoride ions and in vivo aluminum toxicity detection by an aluminum(iii) binding chemosensor.

Aluminum toxicity in biological systems is a well-known issue yet remains as a prevalent and unsolvable problem due to the lack of proper molecular tools that can detect free aluminum(iii) or Al(iii) ions in vivo. Herein, we report a water-soluble photo-induced electron transfer (PET)-based turn-ON/OFF fluorometric chemosensor for the dual detection of Al(iii) and fluoride ions in aqueous media with a nanomolar (∼1.7 × 10-9 M) and picomolar (∼2 × 10-12 M, lowest ever detection so far) detection limit, respectively. Fluoride ions in sea water could be detected as well as the recognition of non-contamination in drinking water. In addition, using live-cell microscopy, Al(iii) ions were detected in live biological samples in vivo to aid establishing the aluminum-toxicity effect.

Development of porphyrin-based chemosensor for highly selective sensing of fluoride ion in aqueous media

A porphyrin-based receptor to sense fluoride ion via hydrogen bonding has been prepared and investigated in aqueous media. The interactions between receptor and fluoride ion are confirmed by absorption and emission spectroscopy, and the influence of pH on the sensor performance has also been investigated. A dramatic color change from wine red to green, and photoswitching from the fluorescent on-state to the non-fluorescent off-state were observed after addition of fluoride ion to chemosensor POR. The detection limit for fluoride ion was calculated to be around 10 µM by both the colorimetric and fluorometric methods, which is under the tolerable amounts in drinking water by WHO guidelines. The Jobs plot showed a 1:2 reaction stoichiometry between POR and fluoride ion, which was further confirmed by mass analysis. The experimental results are fully supported by the DFT theoretical calculations. Furthermore, the changes in structural alignment of POR during fluoride detection were also proposed.

Chemical traffic light: A self-calibrating naked-eye sensor for fluoride

We report a low-cost sensing platform for effective naked-eye detection of fluoride ion in aqueous media. The sensor is based on silicon complex of 5,10,15-tritolylcorrole (SiTTCorr) deposited on paper support and designed in a particular way that permits it to perform in a unique sensing event an internal sensor self-calibration and subsequent analysis of fluoride ion in a concentration range from 20 [Formula: see text]g/L to 200 mg/L with a LOD 9 [Formula: see text]g/L, much lower than the WHO guideline value of 1.5 mg/L for fluoride in drinking water. The influence of tetradodecylammonium chloride (TDACl) anion exchanger addition to the performance of SiTTCorr-based sensors was studied and the sensor with optimal ionophore: exchanger [Formula: see text] 2:1 ratio demonstrated the highest sensitivity. The evident color variation of SiTTCorr-based optode from dark pink to intense green occurred upon addition of increasing concentrations of fluoride. A smartphone application equipped with home-written color intensity analysis software as a detector of developed sensor output permitted fluoride content quantification in bottled water and toothpaste samples. Moreover, since at the quantification step the SiTTCorr color variation was significant for the red component of visible light and increase of fluoride content evidently changed this color from red to yellow and then to green, the developed optode was compared to a kind of chemical traffic light, able to detect the presence of fluoride in permitted, borderline or dangerous concentrations, respectively.

A selective chemosensor and fluorescence probe for relay recognition of cations and fluoride ions in aqueous media with logic gate function

Cation to anion relay recognition was studied for the first time with sequential specificity (Cu2+ → F− or Co2+ → F−) using a fluorescence “ON−OFF−ON” mechanism. L1 is a receptor with high selectivity for F−, Cu2+ and Co2+ ions in the solution of DMSO/H2O with a 9:1 vol ratio. Absorption and fluorescence spectra were used to investigate the sensing process. Fluorescent emission intensity of L1 at 324 is quenched (switch-Off) after the addition of Cu2+ and Co2+. Surprisingly, complex L1 + Cu2+ or L1 + Co2+ is restored with addition of F− into the compound (switch-On). Consequently, implication (from emission) and inhibit (from absorption) logic gates are constructed at molecular level. The gates operate in fluorescence and absorption modes when Cu2+ and F− or Co2+ and F− are used as input materials and the fluorescence intensity signal as outputs. Based on reversible and reproducible system, a sequential memory unit with integrated ‘‘Writing–Reading–Erasing–Reading’’ behavior, is developed.

Coumarin Probe for Selective Detection of Fluoride Ions in Aqueous Solution and Its Bioimaging in Live Cells.

We have synthesized novel coumarin-based fluorescent chemosensors for detection of fluoride ions in aqueous solution. The detection mechanism relied on a fluoride-mediated desilylation triggering fluorogenic reaction and a strong interaction between fluoride and the silicon center. In this work, the hydroxyl-decorated coumarins containing oxysilyl moiety have been synthesized through the aldehyde-functionalized coumarins. The optical responses toward fluoride, as well as aqueous stability studies of both aldehyde and hydroxyl functionalized coumarins, have been investigated. Due to the highest fluorescence enhancement upon the addition of fluoride and good stability in aqueous solution, the hydroxyl-decorated coumarin connected with the bulky tert-butyldiphenyloxysilyl group (-OSitBuPh2) has been selected for further investigation of its potential as a fluoride sensor. This hydroxyl-decorated coumarin can selectively sense fluoride ions in aqueous media (contain 0.8% MeCN) with desirable response times (40 min). The limit of detection of this compound was determined as 0.043 ppm, satisfying the standard fluoride level (0.7 ppm) in drinking water recommended by U.S. Department of Health and Human Services. The application of this silyl-capped coumarin derivative for fluoride analysis in collected water samples displayed satisfactory analytical accuracy (<5% error). Finally, this compound was successfully employed in fluorescence bioimaging of fluoride ions in human liver cancer cells, indicating its excellent cell permeability, ability to retain inside the living cells, and good stability under physiological conditions.

An effective electrochemical sensing platform for fluoride ions based on fluorescein isothiocyanate–MWCNT composite

The intrinsic redox properties of fluorescein isothiocyanate, rather than its fluorescence, were employed as a transducing signal to detect fluoride ions in aqueous media.

Smart fluorescent AIEE active supramolecular polymeric assemblies for selective and quantitative detection of fluoride ions in aqueous media

Abstract A fibrous network of AIEE active polyamine derivative 2 has been developed which exhibits living self-assembly in mixed aqueous media accompanied by solvent dependent morphology transformation. Further, the supramolecular assemblies of polyamine derivative 2 in presence of fluoride ions undergo rigidification to generate highly fluorescent supramolecular polyamine ensemble 2:F−. The mechanism of self-aggregation and fluoride induced aggregation is theoretically and experimentally proved. Additionally, electron rich supramolecular polyamine ensemble 2:F− was utilized for the detection of picric acid with detection limit of 15 ppb.

Carbohydrates in Fluoride Sensing: Use of Cyclodextrin and CNC‐Based Chemical Probes

AbstractDespite significant development in the area, efficient sensing of fluoride ions in aqueous media remained a serious challenge. In this communication we report the design and synthesis of two eco‐friendly carbohydrate‐based probes for the fluorimetric sensing of fluoride ions. The novel probes are fully characterized with NMR, UV‐Vis, FTIR and MALDI‐TOF. The probes showed selective detection of fluoride anion within the permissible limit set by WHO. The organic cellulose nanocomposite (CNC) based probe showed the lowest detection limit among other carbohydrate‐based probes for the detection of fluoride anion. In addition to the excellent sensitivity, these probes are particularly attractive for their bio‐availability and non‐toxic nature.

Alternating Poly(borosiloxane) for Solid State Ultrasensitivity Toward Fluoride Ions in Aqueous Media

Facile synthesis of alternating copolymer poly(borosiloxane) via dehydrocoupling was successfully carried out in the presence of transition metal catalyst at room temperature. The polymer was characterized by NMR and IR spectroscopy. The presence of a single peak in 11B NMR and 29Si NMR supported the alternating sequence of the polymer which was further complimented by the study of specifically designed model reactions. Fluoride ion sensitivity was analyzed by electrochemical methods.. The anion selective electrode prepared using synthesized polymer was found to be extremely sensitive toward fluoride ions (10–10 M in aqueous media) by potentiometric measurements using 0.1 M disodium hydrogen phosphate as supporting electrolyte, Ag/AgCl as reference electrode, and Pt wire as counter electrode.

A gadolinium(iii) complex based dual-modal probe for MRI and fluorescence sensing of fluoride ions in aqueous medium and in vivo.

A novel Gd(iii) complex, Gd(TTA)3-DPPZ, was designed and assembled as a dual-modal probe for the simultaneous fluorescence and magnetic resonance imaging (MRI) detection of fluoride ions in aqueous media and in vivo. In this system, the Gd(iii) center is not only serving as a MRI signal output unit, but also as a binding site for fluoride ions. When appropriate equivalents of fluoride ions were added into the solution of Gd(TTA)3-DPPZ, the replacement of the coordination water led to a decrease of the longitudinal relaxivity (r1) as well as distinct spectroscopic changes, by which MRI/fluorescence dual-modal fluoride ion sensing was achieved. In the presence of fluoride ions, a 2-fold fluorescence emission enhancement of Gd(TTA)3-DPPZ, and a notable decrease of the UV-vis absorption spectrum were observed. The fluorescence detection limit for fluoride ions was established at 70 nM. Gd(TTA)3-DPPZ also exhibits about 75% decrease of the longitudinal relaxivity (r1) upon addition of fluoride ions in aqueous medium. The appropriate blood circulation time of Gd(TTA)3-DPPZ allows its potential application in MRI in vivo. The results demonstrated that Gd(TTA)3-DPPZ could serve as a potential MRI/fluorescence bimodal imaging agent for the specific and high-sensitive sensing of fluoride ions in vivo.

Fluorometric selective detection of fluoride ions in aqueous media using Ag doped CdS/ZnS core/shell nanoparticles

The presence of fluoride ions in drinking water plays an important role in human health. For that reason, maintaining the optimum concentration of fluoride ions in drinking water is essential, as both low and excess (above the permissible level) concentrations can cause different health problems, such as fluorosis, urolithiasis, kidney failure, cancer, and can even lead to death. So, development of a simple and low cost method for the detection of fluoride ions in water is highly desirable. In this study, a fluorometric method based on Ag-CdS/Ag-ZnS core/shell nanoparticles is developed for fluoride ion detection. The method was tested in aqueous solution at different pH values. The selectivity and sensitivity of the fluorescence probe was checked in the presence of other anions (Cl(-), Br(-), I(-), NO3(-) SO4(2-), HCO3(-), HPO4(2-), CH3COO(-), and H2PO4(-)) and found there is no significant interference of these associated ions. The fluoride ion concentration was varied in the range 190-22 800 μg L(-1) and a lower detection limit was obtained as 99.7 μg L(-1).

Molecular logic circuits and a security keypad lock based on a novel colorimetric azo receptor with dual detection ability for copper(II) and fluoride ions

A novel azoimine dye-based colorimetric chemosensor (1) has been designed and synthesised for dual recognition of copper(II) and fluoride ions in aqueous media. Significantly, the outstanding dual-ion recognition properties along with the excellent reversibility prompted us to consider 1 as an ideal candidate for fabrication of multiple logic circuits. According to the response profile of 1 towards Cu2+ and F− inputs, we developed a unique tunable system integrated with one INHIBIT logic gate as well as one OR gate. Also, 1 behaved as a molecular keypad lock with sequential addition of Cu2+ and F− inputs. In accession, a reversible ‘Write–Read–Erase–Read’ function with complementary ‘IMP/INH’ logic gate has been demonstrated through a feedback loop using F− and trifluoroacetic acid as two chemical inputs. To the best of our knowledge, this is the first report where the symmetrical bis azo-azomethine dye has been exploited as a molecular keypad lock.

AIE active pyridinium fused tetraphenylethene: Rapid and selective fluorescent “turn-on” sensor for fluoride ion in aqueous media

Pyridinium functionalized derivative of tetraphenylethene with iodide ion as a counter anion was reported for highly selective detection of fluoride ion in aqueous media. Rapid “turn-on” fluorescence signaling with hypsochromic shift upon addition of micromolar quantities of fluoride ion to the aqueous solution of was attributed to the formation of aggregated amorphous tetraphenylethene units due to the decrease in solvolysis caused by the ion exchange process between fluoride and iodide ion. The ion-exchange induced emission formation due to the formation of less soluble amorphous salts is the novel approach for AIE active turn-on fluorescent sensing analysis. The experimental studies obviously demonstrate the selectivity of designed luminogen for fluoride ion detection when compared with other metals, particularly CN−, and AcO−. The practical applicability of the presented fluorometric method in tap water was also associated with satisfactory results. It is concluded that, such simple and convenient sensing strategy with a great potential for practical applications could provide a promising powerful tool for rapid, sensitive and selective analysis of fluoride ion.

Fluorescent carbon nanodots for optical detection of fluoride ion in aqueous media

In this work, a nanoprobe for sensing fluoride ion in aqueous solution has been introduced. The operation of this system is based on the quenching of the fluorescence signal of carbon nanodots (CDs) with a simple organic receptor. The linear trend in fluorescence signal with respect to fluoride concentration proved that Stern-Volmer equation was adapted successfully to the system with a linear range of 0–26.7mM and LOD value of 1.1×10−4M. This system showed to be nonresponsive toward weak basic anions except for fluoride. Using toothpaste as a real sample, the level of fluoride was successfully measured by this method.

Turn-on fluorescent probe designed for fluoride ion sensing in aqueous media

A NBD-based probe for selective detection of fluoride ion in aqueous media is reported. The probe was designed by applying rules for water solubility and membrane permeability. The probe functions through the fluoride mediated cascade reaction which was studied by 1H NMR, HPLC analysis, UV–vis, and fluorescence spectroscopy. The sensing process was marked by a colour change from colourless to yellow, and an intriguing 120-fold turn-on green fluorescence. Application of the probe for selective detection of fluoride was demonstrated by live-cell imaging.

β-Cyclodextrin and calix[4]arene-25,26,27,28-tetrol capped carbon dots for selective and sensitive detection of fluoride.

In this work we have designed a novel system based on carbon dots prepared from chitosan gel capped with β-cyclodextrin and calix[4]arene-25,26,27,28-tetrol for sensitive and selective detection of fluoride ions in aqueous media. Fluorescent carbon dots prepared from chitosan gel when capped with β-cyclodextrin and calix[4]arene-25,26,27,28-tetrol results in quenching of its fluorescence intensity. Introduction of F(-) ions to carbon dots capped with β-cyclodextrin and calix[4]arene-25,26,27,28-tetrol system results in enhancement and restoration of fluorescence intensity leading to detection of F(-) ion. Minimum detection limit was determined to be ∼6.6 μM. The detection is selective as with other halide ions i.e. Cl(-), Br(-) and I(-) and hydroxyl ion (OH(-)), there is observed decrease of fluorescence intensity. A possible mechanism to justify the observation is also discussed in the paper.

Naked-eye detection of inorganic fluoride in aqueous media using a new azo-azomethine colorimetric receptor enhanced by electron withdrawing groups

A new azo-azomethine receptor, containing active phenolic sites, has been designed and synthesized for quantitative detection and colorimetric sensing of inorganic fluoride ion in aqueous media. The introduction of four electron withdrawing groups into the backbone of the receptor makes the two phenolic groups efficient hydrogen bonding sites. Hence, the receptor is capable of competing with water molecules to detect trace amounts of inorganic fluoride ions in aqueous solutions. Accordingly, the receptor showed a remarkable colour change from light yellow to orange upon the addition of aqueous solution of NaF, enabling naked-eye F− sensing without any spectroscopic instrumentation. The recognition details of F− sensing were also evaluated using UV-Vis spectroscopy and 1H NMR titration techniques. The 1H NMR titration revealed that the colorimetric response was considered to be the direct consequence of hydrogen-bond formation between the phenolic groups of the receptor and fluoride ions followed by deprotonation. Importantly, the current sensor can detect inorganic fluoride in water even at 0.058 ppm, which is lower than the World Health Organization (WHO) permissible level. To the best of our knowledge, there have been very few examples of detection limits lower than the WHO permissible level for detecting fluoride ion in drinking water (below 1 ppm). The designed sensor has also shown highly promising results for the qualitative and quantitative detection of fluoride in real samples like sea water, toothpaste and mouthwash.