Fluoride Ion Sensor Research Articles

Naked eye detection of anions: Dihydrazone receptor-based visual sensing

In this study, we designed and synthesized a novel colorimetric sensor for fluoride ions by integrating a thienodicarbohydrazide framework with salicylaldehyde, resulting in a unique bis-hydrazone-phenol receptor. This sensor exhibited exceptional selectivity for fluoride and acetate ions in nonaqueous environments, with detection visible to the naked eye. Upon interaction with fluoride ions, the receptor underwent a significant red shift in its UV–Visible absorption spectrum, moving from an absorption maximum at 332 nm–380 nm, signalling the recognition event. Acetate ions induced a similar shift. The binding interactions were thoroughly investigated, with a Jobs plot revealing a 1:1 receptor-anion complex formation with fluoride ions and a 1:2 complex with acetate ions. Further validation came from 1H NMR titration, which confirmed the presence of hydrogen bonding interactions between the receptor and the ions. The receptor demonstrated remarkable binding constants of 5.2 × 10⁴ M−2 for acetate and 1.6 × 10⁴ M−1 for fluoride ions, highlighting its strong and selective affinity. Fluorescence titrations further confirmed the receptor's potential as a chemo sensor, showing distinct emission changes in the presence of fluoride and acetate ions. This study not only underscores the receptor's capability for visual detection of fluoride ions in non-aqueous systems but also paves the way for its application in diverse analytical and environmental settings.

The Advent of Bodipy-based Chemosensors for Sensing Fluoride Ions: A Literature Review.

The detection of fluoride ions in water and other sources is crucial because they can harm human health if they exceed the safe limit of 1-1.5 ppm. BODIPY (boron dipyrromethene) dyes are promising fluorophores for chemosensors, and their design and modification have attracted a lot of attention. Their advantages include visible light excitation and emission, high molar absorption coefficients (ε) and fluorescence quantum yields [ϕ (λ)], and flexible scaffold manipulation for various applications. In this article, we review the progress of BODIPY-based sensors for fluoride ions from the early 2000s to the present. We focus on the different scaffold modifications of the sensors and their corresponding responses, as well as the underlying photophysical mechanisms and potential uses of each sensor.

Electrochemical difference between single‐ and poly‐crystalline LaF3 for a compact and low‐price fluoride ion sensor

AbstractFluoride ion sensor electrodes that use polycrystalline LaF3 prepared by low‐temperature sintering can reduce sensor size and fabrication costs; however, decreasing the sintering temperature deteriorates sensor performance. Further, it is unclear why the performance of polycrystalline LaF3 prepared at low temperatures is inferior to that of the single‐crystal LaF3. Thus, in this study, we investigated factors that deteriorate sensor response under low sintering temperatures, such as solution penetration, fluorine conductivity, and ion exchange. To this end, LaF3 was prepared by changing the sintering temperature, and the electrical characteristics and sensor performance were evaluated and compared with those of the single‐crystal LaF3. The sensor performances of LaF3 sintered at 900 °C (−9.3 mV/dec) and 1000 °C (−5.8 mV/dec) were inferior to that of a single‐crystal LaF3 (−49.9 mV/dec). LaF3 prepared by sintering over 800 °C achieved fluorine removal and showed lower ion conductivity and ion exchange compared to that of the single‐crystal LaF3. LaF3 sintered at 700 °C did not show a sensor response because of solution penetration into the through‐pore. Our results confirmed that solution penetration, ion conductivity, and ion exchange influence the sensor performance of LaF3. Finally, we discussed approaches to achieve high sensor performance with LaF3 prepared by low‐temperature sintering. The proposed approaches are expected to contribute to expanding the utility of fluoride ion sensor electrodes with LaF3.

Design of molecular sensors and switches based on luminescent ruthenium-terpyridine complexes bearing active methylene and triphenylphosphonium motifs as anion recognition sites: experimental and DFT/TD-DFT investigation.

Synthesis, characterization and thorough investigation of the photophysical and electrochemical properties of a new category of emissive homo- and heteroleptic Ru(II)-complexes derived from the [4'-(p-triphenylphosphonium methyl phenyl)-2,2':6',2''-terpyridine]bromide (tpy-PhCH2PPh3Br) ligand have been executed in this work. Incorporation of the PhCH2PPh3+Br- group at the terpyridine motif appropriately adjusts the triplet metal-to-ligand charge transfer (3MLCT) and metal-centered (3MC) excited states so that the complexes luminesce at room temperature (RT) having lifetimes within the range of 6.82-9.63 ns. The RT emission characteristics of the complexes get further enhanced via aggregation phenomena through the use of different solvent/non-solvent mixtures (DMSO/H2O and DMSO/PhCH3 mixtures). Temperature dependent emission spectral measurements indicate that the emission intensity, quantum yield and lifetime increase upon dropping down the temperature, thereby designated as the on-state, while the increase of temperature causes a reduction of the said properties, indicating the off-state and the process is fully reversible. Taking advantage of the active methylene group coupled with a phosphonium motif, anion sensing characteristics of the complexes are investigated systematically in DMSO through the use of various optical channels and spectroscopic tools. The complexes are very much sensitive to fluoride and to a lesser extent acetate and dihydrogen phosphate among the studied anions. In essence, the complexes function as sensors for temperature and fluoride ion. Computational investigations were also executed via density functional theory (DFT) and time-dependent (TD)-DFT to obtain a clear understanding of the electronic structures of the metalloreceptors, appropriate assignment of the spectral bands and their mode of interaction with selected anions.

High-selectivity turn-on fluorescence-based fluoride ion detection using histidine-functionalized UiO-66-NH2.

Hisditine-functionalized UiO-66-NH2 (UiO-66-NH2@Hst) as a novel "turn-on" fluorescent probe to detect fluoride ions has been successfully synthesized using the solvothermal method. The results showed that fluoride ion detection gave the best fluorescence response in water media and no response was observed in non-polar solvents. Detection at pH 3-10 produces a relatively similar fluorescence response and decreases quite significantly at pH 11-13. UiO-66-NH2@Hst is very selective and stable towards fluoride ions as evidenced by the appearance of blue luminescence under UV light (λ 365 nm) compared to other ions. A possible mechanism for detecting fluoride ions is through the formation of hydrogen bonds, which results in incremental electron transfer from organic ligands to Zr-oxo clusters. The LoD value obtained in this study was 0.013 ppm, which is smaller than the maximum concentration of fluoride ions in drinking water samples (1.5 ppm) set by the World Health Organization (WHO). Therefore, UiO-66-NH2@Hst can be a candidate fluorescence-based sensor for fluoride ions.

Detection of fluoride ions using carbon quantum dots derived from coal washery rejects via an on–off–on fluorescence mechanism: a smartphone-based image-processing and machine learning approach

An on–off–on fluorescence process-based fluoride ion sensor is developed by using highly fluorescent carbon quantum dots (CQDs) derived from coal washery rejects/waste coal (CWRs) and demonstrated through smartphone.

Hydrogen-bonding receptor substituted BODIPYs as selective ON-OFF fluorimetric sensors for fluoride ions in polar aprotic organic solvents – A molecular-level understanding based on experimental and theoretical studies

We report the facile synthesis of three meso-substituted BODIPYs which can act as fluorimetric chemosensors for detecting fluoride ions in polar aprotic organic solvents with a micromolar detection limit. The substituents at the meso-positions of synthesized BODIPYs are acetamidophenyl (B1), trihydroxyphenyl (B2), and hydroxyquinoline (B3) which show strong absorption (490–510 nm) and emission (515–550 nm) in the visible region. The spectral and quantum mechanical studies indicate that the fluoride ions can interact with the acidic proton of the BODIPYs viz., NH in B1 and OH in B2 and B3 respectively, and results in 1:1 BODIPY-fluoride [BODIPY----HF] adduct. The acidic protons of these BODIPYs are abstracted by fluoride ions resulting in non-fluorescent deprotonated species (turn-OFF state). The time-dependent density functional theory (TDDFT) calculations indicate that the deprotonated adduct is responsible for the fluorescence turn-OFF via the photoinduced electron transfer (PET) mechanism. These non-fluorescent deprotonated adducts can return to the fluorescent BODIPY state by abstracting H+ ions from any protic solvents. Hence, these molecules can act as ON-OFF-ON reversible sensors. The deprotonated adducts show significantly different UV–visible responses for B1, B2 and B3. The binding constant of fluoride ions with BODIPYs (Kb) is calculated to be in the range of 105 –106 M−1 with a limit of detection (LOD) in the range of 0.73–9 ppm. The ON-OFF-ON sensing behaviour of B1 is utilized to construct NOR molecular logic gate based on the two inputs of F- and OH– ions, and the emission intensity at 520 nm as the output. Among these BODIPYs, B2 has the lowest LOD for fluoride ions and shows distinct color change upon deprotonation in the visible region. This property has been utilized to develop portable test-paper strips for the qualitative colorimetric detection of fluoride ions.

Laser‐Patterned Carbon‐Supported Graphitic Carbon Nitride Quantum Dots for Flexible Nanozyme‐Based Fluoride Sensor

AbstractGraphitic carbon nitride quantum dots (g‐CNQDs)‐based colorimetric sensors are typically solution‐based and hence incompatible with wearable electronics. Today's competitive technology demands safe and reliable, high‐performance sensors suitable for integration with sophisticated electronics—all at a low cost. Herein, a flexible and reusable solid‐state fluoride ion sensor manufactured by combining the intriguing surface properties of laser‐patterned carbon (LP‐C) with the sensitivity of g‐CNQDs is reported. LP‐C is obtained by direct IR‐laser writing onto polyimide films, and g‐CNQDs are synthesized via a solvent‐free and zero‐waste green process. The hybrid of LP‐C and g‐CNQDs (g‐CNQDs/LP‐C), mimics the natural enzyme horseradish peroxidase and oxidizes the chromogenic substrate 3,3’,5,5’‐tetramethylbenzidine in the presence of H2O2 in acidic media. The highly selective and user‐friendly nanozyme sensors feature a lower limit of detection of 0.568 ± 0.006 × 10−6 m (23.8 ± 1.5 µg L−1) with linearity in the range of 0.5 × 10−6 to 100 × 10−6 m. A sensing mechanism based on the electronic transitions of g‐CNQDs and LP‐C, the two variants of nitrogen‐containing carbon used in this work, is established. Finally, the device is tested for fluoride ion sensing in natural water samples collected from the Uhl river in Mandi, India.

Fluoride ion sensor based on LaF<sub>3</sub> nanocrystals prepared by low-temperature process

This study addresses the advantages of using a lanthanum fluoride (LaF3) nanocrystals-based fluoride ion sensor. We propose a method that enables the preparation of fluoride ion-selective LaF3 nanocrystals at low temperatures (less than 80 °C) in contrast to the conventional method, wherein high temperatures (1000 °C and above) are required for preparing a single-crystal LaF3. An LaF3 nanocrystal with a diameter below 5 nm in the (001) plane was synthesized and subsequently deposited on a Ti electrode. The sensor exhibited a selective response to fluoride ions. This process does not require high-temperature and vacuum equipment and conditions, thus enabling easy production of fluoride ion sensors.

Fluorenone Appended Colorimetric Sensor for Cascade Detection of Fluoride and Calcium Gluconate with Applications in Solid State and Logic Gate Systems

AbstractA novel fluorenone derived Schiff base chemosensor (1) has been synthesized as a colorimetric sensor for fluoride (F−) ions in CH3CN and characterized by various analytical techniques. The chemosensor 1 perceived high selectivity for F− ion detection in the presence of other anions along with naked eye color change from yellow to orange‐red with quantitative detection limit of 900 nM. The UV‐vis changes, density functional theoretical (DFT) calculations and 1H NMR titration studies pointed to F− ion induced deprotonation of −OH of sensor 1 that has been proposed to be responsible for the observed absorption as well as color changes. The sensor 1 has also been efficiently applied for the solid state concentration dependent naked eye detection of F− ions in the form of filter paper strips and smartphone applications. The in‐situ generated 1‐F− complex was further utilized for cascade recognition of calcium gluconate (CG). The reversible and reproducible changes produced by the addition of F− ions and CG enabled 1 to be used as “INHIBIT” molecular logic system and “SET/RESET” memorized device at the molecular level.

Structural elucidation of N-amidothiourea derived from nicotinic acid hydrazide: A detailed study of its application as selective anion sensor

A novelN-amidothiourea receptor (1), synthesized by the reaction of nicotinic acid hydrazide with phenyl isothiocyanate, was evaluated for the detection of fluoride, acetate, and hydroxide ions selectively over other anions. Receptor1was characterized by various spectroscopic methods, and further structural elucidation of it was done by Single Crystal X-ray diffraction analysis. The efficacy of receptor1as a colorimetric sensor for fluoride ions was observed by an instant colour change from colourless to light yellow, which can be attributed to the H-bonding complex formation between receptor1and anion. The binding characteristics of the thiourea receptor with fluoride ion (F−) showed 1:1 binding stoichiometry at a lower concentration, whereas at a higher concentration, the binding stoichiometry increased to 1:2. The receptor, when treated with acetate and hydroxide ion, showed 1:2 and 1:1 binding stoichiometry, respectively. The binding affinity of receptor1was found to be following the Brønsted acidity order, i.e., OH− > AcO− > F−. Detailed quantum chemical calculations also supported the experimental findings.

Fluoride ions detection in aqueous media by unprecedented ring opening of fluorescein dye: A novel multimodal sensor for fluoride ions and its utilization in live cell imaging

Imidazole functionalized on fluorescein dye was developed as an efficient probe for naked eye and fluorescence determination of fluoride ions. The probe is dramatic color change and very exciting fluorescence turn-on response with the addition fluoride ions. Moreover, fluoride ions triggering leads to the fissure of the spirolactam ring that causes drastic color makes feasible for the naked eye detection of fluoride ions. The mode of binding of fluoride with the probe was proved by 1H NMR titration experiments and the observed photophysical changes were rationalized by use of DFT calculations. This sensor was more applied to detect fluoride ions in real samples and imaging of fluoride ions through fluorescence imaging in living cells.

In situ ligand modulated highly luminescent and stable perovskite quantum dots for fluoride detection

This work presents a new strategy to improve the optical performance of perovskite quantum dots (QDs) and an excellent fluoride ion sensor. Using amino acids like L-alanine or D-alanine ((L/D)Ala) as surface ligands, a series of novel perovskites have been prepared for extremely sensitive and reliable detection of the fluoride ions (F-). Because the (L/D)Ala ligands effectively hinder the non-radiative transitions, the luminescence quantum yield of MAPbBr3 (CH3NH2 =MA) QDs is increased by 89.05%. The high energy of the bond N-H…F for (L/D)Ala QDs makes high selectivity and sensitivity for F-. The sensing capabilities of (L/D)Ala QDs have a linear dynamic range of 0–160 μM and a low detection limit of 3.8 μM with excellent sensitivity and selectivity.

Synthesis and characterization of Schiff’s base-based chemosensor and its detection potential of Fluoride ions

The development of selective and sensitive chemical sensors to overcome fluoride ions is needed, especially for applications in chemical and biological processes. One of the chemical compounds that can act as sensors is the Schiff base compound group. This study aims to synthesis a Schiff base based on salicylaldehyde and as a fluoride ion sensor. The one-pot synthesis approach was carried out in room terms by mixing salicylaldehyde with hydrazine hydrate or phenylenediamine with a molar ratio of 2: 1 in ethanol solvent under stirring for 24 hours. The bright yellow crystal was obtained with a yield of 80% for salicylaldazine (SB). The compounds in the dimethyl sulfoxide (DMSO) solvent tend to be colorless, but in the presence of F-ions, the solution turns orange. The results indicate an interaction between SB1 with F-ions in solution.

Fluoride ion promoted NH deprotonation of dioxaPhlorin with NIR absorption vs. acid induced facile conversion to aromatic dioxaSapphyrin: Synthesis, spectroscopic and theoretical characterization

Synthesis, spectroscopic and solid state structural proof of hitherto unknown highly stable meso-pyrrole appended expanded dioxaphlorin is reported. The macrocycle was susceptible to NH deprotonation upon TBAF titration leading to NIR absorption with vivid colour change to the naked eye paving the way towards the application as a fluoride ion sensor. Contrarily, efficient conversion to aromatic dioxasapphyrin has been anticipated upon trifluoroacetic acid reaction owing to facile elimination of meso-appended pyrrole ring. The conformational preorganzation and anion induced conformational reorganization owing to the base promoted NH deprotonation are thoroughly investigated by various spectroscopic techniques and DFT level theoretical calculations.

Fluorescent Sensor for Fluoride Ions Based on Perylene Diimide Tethered with Siloxane Moieties

Fluorescent Sensor for Fluoride Ions Based on Perylene Diimide Tethered with Siloxane Moieties

A nanofibrous membrane fluorescent sensor for fluoride ions prepared by electrospinning and host-guest interaction

A novel inclusion complexes nanofibrous membrane fluorescent sensor was prepared for recognizing F- via electrospinning and host–guest interaction. The host α-cyclodextrin on the surface of the electrospun nanofiber membrane is assembled into the guest azobenzene molecule which modified with F- fluorescent probe, and the formation of the inclusion complex is fixed on the surface of the nanofibrous membrane without external force, to prepare a novel surface controllable composite nanofiber membrane for F- detection. The inclusion complexes nanofibrous membrane exhibited favourable sensitivity and selectivity for F-. The introduction of F- would result in notable fluorescent decreasing of the membrane, but the other most common anions would not disturb the detection of F-. Moreover, this nanofibrous membrane was not only a fluorescent sensor for detecting F-, but also a good adsorbent for F- in solution.

A novel colorimetric and ratiometric fluoride ion sensor derived from gallic acid

We report a novel colorimetric and ratiometric fluoride ion sensor derived from gallic acid.

Multi-resonance organoboron-based fluorescent probe for ultra-sensitive, selective and reversible detection of fluoride ions

This multiple resonance organoboron-based fluoride ion sensor exhibited a record low detection limit together with good selectivity and reversibility.

Colorimetric ‘naked eye’ sensor for fluoride ion based on isatin hydrazones via hydrogen bond formation: Design, synthesis and characterization ascertained by Nuclear Magnetic Resonance, Ultraviolet–Visible, Computational and Electrochemical studies

A new colorimetric sensor ‘R-IND’ based on isatin hydrazones have been designed and synthesized by simple Schiff base reaction. The anion sensing properties of R-IND were examined, characterized by common spectroscopic techniques such as Fourier Transform-Infrared (FT-IR), Ultraviolet–Visible (UV–Visible), Proton and Carbon Nuclear Magnetic Resonance (1H &13C NMR), Electrospray Ionization Mass Spectroscopy (ESI-MS) and electrochemical studies. The sensor R-IND bearing ortho hydroxy group and amine group acting as binding sites. The sensor R-IND exhibited sensitive and selective sensing towards F− ion over the other competitive anions like Cl−, I−, Br−, H2PO4−, AcO−, CN–, NO3–, ClO4− and HSO4− in 100% Aetonitrile and 20% aqua Acetonitrile media. The bathochromic shift of 222 nm and 228 nm was observed in UV–Vis spectra with a color change from pale yellow to purple which is due to the complex formation between R-IND and F− ion through hydrogen bond formation. This was further accounted by 1H NMR titration. The Job’s plot reveals 1:2 stoichiometry between the host-guest complex. Binding and association constants were found to be 1.72 × 109 M−1, 2.82 × 109 M−1 and 6.0 × 105 M−1, 2.0 × 106 M−1 in 100% ACN and 20% aqua ACN respectively. The detection limit of sensor R-IND was turned out to be 0.45 and 0.41 ppm for F− ion in organic and aqua organic medium which is lesser than World Health Organization (WHO) permission level (1 ppm). The characteristic potential difference of 1.069 V has been observed for R-IND+F− complex in the electrochemical study. Finally, economically viable paper-based colorimetric test strips of R-IND were developed to detect the F− ions in 100% aqueous solution.