"Turn-on" benzophenone based fluorescence and colorimetric sensor for the selective detection of Fe2+ in aqueous media: Validation of sensing mechanism by spectroscopic and computational studies

Rhodamine-based Fluorescent Probe With Quick Response and High Selectivity for Imaging Labile Ferrous Iron in Living Cells and Zebrafish

The transition between its various oxidation states of Iron plays a crucial part in various chemical transformation of cells. Misregulation of iron can give rise to the iron-catalyzed reactive oxygen species disorder which have been linked to a variety of diseases, so it is crucial to monitor the labile iron pool in vivo for clinical diagnosis. According to iron autoxidation and hydrogen abstraction reaction, we reported a novel "off-on" fluorescent probe to response to ferrous (Fe2+) both in solutions and biological systems. The probe responds to Fe2+ with good selectivity toward competing metal ions. What's more, the probe presents significant fluorescent enhancement to Fe2+ in less than 1 min, making real-time sensing in biological system possible. The applications of the probe in bioimaging revealed the changes in labile iron pool by iron autoxidation or diverse stimuli.

Synthesis and structural elucidation of a unique turn-off fluorescent sensor based on oxo-bridged tin (IV) cluster for selective detection of dopamine in biological fluids

An oxo-bridged Sn (IV) Cluster, (TOC) was synthesized and fully characterized by FT-IR, UV-vis, 1H NMR, 119Sn NMR, Mass spectrometry and single crystal X-ray diffraction studies. The single-crystal X-ray analysis revealed that the crystal crystallizes in the monoclinic crystal system possessing the P 21/c space group and exhibited a distorted trigonal bipyramidal geometry. The TOC exhibited a unique turn-off fluorescence response for the selective detection of dopamine (DA) over other analytes. The stoichiometry between the TOC and DA was calculated using Job's plot. The value of the detection limit was found to be 1.33 µM. The Hirshfeld surface analysis was carried out on the crystal structure to investigate the H-H, Cl-H, Cl-Cl, Sn-Cl and Cl-C interaction studies in the molecule. Density Functional Theory (DFT) studies further supported the sensing mechanism, which closely agreed with the experimental results. Furthermore, the TOC chemosensor was used to detect DA in human blood plasma, and molecular docking studies validated the interaction between the chemosensor and protein. Confocal fluorescence imaging studies were carried out and validated TOC sensing ability for DA in human blood plasma.

Synthesis, Crystal Structure and Fluorimetric Study of 2-phenylphthalazin-1(2H)-one: a Highly Selective Florescent Chemosensor for Detection of Fe3+ and Fe2+ Metal Ions

A ligand, 2-phenylphthalazin-1(2H)-one (K), was synthesized by refluxing 2-formylbenzoic acid with phenyl hydrazine in presence of ethanol. FTIR, elemental analysis and single crystal XRD techniques were used to elucidate the structure. Fluorimetric turn-off response was recorded when solution of ligand (K) in DMF was treated with aqueous solution of Fe3+ and Fe2+ metal ions. No specific changes were observed on addition of other metal ions (Pb2+, Cd2+, Mn2+, Zn2+, Ba2+, Ni2+, Al3+, Ag1+, Co2+, Ca2+, Cu2+, Mg2+, Cr3+). Limit of Detection (LOD) was calculated for Fe2 and Fe3+as 2.4 µM and 2.5µM respectively, which is quite below to the recommended value 5.4 µM of the Environment Protection Agency of USA. Association constants for Fe3+ and Fe2+ metal ions were determined as 6 × 10-4 M-1 and 3.6 × 10-4 M-1 respectively. Benesi-Hildebrand plot confirmed 1:1 binding ratio between metal ions and ligand.

Strategies for Improving Selectivity and Sensitivity of Schiff Base Fluorescent Chemosensors for Toxic and Heavy Metals

Toxic cations, including heavy metals, pose significant environmental and health risks, necessitating the development of reliable detection methods. This review investigates the techniques and approaches used to strengthen the sensitivity and selectivity of Schiff base fluorescent chemosensors designed specifically to detect toxic and heavy metal cations. The paper explores a range of strategies, including functional group variations, structural modifications, and the integration of nanomaterials or auxiliary receptors, to amplify the efficiency of these chemosensors. By improving selectivity towards targeted cations and achieving heightened sensitivity and detection limits, consequently, these strategies contribute to the advancement of accurate and efficient detection methods while increasing the range of end-use applications. The findings discussed in this review offer valuable insights into the potential of leveraging Schiff base fluorescent chemosensors for the accurate and reliable detection and monitoring of heavy metal cations in various fields, including environmental monitoring, biomedical research, and industrial safety.

Iminobenzophenone-thiophen hydrazide schiff base: a selective turn on sensor for paramagnetic Fe3+ ion and application in real sample analysis

A highly selective turn-on sensor for paramagnetic Fe³⁺ ions based on (E)-N'-((2-aminophenyl)(phenyl)methylene)thiophene-2-carbohydrazide is successfully synthesized. The sensor BPTH is significantly selective and sensitive towards Fe³⁺ ions over other interfering metal ions especially Cu²⁺ and Co²⁺ ions with a lowest limit of recognition 1.48 × 10^-7 M. The turn-on sensing mechanism involves enhanced charge transfer. Fe³⁺ ion forms strong binding with the ligand with a K_a value about 8.23 × 10⁴ M^-1 and a 1:1 stoichiometric ratio is confirmed by Job's plot experiment. With Fe³⁺ ion, the yellow ligand BPTH change to a green fluorescent and reversible with 1 equivalent of EDTA. Practical application of sensor is demonstrated in real sample analysis.

Highly efficient iodine capture and ultrafast fluorescent detection of heavy metals using PANI/LDH@CNT nanocomposite

Here, the hybrid material of polyaniline/layered double hydroxide@carbonnanotubes (PANI/LDH@CNT) is considered a multifunctional material. Instrumental methods, including FTIR, XRD, TEM, SEM, and TGA/DTA were utilized to characterize PANI/LDH@CNT. The polymerization method created PANI/LDH@CNT as an adsorbent to remove toxic iodine in hexane solution with a capture capacity of 303.20 mg g^-1 during 9 h. It is 900 mg g^-1 in the vapor phase within 24 h. After three cycles, the PANI/LDH@CNT could be regenerated while maintaining 91.90 % iodine adsorption efficiency. Due to the presence of free amine (-N) groups, OH^-, CO₂H, and π-π conjugated structures in the PANI/LDH@CNT, it is also explored for efficient iodine uptake. It was demonstrated that the pseudo-first-order (PFO) and Langmuir model had the optimum correlation with the kinetic and isotherm data, respectively. Moreover, the use of PANI/LDH@CNT is not only limited to iodine capture; it can also be utilized as a sensitive sensor that displays a fluorescence "turn-off" response for Mn⁷⁺ and Cr⁶⁺ ions and a fluorescence "turn-on" response in the case of Al³⁺ ions. The fluorescence intensity of the PANI/LDH@CNT was turned off in the presence of Mn⁷⁺ and Cr⁶⁺ because of the fluorescence inner filter effect (IFE) mechanism. In contrast, the fluorescence intensity was turned on in the case of Al³⁺, relying on the chelation-enhanced fluorescence (CHEF) effect mechanism. Under optimal conditions, the limit of detection (LOD) of 51, 59, and 81 nM for Mn⁷⁺, Cr^6+, and Al³⁺, respectively. According to the literature, this is probably the first example based on PANI/LDH@CNT as a multifunctional hybrid material employed as an adsorbent for capturing radioactive iodine and as a chemosensor for detecting heavy metal ions in aqueous solutions.

Selective turn-on fluorescence sensing of Fe2+ in real water samples by chalcones

The design of fluorescence sensor for selective detection of Fe²⁺ is very important as it is part of different biochemical redox system related to a number of diseases. In many occasion sensors are unable to distinguish Fe²⁺ from Fe³⁺ ions. In the present work, we report simple chalcone type sensors for sensing Fe²⁺ ions in semi aqueous system. The receptors R1 and R2 have showed excellent sensing properties at pH 7 in CH₃OH-H₂O (1:1, v/v) solvent system. The fluorescence emission intensity of the complexes between hosts and Fe²⁺ is least affected by the other competitive metal ions leading to the formation of very tight host-guest complex. The LOD for the R1 and R2 for Fe²⁺ are 1.91 μM and 3.54 μM respectively, which is quite low in compared to the many other reported sensors. The practical applicability of these sensors is determined by the detection of Fe²⁺ in real water samples. So chalcones would be cost effective PET inhibited fluorescence sensor for Fe²⁺.

Synthesis and bioimaging of a BODIPY-based fluorescence quenching probe for Fe3

Iron is the main substance for maintaining life. Real-time determination of ferric ion (Fe³⁺) in living cells is of great significance for understanding the relationship of Fe³⁺ concentration changes with various physiological and pathological processes. Fluorescent probes are suitable for the detection of trace metal ions in cells due to their low toxicity and high sensitivity. In this work, a boron-dipyrromethene-based fluorescent probe (BODIPY-CL) for selective detection of Fe³⁺ was synthesized. The fluorescence emission of BODIPY-CL was determined at 516 nm. In a pH range of 1 to 10, the probe BODIPY-CL exhibits a quenching response to Fe³⁺. Meanwhile, BODIPY-CL showed a highly selective response to Fe³⁺ compared with 16 kinds of metal ions. The stoichiometry ratio of BODIPY-CL bound to Fe³⁺ was nearly 2 : 1. The fluorescence quenching response obtained by the sensor was linear with the Fe³⁺ concentration in the range of 0-400 μM, and the detection limit was 2.9 μM. BODIPY-CL was successfully applied to image Fe³⁺ in cells. This study provides a promising fluorescent imaging probe for further research on the physiological and pathological effects of Fe³⁺.

Facile liquid colorimetric sensor using high-density deep eutectic solvent for trace detection and speciation of iron in milk

An efficient colorimetric sensor was developed using a high-density deep eutectic solvent (HD-DES) for the trace detection and speciation of iron in various milk samples. A liquid colorimetric probe was fabricated by dissolving ferrozine (FZ) in HD-DES prepared from TBABr and PBA. The prederivatization of Fe²⁺ via complexation with FZ on the HD-DES/FZ probe provided the [Fe(FZ)₃]^4- complex, which led to a color change from pale yellow to purple before it was simultaneously extracted by HD-DES. The Fe³⁺ content was calculated by subtracting the amount of Fe²⁺ from the total Fe content following the reduction of Fe³⁺ to Fe²⁺ by L-ascorbic acid in an acid buffer. Under the optimized conditions, the proposed colorimetric sensor exhibited appreciable linearity in the concentration range of 0.003-0.04 mg L^-1, a low limit of detection (0.95 µg L^-1), high enrichment factor (50), and outstanding repeatability. The liquid colorimetric probe was successfully applied for the determination and speciation of iron in milk samples, and the results were compared with those obtained using the standard atomic absorption spectrometry method. Moreover, quantitative analysis was performed on a smartphone using the Image J application to estimate the color intensity change, which eliminated the requirement of sophisticated scientific instruments.

Chromone functionalized pyridine chemosensor for cupric ions detection

A new Schiff base 2-ethoxy-3-{[(6-{[(2-ethoxy-4-hydroxy-2H-chromen-3-yl)methylidene]amino}pyridine-2-yl)imino]methyl}-2H-chromen-4-ol (CD) was synthesized as a result of the condensation of 2,6-diaminopyridine and 3-formyl chromone in 1:2 M ratio and used for cupric ions detection and characterized through FTIR, HRMS and ¹H NMR spectral techniques. The sensing capability of Schiff base for cupric ions as compared to other transition metal ions was examined by absorbance and emission studies. A considerable decrease in emission intensity appeared in Schiff base in the case of cupric ions while irrelevant changes were examined for the rest of the ions. The binding stoichiometry was obtained as 1:2 for CD: Cu²⁺ complex intended from the job's plot which was confirmed through HRMS spectral technique. DFT calculations were carried for the confirmation of structural relationships and absorption-emission data. The Regression coefficient, Limit of detection, and Association constant were obtained as 98.7%, 1.2 × 10^-6 M, and 3.26 × 10⁴ M^-1 respectively using Benesi-Hildebrand (B-H) equation. The sensing power of Schiff base CD to recognize cupric ions was unaltered by the addition of the rest of metal ions, which was authenticated through interference studies. Schiff base CD and its complex with cupric ions were found stable over an extensive time period as revealed by time-reliant studies. The data collected by pH studies revealed that the preferred pH range for detecting cupric ions by Schiff base CD was 6 to 11. The Schiff base was finally utilized for sensing cupric ions in a variety of spiked samples of water like canal water, tap water, groundwater, distilled water.

Ni (II) detection by 2-amino-5-substituted-1,3,4-oxadiazole as a chemosensor using photo-physical method: Antifungal, antioxidant, DNA binding, and molecular docking studies

An oxadiazole derivative 2 was prepared by condensation reaction through cyclization of semicarbazone in the presence of bromine and the structural confirmation was supported by ¹ H and ¹³ C NMR, FT-IR spectroscopy, and LC-MS spectrometry. Its sensing ability was examined towards Ni²⁺ ion with binding constant 1.04 x 10⁵ over the other suitable metal cations (Ca²⁺ , Co²⁺ , Cr³⁺ , Ag⁺ , Pb²⁺ , Fe³⁺ , Mg²⁺ , and K⁺ ) by UV-visible and fluorescence spectroscopic studies and the minimum concentration of Ni²⁺ ion with LOD was found to be 9.4μM. Job's plot method gives the binding stoichiometry ratio of Ni²⁺ ion vs oxadiazole derivative 2 to be 2:1. Furthermore, the intercalative binding mode of oxadiazole derivative 2 with Calf Thymus DNA was supported by UV-Vis, fluorescence, viscosity, cyclic voltammetry, time-resolved fluorescence, and circular dichroism measurements. The molecular docking result gives the binding score for oxadiazole derivative 2 to be -6.5 kcal/mol, which further confirms the intercalative interaction. In addition, the anti-fungal activity of oxadiazole derivative 2 was also screened against fungal strains (C. albicans, C. glabrata, and C. tropicalis) by broth dilution and disc diffusion method. In the antioxidant studies, the oxadiazole derivative 2 showed potential scavenging activity against DPPH and H₂ O₂ free radicals.

A New Spiropyran-Based Fluorescent Probe for Dual Sensing of Ferrous Ion and pH

A new spiropyran-based fluorescent probe was developed for dual detection of Fe²⁺ ion and pH. Addition of Fe²⁺ and Ag⁺ to the probe solution enhanced the fluorescence intensity by 6 and 5 fold, respectively. Addition of Fe³⁺, Hg²⁺ and Ni²⁺ caused slight increase in the fluorescence intensity of the probe. While addition of other common metal ions did not bring about substantial change of the fluorescence. Thus the probe can be used for fluorescence turn-on detection of Fe²⁺ ion in ethanol/water (9:1) medium. The detection limit of the probe for Fe²⁺ is 0.77 µM. The suitable pH range for the probe to detect Fe²⁺ was pH 3 - 9. Other metal ions including Li⁺, Na⁺, K⁺, Ag⁺, Cu²⁺, Zn²⁺, Co²⁺, Ni²⁺, Mn²⁺, Sr²⁺, Hg²⁺, Ca²⁺, Mg²⁺, Al³⁺, Cr³⁺, and Fe³⁺ did not cause marked interference with Fe²⁺ recognition. The color of the probe solution was yellow at pH 1 - 2 and colorless at other pH values. The fluorescence intensity of the probe was low at pH 1 - 12 and increased significantly when the pH was 13 and 14, indicating that the probe can be used as a colorimetric and fluorescent probe for sensing extremely acidic or extremely alkaline conditions through different channels.

Lanthanide-based bis-(3,5-dicarboxy-phenyl)terephthalamide metal–organic frameworks: slow relaxation of magnetization and detection of trace Fe2+ and Fe3+

{[Dy₂(BDPT)_1.5(DMF)₄]·H₂O}_n (1) and [Sm₂(BDPT)_1.5(DMF)₄]_n (2) were prepared with highly sensitive fluorescent detection of trace Fe²⁺ and Fe³⁺. 1 exhibits weak antiferromagnetic interactions with signature of SMM behavior.