Turn-on Fluorescent Chemosensor Research Articles

Thiourea Functionalised Receptor for Selective Detection of Mercury Ions and its Application in Serum Sample.

A thiourea functionalised fluorescent probe 1-phenyl-3-(pyridin-4-yl)thiourea was synthesized and utilised as a fluorescent turn-on chemosensor for the selective recognition of Hg2+ ion over competitive metal ions including Na+, Mn2+, Li+, Cr2+, Ni2+, Ca2+, Cd2+, Mg2+, K+, Co2+, Cu2+, Zn2+, Al3+ and Fe2+ ions based on the inter-molecular charge transfer (ICT). Intriguingly, the receptor demonstrated unique sensing capabilities for Hg2+ in DMSO: H2O (10:90, v/v). The addition of Hg2+ ions to the sensor resulted in a blue shift in the absorption intensity and also enhancement in fluorescence intensity at 435nm. Fluorescence emission intensity increased linearly with Hg2+ concentration ranging from 0 to 80 µL. The detection limit and binding constant were determined as 0.134 × 10-6M and 1.733 × 107M-1, respectively. The sensing behavior of Hg2+ was further examined using DLS, SEM and FTIR. The probe could detect Hg2+ ions across a wide pH range. Furthermore, the receptor L demonstrated good sensing performance for Hg2+ in bovine serum albumin and actual water samples.

A novel chromone Schiff base as Zn2+ turn-on fluorescent chemosensor in a mixed solution.

In this study, a novel fluorescent chemosensor 1 based on chromone-3-carboxaldehyde Schiff base was synthesized and featured through nuclear magnetic resonance (NMR) and mass spectra. Spectroscopic investigation indicated that the fluorescent sensor showed high selectivity toward Zn2+ over other metal ions and that the detection limit of 1 could reach 10-7 M. These indicated that 1 acted as a highly selective and sensitive fluorescence chemosensor for Zn2+ .

A Sensitive Probe of Meso-Cyanophenyl Substituted BODIPY Derivative as Fluorescent Chemosensor for the Detection of Multiple Heavy Metal Ions.

A fluorescent turn-on chemosensor (BA) was constructed by attaching bis(pyridin-2-ylmethyl)-amine (DPA) unit to the BODIPY scaffold. It can give a prominent green/yellow fluorescent response selectivity with each of Zn2+/Hg2+/Cd2+/Ca2+/Mn2+/Pb2+/Al3+. The 1:1 stoichiometry of BA and metal ions was drawn from the analysis of Job's plot. The limit detection of BA in recognition of Zn2+/Hg2+/Cd2+/Ca2+/Mn2+/Pb2+/Al3+ is ranged in 50.8-146.6 nM. There exists a linear relationship between the fluorescence intensity and concentration of metal ions (Zn2+: 4-15 µM). The mechanism of fluorescence signal "turn-on" is based on the photo induced transfer (PET) in the excited state of BA. The coordinated metal ions significantly weakened the electron-donating ability nitrogen atom in DPA, thus recovering the emission character of BODIPY. The substituted group at the phenyl ring in meso-position of BODIPY scaffold determines the recognizable list of metal ions.

New type of tin(IV) complex based turn-on fluorescent chemosensor for fluoride ion recognition: elucidating the effect of molecular structure on sensing property.

A novel type of chemosensor based on tin(IV) complexes incorporating hydroxyquinoline derivatives has been designed and investigated for selectively detecting fluoride ions. Sn(meq)2Cl2 (meq = 2-methyl-8-quinolinol) (complex 1) exhibits a significant enhancement in luminescence upon the introduction of fluoride ions. This enhancement greatly surpasses that observed with Snq2Cl2 and Sn(dmqo)2Cl2 (q = 8-hydroxyquinnoline; dmqo = 5,7-dimethyl-8-quinolinol). Furthermore, complex 1 displays excellent sensitivity and selectivity for fluoride detection in comparison to halides and other anions. As a result, complex 1 serves as an outstanding turn-on fluorescent chemosensor, effectively sensing fluoride ions. The Benesi-Hilderbrand method and Job's plot confirmed that complex 1 associates with F- in a 1 : 2 binding stoichiometry. Also, complex 1 exhibited a large binding constant (pKb = 10.4 M-2) and a low detection limit (100 nM). To gain a deeper insight into the photophysical properties and the underlying mechanism governing the formation of the tin(IV) fluoride complex via halide exchange, we successfully synthesized partially fluorinated Sn(meq)2F0.67Cl1.33 (2) and fully fluorinated Sn(meq)2F2 (3), all of which were characterized through computational studies, thereby elucidating their photophysical properties. DFT studies reveal that converting Sn(meq)2Cl2 to Sn(meq)2F2, an endergonic process, leads to greater stability due to reducing steric hindrance about the metal center. Furthermore, the fluorinated complex significantly increases dipole moment, resulting in high affinity toward the F- ion.

Simple turn-on fluorescent chemosensor for ultrafast and highly selective trace-level detection of Cu2+ ions in aqueous solutions

A benzimidazole-based probe, BIPMA (2-(1H-benzo[d]imidazol-2-yl)-N-(pyridin-2-ylmethyl)aniline), was designed and synthesized to detect Cu2+ ions. BIPMA exhibited a fluorescent “turn-on” mechanism when bound to Cu2+ ions in an acetonitrile/water mixture (5:5, v/v, HEPES 10 mM, pH 7.4) owing to the synergistic effect of the chelation-enhanced fluorescence and internal charge-transfer mechanisms. Moreover, the BIPMA probe effectively detected nanomolar-range concentrations (0–400 nM) of Cu2+ ions in an aqueous system with a detection limit of 4.80 nM; this value is significantly lower than that set by the U.S. Environmental Protection Agency (≈20 μM). Additionally, BIPMA showed an ultrafast response to Cu2+ ions, with a maximum intensity achieved 25 s after adding Cu2+. Furthermore, BIPMA detected Cu2+ ions in solutions with a pH range of 5–11, without being influenced by pH, underscoring its applicability under various physiological conditions. Density functional theory studies revealed that internal charge transfer was responsible for emission. Finally, BIPMA effectively detected Cu2+ ions in real water samples and living cells.

A turn-on fluorescence sensor based on water-soluble amino-pyridyl-benzothiazole-derivatives for measuring cellular Zn2+

Novel amino-pyridyl-benzothiazole-derivatives (PBT) were synthesized through cycloaddition/nucleophilic aromatic substitution reactions for the development of a turn-on fluorescence chemosensor that accurately determines Zn2+ in polar media. The selectivity, water-solubility, and overall analytical response were systematically optimized through incorporation of different aliphatic amines as substituents: pyrrolidine (PBT-Pyn), ethylenediamine (PBT-Et) or 1,3-propylenediamine (PBT-Pr). Those ligands presented intense dual radiative emissions in the blue/green region upon activation with a 395 nm LED, which were attributed to the local excitation and internal energy transfer states. Although no variations were observed upon the interaction of Zn2+ with PBT-Pyn, both turn-off and turn-on responses were observed upon its interaction with PBT-Et. These responses depended on the ligand concentration and the associated inner filter effects. Thereby, PBT-Pr was selected for a deeper evaluation towards photoluminescence determination of Zn2+ due to its exclusive turn-on response and major sensibility obtained at pH 7.0, making it very convenient for analysis in physiological media. Under those conditions, the detection limits were 1.9 µM and 4.7 µM for measurements in aqueous or ethanolic solutions, respectively, with linear ranges up to 40 and 80 μM. The selectivity and good biocompatibility of the chemosensor were demonstrated through cell-viability assays with MCF-7, 3T3-L1 and HT-29 cell lines. The probe was then applied for the real-time epifluorescence imaging of Zn2+, observing emission intensities and distribution profiles that correlated with the concentration and location of the target within living cells.

Development of a Golgi-targeted fluorescent chemosensor for detecting ferrous ions overload under Golgi stress.

Ferrous ion (Fe2+) is a crucial metal ion in the body and participates in the diseases related to oxidation and reduction. Golgi apparatus is the main subcellular organelle of Fe2+ transport in cells, and the stability of its structure is related to the Fe2+ at an appropriate concentration. In this work, a turn-on type Golgi-targeting fluorescent chemosensor Gol-Cou-Fe2+ was rationally designed for sensitive and selective detection of Fe2+. Gol-Cou-Fe2+ showed excellent capacity of detecting exogenous and endogenous Fe2+ in HUVEC and HepG2 cells. It was used to capture the up-regulated Fe2+ level during the hypoxia. Moreover, the fluorescence of sensor was enhanced over time under Golgi stress combining with the reduce of Golgi matrix protein GM130. However, elimination of Fe2+ or addition of nitric oxide (NO) would restore the fluorescence intensity of Gol-Cou-Fe2+ and the expression of GM130 in HUVEC. Thus, development of chemosensor Gol-Cou-Fe2+ provides a new window for tracking Golgi Fe2+ and elucidating Golgi stress-related diseases.

A dual-functional chemosensor based on acylhydrazone derivative for rapid detection of Zn(II) and Mg(II): Spectral properties, recognition mechanism and application studies

In this work, an acylhydrazone derivative (QN62) was developed via the one-step condensation of 6-hydroxy-2-naphthoic hydrazide with quinoline-8-carboxaldehyde. The structure of the QN62 compound was characterized by 1H NMR, 13C NMR, HR-MS (ESI), and X-ray crystallography. As a dual-functional turn-on fluorescence chemosensor, QN62 exhibited rapid recognition for Zn2+ in DMSO-H2O (4:1, v/v) and Mg2+ in ethanol-H2O (9:1, v/v). The enhancement in fluorescence detection was associated with the coordination reaction between QN62 and the target ions, which promoted intramolecular charge transfer and prevented the CN isomerization process. Simultaneously, a rapid color change from colorless to yellowish-green or yellow under UV light (365 nm) was easily visible to the naked eye. Under optimal conditions, the limit of detection and limit of quantification were 32.3 nM and 97.8 nM for Zn2+ and 16.1 nM and 48.9 nM for Mg2+, respectively. The recognition mechanism was reasonably speculated based on analysis of the Job’s plot, HR-MS, 1H NMR, and density functional theoretical calculations. Utilizing silica-gel plates fabricated from the QN62 chemosensor, the visual and rapid identification of Zn2+ and Mg2+ was successfully achieved, which could provide a convenient approach for on-site detection in environmental fields. The QN62 chemosensor could also quantify trace amounts of Zn2+ and Mg2+ in water samples. Furthermore, the cell imaging experiments indicated that QN62 could effectively sense intracellular Zn2+ and Mg2+, providing potential applications in biological systems.

Turn-on fluorogenic sensors based on an anthraquinone signaling unit for the detection of Zn(II) and Cd(II) ions.

Turn-on fluorescent chemosensors based on an anthraquinone moiety, N,N'-(9,10-dioxo-9,10-dihydroanthracene-1,8-diyl)bis(2-(bis(pyridin-2-ylmethyl)amino)acetamide) (1) and N,N'-(9,10-dioxo-9,10-dihydroanthracene-2,6-diyl)bis(2-(bis(pyridin-2-ylmethyl)amino)acetamide) (2), have been successfully synthesized with the overall yields of 61% and 90%, respectively. The structures of both chemosensors 1 and 2 were elucidated using several spectroscopic techniques such as 1H NMR, 13C NMR, 2D-NMR, FTIR and HRMS. The target chemosensor 1 is a promising tool for the detection of trace levels of d10 metal ions, such as Zn(II) and Cd(II) ions, by exhibiting a significant fluorescence enhancement via a turn-on photoinduced electron transfer (PET) mechanism with a rapid and highly reproducible signal, and low detection limit values of 0.408 μM and 0.246 μM, for Zn(II) and Cd(II), respectively.

Shining light on fluoride detection: a comprehensive study exploring the potential of coumarin precursors as selective turn-on fluorescent chemosensors.

In this study, we report a fluoride chemosensor based on the use of a non-fluorescent pre-coumarin, compound 1. This compound undergoes selective fluoride-triggered formation of coumarin 2, with a concomitant turn-on fluorescence signal. Although compound 1 exists as a mixture of alkene isomers (2 : 1 in favor of the E isomer), only the minor Z-isomer undergoes cyclization. Nonetheless, comprehensive computational and experimental studies provide evidence that in situ isomerization of E-1 to Z-1, followed by fluoride-triggered phenolate evolution and intramolecular cyclization, facilitates the generation of coumarin 2 in high yield. Moreover, this system is an effective turn-on fluorescence sensor for fluoride anions, which displays outstanding selectivity (limited response to other commonly occurring analytes), sensitivity (lowest reported limits of detection for this sensor class), and practicality (works in solution and on paper to generate both fluorometric and colorimetric responses). Ongoing efforts are focused on expanding this paradigm to other pre-coumarin scaffolds, which also undergo analyte-specific coumarin formation accompanied by turn-on fluorescence.

Synthesis of a novel hydrazone-based compound applied as a fluorescence turn-on chemosensor for iron(iii) and a colorimetric sensor for copper(ii) with antimicrobial, DFT and molecular docking studies.

Hydrazone-hydrazide-based linkers perform a crucial role in environmental as well as biological fields. Such linkers are employed to detect exact metal ions at a minute level; hence, numerous probes are available. Even though thiophene-based molecules have a unique position in the medicinal arena, only very few chemosensors are reported based on such a moiety. In this current work, a novel hydrazide-hydrazone-based fluorogenic molecule 5-bromo-2-hydroxy-N'-[(1E)-1-(thiophen-2-yl)ethylidene]benzohydrazide (L) has been successfully designed and synthesized. The sensing studies of L demonstrated a ratio metric as well as turn-on-enhanced fluorescence and colorimetric response toward Fe3+ and Cu2+ ions, respectively and it was observed to be insensitive toward various metal ions. The Job plots revealed that the binding stoichiometry of L and metal ions is 2 : 1. In addition, density functional theory (DFT) results strongly suggested that L can be used as a powerful colorimetric sensor for the detection of Cu2+ ions. In vitro antimicrobial activities of L were evaluated by disk diffusion and results revealed good antibacterial activities against E. coli. Further, molecular docking was executed with DNA gyrase (PDB ID: 1KZN) of E. coli and the calculated interaction energy value was found to be -7.7 kcal mol-1. Finally, molecular docking, fluorescence, colorimetry and the HOMO-LUMO energy gap of the compound can provide new insights into developing drugs and detecting metals in biomolecules.

A thiourea-based fluorescent turn-on chemosensor for detecting Hg2+, Ag+ and Au3+ in aqueous medium

A thiourea based fluorescence chemosensor (L) was synthesized and applied for the selective detection of Hg2+, Ag+ and Au3+ions in DMSO-H2O (10:90, v/v). The receptor L showed a weak fluorescence emission in DMSO-H2O due to the photo-induced electron transfer (PET) process. The fluorescence intensity of L was enhanced upon addition of Hg2+, Ag+ and Au3+ ions because of the complexation-induced inhibition of PET process. The 1:1 binding stoichiometry between L and the metal ions (Hg2+, Ag+ and Au3+) was found from the Benesi-Hildebrand plot. The density functional theory (DFT) calculations were performed to explain the binding modes. The estimated binding constants and detection limits of L are found to be 5.87 × 106 M−1 and 5.01 × 10-7 M for Hg2+, 8.78 × 106 M−1 and 2.14 × 10-8 M for Ag+, and 7.93 × 106 M−1 and 34 × 10-7 M for Au3+, respectively. The sensor L was applied to detect Hg2+, Ag+ and Au3+ ions in living Drosophila cell lines. Also, sensor L was employed to detect Hg2+ in soil samples.

Pillar[5]arenes modified tetraphenylethylene as fluorescent chemosensor for paraquat detection

Pesticide pollution has become a severe challenge for harming food quality and human safety. Therefore, it’s urgent to develop sensitive methods to detect and analyse pesticides. Herein, we successfully developed a new turn-on fluorescent chemosensor ( TPE-4P ), a tetraphenyl ethylene derivative modified with four pillar[5]arenes, which could sensitively, selectively, and rapidly detect the pesticide paraquat. In our study, we took full advantage of both the host-guest strategy and aggregation-induced emission (AIE) to achieve fluorescent enhancement of the chemosensor for paraquat, in which four pillar[5]arenes as the recognition units can selectively capture paraquat. The formation of the supramolecular complexes based on the interlaced host-guest interactions effectively restricted the intramolecular single-bond rotation and skeletal vibration, resulting in the intensive fluorescent emission. The detection limit for paraquat was low enough to reach 154.1 nM, and the detection time was short enough to meet the rapid detection conditions. Moreover, the test strips loaded- TPE-4P facilitated the detection process and achieved the semi-quantitative analysis for paraquat in real spiked samples. In addition, TPE-4P could respond to paraquat in living zebrafish obviously. These results suggest that the cooperation of host-guest and AIE chemistry could become useful for the design to detect some appropriate organic molecules. • A turn-on chemosensor was synthesized based on TPE and pillar[5]arene. • The sensor can rapidly, selectively, and sensitively detect pesticide paraquat through host-guest and AIE chemistry. • The sensor can be used in visual determination of paraquat in real samples and zebra fish. • The fabricated test strips can quantitatively detect paraquat. • The cooperation of host-guest and AIE chemistry is useful for the design of chemosensors.

Highly selective turn-on fluorescent chemosensor for the detection of Cr (III) ion in drinking water

An effective and simple carbazole-based Schiff base (CrbPy2) chemosensor for selective recognition of Cr(III) was designed and synthesized. The molecular structure of CrbPy2 was confirmed by NMR and FT-IR spectroscopies, its crystal structure was investigated by XRD analysis and the results were in good agreement with the DFT calculations. The CrbPy2 probe showed high selectivity toward Cr3+ ions in THF/H2O (95/5%) solution. Adding Cr3+ ions to CrbPy2 dilute solution induced a naked eye color change from colorless to yellow accompanied with a fluorescence turn-on. The proposed sensing mechanism was related to chelation-enhanced fluorescence (CHEF) process. The stoichiometry ratio of CrbPy2-Cr3+ complex is 1:1 with an association constant exceeding 3 × 105 M-1. The study of the sensing properties in different pH showed that CrbPy2 can tolerate the detection of Cr3+ ions in a pH range from 6 to 8. The chelating sites of the chemosensor and the coordination geometry of the complex were determined using 1H NMR titrations and MEP calculations. The detection was completed within 2–3 min and the detection limit reaches 1.08 μM. The linear recognition range of Cr(III) is from 1.08 μM to 4 μM making CrbPy2 a suitable probe for real-time identification of unsafe Cr3+ concentration in drinking water.

A simple salicylaldehyde-bearing pyrazine as a turn-on fluorescent chemosensor for Al3+ and Zn2+ recognition and its applications

Abstract A simple fluorescent chemosensor, 5-(diethylamino)-2-((2-(pyrazin-2-yl) hydrazono)methyl)phenol, has been synthesized by Schiff-base condensation reaction. The chemosensor exhibited highly selective and sensitive “off-on” fluorescent responses toward Al3+ and Zn2+ but the signal of fluorescence emission varies. The detection limits were found to be 2.33 × 10−7 M for Al3+ and 1.68 × 10−7 M for Zn2+, respectively. The binding mechanisms between chemosensor and Al3+ or Zn2+ ions were supported by Job′s, 1H NMR, Fourier transform infrared spectra, and MS experiments. The sensing behavior was also studied with molecular logic functions of OR, AND, and NOT gates. In addition, the chemosensor was able to detect Al3+ and Zn2+ by producing distinct color changes observed by the naked eye on sensor-coated swabs. Moreover, the chemosensor was successfully applied to effectively detect Al3+ and Zn2+ in actual water and drug samples.

Selective and sensitive investigation of aluminium contamination from cookware based on novel water-soluble fluorescence turn-on chemosensor

The ubiquitous use of aluminium cookware raises serious concerns about the introduction of aluminium by leaching upon prolonged cooking, especially in acidic foods. To mimic a consumer-relevant exposure scenario, an experimental model design was conceptualized for the estimation of leaching from aluminium sheets in acidic additives under variable cooking conditions. A novel water-soluble receptor (Z)-2-((2-hydroxy-3-methoxybenzylidene)amino)-2-(hydroxymethyl)propane-1,3-diol (VT) was synthesized, which gave a selective and sensitive fluorescence turn-on response towards aluminium ions. The 1:1 binding stoichiometry between VT and Al3+ has been confirmed by Job's plot, which is further supported by 1H NMR, 27Al NMR, HRMS, and DFT studies. Test strips were fabricated for quick semi-quantitative estimation of aluminium ions under UV irradiation. Leaching studies show that on increasing the acidity of solution of acidic additives results in an increased aluminium leaching ranging from 4.95 to 11.43 mg/h. Surface morphology by SEM and AFM shows the pitting corrosion of Al sheets.

A recyclable diacylhydrazone-based turn-on fluorescent chemosensor for detecting Al3+ and its practical applications

A novel diacylhydrazone-based fluorescent sensor HMPD was developed for the sensing of Al3+. In the presence of Al3+, HMPD showed a marked fluorescence increment with a 1:2 stoichiometry of HMPD to Al3+. Detection limit of HMPD to Al3+ was found as 0.76 μM. HMPD could determine Al3+ irrespective of the presence of Ga3+ and In3+. HMPD was satisfactorily applied to the qualification of Al3+ in real water samples and test strips. The sensing process of HMPD to Al3+ was reversible by EDTA application. Binding process of HMPD to Al3+ was proposed through fluorescence and UV–vis spectroscopy, Job plot, FT-IR spectroscopy, ESI-MS, 1H NMR titration and theoretical calculations.

Novel “turn-on” fluorescent sensors for silver (I) based on the nicotinonitriles, containing a tricyanobutadiene moiety

The novel turn-on fluorescent chemosensors for silver ion based on nicotinonitriles, containing a tricyanobutadiene moiety (tricyanopyridine, TCPy) were developed. The enchantment of fluorescent emission can be observed by naked eye, even in the presence of interference cations. The binding mode turned out to be a 1: 1 ratio as determined using Job’s plot.

An easy to make Hg(II) complex as a selective and sensitive fluorescent turn-on chemosensor for iodide in an aqueous solution based on metal ion displacement mechanism

• The rationally designed receptor forms Hg(II) complex easily. • The Hg(II) complex senses I − via turn-on fluorescent in aqueous solution. • The mechanism of sensing involves displacement of metal ion from the complex. • This complex exhibited many advantages than similar in-situ generated Hg(II) complexes. A simple Schiff base ligand ( L ) bearing 3,5-dibromo-2-hyrdoxybenzaldehyde fluorophore moiety has rationally been designed, synthesized and characterized. The Hg(II) complex of L has been synthesized by simply stirring a mixture of L and HgCl 2 in ethanol at RT and the resultant non-fluorescent complex HgL is found to detect iodide ion selectively, with a turn-on fluorescence in H 2 O:DMSO (1:1 v/v) medium. The detection of iodide is performed via the metal ion displacement mechanism with a 1:2 (Probe:Iodide) stoichiometry and binding constant of 1.51x10 4 M −1 . The results indicated that novel HgL complex showed rapid response towards iodide ion with a limit of detection (LOD) as low as 60 nM. Moreover, the sensing mechanism of iodide by the complex is theoretically supported by density functional theory (DFT) and time dependent density functional theory (TD-DFT) calculations. In addition, estimation of iodide in real water samples, table salt and urine sample demonstrate the practical value of the probe.

A symmetric Schiff base fluorescent “turn-on” chemosensor for aluminum (III) ion selective detection based on hydrolysis

A new symmetric Schiff base fluorescence turn-on chemosensor H2L (N,N′-bis[2,4-dihydroxy benzal]-1,5-diamino naphthalene) was designed and synthesized. H2L showed favorable selectivity and sensitivity to Al3+ with a significant color change from yellow to colorless in ethanol. The detection limit of H2L was as low as 11.79 nm. Based on fluorescence titration, 1H NMR and IR results, a plausible recognition mechanism of H2L is suggested to proceed via a hydrolysis process. The hydrolysis constant was calculated to be Kh = 3.0 × 104 M−1.