Turn-on Fluorescent Chemosensor Research Articles

Synthesis and cyanide anion recognition of a new displacement fluorescence chemosensor based on two-branched aurone

A new fluorescence turn-on chemosensor based on two dipyridylamine groups substituted aurone moiety, 4’-2,2’-dipyridylamine-3-2,2’-dipyridylamine aurone (1), was synthesized. The recognition properties of the compound for cyanide anions and copper ions were investigated. Yellow fluorescence of the compound is almost quenched completely because of the complexation between the compound and copper ions. After the subsequent addition of cyanide anions, fluorescence spectrum is recovered to the original status of the compound owing to the strong bonding ability between cyanide anions and copper ions and the removal of copper ions from the complexes. The recognition also can be observed by naked eye. The compound exhibits a good reversibility and can be used repeatedly to recognize cyanide anions for several times.

A colorimetric and turn-on fluorescent chemosensor for selectively sensing Hg2+ and its resultant complex for fast detection of I− over S2−

A novel bipyridine-functionalized turn-on fluorescent chemosensor was successfully synthesized and fully characterized by 1H NMR, 13C NMR and MS, UV–vis and fluorescence spectroscopies. The sensor specifically binds to Hg2+ over other competing ions with a significant fluorescence enhancement as well as a visual colour change under physiological conditions. The detection limit of Hg2+ was as low as 32 nM, confirming very high sensitivity toward Hg2+. Moreover, the fluorescence intensity and colour change of the sensor-Hg2+ was quenched by I− or S2− and was proportional to their concentrations with a detection limit of 0.37 μM and 0.43 μM, respectively. The reaction of I− grabbing Hg2+ from the sensor–Hg2+ finished in 10 s due to a stronger binding force, much faster than that of S2−, which allowed fast detection of I− over S2− even in a competent environment. In addition, the sensor was successfully used for the highly sensitive detection of Hg2+ in living cells.

Pyrene Scaffold as Real-Time Fluorescent Turn-on Chemosensor for Selective Detection of Trace-Level Al(III) and Its Aggregation-Induced Emission Enhancement

A pyrene based fluorescent probe, 3-methoxy-2-((pyren-2yl-imino)methyl)phenol (HL), was synthesized via simple one-pot reaction from inexpensive reagents. It exhibited high sensitivity and selectivity toward Al(3+) over other relevant metal ions and also displayed novel aggregation-induced emission enhancement (AIEE) characteristics in its aggregate/solid state. When bound with Al(3+) in 1:1 mode, a significant fluorescence enhancement with a turn-on ratio of over ∼200-fold was triggered via chelation-enhanced fluorescence through sensor complex (Al-L) formation, and amusingly excess addition of Al(3+), dramatic enhancement of fluorescence intensity over manifold through aggregate formation was observed. The 1:1 stoichiometry of the sensor complex (Al-L) was calculated from Job's plot based on UV-vis absorption titration. In addition, the binding site of sensor complex (Al-L) was well-established from the (1)H NMR titrations and also supported by the fluorescence reversibility by adding Al(3+) and EDTA sequentially. Intriguingly, the AIEE properties of HL may improve its impact and studied in CH3CN-H2O mixtures at high water content. To gain insight into the AIEE mechanism of the HL, the size and growth process of particles in different volume percentage of water and acetonitrile mixture were studied using time-resolved photoluminescence, dynamic light scattering, optical microscope, and scanning electron microscope. The molecules of HL are aggregated into ordered one-dimensional rod-shaped microcrystals that show obvious optical waveguide effect.

A highly selective fluorescent sensor for the detection of Al3+ and CN− in aqueous solution: biological applications and DFT calculations

A new turn-on fluorescent chemosensor 1 was developed to detect both Al3+ and CN− and used for practical and biological applications.

A turn-on fluorescence chemosensor based on a tripodal amine [tris(pyrrolyl-α-methyl)amine]-rhodamine conjugate for the selective detection of zinc ions.

A novel tetradendate ligand derived from a tris(pyrrolyl-α-methyl)amine (H3tpa) and rhodamine-based conjugate (PR) has been designed for use as a sensor, synthesized and characterized spectroscopically. PR {(tris(5-rhodamineiminopyrrol-2-ylmethyl)amine)} serves as a selective colorimetric as well as a fluorescent chemosensor for Zn(2+) in acetonitrile/water (1 : 1, v/v). In the presence of Zn(2+), PR exhibited obvious absorption (558 nm) and emission (577 nm) peaks whose intensity increased along with increasing Zn(2+) concentrations. Titration experiments revealed that a large excess of Zn(2+) was required to saturate the absorption (λmax) and emission intensities. Upon the addition of 1000 equivalents of Zn(2+), the fluorescence intensity of the PR underwent an ∼500-fold increase (Φf = 0.34) with the emission maximum at 580 nm. These kinetics studies demonstrated that the absorption and emission changes were proportional to the Zn(2+) concentration. The color of the solution changed from colorless to a dark pink color. The fluorescence of the PR-Zn(2+) complex can be reversibly restored by using ammonium water or by heating. Competitive ion tests revealed that the intensity of PR-Zn(2+) was not suppressed by excess amounts of other metal ions. The counter anions did not exert obvious influences on the absorption and emission profiles. (1)H-NMR and FT-IR spectroscopic investigations of PR and PR-Zn(2+) revealed that the pyrrole motifs, -C[double bond, length as m-dash]N- groups and spirolactam of rhodamine B are capable of coordinating cation guest species. Because each arm of the tripodal ligand tautomerizes independently, only moderate fluorescence enhancement could be seen until all three -C[double bond, length as m-dash]N- groups were coordinated by zinc, which may be due to the spirolactam ring opening mechanism of the rhodamine unit. Once all three -C[double bond, length as m-dash]N- groups were locked by coordinating with excess of Zn(2+), the isomerization was arrested, and PR exhibited highly enhanced fluorescence. In addition, energy optimized structures of PR were found to be cage-like by Gaussian 09, further supporting that it can access a large excess of Zn(2+). Intriguingly, imaging of HeLa cells by using a confocal microscope revealed that this PR probe could be used for biological applications.

Colorimetric recognition of Cu2+ and fluorescent detection of Hg2+ in aqueous media by a dual chemosensor derived from rhodamine B dye with a NS2 receptor

A rhodamine B derivative bearing a NS2-containing receptor (L) is developed as a dual chemosensor for detection of Cu2+ and Hg2+ in aqueous media. L shows highly sensitive colorimetric response to Cu2+ and selectively turn-on fluorescent response to Hg2+ with very low detection limits of 1.63 and 2.36μM, respectively. The significant absorption enhancement (251-fold) accompanied with a visual color change from colorless to purple upon interaction with Cu2+, making L a suitable “bare-eye” indicator for Cu2+. By means of Job's plot, 1H NMR titration and ESI-MS studies, both 1:1 binding modes (L/Cu2+ and L/Hg2+) are confirmed and a possible sensing mechanism is further proposed. The response behaviours of L toward Cu2+ and Hg2+ are pH independent in a wide range (pH 4.0–9.0). Proof-of-concept experiment demonstrates the potential application of L for trace Cu2+ and Hg2+ detection in complicated environmental water samples. More importantly, the turn-on fluorescent chemosensor L with good membrane-permeable property is successfully applied to microscopic imaging for the detection of Hg2+ in PC3 cells.

Turn-on fluorescent chemosensor for selective detection of Zn2 + in an aqueous solution: Experimental and theoretical studies

A new simple receptor 1 based on the combination of julolidine and 2-(aminomethyl)benzenamine groups was prepared. It exhibited a ‘turn-on fluorescence type’ mode with high selectivity in the presence of Zn2+. Noticeably, receptor 1 could clearly distinguish Zn2+ from Cd2+. The mechanism of fluorescence enhancement of 1 for zinc was explained by theoretical calculations. Moreover, sensor 1 had a sufficiently low detection limit (10.9μM), which is below than the WHO recommendation level (76μM) for drinking water. Therefore, 1 can serve as a practical chemosensor for zinc ion in an aqueous solution.

Fluorescence Turn-on Chemosensor for the Detection of Dissolved CO2 Based on Ion-Induced Aggregation of Tetraphenylethylene Derivative.

Herein, a sensitive fluorimetric assay for dissolved carbon dioxide (dCO2) was developed by using ion-induced self-assembly of a tetraphenylethylene derivative by taking advantage of its aggregation induced emission property. Chitosan, a commercially available polymer having amine functionality was utilized for the ion induced assay. In the presence of dCO2, the amine groups in the chitosan get protonated to convert neutral chitosan to a positively charged species, triggering negatively charged tetraphenylethene derivative (probe 1) to aggregate with it by electrostatic interaction. The aggregation causes intense blue fluorescence output from the system. The extent of the aggregation is reliant on the charge density of polymer, which is equivalent to dCO2 concentration. A linear relationship from 5 to 50 μM of dCO2, with a limit of detection of 5 × 10(-6) M (0.00127 hPa) was obtained. This is the first report for detecting dCO2 utilizing the AIE property.

A highly selective and sensitive turn-on fluorescence chemosensor based on a rhodamine–adenine conjugate for Al3+ in aqueous medium: Bioimaging and DFT studies

Recently, extraordinary progress has been made for the specific detection of environmentally and biologically relevant metal ions in aqueous solution and living cells. A new dye L where rhodamine B is covalently attached to adenine has been synthesized in good yields. This dye is found to be highly specific in detecting of Al3+ ion in presence of excess of biologically relevant metal ions in DMSO/H2O [1:4 (v/v), HEPES buffer, pH=7.1] medium. Upon complexation with Al3+ the dye exhibits a substantially enhanced absorbance intensity at 566nm and fluorescence intensity at 590nm. Besides showing high selectivity, the sensor gives a sensitivity of 0.19µM for Al3+ in both absorbance and fluorescence studies over a wide pH range. The sensitivity is much higher compared to the value mentioned in the guidelines of WHO (7.41µM). Moreover, the dye shows moderately cytotoxicity and can be employed for the detection of intracellular concentration of Al3+ ions in living cells.

Turn-on fluorescence chemosensor for fluoride ions and its applicability in imaging of living cells

The study was easy to prepare fluorescent chemosensor, the urea based triphenylamine conjugated ligand and structurally simple anion probes displayed great selectivity for the fluoride anion over other anions in an aqueous tetrahydrofuran solution. The probe was characterized using NMR spectroscopy, UV–visible, emission spectroscopy and mass spectrometry. The sensor showed spectral shifts and intensity changes in the presence of fluoride anions. The Job’s plot analysis indicates that the binding stoichiometry to be 1:1. Furthermore, by means of confocal fluorescent microscopy experiments, it has been demonstrated that it can be used as a fluorescent probe for monitoring fluoride ions in the living cells.

A Simplified and Turn-on Fluorescence Chemosensor Based on Coumarin Derivative for Detection of Aluminium(III) Ion in Pure Aqueous Solution.

A novel chemosensor L based on coumarin Schiff-base was synthesized and investigated. Sensor L showed remarkable selectivity for Al(3+) in Tris-HCl aqueous buffer solution (pH 7.2), and the selectivity was not affected by the presence of a large excess of other competitive ions. The sensor responded rapidly to Al(3+) in aqueous solutions with a 2:1 stoichiometry. Meanwhile, it indicated significant improvement of quantum efficiency and ideal fluorescent lifetime.

A new colorimetric and turn-on fluorescent chemosensor for Al 3+ in aqueous medium and its application in live-cell imaging

Abstract A new simple Schiff-base ligand 2-Hydroxy-1-naphthaldehyde-(2-pyridyl) hydrazone (HL) was synthesized and characterized as a fluorescent probe. In aqueous solution containing 10% ethanol (Hexamethylenetetramine-HCl buffer, pH5.3), HL selectively binds Al3+to form a 1:1 ligand/metal complex, resulting in a color change from colorless to yellow–green and a significant fluorescence enhancement at 454 nm. The addition of EDTA quenches fluorescence of the HL·Al3+ complex, indicating that HL serves as a reversible chemosensor for Al3+. Under the optimum conditions, the dynamic range of the system was found to be linear up to 4.0 × 10−6 M Al3+ ions with a limit of detection of 36.6 nM. The probe is very effective for detection of intracellular Al3+ through fluorescence microscopic imaging.

A new tetrazole based turn-on fluorescence chemosensor for Zn2+ ions and its application in bioimaging

A new turn-on fluorescent quinolone tetrazole based chemosensor (QT-1) is designed and synthesized which shows high sensitivity and selectivity for Zn2+ ions in aqueous acetonitrile solution. QT-1 probe easily distinguishes Zn2+ ions from Cd2+ ions. Job's plot analysis suggested that the binding of QT-1 and Zn2+ ions is probably a 1:1 stoichiometry. Thus QT-1 can be employed for fluorescent imaging of Zn2+ ions in living cells.

E-Bodipy fluorescent chemosensor for Zn2+ ion

ABSTRACT A novel ethynylpyridine containing E-Bodipy, 2 was synthesized from a Bodipy precursor 1 and its chemosensing properties towards various transition metal ions including Fe3+, Co2+, Cu2+, Zn2+ and Hg2+ were investigated. A large fluorescence enhancement of 2 was observed upon treatment with Zn2+ whereas addition of Fe3+, Co2+, or Cu2+ caused fluorescence quenching of 2, which suggests its potential application as a turn-on fluorescent chemosensor for Zn2+. The photophysical behaviors of 1 and 2 were characterized by spectroscopic and electrochemical methods. In addition, the structure and electronic properties of 1, 2 and its metal complex with Zn2+ were investigated by density functional theory (DFT) calculations.

Intra-molecular hydrogen bonding stabilization based-fluorescent chemosensor for CO2: Application to screen relative activities of CO2 absorbents

A fluorescent turn-on chemosensor for CO2 was developed using intra-molecular hydrogen bonding stabilization. The chemosensor (sodium (anthracen-9-ylmethyl)glycinate (1)) reacts with CO2 and forms chemosensor-CO2 adduct stabilized by strong intra-molecular hydrogen bonds. The stabilization consequently allows sensing CO2 with high sensitivity and the detection limit of this chemosensor for CO2 was estimated to be ∼2 ppm. In addition, the chemosensor was applied to develop an easy screening protocol to evaluate the efficiency of CO2 absorbents. The protocols discriminate the relative ability of CO2 absorbents as strong, intermediate, and weak using easily measured fluorescence changes.

Two fluorescence turn-on chemosensors based on pyrrolo[2,1-a]isoquinoline for detection of Ag+ in aqueous solution

In this study, two water-soluble fluorescent probes based on pyrrolo[2,1-a]isoquinoline derivatives (4a and 4b) were synthesized and characterized by IR, 1H NMR, 13C NMR, MS spectra and elemental analysis for the first time. The obtained compounds (4a and 4b) showed fluorescent ‘turn-on’ phenomenon to Ag+ with limits of detection (LOD) of 0.6 μM (4a) and 0.8 μM (4b) (S/N=3), respectively.

A new turn-on fluorescent chemosensor based on sensitive Schiff base for Mn2+ ion

A Schiff-base fluorescent probe – N,N′-bis((6-(thiophen-3-yl)pyridine-2-yl) methylene) benzene-1,2-diamine (L) – was synthesized and evaluated as a chemoselective Mn2+ sensor. Upon treatment with Mn2+, the complexation of L with Mn2+ resulted in a red-shift with a pronounced enhancement in the fluorescence emission intensity in ethanol solution. Moreover, other common alkali, alkaline earth and transition metal ions failed to induce response or minimal spectral changes. Fluorescence studies on L and L–Mn2+ complex reveal that the quantum yield strongly increases upon coordination. The complex solution of L with Mn2+ ion exhibited reversibility with EDTA and regenerated free ligand for further Mn2+ sensing. The stoichiometric ratio and association constant were evaluated using Benesi–Hildebrand relation giving 1:1 stoichiometry. This further corroborated 1:1 complex formation based on Job’s plot analyses. This chemosensor exhibits a very good fluorescence sensing ability to Mn2+ over a wide acidic pH range. This chemosensor can be used as an important application for detection of Mn2+ in real water samples. Both L and L–Mn2+ complex were optimized using density functional theory and vibrational frequency calculations confirmed that both are at local minima on the potential energy surfaces. The corresponding energy differences between HOMO and LUMO of L and L–Mn2+ complex are 2.210eV and 0.550eV, respectively which implies a low kinetic stability and high chemical reactivity.

A new optical sensor for Al3+/Fe3+ based on PET and chelation-enhanced fluorescence

A simple probe (compound 1) sensing Al3+ or Fe3+ by suppression of photoinduced electron/energy transfer (PET) process and chelation-enhanced fluorescence is described. Compound 1 was prepared from 2-(bromomethyl)benzo[d]thiazole and pyridine-2,6-diamine. Compound 1 showed a much stronger fluorescence response to Al(III) than to Fe(III). The best fluorescence response of 1 to Al3+ was found to be at pH near 7. The results indicated that 1 could be a promising fluorescent turn-on chemosensor for Al3+ or Fe3+. Ratiometric sensing of 1 to Al3+ or Fe3+ was accomplished by plotting the absorbance ratio at 338 to 310 nm versus Al3+ or Fe3+ concentration. The fluorescent turn-on response of 1 to Al3+ or Fe3+ can be attributed to suppression of PET process and chelation-enhanced fluorescence upon binding with Al3+ or Fe3+. The binding mode of 1-Al3+ or 1-Fe3+ was found to be a 1:1 complex based on Job’s plot, electrospray ionization (ESI) mass spectroscopy (MS) data, and density functional theory (DFT) calculation results.

Dual turn-on fluorescent chemosensor for Cu2+ and Hg2+ in aqueous medium based on a water-soluble polyacrylamide containing rhodamine

An acrylic monomer bearing rhodamine 6G group, salicylaldehyde rhodamine 6G hydrazone acrylate (AR6GHS), was synthesized from salicylaldehyde rhodamine 6G hydrazone (R6GHS) and acryloyl chloride in the presence of triethylamine in dry dichloromethane (CH2Cl2) at room temperature. The poly(acrylamide- salicylaldehyde rhodamine 6G hydrazone acrylate) (poly(AM-AR6GHS)) was synthesized by a combiation of AR6GHS and a hydrophilic comonomer acrylamide (AM) with 2,2′-azobis(2-methylpropionitrile) (AIBN) as a thermal initiator in tetrahydrofuran (THF). The resultant AR6GHS and poly(AM-AR6GHS) were identified by FTIR and 1H NMR spectra. The fluorescent characteristic of the poly(AM-AR6GHS) in the aqueous solutions were investigated both in varied pH and in the presence of metal cations. It was found that the copolymeric sensor exhibited “off-on” recognition toward Cu2+ and Hg2+ over a wide range of tested metal ions with remarkably enhanced fluorescent intensities. The poly(AM-AR6GHS) had a good linear response between the relative fluorescence intensity and Cu2+ or Hg2+ concentration. In addition, upon the addition of Cu2+ or Hg2+ into the aqueous solution of poly(AM-AR6GHS), the color changes occurred from colorless to pale pink or pink under visible light, and the emission color of the sensor solution turned from dark to bright greenish yellow or orange yellow under the UV light at 365 nm.

Fluorescence turn-on chemosensor for highly selective and sensitive detection and bioimaging of Al(3+) in living cells based on ion-induced aggregation.

Herein, a new fluorescence turn-on chemosensor 2-(4-(1,2,2-triphenylvinyl)phenoxy)acetic acid (TPE-COOH) specific for Al(3+) was presented by combining the aggregation-induced-emission (AIE) effect of tertaphenylethylene and the complexation capability of carboxyl. The introduction of carboxylic group provides the probe with good water-solubility which is important for analyzing biological samples. The recognition toward Al(3+) induced the molecular aggregation and activated the blue fluorescence of the TPE core. The high selectivity of the probe was demonstrated by discriminating Al(3+) over a variety of metal ions in a complex mixture. A detection limit down to 21.6 nM was determined for Al(3+) quantitation. Furthermore, benefiting from its good water solubility and biocompatibility, imaging detection and real-time monitoring of Al(3+) in living HeLa cells were successfully achieved. The AIE effect of the probe enables high signal-to-noise ratio for bioimaging even without multiple washing steps. These superiorities make this probe a great potential for the functional study and analysis of Al(3+) in complex biosystems.