An off-on fluorescent sensor with high selectivity and sensitivity for Fe(III)

A new fluorescent derivative (1) containing coumarin exhibits Fe(III)-selective strong yellow-green fluorescence in ethanol. This compound could be used as an “off-on” chemosensor and allow the detection of Fe³⁺ by monitoring changes in absorption and fluorescence spectra. Upon addition of Fe³⁺, an overall emission change of 125-fold was observed. High selectivity and sensitivity were observed over other metal ions, mainly due to the spirolactam ring-opening power of Fe³⁺. The detection limit was as low as 5.6?ppb. Photo-induced electron transfer, coupled with intramolecular charge transfer are proposed to account for the observed spectral response.     

A biacylhydrazone-based chemosensor for fluorescence ‘turn-on’ detection of Al3+ with high selectivity and sensitivity

A simple Al³⁺ fluorescent chemosensor (1) based on diacylhydrazone has been designed and synthesized by the condensation reaction of 2-hydroxy naphthaldehyde and metaphthalic hydrazide. The chemosensor 1 displays a specific and sensitive response to Al³⁺ over other cations in DMSO solution. Upon the addition of DMSO solution of Al³⁺, the sensor 1 shows an immediate fluorescence ‘turn-on’ response and emitting strong blue emission with visible color change from colorless to green. The fluorescence quantum yield enhanced from 7.24% to 48.68%. Meanwhile, the fluorescence and UV absorption spectra detection limits of the chemosensor 1 for Al³⁺ were 2.0 × 10^?7 M and 5.6 × 10^?7 M respectively, indicating the high sensitivity of 1 to Al³⁺. Furthermore, test strips based on 1 were fabricated, which could be used as a convenient test kit for the detection of Al³⁺ and an efficient Al³⁺ controlled fluorescent security display materials.     

A quinoline-based selective ‘turn on’ chemosensor for zinc(II) via quad-core complex,and its application in live cell imaging

An efficient quinoline-based fluorescent chemosensor (QLNPY) was successfully developed for the detection of zinc ions (Zn²⁺). This novel chemosensor displayed higher sensitivity and selectivity toward Zn²⁺ over other competitive metal ions accompanying with obvious fluorescence enhancement. The QLNPY-Zn²⁺ complex can be further used as a new fluorescent “turn-off” sensor for pyrophosphate (PPi) and sulfur ion (S^2?) via a Zn²⁺ displacement approach. The limits of detection were calculated to be 3.8 × 10^?8 M for Zn²⁺, 3.7 × 10^?7 M for PPi and 4.9 × 10^?7 M for S^2?. The binding mechanism of QLNPY and Zn²⁺ was investigated through NMR, HR-MS analysis and further studied by crystallographic analysis. Additionally, further application of QLNPY for sequential bioimaging of Zn²⁺ and PPi was studied in HepG2 cells, suggesting that the quinoline-based chemosensor possesses great potential applications for the detection of intracellular Zn²⁺ and PPi in vivo.     

A New Fluorescent Chemosensor for Cu2+ Based on a Dianthracene-Derivative

Abstract

Besides being of interest in photochemistry, photoinduced electron transfer (PET) is a process largely used in the design of fluorescent ion sensing molecules. One of the simplest systems is based on fluorescent aromatic groups linked to amino groups and proposed as possible fluorescent transition metal ion chemosensor [1]. In this case, the fluorescence of the fluorophore “ligths on” when the amino group is complexed. On the other hand, in the absence of metal ions, the fluorescence is quenched by a PET originating from the nitrogen lone electron pairs [2]. We prepared a new fluorescent chemosensor, abbreviated as Ant-NH-O-O-NH-Ant (shown in Fig. 1) in which the intramolecular PET is expected to be efficient. The chemosensor consists of a metal-binding dioxodiamino unit linked to two light-emitting anthracene fragments. This type of supramolecules when irradiated in methanol solution (conc. 1.89—10^?5 M.) at 368 nm displays a characteristic fluorescence spectrum for anthracene group with the most intensive band at 415 nm [Fig. 2(a)]. The emission is slightly enhanced upon coordination of such metal ions as Ni²⁺ and Zn²⁺ by the ligand fragment of the Ant-NH-O-O-NH-Ant molecule [Fig. 2(b) and (d)]. However, much higher intensity of emission is observed in the case of Cu²⁺ complex [see Fig 2(c)]. The fluorescence enhancement is presumably due to suppression of photoinduced fluorophore-to-metal electron-transfer mechanism.     

A turn-on and reversible fluorescence sensor with high affinity to Zn in aqueous solution

A new simple receptor 1 based on aminosalicylimine was prepared. It exhibited an ‘off–on fluorescence type’ mode with high sensitivity in the presence of Zn²⁺. In particular, this chemosensor could clearly distinguish Zn²⁺ from Cd²⁺. Also, it could be a reusable chemosensor because the addition of EDTA quenched the fluorescence of the Zn²⁺-2·1 complex. Furthermore, receptor 1 had a sufficiently low detection limit (68 nM) in aqueous solutions, which implies that 1 could sense the nanomolar concentration of Zn²⁺. Therefore, this sensor has the ability to be a practical system for the monitoring of Zn²⁺ concentrations in aqueous samples.     

Thiazole sulfonamide based ratiometric fluorescent chemosensor with a large spectral shift for zinc sensing

A new thiazole sulfonamide (TTP, 1) based Zn²⁺ selective intrinsic chemosensor has been synthesized and investigated. The chemosensor shows a selective fluorescence enhancement (3.0 fold) with Zn²⁺ over biologically relevant cations (Ca²⁺, Mg²⁺, Na⁺, and K⁺) and biologically non-relevant cations (Cd²⁺) in an aqueous ethanol system. It produces an increase in the quantum yield and a longer emission wavelength shift (64 nm) on Zn²⁺ binding with the potential of a ratiometric assay.     

FRET based selective and ratiometric ‘naked-eye’ detection of CN in aqueous solution on fluorescein–Zn–naphthalene ensemble platform

We have developed a FRET-based ratiometric fluorescent probe for the detection of CN⁻ using a fluorescein–Zn–naphthalene ensemble (NFH·Zn²⁺). The sensing mechanism was ascribed by displacement approach. The chemosensor exhibits high selectivity and sensibility for CN⁻. The speculation was supported by fluorescence emission spectra, UV–vis spectrum, ¹H NMR titration experiments, and mass spectra. The interconversion of probe NFH and NFH·Zn²⁺ via the complexation/decomplexation by the modulation of Zn²⁺/CN⁻ mimics INHIBIT gate. In addition, it also shows an excellent performance in ‘dip stick’ method.     

Detection of Hg2+ ion using highly selective fluorescent chemosensor in real water sample and in-vitro cell study upon breast adenocarcinoma (MCF-7)

A novel rhodamine-based chemosensor (R) was designed and synthesised for selective recognition of Hg²⁺ ion in real water samples collected from different places. The chemosensor was prepared in green condition with high yield. The selectivity of R was examined with various metal ions, among which only Hg²⁺ was identified selectively with off–on mechanism along with enhancement of fluorescence. Metal ions recognition has been carried out using UV–vis and fluorescence studies taking µM concentration of chemosensor R in HEPES buffer. The detection limit of R was calculated and found to be 4.4 × 10^–9 M. Quantum chemical (DFT) calculation was carried out in order to acquire knowledge about the stability of R in presence of Hg²⁺ ions. Cell viability and fluorescence microscopic experiments showed R as cytocompatible and can be used as a fluorescent probe for detecting Hg²⁺ in living cells.     

Supramolecular chemosensor for selective detection of iron in aqueous medium

We have successfully developed a ‘turn-on’ colorimetric chemosensor for Fe³⁺ based on 1,10-phenanthroline. An amide derivative of 1,10-phenanthroline 4 was developed for the selective recognition of Fe³⁺ over Co²⁺, Cr³⁺, Cu²⁺, Mn²⁺, Ni²⁺, Ag⁺ and Zn²⁺ and could measure Fe³⁺ concentration in the range of 15–210 μM by UV–vis spectroscopy. Moreover, the addition of Fe³⁺ to a colourless solution of 4 turned its colour to light pink, indicating that 4 is capable of detecting Fe³⁺ by the naked eye. Compound 4 exhibits a major absorption band centred at 268 which shifted to 278 nm after addition of Fe³⁺, and a shoulder band around 514 nm was also observed. The complexation of Fe³⁺ with 4 was analysed at a different pH and favourable binding was observed at pH 6.2.     

2-羟基-1-萘甲醛缩-2-萘甲酰腙对Zn2+的选择性识别

设计合成了识别Zn²⁺的荧光传感分子--2-羟基-1-萘甲醛缩-2-萘甲酰腙(3)。 通过红外光谱、核磁共振谱和质谱测试技术表征了其结构。 利用其光谱性质研究了该物质对几种过渡金属离子的识别性质,初步探讨了其结合模式。 结果表明,在乙腈介质中,受体分子3表现出对Zn²⁺良好的选择性,Zn²⁺的加入导致受体分子3的吸收光谱在435 nm处出现1新峰,其吸光度逐渐增强,同时于239、302、330、342和387 nm处观察到5个清晰的等吸收点;在516 nm处荧光增强101倍,而其它过渡金属只引起受体分子]3的荧光略微增强。 Job法实验揭示受体分子3与Zn²⁺的结合比为1∶1。     

A highly selective ratiometric fluorescent chemosensor for Zn2+ ion based on a polyimine macrocycle

A new ratiometric fluorescent chemosensor based on a polyimine macrocycle ligand 1 has been synthesized. The chemosensor can exhibit a pronounced fluorescence response and high selectivity to Zn²⁺ ion over other 15 metal ions, including Cd²⁺. Sensor 1 appears an emission peak at 370 nm. Upon the addition of Zn²⁺ ion, the typical emission peak for 1 at 370 nm is obviously quenched, but a new emission peak at around 470 nm appears and shows a large enhancement due to the formation of a 1:1 Zn²⁺-1 complex. In addition, there is a good linear relationship between the fluorescence ratio I_470nm/I_370nm and the concentration of Zn²⁺, which makes a ratiometric assay of Zn²⁺ ion possible.     

A Highly Sensitive and Selective Fluorescence Chemosensor for Cu2+ and Zn2+ Based on Solvent Effect

A novel fluorescence chemosensor 1 based on (R)‐binaphthyl‐salen can exhibit highly sensitive and selective recognition responses toward Cu²⁺ by "turn‐off" fluorescence quench type in THF/H₂O, and Zn²⁺ by "turn‐on" fluorescence enhancement type in CHCl₃/CH₃CN, respectively, suggesting that solvents can dramatically affect the responsive properties of salen‐based chemosensor. In addition, Cu²⁺ can lead to the most pronounced changes of CD spectra without the influence of solvents, which indicates this kind chemosensor can also be used as a sole Cu²⁺ probe based on CD spectra.     

A multichannel thiacalix[4]arene-based fluorescent chemosensor for Zn2+, F− ions and imaging of living cells

Abstract

The fluorescent sensor (3) based on the 1,3-alternate conformation of the thiacalix[4]arene bearing the coumarin fluorophore, appended via an imino group, has been synthesised. Sensing properties were evaluated in terms of a colorimetric and fluorescence sensor for Zn²⁺ and F^?. High selectivity and excellent sensitivity were exhibited, and ‘off-on’ optical behaviour in different media was observed. All changes were visible to the naked eye, whilst the presence of the Zn²⁺ and F^? induces fluorescence enhancement and the formation of a 1:1 complex with 3. In addition, 3 exhibits low cytotoxicity and good cell permeability and can readily be employed for assessing the change of intracellular levels of Zn²⁺ and F^?.     

Dual-signaling fluorescent chemosensor based on bisthiazole derivatives

A new bisthiazole chemosensor (3) with phenolic substituents at the position 2 of the thiazole rings was prepared. The chemosensor 3 acts as a potential dual-function fluorescence chemosensor with Cu²⁺ and Zn²⁺ ions causing complete quenching and ratiometric change of fluorescence, respectively. The mechanism of fluorescence was based on the cation-induced inhibition of excited-state intramolecular proton transfer (ESIPT).     

Design and Synthesis of a Highly Sensitive Off–On Fluorescent Chemosensor for Zinc Ions Utilizing Internal Charge Transfer

Fluorescence imaging is a powerful tool for the visualization of biological molecules in living cells, tissue slices, and whole bodies, and is important for elucidating biological phenomena. Furthermore, zinc (Zn²⁺) is the second most abundant heavy metal ion in the human body after iron, and detection of chelatable Zn²⁺ in biological studies has attracted much attention. Herein, we present a novel, highly sensitive off–on fluorescent chemosensor for Zn²⁺ by using the internal charge transfer (ICT) mechanism. The rationale of our approach to highly sensitive sensor molecules is as follows. If fluorescence can be completely quenched in the absence of Zn²⁺, chemosensors would offer a better signal‐to‐noise ratio. However, it is difficult to quench the fluorescence completely before Zn²⁺ binding, and most sensor molecules still show very weak fluorescence in the absence of Zn²⁺. But even though the sensor shows a weak fluorescence in the absence of Zn²⁺, this fluorescence can be further suppressed by selecting an excitation wavelength that is barely absorbed by the Zn²⁺‐free sensor molecule. Focusing on careful control of ICT within the 4‐amino‐1,8‐naphthalimide dye platform, we designed and synthesized a new chemosensor ( 1 ) that shows a pronounced fluorescence enhancement with a blueshift in the absorption spectrum upon addition of Zn²⁺. The usefulness of 1 for monitoring Zn²⁺ changes was confirmed in living HeLa cells. There have been several reports on 4‐amino‐1,8‐naphthalimide‐based fluorescent sensor molecules. However, 1 is the first Zn²⁺‐sensitive off–on fluorescent sensor molecule that employs the ICT mechanism; most off–on sensor molecules for Zn²⁺ employ the photoinduced electron transfer (PeT) mechanism.     

A reversible fluorescence “ON–OFF–ON” sensor for sequential detection of F− and Cu2+ ions and its application as a molecular-scale logic device and security keypad lock

A new azoimine receptor, R₁, was synthesized by Schiff base condensation of 4-(4-butylphenyl) azophenol and 2,6-diaminopyridine and acts as a colorimetric and fluorometric chemosensor for F^? and also toward Cu²⁺ ions in aqueous environment. UV–Vis absorption and fluorescent emission spectra were employed to study the sensing process. Emission study was performed to examine the dual sensing ability of the obtained probe with sequential addition of F^? followed by Cu²⁺ and vice versa. The receptor is an efficient “ON–OFF” fluorescent probe for the fluoride ion. Also, R₁ + F^? operated as an “OFF–ON” fluorescent sensor for Cu²⁺ ions. Considering emission intensity and absorption wavelength for F^? and Cu²⁺ ions, a molecular system was developed with the ability to mimic the functions of XNOR logic gating on the molecular level. In addition, R₁ behaved as a molecular security keypad lock with F^? and Cu²⁺ inputs. The keypad lock operation is particularly important, as the output of the system depends not only on the proper combination but also on the order of input signals, creating the correct password that can be used to “open” this molecular keypad lock through strong fluorescence emission at 460?nm.     

A highly selective and sensitive dual-channel chemosensor for cyanide based on sulfahydrazone derivative

A colorimetric and fluorescent cyanide probe bearing naphthol and sulfahydrazone groups has been designed and synthesized. This structurally simple probe displays a rapid response and high selectivity for cyanide in DMSO/EtOH (v/v = 2:8) solution. The addition of CN^? to the sensor p-toluenesulfonyl-2-hydroxy-1-naphthylhydrazone (L3) induced a remarkable color change from pale-yellow to yellow, and green fluorescence changed to yellow. The ¹H NMR titration and DFT calculations suggested that the selective sensing process is based on a nucleophilic addition reaction of cyanide to imine. Test strips based on sensor L3 were fabricated, which could act as a convenient and efficient test kit to detect CN^? for “in-the-field” measurements.     

A ‘turn-on’ fluorescent chemosensor based on rhodamine-N-(3-aminopropyl)-imidazole for detection of Al ions

A novel N-(3-aminopropyl)-imidazole-appended rhodamine-based fluorescent chemosensor was synthesized. The sensing behavior and selectivity of the synthesized chemosensor toward metal cations were studied by UV/vis and fluorescence spectroscopy. The chemosensor recognized Al³⁺ ions by a significantly enhanced fluorescence and a visible color change due to opening of the spirolactam ring triggered by the addition of Al³⁺ ions.     

A fluorescent chemosensor for Hg based on naphthalimide derivative by fluorescence enhancement in aqueous solution

Naphthalimide derivative (compound 1) containing hydrophilic hexanoic acid group was synthesized and used to recognize Hg²⁺ in aqueous solution. The fluorescence enhancement of 1 is attributed to the formation of a complex between 1 and Hg²⁺ by 1:1 complex ratio (K = 2.08 × 10⁵), which has been utilized as the basis of fabrication of the Hg²⁺-sensitive fluorescent chemosensor. The comparison of this method with some other fluorescence methods for the determination of Hg²⁺ indicated that the method can be applied in aqueous solution rather than organic solution. The analytical performance characteristics of the proposed Hg²⁺-sensitive chemosensor were investigated. The chemosensor can be applied to the quantification of Hg²⁺ with a linear range covering from 2.57 × 10⁻⁷ to 9.27 × 10⁻⁵ M and a detection limit of 4.93 × 10⁻⁸ M. The experiment results show that the response behavior of 1 toward Hg²⁺ is pH independent in medium condition (pH 4.0–8.0). Most importantly, the fluorescence changes of the chemosensor are remarkably specific for Hg²⁺ in the presence of other metal ions, which meet the selective requirements for practical application. Moreover, the response of the chemosensor toward Hg²⁺ is fast (response time less than 1 min). In addition, the chemosensor has been used for determination of Hg²⁺ in hair samples with satisfactory results, which further demonstrates its value of practical applications.     

Reversible fluorescence sensing of Zn2+ based on pyridine-constrained bis(triazole-linked hydroxyquinoline) sensor

Zinc ion (Zn²⁺) is an important and a most useful biological trace nutrient responsible for the activity of several enzymes. Zn²⁺ concentrations in the environment as well as in the human body increase beyond permissible limits as a consequence of its mining and widespread industrial applications. Such excess Zn²⁺ concentrations are toxic to humans and many aquatic organisms. The magnetic inertness and spin paired electronic configuration of Zn²⁺ makes it hard to detect by common analytical techniques. Therefore, fluorometric detection using chemosensor is the most effective tool for the environmental and biological detection of Zn²⁺. We have developed a novel pyridine-constrained bis(triazole-linked hydroxyquinoline) ligand as a reversible fluorescent chemosensor for Zn²⁺. The symmetrical ligand is highly selective for Zn²⁺ and fluoresces brightly upon complexation compared with other metal ions based on chelation-enhanced fluorescence mechanism. Interestingly, free ligand can be regenerated by treating the ligand–Zn²⁺ complex with aqueous ammonia.