A highly sensitive fluorescent sensor for Cd2+ and Zn2+ based on diarylethene with a pyrene unit

A review on polycyclic aromatic compounds based chemosensors for toxic ions detection - Present and future perspective

This comprehensive review delves into the current landscape and future outlook of chemosensors constructed from polycyclic aromatic compounds (PACs) for the detection of toxic ions. PACs, known for their unique molecular properties, have emerged as key building blocks for the development of chemosensors due to their sensitivity, selectivity, and versatility. The review begins by providing an overview of the existing literature on PAC-based chemosensors, detailing their design principles, structural modifications, and mechanisms of ion recognition. The discussion encompasses various toxic ions, including heavy metals, anions, and other environmental pollutants, showcasing the broad applicability of PAC-based chemosensors in diverse analytical contexts. The review also highlights recent advancements in the field, exploring novel strategies and materials for enhancing the performance of PAC-based chemosensors. Furthermore, the review critically evaluates the current challenges and limitations associated with PAC-based chemosensors, offering insights into potential avenues for future research and technological development.

Zinc-Induced Luminescent l-Valine-Based Pseudopeptidic Soft Bioinspired Materials for Precise Tuning of Nanoassembly

Pseudopeptide-based bioinspired materials are emerging for selective recognition of biologically significant analytes and are applicable in the modern nanoscience field. Therefore, we have developed novel multifunctional C2-symmetric soft pseudopeptides by amino acid l-valine and salicylaldehyde fragments using a series of aliphatic linkers. They are highly selective and sensitive to Zn (II) ions under physiological conditions and reveal significant fluorescence enhancement with the PET mechanism. The molecular self-assembly shows zinc-induced morphological transformation of the rod-shaped assembly into a chain-like morphology. Such a metal-induced hierarchical nano-assembly may have relevance for specific nanobiotechnology applications.

The new role of dipyrromethene chemosensor for absorbance-ratiometic and fluorescence "turn-on" sensing Zn2+ ions in water-organic solutions and real water samples

This study presents a dipyrromethene-based sensitive and selective probe for Zn2+ ions detection in aqueous and water-organic media. The probe demonstrates absorbance-ratiometric and "off-on" fluorescent sensing for Zn2+ in a DMSO/H2O (9:1, v/v) mixture. The 3,3',4,4',5,5'-hexamethyl-2,2'-dipyrromethene (HL), similar to its analogs, exhibits weak fluorescence (with a quantum yield of less than 0.001). However, upon the presence of Zn2+ ions in the sensor HL solution, there is a remarkable increase (up to 200-fold) in fluorescence intensity due to the formation of a stable intramolecular chelate complex [ZnL2]. This complex formation induces a significant hyperchromic effect and a red shift (57 nm) in the characteristic absorption bands. The sensing mechanism of the probe towards Zn2+ ions was thoroughly investigated through absorbance and fluorescent titrations, molar ratio plots, 1H NMR, and DFT/TDDFT studies. The fluorescence response exhibited a strong linear relationship with Zn2+ concentration within the range of 0 to 5.7 × 10-6 mol/L. The detection limit (LOD) and limit of quantitation (LoQ) for Zn2+ were determined as 2 × 10-8 mol/L and 6.6 × 10-8 mol/L, respectively. Moreover, the probe demonstrated high selectivity for Zn2+ ions over other metal ions (Na+, Mg2+, Al3+, Cr3+, Mn2+, Fe3+, Co2+, Ni2+, Cu2+, Pd2+, Cd2+, Hg2+, Pb2+). Test systems in the form of test-strips and cotton-pads were developed based on the dipyrromethene sensor for rapid "naked-eye" detection of zinc ions in water. The sensor was successfully applied for detecting Zn2+ ions in real water samples.

Fabrication of reusable probe impregnated polymer monolithic sensor for the visual detection of Cd2+ in natural waters and cigarette samples

This work demonstrates the fabrication of a simple, low-cost naked-eye colorimetric solid-state sensor model for selective sensing of Cd2+. The sensor was developed using a polymer monolithic architect; namely, poly(n-allylthiourea-co-ethyleneglycol dimethacrylate) (poly(ATU-co-EGD) imbued with the chromophoric probe, 3-(quinoline-8-yldiazenyl)quinoline-2,4-diol (QYQD). The concocted indigenous perforated structural assemblies were studied through various microscopic, spectroscopic, and diffraction techniques. The template possessed a uniform arrangement of interconnected macro/mesoporous networks available for the maximum hooking of the QYQD probe moieties for the rapid and enhanced Cd2+ sensing process. The developed sensor offered an enhanced solid-state color transition response from yellow to dark meron for a proportional concentration increase of Cd2+ exhibiting precise absorption spectra with λmax at 475 nm. The relative stoichiometric binding ratio of the QYQD probe with Cd2+ was observed to be 2:1. The enhanced working conditions of the developed poly(ATU-co-EGD)QYQD sensor were tuned by validating various analytical conditions. The sensor exhibited a linear response signal from 2 to 150 ppb of Cd2+, and the corresponding LOD and LOQ values were 0.31 and 1.03 ppb, respectively. The efficacious performance drive of the sensor was validated in real water and cigarette samples that showed excellent data accuracy with a recovery value of ≥ 99.72% (n = 3).

Recent Advancements in Ion-Pair Receptors

Over the past two decades, non-covalent chemistry has introduced various promising artificial receptors and revolutionized the host-guest chemistry. These versatile receptors have particularly been entertained in sensing and recognizing of diverse neutral molecules and/or ionic entities (e. g. anions, cations and ion-pair) of particular interest. Notably, supramolecular chemistry had given birth to a plethora of important molecules, explored in the chemical, biological, environmental, and pharmacological world to resolve the critical issues related to the human health while keeping environmental concerns in mind. Amongst the various types of supramolecular monotopic receptors (anions, cations, and neutral molecules), heteroditopic receptors (ion-pair receptors) consisting of distinct binding sites in one system for both cation and anion, have gained much interest from the scientific community in recent past because of their unique binding abilities. Interestingly, these promising artificial receptors have shown potential applications in sensing, recognition, transport and extraction processes besides their uses in salt/waste purification. Bearing the importance of these systems in mind, we intended to report the recent developments in ion-pair chemistry. Herein, we divided the whole document into three main sections; first one describes the introduction and history of the ion-pairs receptors. The second portion highlights the synthesis and applications of ion-pair receptors in sensing, recognition, molecular machines, photoswitching behaviour, extraction and transport properties, whereas the last part of this manuscript provides concluding remarks as well as future prospects of ion-pair receptors. We hope that this manuscript will be helpful to stimulating researchers around the globe to find out the hidden opportunities in this and related areas.

Modified polymeric hydrogels for the detection of Zn2+ in E. coli bacterial cells and Zn2+, Cd2+ and Hg2+ in industrial effluents

The article focusses on exploring the real-time application of meta-benziporphodimethene (m-BPDM) embedded polyacrylamide/carboxymethylguargum (PAM/CMG) hydrogel. The hydrogel-based sensor is highly selective for Zn²⁺, Cd²⁺ and Hg²⁺ with no significant response to other competitive cations including Na⁺, K⁺, Ca²⁺, Cr³⁺, Pb²⁺, Mg²⁺, Mn²⁺, Co²⁺, Cu²⁺ in aqueous medium. Initially, the stability of the hydrogel has been examined at different pH conditions. The sensitivity of the hydrogel was found to be 0.5, 1, and 2 ppm in 1, 2 and 3 h for Hg²⁺, Zn²⁺, and Cd²⁺, respectively, at pH 6. The sensor exhibits colour change from red to bluish-green with Zn²⁺, Cd²⁺ and Hg²⁺ in water over other ions. The modified hydrogel matrix displayed a unique naked eye turn-on colorimetric sensor selectivity for Zn²⁺, Cd²⁺ and Hg²⁺ ions in the aqueous solutions of Escherichia coli (E. coli) bacterial cells and industrial effluents. During the detection process, the zinc metal ions released because of cell lysis bind with hydrogel, in the former. The binding of Zn²⁺ causes the change in the colour of hydrogel from red to bluish-green, which was visually detected. The m-BPDM does not leach out and is stable in the hydrogel matrix. The sensing of Zn²⁺, Cd²⁺ and Hg²⁺ was achieved by directly adding hydrogel into industrial effluent without any pretreatment of effluent. The quantitative determination of Zn²⁺, Cd²⁺ and Hg²⁺ in industrial effluent was performed by the atomic absorption spectroscopy technique just to confirm the results obtained with the hydrogel.

Synthesis, characterization and metal ions sensing applications of meta-benziporphodimethene-embedded polyacrylamide/carboxymethyl guargum polymeric hydrogels in water

We have developed a robust procedure for the visual on-site detection of zinc, cadmium and mercury metal ions in an aqueous medium using a polymeric hydrogel matrix-based colorimetric sensor. Zn²⁺, Cd²⁺and Hg²⁺, owing to their biological significant value and environmental harm, have attracted more attention. The selective detection of Zn²⁺, Cd²⁺and Hg²⁺ metal ions has always been challenging due to their closed-shell d¹⁰ electronic configuration which makes them spectroscopically silent. A polyacrylamide/carboxymethyl guargum polymeric hydrogel-based metal ion sensor was synthesized by in situ embedding 11, 16-bis (phenyl)-6, 6, 21, 21-tetramethyl-m-benzi-6,21-porphodimethene (meta-BPDM) in a host hydrogel. The meta-BPDM-embedded hydrogel shows high stability, sensitivity and selectivity when it is dipped into the aqueous solutions of Zn²⁺, Cd²⁺and Hg²⁺ metal ions. During detection, the binding of these metal ions in hydrogel causes hydrogel to change from red to bluish-green which was visually detected and confirmed by UV-visible spectroscopy. The meta-BPDM-embedded polymeric hydrogel was characterized by using solid-state UV-visible spectroscopy, scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, Fourier-transform infrared spectroscopy, energy-dispersive X-ray analysis and its sensing properties were studied. The meta-BPDM-embedded polymeric hydrogel was found to be an excellent colorimetric sensor for Zn²⁺, Cd²⁺ and Hg²⁺ in aqueous medium without leaching of meta-BPDM from the hydrogel. The selectivity to sense these ions is mainly dependent on the binding constant of these metal ions with the meta-BPDM embedded in the hydrogel. The sensitivity of the hydrogel was 0.5, 1, and 2 mg/L with Hg²⁺, Zn²⁺ and Cd²⁺, respectively.

Fabrication of a light-responsive polymer nanocomposite containing spiropyran as a sensor for reversible recognition of metal ions

Poly(spiropyran ethylacrylate-co-glycidyl methacrylate) grafted onto the surface of modified TiO2 (TiO2-g-P(SPEA-co-GMA)) as a novel stimuli-responsive polymer was fabricated and employed as sensor for reversible recognition of metal ions.

Crystal structure of 1-(2-methylphenyl)-2-(2-methylbenzo[b]thienyl)-3,3,4,4,5,5-hexafluorocyclopent-ene, C21H14F6S

C21H14F6S, monclinic, P21/n (no. 14), a = 9.9344(11) Å, b = 16.7106(18) Å, c = 11.6207(13) Å, β = 101.0080(10)°, V = 1893.7(4) Å3, Z = 4, R gt (F) = 0.0491, wR ref (F 2) = 0.1541, T = 296(2) K.

Europium Doped Silicon Quantum Dot As a Novel FRET Based Dual Detection Probe: Sensitive Detection of Tetracycline, Zinc, and Cadmium

The imbalance of Zn²⁺ /Cd²⁺ in the human body can lead to many serious diseases due to the overuse of antibiotics and deposition in animal products. Developing a functional material for detecting is challenging and in demand. Herein, silicon quantum dots (SiQDs) are designed as a functional platform for the detection of tetracycline and Zn²⁺ /Cd²⁺ . The COOH functionalized SiQDs with the emission wavelength of 450 nm are chelated with Eu(NO₃ )₃ to form SiQDs-Eu³⁺ ratio fluorescent probes, which can be used to detect tetracycline (TCs) and Zn²⁺ /Cd²⁺ by fluorescence resonance energy transfer (FRET) principle sequentially. The fluorescent probe showed good linearity between ion concentration and fluorescence enhancement. The detection limit of TCs and Zn²⁺ /Cd²⁺ are 0.2 × 10^-6  m and 3 × 10^-6  m, respectively, when the pH of the solution is 7.4. In addition, the synthesized SiQDs-Eu³⁺ exhibited good stability (from 94.9% to 103.1%). The relative standard deviations (RSD, n = 10) of human serum and urine were both less than 3%. Therefore, the SiQDs-Eu³⁺ ratio fluorescence probe will provide a good application prospect in actual sample detection.

Recent progress in cadmium fluorescent and colorimetric probes

Cadmium is a heavy metal which exists widely in industrial and agricultural production and can induce a variety of diseases in organisms. Therefore, its detection is of great significance in the fields of biology, environment and medicine. Fluorescent probe has been a powerful tool for cadmium detection because of its convenience, sensitivity, and bioimaging capability. In this paper, we reviewed 98 literatures on cadmium fluorescent sensors reported from 2017 to 2021, classified them according to different fluorophores, elaborated the probe design, application characteristics and recognition mode, summarized and prospected the development of cadmium fluorescent and colorimetric probes. We hope to provide some help for researchers to design cadmium fluorescent probes with higher selectivity, sensitivity and practicability.

Cadmium is a heavy metal which exists widely in industrial and agricultural production and can induce a variety of diseases in organisms.

Europium(III) complex fluorescent sensor for dual channel recognition of Sn2+ and Cu2+ ions in water

A new europium(III) complex Eu(tta)₃L₁ (1a) (L₁ = (2-(3,5-dimethoxyphenyl)-1H-imidazo[4,5-f][1,10]phenanthroline), tta = 2-thenoyltrifluoroacetone) has been prepared and synthesized. The structure of complex was completely determined by several different analytical techniques including single-crystal X-ray diffraction, ¹H and ¹³C NMR. The crystal structure of the complex 1a belonged to monoclinic system with the space group P2₁/n. Its fluorescent properties were systematically studied in details by adding different metal ions in deionized water. Upon addition of Sn²⁺, its fluorescence intensity was strengthened and centered at 460 nm. And when Cu²⁺ was added, its fluorescence emission intensity was quenched quickly. The LODs for Sn²⁺ and Cu²⁺ were calculated to be 4.52 × 10^-7 mol L^-1 and 1.11 × 10^-7 mol L^-1, respectively. Furthermore, this sensor was successfully employed to monitor Sn²⁺ and Cu²⁺ in practical samples.

Highly Emissive Water-Soluble Polysulfurated Pyrene-Based Chromophores as Dual Mode Sensors of Metal Ions

Pyrene-based materials have gained considerable attention as stimuli-responsive chemical sensors. We designed a polysulfurated arene system based on a tetra(phenylthio)pyrene core decorated with four carboxylic acid units. Three different regioisomers, ortho, meta and para were studied in organic and aqueous solution. These systems are soluble in water at pH≥8 due to the deprotonation of carboxylic acids. The addition of metal ions cannot only quench the fluorescence of the central pyrene core, but also control the formation of three-dimensional nanoscopic objects in a dual mode function. Several divalent metal ions were tested and compared. Addition of ethylenediaminetetraacetic acid (EDTA) disassembles the non-emissive supramolecular system and restores the initial fluorescence of the pyrene core.

A highly selective sequential recognition probe for Zn2+ and HSO4-/H2PO4- based on a diarylethene chemosensor

A novel diarylethene derivative chemosensor DTP-o connected to Schiff base unit for fluorescent detection of Zn²⁺ and relay-detection of HSO₄^-/H₂PO₄^- was designed and synthesized successfully. DTP-o displayed excellent photochromism and fluorometric sensing toward Zn²⁺ to form DTP-o-Zn²⁺ complex in acetonitrile with the detection limit of 5.62 × 10^-7 M. And the form of DTP-o combined with Zn²⁺ could further be verified by Job's plot titrations and mass spectrometry analysis. Furthermore, the complex of DTP-o-Zn²⁺ showed an excellent characteristic of fluorescent relay-response toward HSO₄^- and H₂PO₄^- with high sensitivity and selectivity. The detection limits for HSO₄^- and H₂PO₄^- were as low as 3.04 × 10^-8 M and 3.41 × 10^-8 M, respectively. Moreover, the sensor DTP-o could also be applied to detect Zn²⁺ on practical samples and test strips with high accuracy.

Fluorescence determination of trace level of cadmium with pyrene modified nanocrystalline cellulose in food and soil samples

Cadmium is one of the most toxic metal that accumulates in the human body via food chain, industrial/agricultural activites. It also has negative effects in organs such as the brain, liver and central nervous system. Therefore, International Agency for Research on Cancer is classified cadmium as "carcinogenic to humans" (group 1). In this work, novel pyrene modified nanocrystalline cellulose (NP-1) was designed as a fluorescence sensor for selective determination of Cd²⁺ in food and soil samples. FTIR, UV-Vis, SEM, TEM and TGA were used for structural, morphological characterizations and thermal properties of NP-1. The experimental conditions such as selectivity, pH, sensor concentration, photostability, time and interaction mechanism were examined and optimized. The LOD was determined as 0.09 μM (10.70 μg/L) which was lower than WHO's permissible limit of cadmium in plant with 0.10-60.00 μM linear working range. Validation of the present method was performed by spike/recovery test and ICP-MS, then fluorescence determination of Cd²⁺ in food and soil samples was succesfully applied. The results indicated that the proposed method based on "turn-on" fluorescence of NP-1 was a simple, sensitive and reliable for rapid determination of Cd²⁺ in real samples with high applicability and stability.

Crystal structure of 4-(2-(benzo[b]thiophen-2-yl)-3,3,4,4,5,5-hexafluorocyclopent-1-en-1-yl)-1,5-dimethyl-1H-pyrrole-2-carbonitrile, C20H12F6N2S

C20H12F6N2S, monoclinic, P21/c (no. 14), a = 8.2091(9) Å, b = 13.9215(16) Å, c = 16.5280(19) Å, β = 94.0670(10)°, V = 1884.1(4) Å3, Z = 4, R gt(F) = 0.0421, wR ref(F 2) = 0.1226, T = 296(2) K.

Crystal structure of (E)-2-(5,5-dimethyl-3-(4-((7-nitrobenzo[c][1,2,5]oxadiazol-4-yl)oxy)styryl)cyclohex-2-en-1-ylidene)malononitrile, C25H19N5O4

C25H19N5O4, triclinic, P1̄ (no. 2), a = 7.5952(11) Å, b = 9.4729(13) Å, c = 16.260(2) Å, α = 76.559(2)°, β = 87.394(2)°, γ = 73.886(2)°, V = 1092.9(3) Å3, Z = 4, R gt(F) = 0.0433, wR ref(F 2) = 0.1293, T = 296(2) K.

Structure of 7-(3,3,4,4,5,5-hexafluoro-2-(2-methylbenzo[b]thiophen-3-yl)cyclopent-1-en-1-yl)-8-methylquinoline, C24H15F6NS

C24H15F6NS, monclinic, P21/n (no. 14), a = 10.5279(11) Å, b = 21.242(2) Å, c = 10.7096(11) Å, β = 119.1850(10)°, V = 2091.0(4) Å3, Z = 4, R gt(F) = 0.0488, wR ref(F 2) = 0.1441, T = 296(2) K.

A diaminomaleonitrile-appended BODIPY chemosensor for the selective detection of Cu2+ via oxidative cyclization and imaging in SiHa cells and zebrafish

A specific Cu²⁺ sensor, 2-amino-3-(BODIPYmethyleneamino)maleonitrile (BDM), was established by a simple dehydration between BODIPY and diaminomaleonitrile. Cu²⁺ could be recognized by BDM over other competing metal ions in acetonitrile with distinct fluorescence emission signal response. Upon the addition of Cu²⁺ to BDM in acetonitrile, the maximum absorption at approximately 530 nm on the longer wavelength side was quenched, and the emission at 530 nm was ignited simultaneously. The fluorescence intensity enhancement could reach a maximum of 204 times the intensity of the BDM blank solution. The fluorescence "off-on" effect is established according to the Cu²⁺-induced fast intramolecular oxidative cyclization reaction, which could be deduced from the formation of an imidazole ring appended to the cyclization product (2-BODIPY-1H-imidazole-4,5-dicarbonitrile, BMC). Single-crystal structure analysis of the sensor BDM and cyclization product BMC further demonstrated this oxidative cyclization. Finally, the Cu²⁺ recognition property of BDM was validated in SiHa cells and living zebrafish. Additionally, the blood-brain barrier of the zebrafish can be penetrated by the BDM dye and the neuron cells in the brain were stained.

A simple fluorescent probe for detection of Ag+ and Cd2+ and its Cd2+ complex for sequential recognition of S2

In this study, we designed and synthesized a simple probe 2-(8-((8-methoxyquinolin-2-yl)methoxy)quinolin-2-yl)benzo[d]thiazole (DQT) for detection of Ag⁺ and Cd²⁺ in a CH₃OH/HEPES (9 : 1 v/v, pH = 7.30) buffer system. Its structure was characterized by NMR, ESI-HR-MS and DFT calculations, and its fluorescence performance was also investigated. Probe DQT showed fluorescence quenching in response to Ag⁺ and Cd²⁺ with low detection limits of 0.42 μM and 0.26 μM, respectively. Importantly, the complexation of the probe with Cd²⁺ resulted in a red shift from blue to green, making it possible to detect Ag⁺ and Cd²⁺ by the naked eye under an ultraviolet lamp. The DQT-Cd²⁺ complex could be used for sequential recognition of S^2-. The recovery response could be repeated 3 times by alternate addition of Cd²⁺ and S^2-. A filter paper strip test further demonstrated the potential of probe DQT as a convenient and rapid assay.

Quinoline- and isoquinoline-derived ligand design on TQEN (N,N,N′,N′-tetrakis(2-quinolylmethyl)ethylenediamine) platform for fluorescent sensing of specific metal ions and phosphate species

Utilizing the unique metal-binding and fluorescent properties of methoxy-substituted (iso)quinolines, varieties of fluorescent probes were developed from TQEN (N,N,N′,N′-tetrakis(2-quinolylmethyl)ethylenediamine) structure.

A solvent-dependent chemosensor for fluorimetric detection of Hg2+ and colorimetric detection of Cu2+ based on a new diarylethene with a rhodamine B unit

A novel solvent-dependent chemosensor based on a diarylethene derivative for fluorescent “turn-on” recognition of Hg²⁺ and colorimetric detection of Cu²⁺ was synthesized, its multi-controllable photoswitchable behaviors with light and chemical stimuli were investigated.