Chemically diverse small molecule fluorescent chemosensors for copper ion

A luminescent ATCUN peptide variant with enhanced properties for copper(II) sensing in biological media

The measurement of labile Cu^II in biological samples is fundamental for understanding Cu metabolism and has been emerging as a promising diagnostic marker for Cu-related pathologies such as Wilson's and Alzheimer's diseases. The use of fluorescent chelators may be useful to circumvent separation steps employed by current methods. For this purpose, we recently designed a selective and suited-affinity turn-off luminescent probe based on a peptide bearing the Cu^II-binding Xxx-Zzz-His (Amino-Terminal Cu^II- and Ni^II-binding, ATCUN) motif and a Tb^III-DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) complex. Here, we present an analogue probe bearing the ATCUN motif variant Xxx-His-His. This probe showed much faster response in biologically-relevant media and higher stability than the previous motif at low pH. These features could be beneficial to the measurement of dynamic Cu^II fluctuations and the application in slightly acidic media, such as urine.

Silicon-based fluorescent platforms for copper(ii) detection in water

The potential of silicon-based fluorescent platforms for the detection of trace toxic metal ions was investigated in an aqueous environment. To this aim, silicon chips were first functionalized with amino groups, and fluorescein organic dyes, used as sensing molecules, were then covalently linked to the surface via formation of thiourea groups. The obtained hybrid heterostructures exhibited high sensitivity and selectivity towards copper(ii), a limit of detection compatible with the recommended upper limits for copper in drinking water, and good reversibility using a standard metal-chelating agent. The fluorophore-analyte interaction mechanism at the basis of the reported fluorescence quenching, as well as the potential of performance improvement, were also studied. The herein presented sensing architecture allows, in principle, tailoring of the selectivity towards other metal ions by proper fluorophore selection, and provides a favorable outlook for integration of fluorescent chemosensors with silicon photonics technology.

A novel fluorescent BODIPY-based probe for detection of Cu2+ and H2S based on displacement approach

A new BODIPY-based fluorescent probe (BC-DPA) was prepared by a simple method for Cu²⁺ detection in aqueous media and living cells. BC-DPA displayed excellent selectivity toward Cu²⁺via fluorescence "turn-off" mode when a mononuclear Cu(Ⅱ) complex is formed. The corresponding BC-DPA-Cu(Ⅱ) complex, whose structure was characterized by X-ray crystallography, has Cu(Ⅱ) in a distorted octahedral geometry. On the basis of the displacement approach, the fluorescence of BC-DPA-Cu²⁺ was recovered in the presence of S^2-, which allowed the system to act as a sensitive "turn-on" sensor for hydrogen sulfide. Furthermore, BC-DPA exhibited noticeable permeability and low cytotoxicity, making it a useful tool to detect Cu²⁺ in biosystems.

A novel near-infrared-emitting aza-boron-dipyrromethene-based remarkable fluorescent probe for Hg2+ in living cells

A new near-infrared (NIR)-emitting aza-boron-dipyrromethene dye with two electron-donating amino groups at 1- and 7-positions has been prepared via several steps of reactions. This probe showed a NIR absorption at 748 nm with an obvious shoulder peak at 634 nm in CH₃CN/H₂O. Interestingly, a NIR fluorescence emission at 843 nm was observed with a large Stokes shift of 95 nm. This novel NIR-emitting aza-boron-dipyrromethene dye was further investigated as a Hg²⁺-sensing fluorescent probe, which selectively bound to Hg²⁺, showing a blue-shifted and sharp absorption band at 695 nm with the disappearance of the shoulder peak at 634 nm. Correspondingly, the color change could be easily seen from blue to green. Interestingly, the emission exhibited an absolutely "turn-on" peak at 725 nm with a significant blue shift by 118 nm (from 843 to 725 nm), due to the efficient inhibition of the intramolecular-charge-transfer process arising from two amino groups. This probe was finally introduced to Hela cells, showing a "OFF-ON" NIR emission upon exposure to Hg²⁺. The overall results confirmed that this novel NIR-emitting aza-boron-dipyrromethene fluorescent probe with a large Stokes shift could serve as a colorimetric and fluorescent "turn-on" sensor for Hg²⁺ in both solutions and living cells.

A multi-functional picolinohydrazide-based chemosensor for colorimetric detection of iron and dual responsive detection of hypochlorite

A novel effective chemosensor HPHN, (E)-6-hydroxy-N'-((2-hydroxynaphthalen-1-yl)methylene) picolinohydrazide, was synthesized. HPHN sensed Fe^3+/2+ with the changes of color from yellow to orange without obvious inhibition from other cations. In addition, HPHN could detect ClO^- by both the color change from yellow to colorless and the fluorescence quenching. The binding modes of HPHN with Fe^3+/2+ and ClO^- were determined to be 1:1 with Job plot and ESI-mass analysis. HPHN displayed low detection limits of 0.29 μM for Fe³⁺ and 0.77 μM for Fe²⁺. For ClO^-, the detection limit was 6.20 μM by colorimetric method and 3.99 μM by fluorescent one, respectively. Moreover, HPHN can be employed to quantify Fe³⁺ and ClO^- in environmental samples and apply to cell imaging for ClO^-.

Ratiometric Detection of Mercury (II) Ions in Living Cells Using Fluorescent Probe Based on Bis(styryl) Dye and Azadithia-15-Crown-5 Ether Receptor

Bis(styryl) dye 1 bearing N-phenylazadithia-15-crown-5 ether receptor has been evaluated as a ratiometric fluorescent chemosensor for mercury (II) ions in living cells. In aqueous solution, probe 1 selectively responds to the presence of Hg²⁺ via the changes in the emission intensity as well as in the emission band shape, which is a result of formation of the complex with 1:1 metal to ligand ratio (dissociation constant 0.56 ± 0.15 µM). The sensing mechanism is based on the interplay between the RET (resonance energy transfer) and ICT (intramolecular charge transfer) interactions occurring upon the UV/Vis (380 or 405 nm) photoexcitation of both styryl chromophores in probe 1. Bio-imaging studies revealed that the yellow (500-600 nm) to red (600-730 nm) fluorescence intensity ratio decreased from 4.4 ± 0.2 to 1.43 ± 0.10 when cells were exposed to increasing concentration of mercury (II) ions enabling ratiometric quantification of intracellular Hg²⁺ concentration in the 37 nM-1 μM range.

The Role of 8-Amidoquinoline Derivatives as Fluorescent Probes for Zinc Ion Determination

Mass-spectrometry-based and X-ray fluorescence-based techniques have allowed the study of the distribution of Zn2+ ions at extracellular and intracellular levels over the past few years. However, there are some issues during purification steps, sample preparation, suitability for quantification, and the instruments' availability. Therefore, work on fluorescent sensors based on 8-aminoquinoline as tools to detect Zn2+ ions in environmental and biological applications has been popular. Introducing various carboxamide groups into an 8-aminoquinoline molecule to create 8-amidoquinoline derivatives to improve water solubility and cell membrane permeability is also a recent trend. This review aims to present a general overview of the fluorophore 8-aminoquinoline and its derivatives as Zn2+ receptors for zinc sensor probes. Various fluorescent chemosensor designs based on 8-amidoquinoline and their effectiveness and potential as a recognition probe for zinc analysis were discussed. Based on this review, it can be concluded that derivatives of 8-amidoquinoline have vast potential as functional receptors for zinc ions primarily because of their fast reactivity, good selectivity, and bio-compatibility, especially for biological applications. To better understand the Zn2+ ion fluorophores' function, diversity of the coordination complex and geometries need further studies. This review provides information in elucidating, designing, and exploring new 8-amidoquinoline derivatives for future studies for the improvement of chemosensors that are selective and sensitive to Zn2+.

Polyoxometalate based ionic crystal: dual applications in selective colorimetric sensor for hydrated ZnCl2 and antimicrobial activity

One-pot synthesis of POM-salt ([Himi]₄[SiMo₁₂O₄₀] (1)) was achieved by mixing silicomolybdic acid and imidazole in acidic conditions and characterized by FTIR, TGA, SEM, EDX, ICP-OES and XPS.

Hydrazone-Based Small-Molecule Chemosensors

The hydrazone functional group is widely applied in several fields. The versatility and large use of this chemotype are attributed to its easy and straightforward synthesis and unique structural characteristics which is useful for different chemical and biological purposes. Recently hydrazone scaffold has been widely adopted in the design of small-molecule fluorescent and colorimetric chemosensors for detecting metals and anions because of its corresponding non-covalent interactions. This chapter provides an overview of hydrazone-based fluorescent and colorimetric chemosensors for anions and metals of biological interest, with their representative rational designs in the last 15 years. We hope this chapter inspires the development of novel and powerful fluorescent and colorimetric chemosensors for a broad range of applications.

Internet of Things-Enabled Aggregation-Induced Emission Probe for Cu2+ Ions: Comprehensive Investigations and Three-Dimensional Printed Portable Device Design

Herein, we have developed a novel aggregation-induced emission (AIE) probe and three-dimensional (3D) printed portable device for copper (Cu²⁺) sensing in an aqueous medium. A ubiquitous synthetic route has been employed to devise the anthracene-conjugated imidazo[1,5-a]pyridine (TL19) probe as a unique anchor for Cu²⁺ ions. The TL19 is meticulously characterized through pivotal spectroscopic techniques, and the satisfactory results were obtained. The solvatochromic analysis and density functional theory calculations cohesively reveal that the TL19 exhibits the intramolecular charge transfer transition upon photoexcitation. Intriguingly, the TL19 exhibits spherically shaped nanoaggregates and enhanced fluorescence in DMSO/water (10:90) mixtures. This fluorescent nanoaggregate instantaneously responded toward the detection of Cu²⁺ via a deaggregation mechanism. The detection limit is found to be 9 pM in an aqueous medium. Further, the detection of Cu²⁺ in the HeLa cells has also been achieved due to bright green fluorescence, photostability, and biocompatibility nature of TL19 aggregates. On the other hand, an internet of things (IoT)-embedded 3D printed portable device is constructed for the detection of Cu²⁺ ions in real water samples. The Cu²⁺ detection is achieved through an IoT device, and results were acknowledged through an android application in 3.32 s round-trip time. Thus, the IoT-enabled AIE probe could be a prospective device for Cu²⁺ detection in a constrained environment.

A novel dihydro phenylquinazolinone-based two-in-one colourimetric chemosensor for nickel(ii), copper(ii) and its copper complex for the fluorescent colourimetric nanomolar detection of the cyanide anion

Currently, considerable efforts have been devoted to the detection and quantification of hazardous multi-analytes using a single probe. Herein, we have developed a simple, environment-friendly colourimetric sensor for the sensitive, selective and rapid detection of Ni2+ and Cu2+ ions using a simple organic Schiff base ligand L in methanol-Tris-HCl buffer (1 : 1 v/v, 10 mM, pH = 7.2). The probe L exhibited a binding-induced colour change from colourless to yellow and fluorescence quenching in the presence of both Ni2+ and Cu2+ ions. The interactions between L and the respective metal ions were studied by Job's plot, electrospray ionisation-mass spectrometry (ESI-MS), Fourier-transform infrared spectroscopy (FT-IR), density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations. The limit of detection (LOD) of L towards Ni2+ and Cu2+ was calculated to be 7.4 × 10-7 M and 4.9 × 10-7 M, respectively. Furthermore, the L-Cu2+ complex could be used as a new cascade fluorescent-colourimetric sensor to detect CN- ions with a very low level of detection (40 nM). Additionally, L could operate in a wide pH range, and thus was successfully applied for the detection and quantification of Ni2+ and Cu2+ in environmental samples, and for building OR- and IMPLICATION-type logic gates.

A dual-functional fluorescent probe for sequential determination of Cu2+/S2- and its applications in biological systems

A new acylhydrazine-derived Schiff base fluorescence probe DMI based on "ON-OFF-ON" fluorescence strategy was presented in this paper. Probe DMI could detect Cu²⁺ selectively and sensitively with dramatic fluorescence quenching in CH₃OH-PBS (v/v = 3:7) mixed solution. Once the complex DMI-Cu²⁺ interacted with S^2-, 10.67-folds fluorescence increase was induced via a displacement mechanism under the same experimental conditions. The corresponding detection limits for Cu²⁺ and S^2- were calculated to be 1.52 × 10^-8 M and 1.79 × 10^-8 M, respectively. The structures of DMI and DMI-Cu²⁺ were systematically characterized by Job's plot analysis, ESI-MS, IR, X-ray diffraction and density functional theory calculations. Furthermore, fluorescence imaging in MCF-7 cells and zebrafish demonstrated the probe DMI could act as a useful tool to monitor and track intracellular Cu²⁺ and S^2-, which was encouraged by remarkable fluorescence performance and low cytotoxicity. Importantly, the complex DMI-Cu²⁺ could be applied to detect corrupt blood samples, which could estimate the time of death.

Thiophene-phenylquinazoline probe for selective ratiometric fluorescence and visual detection of Fe(iii) and turn-off fluorescence for I- and its applications

A 2,5-bis(4-phenylquinazolin-2-yl)thiophene (BQT) probe is designed, synthesized and explored for selective ratiometric fluorescence and visual detection of Fe³⁺ and as a turn-off fluorescence probe for I^- anion. BQT is colorless and has blue emission in CH₃CN solution. BQT selectively complexes with Fe³⁺, turns its solution from colorless to greenish yellow and enables the ratiometric sensing of Fe³⁺ with limit of detection (LOD) and limit of quantitation (LOQ) of 2 × 10^-8 M and 6.1 × 10^-8 M, respectively. Binding constant of BQT with Fe³⁺ is found to be 4.1 × 10^-4 M^-1. BQT is also able to sense I^- anion present in aqueous solution by selectively turning colorless to yellow and fluorescence quenching with a LOD of 1.7 × 10^-7 M and LOQ of 5.2 × 10^-7 M. BQT sensing ability is not influenced by the presence of other metal ions and anions in the vicinity. The BQT-Fe³⁺ complex is thoroughly characterized using MALDI-TOF, NMR and Job's plot. A reversibility experiment with EDTA suggests BQT is a reversible fluorescent chemosensor for Fe³⁺ ions. The spectroscopic data of BQT and its complexes are employed to construct a field test kit for qualitative analysis and INHIBIT logic gate.

From Zn(II) to Cu(II) Detection by MRI Using Metal-Based Probes: Current Progress and Challenges

Zinc and copper are essential cations involved in numerous biological processes, and variations in their concentrations can cause diseases such as neurodegenerative diseases, diabetes and cancers. Hence, detection and quantification of these cations are of utmost importance for the early diagnosis of disease. Magnetic resonance imaging (MRI) responsive contrast agents (mainly Lanthanide(+III) complexes), relying on a change in the state of the MRI active part upon interaction with the cation of interest, e.g., switch ON/OFF or vice versa, have been successfully utilized to detect Zn2+ and are now being developed to detect Cu2+. These paramagnetic probes mainly exploit the relaxation-based properties (T1-based contrast agents), but also the paramagnetic induced hyperfine shift properties (paraCEST and parashift probes) of the contrast agents. The challenges encountered going from Zn2+ to Cu2+ detection will be stressed and discussed herein, mainly involving the selectivity of the probes for the cation to detect and their responsivity at physiologically relevant concentrations. Depending on the response mechanism, the use of fast-field cycling MRI seems promising to increase the detection field while keeping a good response. In vivo applications of cation responsive MRI probes are only in their infancy and the recent developments will be described, along with the associated quantification problems. In the case of relaxation agents, the presence of another method of local quantification, e.g., synchrotron X-Ray fluorescence, single-photon emission computed tomography (SPECT) or positron emission tomography (PET) techniques, or 19F MRI is required, each of which has its own advantages and disadvantages.

Recent Developments in Fluorescent Materials for Heavy Metal Ions Analysis From the Perspective of Forensic Chemistry

Forensic chemistry deals with the analysis of various types of physical evidences related to crime, corresponding to the detection of target substances or elements in complex matrices. There is a vital need for highly selective, rapid, and sensitive biosensing technologies in heavy metal ions analysis especially those from living persons, autopsy, food, water, soil, and other identified substances at very preliminary stages. Fluorescent materials-based method for heavy metal ions detection is one of the most important analytical methods, resulting in the ability to measure analytes in complex matrices with unsurpassed selectivity and sensitivity. In this mini review, different fluorescent materials-based analytical methods aiming at several heavy metal ions detection are exclusively reviewed through a comprehensive literature survey. In addition, current challenges to achieve integrated evidence analysis process are briefly discussed to provide an outlook for heavy metal ions detection based on fluorescent analytical methods in the forensic chemistry field.

Switching of C-C and C-N Coupling/Cleavage for Hypersensitive Detection of Cu2+ by a Catalytically Mediated 2-Aminoimidazolyl-Tailored Six-Membered Rhodamine Probe

A robust six-membered rhodamine spirocyclic probe 1 containing a versatile 2-aminoimidazolyl moiety was elaborately designed and synthesized via an attractive C-C and C-N coupling strategy to improve the performance in the detection of ultralow transition metal ions. Probe 1 allowed the highly hypersensitive detection of Cu²⁺ with a superior picomolar limit of detection (35 pM) and nanomolar naked-eye performance (80 nM) via the switching of C-C and C-N cleavage by a catalytic hydrolysis mode.

Photostable Ag(I)-Based Metal-Organic Framework: Synthesis, Structure, and Photocatalytic Selective Oxidation Properties

For Ag(I)-based photocatalysts, the photoreduction of Ag⁺ to metallic Ag is an unignorable issue, which is the major reason for their instability. If electrically neutral excitons rather than electrons were produced over Ag(I)-based photocatalysts, the photoreduction of Ag⁺ is expected to be greatly suppressed. To check this assumption, a Ag-based metal-organic framework containing pyrene, which is in favor of exciton production, is synthesized (denoted as Ag-PTS-BPY) and the structure is solved via single-crystal X-ray diffraction. Ag-PTS-BPY is applied in the photocatalytic selective oxidation of methyl phenyl sulfide, which displays high conversion and selectivity. As expected, no metallic Ag is formed after five cycles of reaction according to the results of X-ray diffraction, Fourier transform infrared, and X-ray photoelectron spectroscopy, and the high conversion is also maintained. The participation of excitons suppresses the involvement of electrons, which are believed to be the reason for the high stability of Ag-PTS-BPY.

A turn-on red-emitting fluorescent probe for determination of copper(II) ions in food samples and living zebrafish

Herein, we developed a turn-on red-emitting fluorescent probe for the sensitive and selective detection of copper ions (Cu²⁺) in food samples and living zebrafish. The probe employs a hemicyanine scaffold as the fluorophore and a 2-pyridinecarbonyl group as the recognition receptor and quenching moiety. The 2-pyridinecarbonyl moiety can be specifically cleaved by Cu²⁺ and results in an approximately 18-fold fluorescence enhancement of the probe, thereby providing a fluorescence turn-on assay for Cu²⁺. Additionally, the probe exhibited excellent selectivity, high sensitivity, a broad linear relationship (0.020 to 8.0 μM), and a low limit of detection (4.0 nM, S/N = 3) for Cu²⁺. Concomitantly, the probe exhibited satisfactory analytical performance when used with actual food samples. Moreover, the probe could be used for in situ determination of Cu²⁺ in both living plant tissues and in living zebrafish.

Croix CM, Koide K. Using Ligand-Accelerated Catalysis to Repurpose Fluorogenic Reactions for Platinum or Copper

The development of a fluorescent probe for a specific metal has required exquisite design, synthesis, and optimization of fluorogenic molecules endowed with chelating moieties with heteroatoms. These probes are generally chelation- or reactivity-based. Catalysis-based fluorescent probes have the potential to be more sensitive; however, catalytic methods with a biocompatible fluorescence turn-on switch are rare. Here, we have exploited ligand-accelerated metal catalysis to repurpose known fluorescent probes for different metals, a new approach in probe development. We used the cleavage of allylic and propargylic ethers as platforms that were previously designed for palladium. After a single experiment that combinatorially examined >800 reactions with two variables (metal and ligand) for each ether, we discovered a platinum- or copper-selective method with the ligand effect of specific phosphines. Both metal-ligand systems were previously unknown and afforded strong signals owing to catalytic turnover. The fluorometric technologies were applied to geological, pharmaceutical, serum, and live cell samples and were used to discover that platinum accumulates in lysosomes in cisplatin-resistant cells in a manner that appears to be independent of copper distribution. The use of ligand-accelerated catalysis may present a new blueprint for engineering metal selectivity in probe development.

A dicyanoisophorone-based highly sensitive and selective near-infrared fluorescent probe for sensing thiophenol in water samples and living cells

Thiophenol (PhSH) is an important sulfhydryl compound in organic synthesis, but it is also a volatile environmental pollutant with high toxicity to organisms. Herein, we reported a novel near-infrared (NIR) probe (1) for turn-on fluorescence detection of PhSH. The probe was prepared by coupling 2,4-dinitrophenyl (DNP) to a dicyanoisophorone-based fluorophore (2). PhSH can specifically perform a nucleophilic aromatic substitution on probe 1 and result in the release of fluorophore 2, thus achieving a turn-on fluorescence response (λ_em = 693 nm). A dramatic color change from red (λ_abs = 525 nm) to blue (λ_abs = 668 nm) was also observed. This fluorescent assay displayed a large Stokes shift (∼133 nm) and a high sensitivity for PhSH, as well as a low detection limit (34 nM). Moreover, probe 1 was successfully applied to monitor PhSH in real water samples and image PhSH in living cells.

Selective Coordination of Cu2+ and Subsequent Anion Detection Based on a Naphthalimide-Triazine-(DPA)2 Chemosensor

A new fluorescent chemosensor for copper (II) and subsequent anion sensing was designed and fully characterized. The sensor consisted of a 1,8-naphthalimide core, bearing two terminal dipicolylamine (DPA) receptor units for binding metal cations, and an ethoxyethanol moiety for enhanced water solubility. The DPA units are connected to position 4 of the fluorophore via a triazine-ethylenediamine spacer. Fluorescence titration studies of the chemosensor revealed a high selectivity for Cu²⁺ over other divalent ions, the emissions were strongly quenched upon binding, and a stability constant of 5.52 log units was obtained. Given the distance from DPA chelating units and the fluorophore, quenching from the Cu²⁺ complexation suggests an electron transfer or an electronic energy transfer mechanism. Furthermore, the Cu²⁺-sensor complex proved to be capable of sensing anionic phosphate derivatives through the displacement of the Cu²⁺ cation, which translated into a full recovery of the luminescence from the naphthalimide. Super-resolution fluorescence microscopy studies performed in HeLa cells showed there was a high intracellular uptake of the chemosensor. Incubation in Cu²⁺ spiked media revealed a strong fluorescent signal from mitochondria and cell membranes, which is consistent with a high concentration of ATP at these intracellular sites.

Fluorescent detection of S2- based on ZnMOF-74 and CuMOF-74

The detection of S^2- is of great significance because excess S^2- can lead to a variety of serious physiological diseases. Here, two metal-organic frameworks (MOFs), ZnMOF-74 and CuMOF-74, were synthesized by using 2,5-dihydroxy terephthalic acid with strong fluorescence as organic ligand and Zn²⁺ or Cu²⁺ as central coordination ions for S^2- detection. Both as-prepared ZnMOF-74 and CuMOF-74 displayed nanospheres with a diameter of about 100 nm. Under the excitation of 353 nm, the ZnMOF-74 had a characteristic emission peak at 537 nm and the CuMOF-74 had a characteristic emission peak at 528 nm under excitation of 356 nm. The interaction of S^2- and Zn²⁺ weakened the fluorescence of ZnMOF-74 but the interaction of S^2- with Cu²⁺ to form CuS restored the fluorescence of CuMOF-74, so the ZnMOF-74 and CuMOF-74 were exploited as a fluorescent nanosensor for sensing S^2-. The ZnMOF-74 sensor has a good linear range of 19.6 nmol L^-1-90.0 μmol L^-1, and the limit of detection was as low as 6.53 nmol L^-1. The CuMOF-74 sensor has a good linear relationship with II₀ in the S^2- concentration range of 1.50 nmol L^-1-125 μmol L^-1, and the limit of detection was 1.50 nmol L^-1. The proposed ZnMOF-74 and CuMOF-74 sensor could also detect S^2- in actual samples.

An unprecedented polyhydroxycarboxylic acid ligand bridged multi-EuIII incorporated tellurotungstate and its luminescence properties

The first polyhydroxycarboxylic acid ligand bridged multi-EuIII-incorporated tellurotungstate K14H10[Eu4(H2O)4W6(H2glu)4O12(B-α-TeW9O33)4]·60H2O (H6glu = d-gluconic acid) (1) was synthesized via an organic ligand-driven self-assembly strategy. The polyhydroxycarboxylic acid ligand bridged tetrameric polyoxoanion [Eu4(H2O)4W6(H2glu)4O12(B-α-TeW9O33)4]24- in 1 can be viewed as an aggregation of four trivacant Keggin [B-α-TeW9O33]8- fragments and an innovative heterometallic [Eu4(H2O)4W6(H2glu)4O12]8+ cluster, in which four high-coordinate polyhydroxy flexible H2glu4- ligands chelate W and Eu centers through carboxyl and hydroxyl groups, giving rise to a heterometallic cluster. The hexagonal packing of the tetrameric polyoxoanions in 1 along the c axis provides excellent porous channels, which greatly increases the specific surface area of the whole framework and may be of benefit for fluorescence sensing in aqueous solution. 1 can function as a "turn-off" luminescence sensor to detect Cu2+ ions in aqueous solution. The limit of detection (LOD) of the 1-sensor is 8.82 × 10-6 mM, which is the lowest among the reported polyoxometalate-based fluorescence sensors. As for the Cu2+-quenching system, it can function as an "off-on" sensor to detect cysteine in an aqueous system, affording a LOD of 1.75 × 10-4 mM. This work opens up an avenue to broaden the applications of polyoxometalate-based materials in the optical intelligence detection field.

Aromatic and heteroaromatic azacrown compounds: advantages and disadvantages of rigid macrocyclic ligands

Current approaches to the synthesis of aromatic and heteroaromatic azamacrocycles and their derivatives are summarized and systematized. The relationship between the structure of azacrown compounds and their complexation behaviour towards metal cations is analyzed. The diversity of practical applications of azamacrocyclic derivatives in medicine, biology and analytical and organic chemistry, as well as for the design of molecular devices is demonstrated.

The bibliography includes 307 references.

A novel near-infrared turn-on and ratiometric fluorescent probe capable of copper(ii) ion determination in living cells

A near-infrared ratiometric fluorescent probe CR-Ac based on a coumarin-benzopyrylium platform has been developed for selective detection of Cu2+. The cell imaging data revealed the capabilities of CR-Ac in monitoring the dynamic changes of subcellular Cu2+ and the quantification of Cu2+ levels in living cells.

A novel tetrapeptide fluorescence sensor for early diagnosis of prostate cancer based on imaging Zn2+ in healthy versus cancerous cells

Zinc as a biomarker can be used to diagnose the early stage prostate cancer, while ZIP1 protein, a zinc transporter is significantly down-regulated in prostate cancer cells. This behavior leads to the apparent alteration of the enrichment ability for zinc between early prostate cancer tissues and healthy tissues. This difference inspires us to develop a novel Zn²⁺ sensor that applies to the clinic diagnosis of early prostate cancer. We designed a tetrapeptide sensor H₂L (Dansyl-Gly-Pro-Trp-Gly-NH₂) according to the photo-induced electron transfer principle (PET), and it performed adequately in Zn²⁺ imaging of prostate cell lines. Based on the assessment of Zn²⁺ enrichment ability, there was distinctly lower Zn²⁺ concentrate in prostate cancer cell lines than healthy prostate epithelial cells. Furthermore, H₂L displayed high sensitivity with a detection limit as low as 49.5 nM, and high specificity for Zn²⁺ detection. Also the low toxicity and the superior cell permeability of H₂L made the imaging of Zn²⁺ ions detection safe and rapid. We expect that H₂L to be a powerful tool for early diagnosis of prostate cancer and a good indicator for the precise resection of cancer tissue during surgery.

Recent progress in chemosensors based on pyrazole derivatives

Colorimetric and fluorescent probes based on small organic molecules have become important tools in modern biology because they provide dynamic information concerning the localization and quantity of the molecules and ions of interest without the need for genetic engineering of the sample. In the past five years, these probes for ions and molecules have attracted great attention because of their biological, environmental and industrial significance combined with the simplicity and high sensitivity of absorption and fluorescence techniques. Moreover, pyrazole derivatives display a number of remarkable photophysical properties and wide synthetic versatility superior to those of other broadly used scaffolds. This review provides an overview of the recent (2016-2020) findings on chemosensors containing pyrazole derivatives (pyrazoles, pyrazolines and fused pyrazoles). The discussion focuses on the design and physicochemical properties of chemosensors in order to realize their full potential for practical applications in environmental and biological monitoring (sensing of metal ions, anions, explosives, and biomolecules). We also present our conclusions and outlook for the future.

Silk Fibroin-Confined Star-Shaped Decahedral Silver Nanoparticles as Fluorescent Probe for Detection of Cu2+ and Pyrophosphate

A green, one-step method for the fabrication of silk fibroin (SF) protected silver decahedral nanoparticles (SF@AgNPs) has been developed. High-resolution transmission electron microscopy characterization demonstrated that the silver decahedral nanoparticles can provide more binding sites with (111) facets. Moreover, a facile strategy based on Cu²⁺ mediated SF@AgNPs was reported as an on-off-on fluorescent system for the detection of Cu²⁺, and the SF@AgNPs can be also used for the determination of pyrophosphate ion (P₂O₇^4-, PPi). The fluorescence of SF@AgNPs was quenched by Cu²⁺ as a complex formed between SF and Cu²⁺ and was restored when PPi was introduced into the system due to the higher binding affinity between PPi and Cu²⁺. Herein, a novel SF@AgNPs-Cu²⁺ fluorescent probe for Cu²⁺ and PPi detection is presented. The proposed assay shows a linear relationship at a Cu²⁺ concentration range from 1 to 6 μM with a detection limit of 33.3 nM. This simple, reliable, selective, and environmentally friendly fluorescent probe also has a wide concentration range from 100 to 700 μM with a detection limit of 6.7 μM for PPi. The 16 types of anions lead to negligible changes in the SF@AgNPs-Cu²⁺ complexes, while restoring the fluorescence intensity of the complexes when added with PPi. Additionally, it is demonstrated that the SF@AgNPs-based fluorescent assay works in real biological samples. It suggests that this proposed method has the potential for application in the clinical detection of Cu²⁺ and PPi.