Recent Development on Copper-Sensor and its Biological Applications: A Review

Metal ion recognition is one of the most prospective research topics in the field of chemical sensors due to its wide range of clinical, biological and environmental applications. In this context, hydrazones are well known compounds that exhibit metal sensing and several biological properties due to the presence of N=CH- bond. Some of the biological properties includes anti-cancer, anti-tumor, anti-oxidant, anti-microbial activities. Hydrazones are also used as a ligand to detect metal ion as well as to generate metal complexes that exhibit medicinal properties. Thus, in recent years, many attempts were made to develop novel ligands with enhanced metal sensing and medicinal properties. In this review, some of the recent development on the hydrazones and their copper complexes are covered from the last few years from 2015-2023. These includes significance of copper ions, synthesis, biological properties, mechanism and metal sensing properties of some of the copper complexes were discussed.

Coordination Chemistry of Mixed-Donor Pyridine-Containing Macrocyclic Ligands: From Optical to Redox Chemosensors for Heavy Metal Ions

2,8-Dithia-5-aza-2,6-pyridinophane (L1) has been used as a receptor unit in the construction of the conjugated redox chemosensor 5-ferrocenylmethyl-2,8-dithia-5-aza-2,6-pyridinophane (L3). In order to further explore the coordination chemistry of L1, and comparatively, that of its structural analogue 2,11-dithia-5,8-diaza-2,6-pyridinophane (L2), featuring two secondary nitrogen atoms in the macrocyclic unit, the crystal structures of the new synthesised complexes [Pb(L1)(ClO4)2]·½CH3CN, [Cu(L2)](ClO4)2·CH3CN and [Cd(L2)(NO3)]NO3 were determined by X-ray diffraction analysis. The electrochemical response of L3 towards the metal ions Cu2+, Zn2+, Cd2+, Hg2+, and Pb2+ was investigated by cyclic voltammetry (CV) in CH2Cl2/CH3CN 0.25:1 (v/v) mixture. Upon addition to L3 of increasing amounts of the aforementioned metal cations, the wave corresponding to the Fc+/Fc redox couple of the un-complexed L3 was gradually replaced by a new reversible wave at more positive potentials and corresponding to the Fc+/Fc redox couple of the complexed ligand. The maximum anodic shift of the ferrocene oxidation wave is observed in the presence of Pb2+ (230 mV), to which corresponds a reaction coupling efficiency (RCE) value as large as 7.9 × 103. The response selectivity of L3 is discussed in reference to the optical selectivity observed for conjugated chemosensors featuring L1 as receptor unit and different fluorogenic fragments as signalling units.

A novel light-harvesting ZIF-9-TCPP as a promising FRET-based ratiometric fluorescence probe for sperm mobility

The concentration of zinc ions in semen is significantly correlated with sperm viability and male fertility. In this work, a reliable ratiometric fluorescence probe (ZIF-9-TCPP) based on the efficient Förster resonance energy transfer (FRET) process between two luminophores, benzimidazole (BIM) and meso-tetra (4-carboxyphenyl) porphyrin (TCPP) for Zn2+ detection has been constructed, where the emissions of BIM and TCPP are used as reference and detection signals. The proximity of BIM and TCPP in one framework (ZIF-9-TCPP) and the overlapped spectra between BIM and TCPP afford the attainment of a highly efficient FRET (around 90% efficiency). Efficient FRET improves the fluorescence intensity of porphyrin to enhance the sensitivity of detection. The unique spectral shift resulting from Zn2+ binding to the porphyrin ring ensures the selectivity of detection. In addition, the response mechanism of the proposed ratiometric probes to Zn2+ has been investigated. This work provides a convenient way to design an efficient FRET system and a promising method for sperm mobility detection.

Fluorophore-quencher complexes (Cu2+/Al3+) of coumarin Schiff bases as chemosensors for the detection of L-glutamic acid and L-arginine: in vitro and in vivo studies

This study reports the development of new probes RR1 ((1E)-1-(1-(6-bromo-2-oxo-2H-chromen-3-yl)ethylidene)ethyl thiosemicarbazone) and RR2 ((1E)-1-(1-(6-bromo-2-oxo-2H-chromen-3-yl)ethylidene)phenyl thiosemicarbazone), which selectively showed fluorescence turn 'OFF' response towards Cu2+ and Al3+. Further, complexes of RR1-Cu2+ and RR2-Al3+ acted as chemosensors for the detection of L-amino acids. RR1-Cu2+ selectively detected L-arginine (fluorescence turn 'ON'), and RR2-Al3+ selectively detected L-glutamic acid (fluorescence turn 'ON'). The existence of the fluorophore-quencher complexes RR1-Cu2+ and RR2-Al3+ was confirmed by theoretical studies. Further, the chemosensors RR1-Cu2+ and RR2-Al3+ have three possible structural isomers (RR1-Cu2+-L-arginine - A, B and C) and (R2-Al3+-L-glutamic acid - D, E and F), as confirmed by theoretical studies. In vitro bio-imaging of the probes (RR1 and RR2), complexes (RR1-Cu2+ and RR2-Al3+) and complexes associated with L-arginine (RR1-Cu2+-L-arginine) and L-glutamic acid (R2-Al3+-L-glutamic acid) was performed in the MDA-MB-231 cell line using their IC50 concentrations. In addition, in vivo live cell imaging studies were conducted using C. elegans as the model organism.

A Novel Rhodamine B Derivative as a "Turn-on" Fluorescent Sensor for Cu2+ with High Selectivity and Sensitivity

The number of "turn-on" fluorescent probes for Cu2+ is relatively limited, and interference from other metal cations presents a significant challenge for these sensors. In this study, we synthesized and characterized a rhodamine B-based sensor, designated as RBHP, using 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (PMBP) and rhodamine B hydrazide. Selectivity, sensitivity, solvent effects, water content, and pH of RBHP in relation to Cu²⁺ were conducted. RBHP exhibited an exceptionally low fluorescence background signal in acetonitrile and demonstrated a "turn-on" fluorescent response to Cu²⁺. The PMBP-based acylhydrazone moiety and acetonitrile as the detection solvent are crucial for the selective detection. RBHP shows potential as a highly selective and sensitive fluorescent sensor for Cu2+.

A Pyridinium fluorophore for the detection of zinc ions under autophagy conditions

Molecular probes for sensing and imaging of various analytes and biological specimens are of great importance in clinical diagnostics, therapy, and disease management. Since the cellular concentration of free Zn2+ varies from nanomolar to micromolar range during cellular processes and the high affinity Zn2+ imaging probes tend to saturate at lower concentrations of free Zn2+, fluorescence based probes with moderate binding affinity are desirable in distinguishing the occurrence of higher zinc concentrations in the cells. Herein, we report a new, pentacyclic pyridinium based probe, PYD-PA, having a pendant N,N-di(pyridin-2-ylmethyl)amine (DPA) for Zn2+ detection in the cellular environment. The designed probe is soluble in water and serves as a mitochondria targeting unit, whereas the pendent DPA acts as the coordination site for Zn2+. PYD-PA displayed a threefold enhancement in fluorescence intensity upon Zn2+ binding with a 1:1 binding stoichiometry. Further, the probe showed a selective response to Zn2+ over other biologically relevant metal ions with a moderate binding affinity (Ka = 6.29 × 104 M-1), good photostability, pH insensitivity, and low cytotoxicity. The demonstration of bioimaging in SK-BR-3 breast cancer cell lines confirmed the intracellular Zn ion sensing ability of the probe. The probe was successfully applied for real time monitoring of the fluctuation of intracellular free zinc ions during autophagy conditions, demonstrating its potential for cellular imaging of Zn2+ at higher intracellular concentrations.

A novel organic chromo-fluorogenic optical sensor for detecting chromium ions

Sensing trivalent chromium ion (Cr(III)) is widely applied in different areas, such as clinical analysis, marine, environmental monitoring, or even chemical industry applications. Cr(III) has a significant role in the physiological process of human life. It is classified as an essential micronutrient for living organisms. Herein, we developed and designed a novel optical Cr(III) ions sensor film. The investigated sensor has a relatively small dynamic range of 1.24 × 10-3 to 0.5 μM. We report a highly sensitive optical sensor film for Cr(III) ions based on diethyl 3,4-diaminothieno[2,3-b]thiophene-2,5-dicarboxylate (3D) probe. The optical characteristics of the chemical probe exhibit substantial emission at 460 nm under 354 nm excitation. Besides, the interaction of the Cr(III) ions with 3D involves a complex formation with a 2:1 (metal: ligand) ratio, which is convoyed by the main peak enhancement that centered at 460 nm of 3D, and the main peak is red-shifted to 480 nm. The easily discernible fluorescence enhancement effect is a defining characteristic of the complexation reaction between the 3D probe and Cr(III). On the basis of the substantial fluorescence mechanism caused by the formation of a (Cr(III)-3D complex, which inhibits the photo-induced electron transfer (PET) process, the devised optical sensor was proposed. This film exhibits exceptional sensitivity and selectivity due to its notable fluorescence properties, stock shift of less than 106 nm, and detection capabilities at a significantly low detection limit of 0.37 × 10-3 μM. The detection procedure is executed by utilizing a physiological pH medium (pH = 7.4) with a relative standard deviation RSDr (1 %, n = 3). In addition, the 3D sensor demonstrates a high degree of affinity for Cr(III), as determined by the calculation of its binding constant to be 1.40 × 106. We present an impressive optical sensor that is constructed upon a three-dimensional molecule.

Highly Selective Turn-on Fluorescence Sensor for Cd2+ Ions by Tripodal Organic Ligand

Organic fluorescence sensor for selectively detecting and quantifying toxic heavy metal ions has received significant interest due to their environmental hazards. Herein, we have designed and synthesized a simple tripodal Schiff base ligand (1) based on hydroxy-naphthaldehyde and tris(2-aminoethyl)amine (TREN) and demonstrated highly selective turn-on fluorescence sensing of Cd2+ ions. The free ligand did not show any fluorescence in DMF. In contrast, Cd2+ (10- 4 M) addition exhibited a strong enhancement of fluorescence at 450 nm. Interestingly, other metal ions including Zn2+, which exhibit similar chemistry, did not show any turn-on fluorescence. The concentration-dependent studies of 1 with Cd2+ showed the detection limit of 6.78 × 10- 8 M. NMR spectra of 1 with Cd2+ and computational studies were performed to understand the mechanism of sense.

Broadband-Tunable Vanadium Dioxide (VO2)-Based Linear Optical Cavity Sensor

Sensors fabricated by using a silicon-on-insulator (SOI) platform provide promising solutions to issues such as size, power consumption, wavelength-specific nature of end reflectors and difficulty to detect ternary mixture. To address these limitations, we proposed and investigated a broadband-thermally tunable vanadium dioxide (VO2)-based linear optical cavity sensor model using a finite element method. The proposed structure consists of a silicon wire waveguide on a silicon-on-insulator (SOI) platform terminated with phase-change vanadium oxide (VO2) on each side to provide light confinement. A smooth transmission modulation range of 0.8 (VO2 in the insulator state) and 0.03 (VO2 in the conductive phase state) in the 125 to 230 THz spectral region was obtained due to the of Fabry-Pérot (FP) effect. For the 3.84 μm cavity length, the presented sensor resulted in a sensitivity of 20.2 THz/RIU or 179.56 nm/RIU, which is approximately two orders of magnitude higher than its counterparts in the literature. The sensitivity of the 2D model showed direct relation with the length of the optical cavity. Moreover, the change in the resonating mode line width Δν of approximately 6.94 THz/RIU or 59.96 nm/RIU was also observed when the sensor was subjected to the change of the imaginary part k of complex refractive index (RI). This property of the sensor equips it for the sensing of aternary mixture without using any chemical surface modification. The proposed sensor haspotential applications in the areas of chemical industries, environmental monitoring and biomedical sensing.

Triazole-linked amidopyrene-tagged fluorometric probe for Au3+ ions and pH control aggregation-induced emission

In this paper, an amidopyrene-tagged reversible fluorescence probe 1 has been constructed for the detection of Au(III) ions in H2O/CH3CN (4/1, v/v). It is used to identify the Au(III) ions over several metal ions with excellent sensitivity (LOD: 0.061 µM). The fluorescence quenching of 1 with Au(III) ions might be attributed to the reverse PET process. Probe 1 recognized Au(III) by forming tetravalent geometry with the amide -NH, triazole moiety, free water, and Cl- ion in 1:1 binding mode, which is evidenced by the DFT calculations, FT-IR spectroscopy, and HRMS value of the complex. The application utility of probe 1 was ascertained from the recovery of Au(III) ions from different sources of natural water samples. Interestingly, molecule 1 also showed aggregation-induced emission behavior at basic pH (>10) in H2O/CH3CN medium with high water content. The AIE might be attributed to the formation of self-associates of 1 upon the intermolecular H-bonding interactions between water and donor atom(s) of 1 or the increased polarity of the solvent medium.

A fluorescent magnetic core-shell nanosensor for detection of copper ions in natural waters

A nanosensor based on magnetic core-shell nanoparticles functionalized with rhodamine derivative, N-(3-carboxy)acryloyl rhodamine B hydrazide (RhBCARB), using (3-aminopropyl)triethoxysilane (APTES) as a linker, has been synthesized for detection of Cu(II) ions in water. The magnetic nanoparticle and the modified rhodamine were fully characterized, showing a strong orange emission sensitive to Cu(II) ions. The sensor shows a linear response from 10 to 90 µg L^-1, detection limit of 3 µg L^-1 and no interference of Ni(II), Co(II), Cd(II), Zn(II), Pb(II), Hg(II) and Fe(II) ions. The nanosensor performance is similar to those described in the literature, being a viable option for the determination of Cu(II) ions in natural waters. In addition, the magnetic sensor can be easily removed from the reaction medium with the aid of a magnet and its signal recovered in acidic solution, allowing its reuse in subsequent analysis.

Simple colorimetric copper(II) sensor - Spectral characterization and possible applications

New o-hydroxyazocompound L bearing pyrrole residue was obtained in the simple synthetic protocol. The structure of L was confirmed and analyzed by X-ray diffraction. It was found that new chemosensor can be successfully used as copper(II) selective spectrophotometric regent in solution and can be also applied for the preparation of sensing materials generating selective color signal upon interaction with copper(II). Selective colorimetric response towards copper(II) is manifested by a distinct color change from yellow to pink. Proposed systems were effectively used for copper(II) determination at concentration level 10^-8 M in model and real samples of water.

Design and Synthesis of a Novel ICT Bichromophoric pH Sensing System Based on 1,8-Naphthalimide Fluorophores as a Two-Input Logic Gate and Its Antibacterial Evaluation

The synthesis, sensor activity, and logic behavior of a novel 4-iminoamido-1,8-naphthalimide bichromophoric system based on a "fluorophore-receptor" architecture with ICT chemosensing properties is reported. The synthesized compound showed good colorimetric and fluorescence signaling properties as a function of pH and proved itself as a promising probe for the rapid detection of pH in an aqueous solution and base vapors in a solid state. The novel dyad is able to work as a two-input logic gate with chemical inputs H⁺ (Input 1) and HO^- (Input 2) executing INHIBIT logic gate. The synthesized bichromophoric system and the corresponding intermediates demonstrated good antibacterial activity toward Gram (+) and Gram (-) bacteria when compared with the Gentamycin standard.

Colorimetric Probe for Mn2+ Using a Mixture of an Anionic Dye and a Cationic Polyelectrolyte in an Aqueous Solution

A novel colorimetric probe for Mn²⁺ was easily prepared by mixing negatively charged alizarin complexone (ALC) with positively charged poly[bis(2-chloroethyl)ether-alt-1,3-bis[3-(dimethylamino)propyl]urea] (PQ-2) in aqueous solutions at pH 6.0. Upon adding Mn²⁺ to ALC alone, the solution underwent no distinct color change, while the mixture displayed selective detection of Mn²⁺ over different physiological and environmentally significant metal ions by an efficient naked-eye color change from red to purple. The detection of Mn²⁺ by the mixture was achieved from the electrostatic interactions between ALC and PQ-2. The quantitative determination of Mn²⁺ was obtained by spectrophotometric measurement and naked-eye observation. This sensing strategy can be an attractive approach for the development of new colorimetric probes due to the advantages such as no organic synthesis, facile fabrication, and simple visual detection.

Synthesis, Characterization, Optical Properties, Molecular Modeling and Urease Inhibition Analysis of Organic Ligands and Their Metal Complexes

Recently, screening of efficient urease inhibitors by employing organic small molecules metalloderivatives interests the scientific community due to their efficacy for treatment of urease triggered health complications. This study comprises the synthesis, urease inhibition activity, optical analysis and molecular modeling of hydrazinecarbothioamide and hydrazinecarboxamide metalloderivatives. Characterization of synthesized materials was done by UV-visible, fluorescence, NMR and FTIR spectroscopic analysis. Metalloderivatization of ligands induce increment in urease inhibition potential and effect was prominent for copper complexes with 10-fold enhancement, cobalt complex with 3.5 fold's enhancement and palladium with 2-fold increment in the inhibition efficacy toward urease when it was compared with reference urease inhibitor. Zinc and iron complexes cause declined urease inhibition activity of the bare ligand. The overall activity of hydrazinecarbothioamide slightly exceeds than that of hydrazinecarboxamide, possibly due to larger complexation ability of sulfur-based ligand in comparison to oxygenated derivatives i.e., hydrazinecarboxamide. The enzyme inhibition kinetics for the most active complexes represent the mixed type urease inhibition for 3a and competitive urease inhibition for 5a, as determined by Lineweaver-Burk plots. The docked scoring values for both the ligands were calculated to be 61.34, 64.72, 56.68, 62.94, 64.98 and 58.98. Three active hydrogen bonds were observed in docking complex upon computational analysis of most potent metallodrug 3a inside active region of targeted protein.

Multicolor Emissive Phosphorescent Iridium(III) Complexes Containing L-Alanine Ligands: Photophysical and Electrochemical Properties, DFT Calculations, and Selective Recognition of Cu(II) Ions

Three novel Ir(III) complexes, (ppy)₂Ir(L-alanine) (Ir1) (ppy = 2-phenylpyridine), (F₄ppy)₂Ir(L-alanine) (Ir2) (F₄ppy = 2-(4-fluorophenyl)pyridine), and (F_2,4,5ppy)₂Ir(L-alanine) (Ir3) (F_2,4,5ppy = 2-(2,4,5-trifluorophenyl)pyridine), based on simple L-alanine as ancillary ligands were synthesized and investigated. Due to the introduction of fluorine substituents on the cyclometalated ligands, complexes Ir1-Ir3 exhibited yellow to sky-blue emissions (λ_em = 464-509 nm) in acetonitrile solution. The photoluminescence quantum yields (PLQYs) of Ir1-Ir3 ranged from 0.48-0.69, of which Ir3 with sky-blue luminescence had the highest PLQY of 0.69. The electrochemical study and density functional theory (DFT) calculations show that the highest occupied molecular orbital (HOMOs) energy of Ir1-Ir3 are stabilized by the introduction of fluorine substituents on the cyclometalated ligands, while L-alanine ancillary ligand has little contribution to HOMOs and lowest unoccupied molecular orbitals (LUMOs). Moreover, Ir1-Ir3 presented an excellent response to Cu²⁺ with a high selectivity, strong anti-interference ability, and short response time. Such a detection was based on significant phosphorescence quenching of their emissions, showing the potential application in chemosensors for Cu²⁺.

Polymer based nanocomposites: A strategic tool for detection of toxic pollutants in environmental matrices

A large fraction of population is suffering from waterborne diseases due to the contaminated drinking water. Both anthropogenic and natural sources are responsible for water contamination. Revolution in industrial and agriculture sectors along with a huge increase in human population has brought more amount of wastes like heavy metals, pesticides and antibiotics. These toxins are very harmful for human health, therefore, it is necessary to sense their presence in environment. Conventional strategies face various problems in detection and quantification of these pollutants such as expensive equipment and requirement of high maintenance with limited portability. Recently, nanostructured devices have been developed to detect environmental pollutants. Polymeric nanocomposites have been found robust, cost effective, highly efficient and accurate for sensing various environmental pollutants and this is due to their porous framework, multi-functionalities, redox properties, great conductivity, catalytic features, facile operation at room temperature and large surface area. Synergistic effects between polymeric matrix and nanomaterials are responsible for improved sensing features and environmental adaptability. This review focuses on the recent advancement in polymeric nanocomposites for sensing heavy metals, pesticides and antibiotics. The advantages, disadvantages, operating conditions and future perspectives of polymeric nanocomposites for sensing toxic pollutants have also been discussed.

Metal-Enhanced Hg2+-Responsive Fluorescent Nanoprobes: From Morphological Design to Application to Natural Waters

Metal-enhanced fluorescence (MEF) is a powerful tool in the design of sensitive chemical sensors by improving brightness and photostability of target-responsive fluorophores. Compounding these advantages with the modest hardware requirements of fluorescence sensing compared to that of centralized elemental analysis instruments, thus expanding the use of MEF to the detection of low-level inorganic pollutants, is a compelling aspiration. Among the latter, monitoring mercury in the environment, where some of its species disseminate through the food chain and, in time, to humans, has elicited a broad research effort toward the development of Hg²⁺-responsive fluorescent sensors. Herein, a Hg²⁺-sensitive MEF-enabled probe was conceived by grafting a Hg²⁺-responsive fluorescein derivative to concentric Ag@SiO₂ NPs, where the metallic core enhances fluorescence emission of molecular probes embedded in a surrounding silica shell. Time-resolved fluorescence measurements showed that the fluorophore's excited-state lifetime decreases from 3.9 ns in a solid, coreless silica sphere to 0.4 ns in the core-shell nanoprobe, granting the dye a better resistance to photobleaching. The Ag-core system showed a sizable improvement in the limit of detection at 2 nM (0.4 ppb) compared to 50 nM (10 ppb) in silica-only colloids, and its effectiveness for natural water analysis was demonstrated. Overall, the reported nanoarchitecture hints at the potential of MEF for heavy metal detection by fluorescence detection.

A Zinc (II) Complex Comprising Aminoethyl-Nitropyridine Derived N,N,O-Donor Schiff Base Ligand Serves as an Efficient ON-OFF Probe for Cu (II)

A new fluorescent zinc (II) complex based probe 1 encompassing a Schiff base (E)-2-methoxy-6-((2-(5-nitropyridin-2-ylamino)ethylimino)methyl)phenol (HL) has been designed, synthesized and used for the highly selective detection of Cu²⁺ . Ligand HL and complex 1 have been characterized by various spectroscopic techniques such as ¹ H, ¹³ C-NMR, FT-IR, HR-MS, UV/vis and fluorescence studies. Ligand HL did not exhibit any considerable change in fluorescence in presence of various cations. Notably, its Zn (II)-complex 1 exhibited highly selective 'Turn-OFF' fluorescence signalling toward Cu²⁺ which remains uninterrupted with competing analytes. Probe 1 interacts with Cu²⁺ in 1:2 (1: Cu²⁺ ) stoichiometry as estimated through Job's plot. Moreover, selectivity of 1 was further confirmed through interaction of 1+ Cu²⁺ complex with some possible interfering metal ions inducing insignificant response. Additionally, association and quenching constant have been determined to be 3.30 × 10⁴ M^-1 and 0.21× 10⁵ M^-1 through Benesi-Hildebrand method and Stern-Volmer plot, respectively.

A Novel Reversible Fluorescent Probe for Cu2+and S2-Ions and Imaging in Living Cells

A novel fluorescent probe TSOC (thiazole salicylaldehyde oxazole chlorinated) was synthesized based on benzothiazole conjugated olefinic bond with salicylicaldehyde unit as fluorophore and a phenyl oxazole unit as bonding unit. The probe could reversibly detect of Cu2+ and S2- over other common ions with longer emission and large stokes shift in an aqueous solution at pH 7.3 (DMSO-Hepes, v/v, 5:1, 10 mM). The bonding mechanism was supported through the titration experiment of fluorescence and absorption spectroscopy, 1H-NMR titration, HR-MS and DFT calculations. Moreover, the probe further exhibited good cell permeability and were successfully used to visualize Cu2+ and S2- in living cells.

The Schiff Base Probe With J-aggregation Induced Emission for Selective Detection of Cu2

Here, three Schiff bases 3a-c, differing by the substitutions (-H, -Cl, and -N(CH₃)₂) on the phenyl ring, have been designed and synthesized via the reaction of ortho-aminophenol with benzaldehyde, 2,4-dichlorobenzaldehyde and para-dimethylamine benzaldehyde in 1:1 molar ratio with favourable yields of 89-92%, respectively. Their structural characterizations were studied by FT-IR, NMR, MALDI-MS and elemental analysis. The fluorescence behaviours of compounds 3a and 3b exhibited a severe aggregation caused quenching (ACQ) effect in EtOH/water system. On the contrary, compound 3c had an obvious J-aggregation induced emission (AIE) feature in EtOH/water mixture (v/v = 1:1), and exhibited excellent sensitivity and anti-interference towards Cu²⁺ with the limit of detection (LOD) of 1.35 × 10^-8 M. Job's plot analysis and MS spectroscopic study revealed the 2:1 complexation of probe 3c and Cu²⁺. In addition, probe 3c was successfully applied to the determination of Cu²⁺ in real aqueous samples.

A reasonably constructed fluorescent chemosensor based on the dicyanoisophorone skeleton for the discriminative sensing of Fe3+ and Hg2+ as well as imaging in HeLa cells and zebrafish

In this study, a new fluorescent sensor dicyanoisophorone Rhodanine-3-acetic acid (DCI-RDA) (DCI-RDA) has been developed by employing a DCI-based push–pull dye as the fluorophore and RDA as the recognition moiety for the simultaneous sensing of Fe³⁺ and Hg²⁺ with a large Stokes Shift (162 nm), high selectivity and sensitivity, and low LOD (1.468 μM for Fe³⁺ and 0.305 μM for Hg²⁺). In particular, DCI-RDA has a short response time (30 s). The Job's plot method in combination with ¹H NMR titration and theoretical calculations was used to determine the stoichiometry of both DCI-RDA-Fe³⁺/Hg²⁺ complexes to be 1 : 1. Moreover, DCI-RDA is applied as a fluorescent probe for imaging in HeLa cells and zebrafish, indicating that it can be potentially applied for Fe³⁺/Hg²⁺ sensing in the field of biology.

A new fluorescent sensor dicyanoisophorone rhodanine-3-acetic acid has been developed by employing a DCI-based push–pull dye as the fluorophore and RDA as the recognition moiety for the simultaneous sensing of Fe³⁺ and Hg²⁺.

Highly Selective and Sensitive Colorimetric and Fluorescent Chemosensors for Rapid Detection of Cyanide Anions in Aqueous Medium: Investigation on Supramolecular Recognition of Tweezer‑shaped Salophenes

Three tweezer‑shaped salophenes having catechols (1), phenols (2) and anisoles (3) units in conjunction to the dipodal Schiff bases have been applied for the optical sensing of cyanide (CN¯) ions in CH3CN-H2O (7:3) as solvent of choice. Among them, compounds 1 and 2 recognized CN¯, relying on distinct color and spectral changes. They are easy-to-use probes that exhibit extremely high sensitivity (limit of detection = 1-10 nM), rapid response (5 s) and excellent selectivity. Moreover, the visual detection and concentration determination of CN¯ by solution test kits of both sensors are the advantages for the practical applications. Based on the fluorescence and NMR spectroscopy, as well as the OH¯ and reversibility experiments, the explicit effect of hydroxyl groups on sensing and as well the different recognition of 1 and 2 toward CN¯ ions was proved. While probe 1 senses CN¯ via deprotonation, probe 2 recognizes it through an intramolecular aldimine condensation cyclization, leading to formation of anions of dihydroxyquinoxaline 4. This chemodosimetry is being reported for the first time in a Schiff's base. Furthermore, the similarity of fluorescence and NMR responses of 2 and 4 toward CN¯ supports the proposed process.

Deep Learning Insights into Lanthanides Complexation Chemistry

Modern structure-property models are widely used in chemistry; however, in many cases, they are still a kind of a "black box" where there is no clear path from molecule structure to target property. Here we present an example of deep learning usage not only to build a model but also to determine key structural fragments of ligands influencing metal complexation. We have a series of chemically similar lanthanide ions, and we have collected data on complexes' stability, built models, predicting stability constants and decoded the models to obtain key fragments responsible for complexation efficiency. The results are in good correlation with the experimental ones, as well as modern theories of complexation. It was shown that the main influence on the constants had a mutual location of the binding centers.

ESIPT-AIE active Schiff base based on 2-(2'-hydroxyphenyl)benzo-thiazole applied as multi-functional fluorescent chemosensors

Three AIE (aggregation-induced emission)-ESIPT (excited-state intramolecular proton transfer) active 2-(2-hydroxyphenyl)benzothiazole derivatives, HL¹, HL² and HL³ with one, two and three rotatable phenyl groups, were obtained and characterized. Their AIE properties in THF/HEPES solution were investigated in detail. HL² shows the best AIE performance with 71-fold fluorescence enhancement, while HL³ only shows a 9-fold enhancement. With the AIE property, HL¹ and HL² could act as fluorescence chemosensors to detect Cu²⁺ ions via the "turn off" mode in THF/HEPES media. With the ESIPT property, HL¹ and HL² could also detect Zn²⁺ ions via the "turn on" mode in EtOH/HEPES media. During the detection process, both demonstrate rapid response and high contrast before and after the addition of metal ions. The species formed in the detection system were investigated. The results of X-ray single-crystal diffraction confirm that Zn²⁺ is coordinated with the oxygen atom and Schiff base nitrogen atom instead of the benzothiazole nitrogen atom in the tetrahedron geometry. Moreover, the chemosensors were successfully constructed into handy fluorescence test papers for Cu²⁺ and Zn²⁺ detection.

"Turn-on" fluorescent probes based on Rhodamine B/amino acid derivatives for detection of Fe3+ in water

Five kinds of Fe³⁺ fluorescent probes (RhB-Gly, RhB-Ala, RhB-Try, RhB-Cys, and RhB-His) were synthesized and characterized by NMR and mass spectrometry, based on the "OFF-ON" mechanism of Rhodamine B derivatives. The RhB-His based probe showed remarkable sensing performance toward the detection for Fe³⁺ and showed high selectivity for Fe³⁺ in the presence of other metal ions (such as Fe²⁺, Hg²⁺, Zn²⁺, Ba²⁺, Al³⁺, Co²⁺, Cd²⁺, K⁺, Na⁺, Mn²⁺, Pd²⁺, Pb²⁺, Ca²⁺, Ni²⁺, Cu²⁺, and Ag⁺), in PBS buffer solution (containing 2% of EtOH, pH 7.4, 1.0 mmol/L). The enhancement of the fluorescence was linearly proportional with the concentration Fe³⁺ (from 0 to 20 μmol/L), while the detection limit reached 0.88 μmol/L with a response time of 15 s. The RhB-His probe was successfully applied to investigate real samples and living cell imaging.

Active Bromoaniline-Aldehyde Conjugate Systems and Their Complexes as Versatile Sensors of Multiple Cations with Logic Formulation and Efficient DNA/HSA-Binding Efficacy: Combined Experimental and Theoretical Approach

Two fluorescence active bromoaniline-based Schiff base chemosensors, namely, (E)-4-bromo-2-(((4-bromophenyl)imino)methyl)phenol (HL1 ) and (E)-2-(((4-bromophenyl)imino)methyl)phenol (HL2 ), have been employed for the selective and notable detection of Cu2+ and Zn2+ ions, respectively, with the simultaneous formation of two new metal complexes [Cu(L1)2] (1) and [Zn(L2)2] (2). X-ray single crystal analyses indicate that complexes 1 and 2 are tetra-coordinated systems with substantial CH...π/π...π stacking interactions in the solid-state crystal structures. These two complexes are exploited for the next step detection of Al3+ and Hg2+ where complex 2 exhibits impressive results via turn-off fluorescence quenching in (DMSO/H2O) HEPES buffer medium. The sensing phenomena are optimized by UV-vis spectral analyses as well as theoretical calculations (density functional theory and time-dependent density functional theory). The combined detection phenomena of the ligand (HL2 ) and complex 2 are exclusively utilized for the first time to construct a molecular memory device, intensifying their multisensoric properties. Furthermore, the DNA- and human serum albumin (HSA)-binding efficacies of these two complexes are examined by adopting electronic and fluorometric titration methods. Complex 2 shows a higher DNA-binding ability in comparison with complex 1, whereas in the case of HSA, the reverse situation is observed. Finally, the binding modes of both the complexes with DNA and HSA have been investigated through molecular docking studies, suggesting good agreement with the experimental results.

Sequence-defined oligomer as a modular platform for selective sub-picomolar detection and removal of Hg2+

A modular synthetic platform for selective sensing and removal of Hg2+ was developed.

A novel highly sensitive dual-channel chemical sensor for sequential recognition of Cu2+ and CN− in aqueous media and its bioimaging applications in living cells

A simple and unique dual-channel chemical probe (DH) was designed and synthesized, which not only realized sequential recognition of Cu2+ and CN− by colorimetric and fluorometric methods, but also realized fluorescence detection of CN−.