Highly sensitive and selective colorimetric and off-on fluorescent chemosensor for Cu2+ in aqueous solution and living cells

A Reversible Fluorescent Chemosensor for the Selective Detection of Cu2+ and CN- ions by Displacement Approach

A novel fluorescence chemosensor BDP (2-(1-(benzothiazol-2-yl)-5-(4-(diphenylamino)phenyl)-4,5-dihydro-1H-pyrazol-3-yl)phenol) has been synthesized and its sensing behavior has been screened towards various cations by absorption, emission and mass spectroscopic techniques. The probe BDP detects Cu2+ ions preferentially over other metal ions, and the resulting BDP-Cu2+ ensemble acts as a secondary sensor for cyanide anion detection over other anions. The fluorescence intensity of the probe BDP is quenched when it comes into contact with Cu2+ ions, but it is increased reversibly when it comes into contact with cyanide anion, according to spectroscopic measurements. Along with this, optical studies indicate that the sensor BDP has capability to sense Cu2+ and CN- ions selectively over other examined competitive ions with the LOD of 2.57×10-8 M and 2.98×10-8 M respectively. The detection limit of Cu2+ ions is lower than the WHO recommended Cu2+ ions concentration (31.5 µM) in drinking water. On the basis of "on-off-on" fluorescence change of the probe BDP upon interaction with Cu2+ and CN- ions, a possible mechanism for this selective sensing behavior was presented and IMPLICATION logic gate was successfully designed. Furthermore, cell imaging investigations were used to investigate the probe BDP's biological applicability.

Small-Molecule Fluorescent Probes for Binding- and Activity-Based Sensing of Redox-Active Biological Metals

Although transition metals constitute less than 0.1% of the total mass within a human body, they have a substantial impact on fundamental biological processes across all kingdoms of life. Indeed, these nutrients play crucial roles in the physiological functions of enzymes, with the redox properties of many of these metals being essential to their activity. At the same time, imbalances in transition metal pools can be detrimental to health. Modern analytical techniques are helping to illuminate the workings of metal homeostasis at a molecular and atomic level, their spatial localization in real time, and the implications of metal dysregulation in disease pathogenesis. Fluorescence microscopy has proven to be one of the most promising non-invasive methods for studying metal pools in biological samples. The accuracy and sensitivity of bioimaging experiments are predominantly determined by the fluorescent metal-responsive sensor, highlighting the importance of rational probe design for such measurements. This review covers activity- and binding-based fluorescent metal sensors that have been applied to cellular studies. We focus on the essential redox-active metals: iron, copper, manganese, cobalt, chromium, and nickel. We aim to encourage further targeted efforts in developing innovative approaches to understanding the biological chemistry of redox-active metals.

Configuration of super-fast Cu2+-responsive chemosensor by attaching diaminomaleonitrile to BODIPY scaffold for high-contrast fluorescence imaging of living cells

A highly fluorescent Cu2+-responsive sensor, 2-amino-3-(BODIPYmethyleneamino)maleonitrile (BD) was constructed by attaching diaminomaleonitrile to a BODIPY scaffold. Cu2+ can be selectively recognized on a 2-s time-scale by way of fluorescence emission. When Cu2+ and BD coexist in solution, typical BODIPY emission was observed and the emission intensity could be increased to 334 times that of the blank dye solution. The mechanism of fluorescence increase is based on the generation of highly fluorescent species by Cu2+-triggered oxidative cyclization of the attached diaminomaleonitrile. The absolute fluorescence quantum yield (AFQY) of the cyclization product is 98% determined by integrating sphere. The highly emissive character can be attributed to the imidazole ring and dicarbonitrile on the BODIPY scaffold. It surpasses the meso-phenyl substituted analogue in AFQY and detection limits (DL). The specific Cu2+ recognition behavior was also validated in Hela cells with high-contrast fluorescence images.

A Rhodamine-coumarin Triazole Conjugate as a Fluorescent Chemodosimeter for Cu(II) Detection and its Application in Live Cell Bioimaging

A rhodamine-triazole fluorescent probe bearing a coumarin moiety RTC was synthesized using the Cu(I)-catalyzed click reaction. The rhodamine-triazole conjugate was highly selective to Cu2+ among other metal ions, including Ca2+, Co2+, Cu2+, Cd2+, Mg2+, Fe2+, Fe3+, Hg2+, Zn2+, Ni2+, Pd2+ and Pb2+ in physiological conditions. Upon the addition of Cu2+, the colorless RTC solution turned pink and exhibited a significant fluorescence emission centered at 578 nm. The binding of Cu2+ induced a hydrolysis reaction, leading to a release of the coumarin unit from the rhodamine probe, as confirmed by mass spectrometric data. From the fluorescence titration, the detection limit of RTC for Cu2+ was determined to be 21 nM (1.3 ppb). The sensor was responsive to Cu2+ in a wide pH range and successfully applied to monitor Cu2+ in HEK293T cells by confocal fluorescence imaging.

Influence of ortho group in rhodamine B hydrazide based Schiff base for selective recognition of Cu2+ and Fe3+ ions: A mechanistic approach by DFT and colorimetric studies

Herein we have implemented a computational approach in designing sensor molecules for the selective recognition of Cu²⁺ and Fe³⁺ ions. Seven rhodamine B hydrazide-based Schiff base derivatives were designed and analysed their chemosensing properties against Cu²⁺ and Fe³⁺ ions in ethanol solution theoretically. The theoretical calculations revealed that the selective recognition of Cu²⁺ and Fe³⁺ ions takes place via spirolactam ring-opening and there is a pivotal role of ortho substituents and N-heteroatoms. The two best chemosensors were synthesised and used for the detection of Cu²⁺ and Fe³⁺ ions by colorimetric methods.

Dual-mode colorimetric/fluorescent chemosensor for Cu2+/Zn2+ and fingerprint imaging based on rhodamine ethylenediamine bis(triazolyl silsesquioxane)

A novel dual functional and visual rhodamine ethylenediamine bis(triazolyl silsesquioxane) (RBS) chemosensor was successfully synthesized using "click" chemistry. The results have unambiguously demonstrated that RBS can act in fluorescent and colorimetric sensing of Cu²⁺ and Zn²⁺ by their respective coordination with triazole structures and, more importantly, it has also been found that triazole-amide of RBS could turn on chelation-enhanced fluorescence (CHEF) of Cu²⁺. Remarkably, the addition of Cu²⁺ triggered an enhanced fluorescent emission by 63.3-fold (ϕ_F = 0.41), while Zn²⁺ enhanced it 48.3-fold (ϕ_F = 0.29) relative to the original RBS (ϕ_F = 0.006) in acetonitrile (MeCN) solvent. The fluorescent limit of detection for Cu²⁺ and Zn²⁺ is similar and fall within 3.0 nM, while under colorimetric sensing the responses were 2.14 × 10^-8 and 4.0 × 10^-8 mol L^-1, respectively. Moreover, the effective sensing profile of RBS and extended applications of RBS-Cu²⁺ and RBS-Zn²⁺ for fingerprinting detection and imaging were observed with adequate sensitivity, stability and legibility under the dual visual responses.

A Recent Update on Rhodamine Dye Based Sensor Molecules: A Review

Herein we have discussed such important modified rhodamine compounds which have been used as chemosensors for the last 7-8 years. This review covered some chemosensors for the detection of metal ions like Al(III), Cu(II), Hg(II), Co(II), Fe(III), Au(III), Cr(III), and some anion like CN-. The selectivity, sensitivity, photophysical properties (i.e., UV-Vis spectral studies, fluorescence studies giving special emphasis to absorption wavelength in UV-Vis spectra and excitation and emission wavelength in fluorescence spectra), binding affinity, the limit of detection, and the application of those chemosensors are described clearly. Here we have also discussed some functionalized rhodamine-based chemosensors that emit in the near-infrared region (NIR) and can target lysosomes and detect lysosomal pH. Their versatile applicability in the medicinal ground is also delineated. We have focused on the photophysical properties of spirolactam rhodamine photoswitches and applications in single-molecule localization microscopy and volumetric 3D light photoactivable dye displays. The real-time detection of radical intermediates has also been exemplified.

Enhanced small green fluorescent proteins as a multisensing platform for biosensor development

Engineered light, oxygen, and voltage (LOV)-based proteins are able to fluoresce without oxygen requirement due to the autocatalytic incorporation of exogenous flavin as a chromophore thus allowing for live cell imaging under hypoxic and anaerobic conditions. They were also discovered to have high sensitivity to transition metal ions and physiological flavin derivatives. These properties make flavin-binding fluorescent proteins (FPs) a perspective platform for biosensor development. However, brightness of currently available flavin-binding FPs is limited compared to GFP-like FPs creating a need for their further enhancement and optimization. In this study, we applied a directed molecular evolution approach to develop a pair of flavin-binding FPs, named miniGFP1 and miniGFP2. The miniGFP proteins are characterized by cyan-green fluorescence with excitation/emission maxima at 450/499 nm and a molecular size of ∼13 kDa. We carried out systematic benchmarking of miniGFPs in Escherichia coli and cultured mammalian cells against spectrally similar FPs including GFP-like FP, bilirubin-binding FP, and bright flavin-binding FPs. The miniGFPs proteins exhibited improved photochemical properties compared to other flavin-binding FPs enabling long-term live cell imaging. We demonstrated the utility of miniGFPs for live cell imaging in bacterial culture under anaerobic conditions and in CHO cells under hypoxia. The miniGFPs’ fluorescence was highly sensitive to Cu(II) ions in solution with K_d values of 67 and 68 nM for miniGFP1 and miniGFP2, respectively. We also observed fluorescence quenching of miniGFPs by the reduced form of Cu(I) suggesting its potential application as an optical indicator for Cu(I) and Cu(II). In addition, miniGFPs showed the ability to selectively bind exogenous flavin mononucleotide demonstrating a potential for utilization as a selective fluorescent flavin indicator. Altogether, miniGFPs can serve as a multisensing platform for fluorescence biosensor development for in vitro and in-cell applications.

Macroporous perovskite nanocrystal composites for ultrasensitive copper ion detection

Accumulation of heavy metal ions, including copper ions (Cu²⁺), presents a serious threat to human health and to the environment. A substantial amount of research has focused on detecting such species in aqueous solutions. However, progress towards ultrasensitive and easy-to-use sensors for non-aqueous solutions is still limited. Here, we focus on the detection of copper species in hexane, realising ultra-sensitive detection through a fluorescence-based approach. To achieve this, a novel macroporous composite material has been developed featuring luminescent CsPbBr₃ nanocrystals (NCs) chemically adhered to a polymerized high internal phase emulsion (polyHIPE) substrate through surface thiol groups. Due to this thiol functionality, sub-monolayer NC formation is realised, which also renders outstanding stability of the composite in the ambient environment. Copper detection is achieved through a direct solution based immersion of the CsPbBr₃-(SH)polyHIPE composite, which results in concentration-dependent quenching of the NC photoluminescence. This newly developed sensor has a limit of detection (LOD) for copper as low as 1 × 10^-16 M, and a wide operating window spanning 10^-2 to 10^-16 M. Moreover, the composite exhibits excellent selectivity among different transition metals.

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.

A FRET-based ratiometric fluorescent probe for hydrogen polysulfide detection in living cells and zebrafish

Hydrogen polysulfide (H₂S_n, n > 1) is an important active sulfur molecule (RSS) in organisms, which have been considered to be involved in redox signaling and cytoprotective processes. In this work, in order to quickly and accurately detect H₂S_n in biosystems, 2-fluoro-5-nitrobenzoic ester was used as the response moiety for H₂S_n, and the FRET strategy was adopted to effectively connect the donor (6-hydroxy-2-naphthoic acid) and acceptor (4-substituted-1,8-naphthalimide) to construct a new ratiometric H₂S_n fluorescent probe NPNA-H₂S_n. NPNA-H₂S_n exhibited a more than ∼ 8.0-fold ratio enhancement towards H₂S_n at I₄₅₀/I₅₂₆ and a very high sensitivity with a very low detection limit of 40.3 nM. Impressive, NPNA-H₂S_n was further used for fluorescence imaging of H₂S_n in living cells and zebrafish, which showed high-clear ratiometric images. Therefore, we have demonstrated that NPNA-H₂S_n could be applied for ratiometric images of endogenous H₂S_n in living biosystems and provide a powerful molecular tool for evaluating the physiological and pathological functions of H₂S_n.

A dansyl-based fluorescent probe for sensing Cu2+ in aqueous solution

A fluorescent probe based on a glycyl-L-tyrosine-modified dansyl derivative (D-GT) is designed and synthesized. D-GT demonstrated great detection performance toward Cu²⁺ in an aqueous solution. Fluorescence quenching occurred due to the coordination of Cu²⁺ with D-GT. The sensitive detection of D-GT to Cu²⁺ was applied in aqueous solution within a wide pH span (6-12). A 1:1 coordinate stoichiometric way and an association constant of 6.47 × 10⁴ M^-1 between D-GT and Cu²⁺ were determined. The measured detection limit for Cu²⁺ in HEPES buffer solution (10 mM, pH 7.4) was 0.69 μM. The probe displayed an appropriate sensitivity toward Cu²⁺ in real drinking water samples and living cells, which reveals the potential applications of D-GT in complicated environments.

Excellent fluorescence detection of Cu2+in water system using N-acetyl-L-cysteines modified CdS quantum dots as fluorescence probe

View of the negative influence of metal ions on natural environment and human health, fast and quantitative detection of metals ions in water systems is significant. Ultra-small grain size CdS quantum dots (QDs) modified with N-acetyl-L-cysteines (NALC) (NALC-CdS QDs) are successfully prepared via a facile hydrothermal route. Based on the changes of fluorescence intensity of NALC-CdS QDs solution after adding metal ions, the fluorescence probe made from the NALC-CdS QDs is developed to detect metal ions in water systems. Among various metal ions, the fluorescence of NALC-CdS QDs effectively quenched by the addition of Cu²⁺, the probe shows high sensitivity and selectivity for detecting Cu²⁺in other interferential metal ions coexisted system. Importantly, the fluorescence intensity of NALC-CdS QDs changes upon the concentration of Cu²⁺, the probe displays an excellent linear relationship between the fluorescence quenching rate and the concentration of Cu²⁺in ranging from 1 to 25μM. Besides, the detected limitation of the probe towards Cu²⁺as low as 0.48μM. The measurement of Cu²⁺in real water sample is also carried out using the probe. The results indicate that NALC-CdS QDs fluorescence probe may be a promising candidate for quantitative Cu²⁺detection in practical application.

Synthesis of trisubstituted hydrazine via MnO2-promoted oxidative coupling of N,N-disubstituted hydrazine and boronic ester

A MnO2-promoted oxidative coupling process between N,N-disubstituted hydrazine and boronic ester is reported. A 1,1-diazene species is firstly generated upon oxidation of a hydrazine substrate in the presence of MnO2 which then interacts with boronic ester to form the key intermediate boron-ate complex, followed by migration from boron to nitrogen to form a new C-N bond. This new finding provides mild, scalable, and operationally straightforward access to trisubstituted hydrazine.

A Benzothiazole-Based Fluorescence Turn-on Sensor for Copper(II)

A new benzothiazole-based chemosensor BTN (1-((Z)-(((E)-3-methylbenzo[d]thiazol-2(3H)-ylidene)hydrazono)methyl)naphthalen-2-ol) was synthesized for the detection of Cu²⁺. BTN could detect Cu²⁺ with "off-on" fluorescent response from colorless to yellow irrespective of presence of other cations. Limit of detection for Cu²⁺ was determined to be 3.3 μM. Binding ratio of BTN and Cu²⁺ turned out to be a 1:1 with the analysis of Job plot and ESI-MS. Sensing feature of Cu²⁺ by BTN was explained with theoretical calculations, which might be owing to internal charge transfer and chelation-enhanced fluorescence processes.

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.

Preparation of a new fluorescence nanochemosensor for Sn(II) ions by a modified nanoprecipitation method

A new dialdehyde was designed and synthesized containing naphthalene groups, and then its macrocycle was prepared with 1,4-diaminobuthan. A modified nanoprecipitation method has been reported for the preparation of the nanoparticles. In this method, to obtain nanoparticles with small particle sizes, the nucleation rate was increased with decreasing of the mixing time. The organic nanoparticles were used for turn-off fluorescence response of low concentration of Sn²⁺ ions over cations such as Cs⁺, K⁺, Na⁺, Ba²⁺, Ca²⁺, Mg²⁺, Al³⁺, Pb^2+, Zn²⁺, Cu²⁺, Ni²⁺, Co²⁺, Fe²⁺, Mn²⁺, Ag⁺, Cd²⁺, and Hg²⁺ and ions in aqueous buffer solution. The limit of detection was 5.4 nM.

A naked-eye colorimetric sensor based on chalcone for the sequential recognition of copper(ii) and sulfide ions in semi-aqueous solution: spectroscopic and theoretical approaches

A chalcone-based new colorimetric sensor A01 for the sequential detection of Cu²⁺ and S²⁻ ions.

The impact of metal coordination on the assembly of bis(indolyl)methane-naphthalene-diimide amphiphiles

The self-assembly and coordination of amphiphiles comprised of naphthalenediimide (NDI) and bis(indolyl)methane (BIM) chromophores were investigated as a function of pH and metal. As observed by TEM, SEM and AFM imaging, the self-assembly of NDI-BIM 1 produced irregular nanostructures at neutral pH in CH3CN-H2O (1 : 1); whereas, well-defined nanotubes were observed at pH 2. Conversely, Fmoc-protected, NDI-BIM 2 formed nanotubes at neutral pH and nonspecific aggregates at pH 2. Upon coordination of Cu2+ ions to the bis(indoyl)methane moiety, a reorganization from nanotubes to vesicular structures was observed.

Coumarin-Based Reversible Fluorescent Probe for Selective Detection of Cu2+ in Living Cells

Copper ion plays an important role in many biological processes in human body. H₂S is considered as the third gasses transmitter after carbon monoxide and nitric oxide. Here a novel ICT-based fluorescent ON-OFF-ON probe for Cu²⁺ and H₂S detection was developed. Selectivity and sensitivity of probe was confirmed in aqueous Tris-HCl buffer (10 mM, pH 7.4, containing 90% acetonitrile). Probe DF-CU shows high selectivity over other analytes. The degree of fluorescence quenching is linearly associated with the concentration of Cu²⁺ (R² = 0.9919). The limit of detection (LOD, calculated according to the 3σ/slope) for Cu²⁺ was 6.4 μM. Probe can work in almost all pH. The probe shows a very fast response to Cu²⁺ (within 10 s). Its response to copper ion could be reversed by H₂S. The complex of probe with Cu²⁺ could be used for H₂S detection. Furthermore, this ON-OFF-ON fluorescent probe successfully applied in the living cells for the detection of Cu²⁺ and H₂S.

Unraveling the Origin of Differentiable 'Turn-On' Fluorescence Sensing of Zn2+ and Cd2+ Ions with Squaramides

A squaramide ring conjugated with Schiff-bases decorated with hydroxy and methoxy functional groups differentially senses zinc and cadmium ions, which turn on the fluorescence. The feebly emitting free ligands light up in the presence of zinc and cadmium acetates, with the acetate ion playing a pivotal role as a conjugate anion. The selective and differentiable emission responses for zinc and cadmium ions make these ligands efficient multi-analyte sensing agents. Furthermore, these ligands could be used to differentially sense zinc and cadmium ions even in aqueous environments. The NMR investigations reveal marginal differences in the binding of zinc and cadmium ions to the ligands, whereas density functional theory calculations suggest the different extent of ligand-to-metal charge transfer (LMCT) contributes to the differential behavior. Finally, comparison of the excited-state dynamics of free ligand and the metal complexes reveal the appearance of longer lifetime (about 500-700 ps) component with complexation, due to rigidified molecular skeleton, thereby impeding the non-radiative processes.

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 colorimetric biosensor for simultaneous ochratoxin A and aflatoxins B1 detection in agricultural products

Colorimetric biosensors have been widely applied to mycotoxins testing. However, the colorimetric assay previously reported used a single color to detect one mycotoxin, and there were few reports on the simultaneous detection of multiple mycotoxins. In this work, a colorimetric biosensor for dual mycotoxins detection was developed. A Fe₃O₄/GO based platform for aflatoxins B1 (AFB1) detection and a Fe₃O₄@Au based platform for ochratoxin A (OTA) detection were fabricated. The quantification of OTA and AFB1 was respectively achieved by the release of thymolphthalein under alkaline conditions and 3,3',5,5'-tetramethylbenzidine was catalyzed by Au NPs under acidic conditions. Because of different conditions, two sensing methods didn't interfere with each other but could provide a higher detection efficiency. The detection range of AFB1 is 5-250 ng·ml^-1 and that of OTA is 0.5-80 ng·ml^-1. This biosensor has been successfully applied in real sample detection, which has a broad application prospect in fields of food safety.

Retinal-based polyene fluorescent probe for selectively detection of Cu2+ in physiological saline and serum

Retinal is a flexible natural chromophore and widely present in organisms. The slender conjugated polyene structure retinal is conducive to entering protein structure. In this work, a novel turn-on fluorescent probe for Cu²⁺ based on retinal and phenylenediamine was designed and synthesized. The probe achieved recognition of copper ions in human serum complex protein environment. Furthermore, the high sensitivity, selectivity for Cu²⁺ and the sensing mechanism was also investigated.

Effect of n-alkyl substitution on Cu(ii)-selective chemosensing of rhodamine B derivatives

Rhodamine B hydrazide-based molecular probes (1-10) were synthesized by derivatization with n-alkyl chains of different lengths at the hydrazide amino end. These probes exhibited selective absorption (A∼557) and fluorescence (I∼580) 'off-on' signal transduction along with a colourless → magenta colour transition in the presence of Cu(ii) ions among all the competitive metal ions investigated. The effective coordination of these probes to Cu(ii) ions under the investigated environment forming [Cu·L]2+ (L = 1-5) and [Cu·L2]2+ (L = 6-10) complexes led to their spiro-ring opening, which in turn was expressed through signatory spectral peaks of ring-opened rhodamine. All these probes exhibited Cu(ii) selectivity in signalling despite structural modifications to the core receptor unit through variation of the nature of the alkyl substituents. However, the sensitivity of the signalling and kinetics of the spiro-ring opening varied and could be correlated with the number of carbon atoms present in the n-alkyl substituents. Structural elucidation with X-ray diffraction and X-ray photoemission spectroscopic analyses provided further insight into the structure-function correlation in their Cu(ii) complexes. These probes with Cu(ii) coordination showed selectivity in signalling, high complexation affinity (log Ka = 4.8-8.8), high sensitivity (LOD = 4.1-80 nM), fast response time (rate = 0.0017-0.0159 s-1) and reversibility with counter anions, which ascertained their potential utility as chemosensors for Cu(ii) ion detection.

Pyrene-appended bipyridine hydrazone ligand as a turn-on sensor for Cu2+ and its bioimaging application

A pyrene-appended bipyridine hydrazone-based ligand, HL, was synthesized and characterized by spectroscopic methods. Upon complexation with Cu(ii), HL formed a hexanuclear paddlewheel metal–organic macrocycle (MOM) via self-assembly with a high association constant with the molecular formula of [Cu₆L₆(NO₃)₆]. Intermolecular and intramolecular π–π interactions were demonstrated in this hexanuclear Cu(ii) complex. Further, it was observed that HL had the potential to detect a trace level of Cu(ii) ion selectively among a wide range of biologically relevant metal ions in aqueous medium at physiological pH. Using HL, it was feasible to sense copper(ii) ions in living cells due to its good cell permeability and high solubility under physiological conditions along with its high IC₅₀ value. The low detection limit, high sensitivity and good reproducibility make this Cu–sensor very promising. The complex (MOM) formed between the ligand and Cu(ii) was found to be 1 : 1 on the basis of fluorescence titrations and was confirmed by ESI-MS. Moreover, single-crystal study of the hexanuclear self-assembled fluorescent species provided better insight into its chemistry, e.g. coordination environment and binding mode, unlike most of the metal sensors due to the lack of a single-crystal structure of the metal sensor complex. Cytotoxicity assay and bioimaging were performed in living cells (Vero cells), giving green fluorescent images. Fluorescence lifetime measurements and theoretical calculations were carried out. The morphology and topographic details on the surface of the metal–organic macrocycle (MOM) were studied by field-emission scanning electron microscopy (FESEM).

A pyrene-based “turn-on” Cu(ii) sensor provides a chemiluminescent Cu₆ metal organic macrocycle (MOM) applicable for live cell imaging.

Macrocyclic "tet a" derived colorimetric sensor for the detection of mercury cations and hydrogen sulphate anions and its bio-imaging in living cells

A mono-N-substituted probe L containing a bromosalicylaldehyde pendant arm attached to a tetraazamacrocyclic "tet a" moiety was synthesized via straight forward reaction. The probe L crystallizes in a monoclinic P2₁/n space group. The probe L displayed quick sensitivity and selectivity towards Hg²⁺ ions due to its hopeful Chelation Enhancement Quenching (CHEQ) feature. Interestingly, the probe L exhibits turn-off fluorescence response to Hg²⁺ ion and turn-on fluorescence signals to HSO₄^- ions. When the probe L was complexed with HSO₄^- in 1:1 mode (L + HSO₄^- formation), improved turn-on fluorescence emission was detected due to the chelation enhanced fluorescence effect through sensor complex. The macrocyclic "tet a" probe L exhibited a binding constant value of 3.89 × 10⁶ M^-1 and 5.58 × 10⁵ M^-1 for Hg²⁺ and HSO₄^-, respectively. Probe L exhibited good selectivity to Hg²⁺ rather than other common metal ions and HSO₄^- over other common anions. The limit of detection (LOD) of Hg²⁺ and HSO₄^- were found to be 1 nM and 7 μM, respectively. The time-resolved fluorescence emission single-photon counting study was used to determine the average lifetime value for the probe L and L + HSO₄^- ions as 0.47 and 1.02 ns, respectively. The practical application of the probe in visualizing intracellular Hg²⁺ and HSO₄^- ions distribution in live Artemia salina was demonstrated. Furthermore, the probe L with Hg²⁺cations was found to be cytotoxic against breast cancer cells in nature and can be delivered as an anticancer agent. Besides the probe L with HSO₄^- exhibit strong fluorescence emission with low cytotoxicity, and it can be recommended for live-cell imaging.

A Luminescent Probe for Ratiometric Optical Detection of HgII and Turn-On Fluorescent Sensing of CuII

Luminescent detection of heavy metals continues to be of growing importance considering their increasing inseparable roles in modern day lifestyle. To this end, we report a simple yet interesting thiourea derivative that results in detection of Cu^II in a turn-on fashion via a chemodosimetric redox reaction leading to oxidative cyclization of the chemosensor molecule. Elaborate studies with regard to the sensing process have been performed along with the proposal of a plausible cyclization mechanism of the molecule. Furthermore, the probe optically detects Hg^II , yet another heavy metal of prime importance, discernable even to the naked eye. The occurrence of a coordination complex has been proved by UV/Visible spectroscopic experiments as well as ESI-mass spectrometry.

Ex vivo detection of cadmium-induced renal damage by using confocal Raman spectroscopy

Cadmium (Cd) is a toxic heavy metal which is harmful to environment and organisms. The reabsorption of Cd in kidney leads it to be the main damaged organ in animals under the Cd exposure. In this work, we applied confocal Raman spectroscopy to map the pathological changes in situ in normal and Cd-exposed mice kidney. The renal tissue from Cd-exposed group displayed a remarkable decreasing in the intensity of typical peaks related to mitochondria, DNA, proteins and lipids. On the contrary, the peaks of collagen in Cd-exposed group elevated significantly. The components in each tissue were identified and distinguished by principal component analysis. Furthermore, all the biological investigations in this study were consistent with the Raman spectrum detection, which revealed the progression and degree of lesion induced by Cd. The confocal Raman spectroscopy provides a new perspective for in situ monitoring of substances changes in tissues, which exhibits more comprehensive understanding of the pathogenic mechanisms of heavy metals in molecular toxicology.

Crystal structure of (E)-N′-((1,6-dihydropyren-1-yl)methylene)isonicotinohydrazide — methanol (1/1), C24H19N3O2

C24H19N3O2, monoclinic, P21/c (no. 14), a = 11.0629(2) Å, b = 10.4583(2) Å, c = 16.0432(3) Å, β = 92.373(2)°, V = 1854.59(7) Å3, Z = 4, Rgt(F) = 0.0435, wRref(F2) = 0.1269, T = 116.2(3) K.

Online, Continuous, and Interference-Free Monitoring of Trace Heavy Metals in Water Using Plasma Spectroscopy Driven by Actively Modulated Pulsed Power

This work presents the development of an online continuous heavy metals monitoring system using optical emission spectroscopy of plasma in water. The plasmas were driven by actively modulated pulsed power (AMPP) to control the plasma and its emission behavior in solutions with a wide range of conductivity. The AMPP quantified in situ the solutions' conductivity and modulated in real time the pulse width based on the conductivity. We demonstrated the online monitoring of the metallic elements. The results show that multiple metallic elements, namely Pb and Zn, can be independently and simultaneously detected with less than a 10% variation in the corresponding optical emission lines in solutions with a wide range of conductivity. An alert system was integrated to demonstrate the capability of an instant warning via e-mail once metallic elements were detected. Finally, we demonstrated that this system was robust even with the existence of several interferences and able to perform online continuous monitoring for days. We believe the system using plasma spectroscopy with AMPP for online monitoring of metals in water will have a significant impact on the fields of environmental monitoring and protection.

A nitroxyl-responsive near-infrared fluorescent chemosensor for visualizing H2S/NO crosstalk in biological systems

We present a near-infrared (NIR) fluorescent probe, NR-HNO, which was successfully applied to visualizing H2S/NO "crosstalk" by the fluorescence detection of nitroxyl with a fast response time (5 min) and a large Stokes shift (131 nm) in living cells and tissue; it was also used to image nitroxyl in live mice.