A fluorescent anion sensor that works in neutral aqueous solution for bioanalytical application

Development of a fast fluorescent probe for sensitive detection of glutathione in 100 % aqueous solution and its applications in real samples, oxidative stress model and ferroptosis model

Glutathione (GSH) plays a crucial role in several physiological processes, including anti-oxidation and heavy metal detoxification. GSH is produced endogenously in the human body and can also be obtained through diet. The development of fast, highly sensitive, and multi-application fluorescent probes remains a challenging task. In this study, we have designed and synthesized a coumarin-based fluorescent probe (NFRF) for the sensitive and rapid detection of GSH in 100 % aqueous solution. By loading probe NFRF on the filter paper, the real-time visual detection of GSH is achieved in both daylight and fluorescence modes, providing a convenient, economical and rapid on-site detection tool. Probe NFRF could be used for the detection of GSH in real samples, with recoveries rates of 81.74 %-115.12 %. Notably, the probe imaged changes in GSH concentrations in oxidative stress environments and during ferroptosis. This work provides a prospective method for GSH detection in food and complex biological systems.

Polymer-Based Long-Lived Phosphorescence Materials over a Broad Temperature Based on Coumarin Derivatives as Information Anti-Counterfeiting

The development of new polymer-based room-temperature phosphorescence materials is of great significance. By a special molecule design and a set of feasible property-enhancing strategies, coumarin derivatives (CMDs, M_a-M_f) were doped into polyvinyl alcohol (PVA), polyacrylamide (PAM), corn starch, and polyacrylonitrile (PAN) as information anti-counterfeiting. CMDs-doped PVA and CMDs-doped corn starch films showed long-lived phosphorescence emissions up to 1246 ms (M_a-PVA) and 697 ms (M_a-corn starch), reaching over 10 s afterglow under naked eye observation under ambient conditions. Significantly, CMDs-doped PAM films can display long-lived phosphorescence emissions in a wide temperature range (100-430 K). For example, the M_e-PAM film has a phosphorescence lifetime of 16 ms at 430 K. The use of PAM with the strong polarity and rigidity has expanded the temperature range of long-life polymer-based phosphorescent materials. The present long-lived phosphorescent systems provide the possibility for developing new polymer-based organic afterglow materials with robust phosphorescence.

Tailoring the band-gap, optical and fluorescent properties of 3,5-diaminobenzoic acid via functionalization with chemical groups: A DFT study

3,5-diaminobenzoic acid (3,5-DABA) with chemical formula C₇H₈N₂O₂ was functionalized with CH₃-, OH-, NH₂- and NO₂- to obtain: CH₃-3,5 DABA, OH-3,5 DABA, NH₂-3,5DABA and NO₂-3,5DABA. These molecules were built with Gauss view 6.0 and their structural, spectroscopic, optoelectronic and molecular properties were investigated using density functional theory (DFT). B3LYP (Becke's 3-parameter exchange functional with Lee-Yang-Parr correlation energy) functional and 6-311+ G (d, p) basis set were used to understand their reactivity, stability and optical activity. Integral equation formalism polarizable continuum model (IEF - PCM) was used to calculate the absorption wavelength, energy required to excite the molecules and oscillator strength. Our results reveal that the functionalization of 3,5 DABA with the groups caused a decrease of the energy gap from 0.1563 eV, to 0.1461 eV, 0.13818 eV and 0.13811 eV in NO₂-3,5DABA, OH-3,5DABA and NH₂-3,5DABA respectively. The lowest energy gap of 0.13811 eV for NH₂-3,5DABA is in good agreement with its highest reactivity value (global softness of 7.240). The most observed significant donor - acceptor NBO interactions where found to occur between *ΠC16-O17 → *ΠC1-C2, *ΠC3-C4→ *ΠC1-C2, *ΠC1-C2 → *ΠC5-C6, *ΠC3-C4 → *ΠC5-C6, *ΠC2-C3 →*ΠC4-C5 natural bond orbitals having second- order stabilization energies of 101.95 kcal/mol, 368.41 kcal/mol, 174.51 kcal/mol, 255.63 kcal/mol and 235.92 kcal/mol in 3,5-DABA, CH₃-3,5-DABA, OH-3,5-DABA, NH₂-3,5-DABA and NO₂-3,5-DABA respectively. The highest perturbation energy was observed in CH₃-3,5DABA while the lowest perturbation energy was observed in 3,5DABA. The absorption band of the compounds were observed in the order: NH₂-3,5DABA (404 nm) > N0₂-3,5DABA (393 nm) > OH-3,5DABA (386 nm) > 3,5DABA (349 nm) > CH3-3,5DABA (347 nm).

Argentivorous molecules with chromophores: dependence of their fluorescence intensities on the distance between a donor and an acceptor

We have prepared new argentivorous molecules (L2 and L3) having different linker lengths between cyclen and anthracene units. The structures of Ag⁺ complexes with the new ligands were investigated in solution and solid states. The silver(I) ion-induced ¹H NMR and UV-vis spectral changes of L2 and L3 showed the presence of 1 : 1 complexes. The solid-state structures of the Ag⁺ complexes with L2 and L3 are stable 1 : 1 complexes because four aromatic side-arms wrap the Ag⁺ incorporated in the cyclen unit. A photo-induced electron transfer (PET) effect that depends on the length of the linker connecting the nitrogen atoms of cyclen to the chromophore is also investigated. The result indicates a linear (log) correlation between the donor-chromophore average distances of the optimized structures calculated by DFT calculations and fluorescence intensities (log I), and the PET effect becomes ineffective at about 12 Å in this system.

Fashionable Co-operative Sensing of Bivalent Zn2+ and Cd2+ in Attendance of OAc- by Use of Simple Sensor: Exploration of Molecular Logic Gate and Docking Studies

The Schiff-base probe H₂VL [6,6'-((1E,1'E)-hydrazine-1,2 diylidenebis(methanylylidene))bis(2-methoxyphenol)] is synthesized and structurally characterized by single crystal X-ray diffraction (SCXRD). H₂VL is able to detect selectively acetate ion (OAc-) colorimetrically over other anions with 1:1 co-ordination. The detection limit is found to be 4.93 µM. On the other hand, fluorescence intensity of the receptor is drastically enhanced with Zn²⁺ and Cd²⁺ in the presence of acetate as counter anion. N, N-Dimethyl formamide (DMF) or Dimethylsulphoxide (DMSO) and acetate (OAc-) was the best solvent and counter anion for Zn²⁺/Cd²⁺ -sensing compared with other solvents and anions, respectively. Detection limit for Zn²⁺ and Cd²⁺ are calculated to be 1.94 µM and 1.99 µM, respectively. The strong selective emissive behavior could be attributed to the CHEF (chelation-enhanced fluorescence) process. According to the changes in output emission intensity in DMSO in response to the set of ions (Zn²⁺, Cd²⁺ and OAc¯) as input variables, the function of 3-input multifunctional molecular logic circuits has been demonstrated. The molecular docking studies of H₂VL with DNA and BSA are also performed to confirm its possible bioactivity.

Fluorescent probes for the detection of disease-associated biomarkers

Fluorescent probes have emerged as indispensable chemical tools to the field of chemical biology and medicine. The ability to detect intracellular species and monitor physiological processes has not only advanced our knowledge in biology but has provided new approaches towards disease diagnosis. In this review, we detail the design criteria and strategies for some recently reported fluorescent probes that can detect a wide range of biologically important species in cells and in vivo. In doing so, we highlight the importance of each biological species and their role in biological systems and for disease progression. We then discuss the current problems and challenges of existing technologies and provide our perspective on the future directions of the research area. Overall, we hope this review will provide inspiration for researchers and prove as useful guide for the development of the next generation of fluorescent probes.

Enzyme assays with supramolecular chemosensors - the label-free approach

Enzyme activity measurements are essential for many research areas, e.g., for the identification of inhibitors in drug discovery, in bioengineering of enzyme mutants for biotechnological applications, or in bioanalytical chemistry as parts of biosensors. In particular in high-throughput screening (HTS), sensitive optical detection is most preferred and numerous absorption and fluorescence spectroscopy-based enzyme assays have been developed, which most frequently require time-consuming fluorescent labelling that may interfere with biological recognition. The use of supramolecular chemosensors, which can specifically signal analytes with fluorescence-based read-out methods, affords an attractive and label-free alternative to more established enzyme assays. We provide herein a comprehensive review that summarizes the current state-of-the-art of supramolecular enzyme assays ranging from early examples with covalent chemosensors to the most recent applications of supramolecular tandem enzyme assays, which utilize common and often commercially available combinations of macrocyclic host molecules (e.g. cyclodextrins, calixarenes, and cucurbiturils) and fluorescent dyes as self-assembled reporter pairs for assaying enzyme activity.

Metal-free colorimetric detection of pyrophosphate ions by the peroxidase-like activity of ATP

Pyrophosphate (P₂O₇^4-, PPi) plays a vital role in ecological environment. Its elevated levels in water bodies can lead to eutrophication. Hence, its detection is extremely significant. Whereas most of the existing methods for the actual detection of PPi may cause environmental pollution or suffer from operational complexity. In this study, we introduced a sensitive and selective method for detecting PPi based on the fact that PPi can inhibit the peroxidase-like activity of adenosine 5'-triphosphate (ATP). This strategy not only eliminated the complexity of material preparation (ATP is commercialized), but also addressed the general need for metal ions in detecting PPi. The dynamic range of PPi detection was 1.0-200 μM and the detection limit was 74 nM. In addition, this strategy had been successfully applied to the determination of PPi in tap water and lake water. This work extends the application of natural biological small molecule ATP in the analysis and provides an innovative thought for the metal-free detection of PPi.

A chromone-based multi-selective sensor: applications in paper strips and real sample

A chromone-based multi-selective sensor: applications in a paper strip and real sample.

Fluorescein Based Three-channel Probe for the Selective and Sensitive Detection of CO32- Ions in an Aqueous Environment and Real Water Samples

We have constructed a novel fluorescein-based fluorescent chemosensor, FL-In, functionalised with an indole moiety and capable of sensing by both the optical "turn-on" and electrochemical detection of carbonate ions (CO₃^2-) in aqueous media. The probe exhibits excellent selectivity and a low detection limit (0.27 µM) regarding carbonate ions by a possible coordination and hydrolysis reaction mechanism. The developed probe successfully detected CO₃^2- ions in different samples of water. Also, in a simple filter paper experiment, we documented its ability to allow the monitoring of CO₃^2- with the naked eye.

Distinct Tetracyanoquinodimethane Derivatives: Enhanced Fluorescence in Solutions and Unprecedented Cation Recognition in the Solid State

Tetracyanoquinodimethane (TCNQ) is known to react with various amines to generate substituted TCNQ derivatives with remarkable optical and nonlinear optical characteristics. The choice of amine plays a crucial role in the outcome of molecular material attributes. Especially, mono/di-substituted TCNQ's possessing strong fluorescence in solutions than solids are deficient. Furthermore, cation recognition in the solid-state TCNQ derivatives is yet undetermined. In this article, we present solution-enhanced fluorescence and exclusive solid-state recognition of K⁺ ion achieved through the selection of 4-(4-aminophenyl)morpholin-3-one (APM) having considerable π-conjugation and carbonyl (C=O) functionality, particularly in the ring. TCNQ when reacted with APM, in a single-step reaction, resulted in two well-defined distinct compounds, namely, 7,7-bis(4-(4-aminophenyl)morpholin-3-ono)dicyanoquinodimethane (BAPMDQ [1], yellow) and 7,7,8-(4-(4-aminophenyl)morpholin-3-ono)tricyanoquinodimethane (APMTQ [2], red), with increased fluorescence intensity in solutions than their solids. Crystal structure investigation revealed extensive C-H-π interactions and strong H-bonding in [1], whereas moderate to weak interactions in [2]. Surprisingly, simple mechanical grinding during KBr pellet preparation with [1, 2] triggered unidentified cation recognition with a profound color change (in ∼1 min) detected by the naked eye, accompanied by a drastic enhancement of fluorescence, proposed due to the presence of carbonyl functionality, noncovalent intermolecular interactions, and molecular assemblies in [1, 2] solids. Cation recognition was also noted with various other salts as well (KCl, KI, KSCN, NH₄Cl, NH₄Br, etc.). Currently, the recognition mechanism of K⁺ ion in [1, 2] is demonstrated by the strong electrostatic interaction of K⁺ ion with CO and simultaneously cation-π interaction of K⁺ with the phenyl ring of APM, supported by experimental and computational studies. Computational analysis also revealed that a strong cation-π interaction occurred between the K⁺ ion and the phenyl ring (APM) in [2] than in [1] (ΔG _binding calculated as ∼16.3 and ∼25.2 kcal mol^-1 for [1] and [2], respectively) providing additional binding free energy. Thus, both electrostatic and cation-π interactions lead to the recognition. Scanning electron microscopy of drop-cast films showed microcrystalline "roses" in [1] and micro/nano "aggregates" in [2]. Optical band gap (∼3.565 eV) indicated [1, 2] as wide-band-gap materials. The current study demonstrates fascinating novel products obtained by single-pot reaction, resulting in contrasting optical properties in solutions and experiencing cation recognition capability exclusively in the solid state.

ESIPT silent and mitochondrial-targeted rapid response for SO2 regulated by pyridinium and its real-time detection in living cells

ESIPT has been widely used in fluorescence recognition because of its advantages such as large Stokes shift.

Mechanistic Insight of Sensing Hydrogen Phosphate in Aqueous Medium by Using Lanthanide(III)-Based Luminescent Probes

The development of synthetic lanthanide luminescent probes for selective sensing or binding anions in aqueous medium requires an understanding of how these anions interact with synthetic lanthanide probes. Synthetic lanthanide probes designed to differentiate anions in aqueous medium could underpin exciting new sensing tools for biomedical research and drug discovery. In this direction, we present three mononuclear lanthanide-based complexes, EuLCl₃ (1), SmLCl₃ (2), and TbLCl₃ (3), incorporating a hexadentate aminomethylpiperidine-based nitrogen-rich heterocyclic ligand L for sensing anion and establishing mechanistic insight on their binding activities in aqueous medium. All these complexes are meticulously studied for their preferential selectivities towards different anions such as HPO₄²⁻, SO₄²⁻, CH₃COO⁻, I⁻, Br⁻, Cl⁻, F⁻, NO₃⁻, CO₃²⁻/HCO₃⁻, and HSO₄⁻ at pH 7.4 in aqueous HEPES (2-[4-(2-hydroxyethyl)piperazin-1-yl]ethanesulfonic acid) buffer. Among the anions scanned, HPO₄²⁻ showed an excellent luminescence change with all three complexes. Job’s plot and ESI-MS support the 1:2 association between the receptors and HPO₄²⁻. Systematic spectrophotometric titrations of 1–3 against HPO₄²⁻ demonstrates that the emission intensities of 1 and 2 were enhanced slightly upon the addition of HPO₄²⁻ in the range 0.01–1 equiv and 0.01–2 equiv., respectively. Among the three complexes, complex 3 showed a steady quenching of luminescence throughout the titration of hydrogen phosphate. The lower and higher detection limits of HPO₄²⁻ by complexes 1 and 2 were determined as 0.1–4 mM and 0.4–3.2 mM, respectively, while complex 3 covered 0.2–100 μM. This concludes that all complexes demonstrated a high degree of sensitivity and selectivity towards HPO₄²⁻.

Sub-ppb mercury detection in real environmental samples with an improved rhodamine-based detection system

A new procedure is described for the determination of Hg²⁺ ions in water samples. A Rhodamine based fluorescent sensor was synthesized and the experimental conditions were specifically optimized for application to environmental samples, which requires low detection limits and high selectivity in competitive experiments with realistic concentrations of other metal ions. Incorporation of a Rhodamine-6G fluorophore to a previously described sensor and optimization of the buffer system (detection with acetic acid at pH 5.25) enabled significant enhancement of the sensitivity (detection limit = 0.27 μg L^-1) and selectivity. The optimized procedure using high-throughput microplates has been applied to tap and river waters with good results.

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.

Binuclear and tetranuclear Zn(ii) complexes with thiosemicarbazones: synthesis, X-ray crystal structures, ATP-sensing, DNA-binding, phosphatase activity and theoretical calculations

Two Zinc(ii) complexes [Zn₄(L¹)₄]·2H₂O (1) and [Zn₂(L²)₂]·2H₂O (2) of pyruvaldehydethiosemicarbazone ligands are reported. The complexes were characterized by elemental analysis, IR, NMR, UV-vis spectroscopy and by single-crystal X-ray crystallography. X-ray crystal structure determinations of the complexes show that though Zn : ligand stoichiometry is 1 : 1 in both the complexes, the molecular unit is tetranuclear for 1 and binuclear for 2. Both the complexes show selective sensing of ATP at pH 7.4 (0.01 M HEPES) in CH₃CN–H₂O (9 : 1) medium in the presence of other anions like AcO⁻, NO₃⁻, F⁻, Cl⁻, H₂PO₄⁻, HPO₄²⁻ and P₂O₇²⁻. The UV-titration experiments of complexes 1 and 2 with ATP results in binding constants of 2.0(±0.07) × 10⁴ M⁻¹ and 7.1(±0.05) × 10³ M⁻¹ respectively. The calculated detection limits of 6.7 μM and 1.7 μM for 1 and 2 respectively suggest that the complexes are sensitive detectors of ATP. High selectivity of the complexes is confirmed by the addition of ATP in presence of an excess of other anions. DFT studies confirm that the ATP complexes are more favorable than those with the other inorganic phosphate anions, in agreement with the experimental results. Phosphatase like activity of both complexes is investigated spectrophotometrically using 4-nitrophenylphosphate (NPP) as a substrate, indicating the complexes possess significant phosphate ester hydrolytic efficiency. The kinetics for the hydrolysis of the substrate NPP was studied by the initial rate method at 25 °C. Michaelis–Menten derived kinetic parameters indicate that rate of hydrolysis of the P–O bond by complex 1 is much greater than that of complex 2, the k_cat values being 212(±5) and 38(±2) h⁻¹ respectively. The DNA binding studies of the complexes were investigated using electronic absorption spectroscopy and fluorescence quenching. The absorption spectral titrations of the complexes with DNA indicate that the CT-DNA binding affinity (K_b) of complex 1 (2.10(±0.07) × 10⁶ M⁻¹) is slightly greater than that of 2 (1.11(±0.04) × 10⁶ M⁻¹). From fluorescence spectra the apparent binding constant (K_app) values were calculated and they are found to be 5.41(±0.01) × 10⁵ M⁻¹ for 1 and 3.93(±0.02) × 10⁵ M⁻¹ for 2. The molecular dynamics simulation demonstrates that the Zn(ii) complex 1 is a good intercalator of DNA.

A binuclear and a tetranuclear zinc(ii) of pyruvaldehyde thiosemicarbazone show selective sensing of ATP at pH 7.4 (0.01 M HEPES) in CH₃CN–H₂O (9 : 1) medium. The DNA binding and phosphatase activities of the complexes are also reported.

Sensing Zn2+ in Aqueous Solution with a Fluorescent Scorpiand Macrocyclic Ligand Decorated with an Anthracene Bearing Tail

Synthesis of the new scorpiand ligand L composed of a [9]aneN3 macrocyclic ring bearing a CH2CH2NHCH2-anthracene tail is reported. L forms both cation (Zn2+) and anion (phosphate, benzoate) complexes. In addition, the zinc complexes of L bind these anions. The equilibrium constants for ligand protonation and complex formation were determined in 0.1 M NaCl aqueous solution at 298.1 ± 0.1 K by means of potentiometric (pH-metric) titrations. pH Controlled coordination/detachment of the ligand tail to Zn2+ switch on and off the fluorescence emission from the anthracene fluorophore. Accordingly, L is able to sense Zn2+ in the pH range 6-10 down to nM concentrations of the metal ion. L can efficiently sense Zn2+ even in the presence of large excess of coordinating anions, such as cyanide, sulphide, phosphate and benzoate, despite their ability to bind the metal ion.

A Dual Emissive Coumarin-urea Derivative with an Electron-withdrawing Substituent in the Presence of Acetate Anion

We investigated the fluorescent properties, including the excited-state intermolecular proton transfer, of urea derivatives comprising a coumarin ring, which is a widely used fluorophore. We prepared two different coumarin-urea derivatives, 6CU and 7CU, which bear a urea-based substituent at the 6 and 7 positions of a coumarin ring, respectively. In the presence of the acetate ion, 7CU showed additional tautomer fluorescence emission with respect to 6CU, indicating that tautomer formation depends on the positions of the urea-based substituent on the coumarin ring. Thus, the resonance structures of urea derivatives might play an important role in the behavior of dual fluorescence, which is an important phenomenon applicable to photochemical anion sensing. Moreover, in order to further improve the fluorescence properties of the mentioned derivatives, a CF₃ group was introduced in a phenyl ring opposite to a coumarin ring. The fluorescence quantum yield of 7CUCF₃ thus synthesized was 65 times as large as that of 7CU, an observation that renders 7CUCF₃ a suitable anion sensor candidate. The results of this study will contribute to the development of new molecular designs for highly fluorescent sensing.

Signal-on fluorescence assay for pyrophosphate ions based on DNA-stabilized silver nanoclusters

Pyrophosphate anion (P₂ O₇ ^4- , PPi) is considered as a potential biomarker for arthritic diseases because high levels of PPi may result in calcium pyrophosphate dehydrate crystal deposition diseases. In this study, a simple fluorescence method for PPi was demonstrated by organic integration of the efficient fluorescence quenching ability of copper ions to DNA-scaffolded silver nanoclusters and the strong affinity of PPi towards copper ions. This simple fluorescence sensor showed a low detection limit (0.28 μM based on signal/noise = 3) towards the detection of PPi. Practical application of this method was also validated by detection of PPi in the synovial fluid.

A copper(ii)-dipicolylamine-coumarin sensor for maltosyltransferase assay

A Cu(ii)-[di(2-methylpyridyl)methylamino]coumarin fluorescence turn-on sensor (Cu-1b) is designed to detect phosphate ions with K_ass = 1.4 × 10⁵ M^-1 in HEPES buffer. Cu-1b is applied to probe the GlgE-catalyzed maltose-transfer reaction of α-maltose-1-phosphate to α-1,4-glucan with concomitant release of phosphate ions in Mycobacterium tuberculosis.

Conformational Selection in Anion Recognition: cGMP-Selective Binding by a Naphthalimide-Functionalized Amido-Amine Macrocycle

Amido-amine macrocycles with two and four naphthalimide dyes were designed to bind nucleoside monophosphates and oligonucleotides in an aqueous buffered solution. Anion-templated synthesis was used to direct the macrocyclization reaction to the [2+2] product, while high dilution conditions favored the formation of the [4+4] macrocycle with an unprecedented geometry, as revealed from the X-ray analysis. The [2+2] product was found to exhibit a remarkable binding strength and fluorescence response for cyclic guanosine monophosphate (cGMP) in an aqueous solution. To our knowledge, this is the first synthetic receptor for cGMP, which also demonstrates a high preference to bind guanine-rich sequences accomplished by a strong fluorescence quenching. The receptor conformation is very sensitive to the guest structure in an aqueous solution, thus modeling the adaptive behavior of proteins. The study of synthetic systems with a detectable conformational equilibrium represents a great potential for understanding highly specific and tightly regulated interactions in biological systems.

Azaindole-BODIPYs: Synthesis, fluorescent recognition of hydrogen sulfate anion and biological evaluation

The synthesized and sensing capability of two novel azaindole substituted mono and distyryl BODIPY dyes against bisulfate anion were reported. Structural characterizations of the targeted compounds were conducted by using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, ¹H and ¹³C NMR spectroscopies. Photophysical properties of the azaindole substituted BODIPY compounds were investigated employing absorption and fluorescence spectroscopies in acetonitrile solution. It was found that the final compounds 3 and 4 exhibited exclusively selective and sensitive turn-off sensor behavior on HSO₄^- anion. Additionally, the stoichiometry ratio of the targeted compounds to bisulfate anion was measured 0.5 by Job's method. Also, density function theory was performed to the optical response of the sensor for targeted compounds. Furthermore, the cytotoxicity of Azaindole-BODIPYs was examined against living human leukemia K562 cell lines.

A coumarin based highly sensitive fluorescent chemosensor for selective detection of zinc ion

A very effective and highly sensitive fluorescent chemosensor, based on 4-hydroxycoumarin skeleton substituted by benzothiazole moiety was synthesized and investigated for the detection of zinc ion. This chemosensor displays highly selective and sensitive fluorescence enhancement to Zn²⁺ over other metal ions examined in solution and in biological systems. The detection limit for the fluorescent chemosensor 1 toward Zn²⁺ was 3.58 × 10^-8 M. A simple and efficient approach was improved for the synthesis of chemosensor 1 starting from 4-hydroxycoumarin.

A new multifunctional benzimidazole tagged coumarin as ratiometric fluorophore for the detection of Cd2+/F- ions and imaging in live cells

A novel multifunctional ratiometric fluorescent probe has been designed and synthesized for the selective recognition of Cd²⁺/F^- ions. The probe (3)-((2)-(1H-benzoimidazole-2-yl)-phenylimino) methyl-4-chloro-methyl-2H-chromen-2-ene (BIMC) displays excellent ratiometric responses towards Cd²⁺/F^- ions over the tested cations/anions. The lowest detection limits observed for Cd²⁺ and F^- are 1.5 × 10^-10 mol/l and 1.2 × 10^-10 mol/l respectively. Job's plot and Electro spray Ionization mass spectral (ESI-MS) studies confirms 1:1 binding stoichiometry of BIMC with Cd²⁺/F^- ions, which is further evidenced by ¹H NMR titration studies. The reversibility studies of BIMC with Cd²⁺ have been investigated using ethylenediaminetetraacetic acid (EDTA). Upon binding to Cd²⁺/F^- ions, the probe features strong ratiometric response in both UV-Visible and fluorescence spectra due to the inhibition of intramolecular charge transfer (ICT). Furthermore, the mechanism of ICT has been rationalized via solvatochromism and DFT calculations.

Hairpin-shaped DNA Templated Copper Nanoparticles for Fluorescence Detection of Adenosine Triphosphate Based on Ligation-mediated Exonuclease Cleavage

DNA-templated copper nanoparticles (CuNPs) have recently received considerable interest as functional fluorescent probes for biochemical analysis. In this work, a novel ATP-dependent ligation reactions (ATP-DLR) based ATP assay strategy was proposed by using hairpin-shaped (HS) DNA templated CuNPs as a fluorescent probe. Nick sealing by T4 DNA ligase leads to the formation of intact HS DNA, which can resist the exonuclease cleavage and be taken as the template for CuNPs formation, resulting in strong fluorescence. The proposed ATP detection is label free, sensitive and highly selective, and it has good linearity from 0.02 to 4 μM and a detection limit of 7 nM. This strategy is expected to promote the exploitation and application of DNA-templated CuNPs in biochemical and biomedical studies, and holds great promise in fluorescence detection for other ligation-related biomolecules.

Selective and sensitive fluorescent and colorimetric chemosensor for detection of CO32- anions in aqueous solution and living cells

A new colorimetric and fluorescent chemosensor for visual determination of carbonate ions was developed by the microwave assisted solvent free synthesis of 7,8-dihydroxy-3-(4-methylphenyl) coumarin (DHMC). The structural characterization of DHMC was confirmed by microanalysis and spectroscopy methods (MALDI-TOF, FT-IR, ¹H NMR, ¹³C NMR, and 2D HETCOR). The binding behaviors of DHMC were investigated towards various anions by UV-vis and fluorescence spectroscopy. DHMC showed a selective and sensitive fluorometric and colorimetric responses towards carbonate ion over other anions. The detection limit of CO₃^2- was found to be 1.03 µM. Moreover, the fluorescence imaging in living cells suggests that DHMC has a great potential in the biological imaging application. It has been demonstrated that DHMC can be used as a rapid and reliable sensor for the determination of carbonate anion in a variety of practical applications.

A hydrazone based probe for selective sensing of Al(iii) and Al(iii)-probe complex mediated secondary sensing of PPi: framing of molecular logic circuit and memory device and computational studies

A hydrazone-based conjugate acts as a dual channel sensor towards Al³⁺and PPi in H₂O–MeOH with excellent sensing capability in live cells.

A fluorescent turn-on probe for cyanide anion detection based on an AIE active cobalt(ii) complex

A Co(ii) complex based on an AIE-active tetraarylethylene ligand displays selective fluorescence enhancement in the presence of cyanide anion in aqueous solution.

Use of a small molecule as an initiator for interchain staudinger reaction: A new ATP sensing platform using product fluorescence

We demonstrated that a small molecule induced interchain Staudinger reaction can be employed for highly selective detection of adenosine triphosphate (ATP), an important energy-storage biomolecule. A designed ATP split aptamer (A1) was first functionalized with a weakly fluorescent coumarin derivative due to an azide group (azido-coumarin). The second DNA strand (A2) was covalently linked with triphenylphosphine, which could selectively and efficiently reduce azido to amino group through the Staudinger reaction. The A2 was then hybridized with a half of another designed longer DNA strand (T1). The second half of T1 was a split aptamer and selectively recognized ATP with A1 to form a sandwich structure. The specific interaction between ATP and the aptamers drew the two functionalized DNA strands (A1 and A2) together to initiate the interchain Staudinger reduction at fmol-nmol concentration level, hence produced fluorescent 7-aminocoumarin which could be used as an indicator for the presence of trace ATP. The reaction process had a concentration dependent manner with ATP in a large concentration range. Such a strategy of interchain Staudinger reaction can be extended to construct biosensors for other small functional molecules on the basis of judiciously designed aptamers.

Red luminescence control of Eu(iii) complexes by utilizing the multi-colored electrochromism of viologen derivatives

The electroresponsive switching of red photoluminescence based on the electrochemical coloration of cyan-magenta-green (CMG) viologen components was achieved by combining a luminescent Eu³⁺ chelate and viologen derivatives, resulting in CMG coloration in a single cell. The cell coloration was controlled by an electrochromic (EC) reaction, which also modulated the photoluminescence of the Eu³⁺ chelate with high contrast, by transferring energy from the excited state of the Eu³⁺ ion to the colored states of EC molecules. Cyclic voltammograms, photoluminescence spectra, absorption spectra, luminescence quantum yields, and luminescence lifetimes were measured to clarify the differences between the luminescence quenching and energy transfer efficiencies for each C, M, and G coloration associated with the electrochromism. Thus, the spectral overlap between the luminescence band of the Eu³⁺ chelate and the absorption band of the colored EC molecules was proven to affect the efficiency of luminescence modulation.

Furan and Julolidine-Based "Turn-on" Fluorescence Chemosensor for Detection of F- in a Near-Perfect Aqueous Solution

A new fluorescent sensor 1, containing furan and julolidine moieties linked through a Schiff-base, has been synthesized. Distinct "turn-on" fluorescence enhancement of 1 was observed upon the addition of F^- in a near-perfect aqueous solution. The binding capabilities of 1 with F^- were studied by using fluorescent spectroscopic techniques, ESI-mass analysis and NMR titration measurements. The detection limit for the analysis of F^- was found to be 10.02 μM, which is below the WHO guideline (79 μM) for drinking water. Practically, the sensing ability of 1 for F^- was successfully applied in real water samples. The sensing mechanism for F^- was proposed to be the ICT mechanism via the hydrogen bonding, which was well explained by theoretical calculations.

Fluorescence Sensing of Inorganic Phosphate and Pyrophosphate Using Small Molecular Sensors and Their Applications

The aim of this contribution is to provide an introduction and a brief summary of the principle of fluorescence molecular sensors specific to inorganic phosphate (Pi) and inorganic pyrophosphate (PPi) as well as their applications. In our introduction we describe the impact of both Pi and PPi in the living organism and in the environment, followed by a description of the principle of fluorescence molecular sensors and the sensing mechanism in solution. We then focus on exciting research which has emerged in recent years on the development of fluorescent sensors specific to Pi and PPi, categorized by chemical interactions between the sensor and the target molecule, such as hydrogen bonding, coordination chemistry, displacement assay, aggregation induced emission or quenching, and chemical reactions.

A direct method for the N-tetraalkylation of azamacrocycles

An efficient protocol for the direct synthesis of N-tetraalkylated derivatives of the azamacrocycles cyclam and cyclen has been developed, using a partially miscible aqueous–organic solvent system with propargyl bromide, benzyl bromide, and related halides. The method works most effectively when the reaction mixture is shaken, not stirred. A crystal structure of the N-tetrapropargyl cyclam derivative 1,4,8,11-tetra(prop-2-yn-1-yl)-1,4,8,11-tetraazacyclotetradecane diperchlorate is reported.