Recent progress in hydrogen sulphide (H 2 S) sensors by metal displacement approach

Tuning the amphiphilicity of terpyridine-based fluorescent probe in water: Assembly and disassembly-controlled H g2+ sensing, removal, and adsorption of H2S

A water-soluble terpyridine-based cationic fluorescent probe (SP-TPy) was synthesized, which emerged with pH-dependent amphiphilicity, resulting in self-assembly and disassembly in aqueous media with the aggregation-induced emission (AIE) property. In neutral water (pH 7.4), a moderate sensing response to Hg²⁺ ions was given by the self-assembly of SP-TPy. However, in acidic aqueous media, the monomer of SP-TPy not only appeared to be highly selective and sensitive for Hg²⁺ ions, but also displayed highly efficient removal of Hg²⁺ ions from solution by rapid precipitation, which was attributed to the coordination-triggered reassembly of SP-TPy. The removal efficiency of SP-TPy for Hg²⁺ was found to be over 99%. Further study indicated that the precipitates were composed of various polyhedral porous frameworks, a property that was further used to adsorb H₂S gas to form HgS complexes with higher uptake capacities. In addition, SP-TPy can be efficiently regenerated and recycled using a simple treatment with acidic water after adsorption of the H₂S gas.

Synthesis, crystal structures and magnetic and electrochemiluminescence properties of three manganese(II) complexes

Three novel complexes, namely, penta-μ-acetato-bis(μ2-2-{[2-(6-chloropyridin-2-yl)hydrazinylidene]methyl}-6-methoxyphenolato)-μ-formato-tetramanganese(II), [Mn4(C13H11ClN3O2)2(C2H3O2)5.168(CHO2)0.832], 1, hexa-μ2-acetato-bis(μ2-2-{[2-(6-bromopyridin-2-yl)hydrazinylidene]methyl}-6-methoxyphenolato)tetramanganese(II), [Mn4(C13H11BrN3O2)2(C2H3O2)6], 2, and catena-poly[[μ2-acetato-acetatoaqua(μ2-2-{[2-(6-chloropyridin-2-yl)hydrazinylidene]methyl}-6-methoxyphenolato)dimanganese(II)]-μ2-acetato], [Mn2(C13H11ClN3O2)(C2H3O2)3(H2O)] n , 3, have been synthesized using solvothermal methods. Complexes 1–3 were characterized by IR spectroscopy, elemental analysis and single-crystal X-ray diffraction. Complexes 1 and 2 are tetranuclear manganese clusters, while complex 3 has a one-dimensional network based on tetranuclear Mn4(L 1)2(CH3COO)6(H2O)2 building units (L 1 is 2-{[2-(6-chloropyridin-2-yl)hydrazinylidene]methyl}-6-methoxyphenolate). Magnetic studies reveal that complexes 1–3 display dominant antiferromagnetic interactions between MnII ions through μ2-O bridges. In addition, 1–3 also display favourable electrochemiluminescence (ECL) properties.

Pyrene derivative-functionalized mesoporous silica-Cu2+ hybrid ensemble for fluorescence "turn-on" detection of H2S and logic gate application in aqueous media

The ensemble system PyH-SBA-15-Cu²⁺ was obtained via coordination interaction of pyrene derivative-functionalized mesoporous SBA-15 and Cu²⁺, and applied for the selective and sensitive detection of H₂S over pH 6.0-12.0 in aqueous media. The sensing strategy was designed on the basis of the H₂S-induced dissolution of Cu²⁺ from PyH-SBA-15-Cu²⁺. Cu²⁺ has good binding affinity to N atoms in PyH-SBA-15; therefore, the organic-inorganic hybrid ensemble PyH-SBA-15-Cu²⁺ was formed, which is nonfluorescent in aqueous solution because of the Cu²⁺-promoted emission quenching of PyH-SBA-15. The addition of H₂S induces the dissolution of PyH-SBA-15-Cu²⁺ by the formation of stable CuS, thereby producing fluorescence revival of PyH-SBA-15. The correlative "turn-on" fluorescence signals of this ensemble system are linearly proportional to [H₂S] in the concentration region of 0-1.0 × 10^-4 M, showing a low detection limit of 3.7 × 10^-7 M. Other common anions do not induce distinct fluorescence changes. When using the fluorescence intensity signal changes of PyH-SBA-15 as outputs and Cu²⁺ and S^2- as inputs, PyH-SBA-15 can act as an XNOR logic gate.

Development of “dual-key-and-lock” responsive probes for biosensing and imaging

Recent advances in the development of “dual-key-and-lock” responsive probes for accurate detection of various biomolecules are reviewed.

Copper Complex-Embedded Vesicular Receptor for Selective Detection of Cyanide Ion and Colorimetric Monitoring of Enzymatic Reaction

Detection of environmentally important ion cyanide (CN^-) has been done by a new method involving displacement of both metal and indicator, metal indicator displacement approach (MIDA) on the vesicular interface. Terpyridine unit was selected as the binding site for metal (Cu²⁺), whereas Eosin-Y (EY) was preferred as an indicator. About 150 nm sized nanoscale vesicular ensemble (Lip-1.Cu) has shown good selectivity and sensitivity for CN^- without any interference from other biologically and environmentally important anions. Otherwise, copper complexes are known for the interferences of binding with phosphates and amino acids. The Lip-1.Cu nanoreceptor also has the possibility to be used for real-time colorimetric scanning for the released HCN via enzymatic reactions. Lip-1.Cu has several superiorities over the other reported sensor systems. It has worked in 100% aqueous environment, fast response time with colorimetric monitoring of enzymatic reaction, and low detection limit.

Electronically-tuned triarylmethine scaffolds for fast and continuous monitoring of H2S levels in biological samples

A sensor for the detection and quantification of H2S in biological samples should ideally meet a set of criteria such as fast detection, high sensitivity in the desired concentration range, high selectivity, non-interference from biomolecules like proteins, ease of synthesis, long-term stability and water solubility. Although a number of H2S probes are known, none of them possess all the above attributes that are relevant for practical applications. As part of a program to develop reliable chemical probes for continuous monitoring of this gasotransmitter in the blood plasma of sepsis-prone individuals in post-operative wards, we have looked at the possibility of improving the reactivity and selectivity profile of triarylmethine dyes towards different nucleophiles. After achieving high sensitivity through electronic control, the interference from sulfite, thiosulfate and metabisulfite was addressed by introducing a metal salt-mediated desulfuration step that results in dye regeneration selectively from its H2S adduct. Typically, if the analyte contains only H2S, the loss of absorbance in the first step gets completely reinstated after the second step; absorbance changes in both steps vary linearly with sulfide concentration and either of these two steps can be used for the quantification of H2S with the help of standard plots. In the presence of interfering ions, the first step will show decolourization due to the presence of all of them whereas only the H2S-adduct will undergo desulfuration in the second step which can be used for quantification. The decolourization step is instantaneous while the desulfuration requires only about 50 s, making the entire protocol complete in less than a minute. The methodology optimized here also meets the requirements mentioned above for real-life applications.

Modulation of fluorescence sensing properties of coumarin-based fluorescent probe for H2S and its application in cell imaging

A coumarin-based turn on probe, named 3-((E)-3-(1H-indol-3-yl)acryloyl)-2H-chromen-2-one(IAC) was designed and synthesized for the detection of H₂S in aqueous medium. IAC showed no obvious red fluorescence in Tris-HCl(pH = 7.2, 60% DMF), a 28.2-fold fluorescence enhancement was found when 40 equiv. H₂S was added. Other analytes such as anions, metal ions and GSH, Cys, Gly did no significant fluorescence enhancement at 580 nm to IAC. The red fluorescence enhancement mechanism between IAC and H₂S was considered by DFT and ESI-MS. Overall, IAC was successfully applied in cell imaging.

Triazole-Coupled Benzimidazole-Based Fluorescent Sensor for Silver, Bromide, and Chloride Ions in Aqueous Media

A triazole-coupled benzimidazole-based fluorescent probe S1 with nitrogen and oxygen binding sites was synthesized and its properties as a probe for cations were investigated. Probe S1 was found to be highly selective toward Ag⁺ ions in aqueous media. The fluorescence intensity of S1 was quenched as a function of the concentration of Ag⁺ ions in the presence of potential interfering cations with a detection limit of 2.70 μM. The resulting S1-Ag⁺ complex was subsequently studied for its anion recognition abilities and found to recognize Br^- and Cl^- ions, revealing the concentration-dependent fluorescence enhancement with detection limits of 22.2 and 23.0 μM, respectively. Revival of the fluorescence profile of probe S1 indicated that Ag⁺ ion was released from the S1-Ag⁺ complex. Probe S1 is a sensor that can be single-handedly utilized for the qualitative and quantitative determination of Ag⁺, Br^-, and Cl^- ions in aqueous media.

Turn-On Fluorescence Probe for Nitric Oxide Detection and Bioimaging in Live Cells and Zebrafish

An effective bioanalytical method for rapid, sensitive, specific, and in situ sensing of nitric oxide (NO) is the key for further unveiling the biological functions of this gasotransmitter molecule in vitro and in vivo. In this contribution, a new fluorescence probe for sensing and imaging of NO in live systems was developed. The probe, FP-NO, was designed by exploring a novel sensing mechanism, i.e., the rotation of the N-N single bond of a coumarin derivative. FP-NO was prepared by incorporating a recognition unit, thiosemicarbazide moiety into a coumarin fluorophore. The weakly fluorescent FP-NO quickly and selectively reacts with NO to form a highly fluorescent product, FP-P. Such an enhancement of fluorescence emission allows NO detection with high sensitivity. The detection limit was 47.6 nM. The reaction mechanism was validated by HRMS titration analysis and the "OFF-ON" fluorescence response mechanism was rationalized by theoretical computation. FP-NO is biocompatible and live cell membrane permeable. The feasibility of FP-NO as the fluorescence probe for imaging and flow cytometry analysis of exogenous NO in MCF-7 cells and exogenous NO production in inflamed J774A.1 macrophage cells was then evaluated. Visualization of exogenous and endogenous NO production in live zebrafish was then achieved, implying the potential application of FP-NO in the studies of the NO roles in live organisms.

Sequential displacement strategy for selective and highly sensitive detection of Zn2+, Hg2+ and S2- ions: An approach toward a molecular keypad lock

A thiocarbonohydrazone locked salicylidene based macrocycle ligand L has been synthesized and its ion sensing properties were examined by UV-visible and fluorescence spectroscopy. The macrocycle serves as a highly selective colorimetric sensor for Hg²⁺ ions while it acts as an excellent fluorescent sensor for Zn²⁺ ions by exhibiting a green fluorescence at 498 nm even in the presence of interfering ions. A detailed analysis of binding characteristics such as complex stoichiometry, association constant and detection limits of L toward Hg²⁺ and Zn²⁺ ions were evaluated by UV-visible and fluorescence experiments which revealed a stronger binding affinity and higher detection limit of L toward the mercury ions. Further, the sequential displacement strategy for the chromofluorogenic detection of Zn²⁺, Hg²⁺ and S^2- ions by ligand L, has been studied comprehensively. Finally, the ion-responsive fluorescence output signal of L were employed to design a molecular keypad lock which could be accessible by two users having two different set of chemical passwords (inputs) through distinguishable optical trajectories.

A luminescent on–off probe based calix[4]arene linked through triazole with ruthenium(ii) polypyridine complexes to sense copper(ii) and sulfide ions

The supramolecular sensor Ru2L was designed by joining a bis-ruthenium(ii) polypyridyl complex with a p-tert-butyl calix[4]arene platform through a 1,2,3-triazole linker and used for sensing of copper(ii) and sulfide ions by fluorescence.

A turn-on fluorescent probe with a dansyl fluorophore for hydrogen sulfide sensing

Hydrogen sulfide (H₂S) is a biologically relevant molecule that has been newly identified as a gasotransmitter and is also a toxic gaseous pollutant. In this study, we report on a metal complex fluorescent probe to achieve the sensitive detection of H₂S in a fluorescent “turn-on” mode. The probe bears a dansyl fluorophore with multidentate ligands for coordination with copper ions. The fluorescent “turn-on” mode is facilitated by the strong bonding between H₂S and the Cu(ii) ions to form insoluble copper sulfide, which leads to the release of a strongly fluorescent product. The H₂S limit of detection (LOD) for the proposed probe is estimated to be 11 nM in the aqueous solution, and the utilization of the probe is demonstrated for detecting H₂S in actual lake and mineral water samples with good reproducibility. Furthermore, we designed detector vials and presented their successful application for the visual detection of gaseous H₂S.

H₂S turn on the fluorescence of DNS–Cu complex probe.

Selective Detection of H2S by Copper Complex Embedded in Vesicles through Metal Indicator Displacement Approach

A new approach for the detection of hydrogen sulfide (H₂S) was constructed within vesicles comprising phospholipids and amphiphilic copper complex as receptor. 1,2-Distearoyl- sn-glycero-3-phosphocholine (DSPC) vesicles with embedded metal complex receptor (1.Cu) sites have been prepared. The vesicles selectively respond to H₂S in a buffered solution and show colorimetric as well as spectral transformation. Other analytes such as reactive sulfur species, reactive nitrogen species, biological phosphates, and other anions failed to induce changes. The H₂S detection is established through a metal indicator displacement (MIDA) process, where Eosin-Y (EY) was employed as an indicator. Fluorescence, UV-vis spectroscopy, and the naked eye as the signal readout studies confirm the high selectivity, sensitivity, and lower detection limit of the vesicular receptor. The application of vesicular receptors for real sample analysis was also confirmed by fluorescence live cell imaging.

Interaction of monohydrogensulfide with a family of fluorescent pyridoxal-based Zn(ii) receptors

We studied the reactivity of HS⁻ with a family of fluorescent zinc complexes. In the case of complexes 1 and 3, we have evidence that the interaction with HS⁻ results in the displacement of the coordinated ligand from the Zn center. For complex 2, our data points to the coordination of HS⁻ to the metal center likely assisted by hydrogen bondings with the OH of the pyridoxal moiety.

A novel near-infrared fluorescent probe for highly selective recognition of hydrogen sulfide and imaging in living cells

A novel near-infrared fluorescent probe (L) based on a 1,4-diethyl-1,2,3,4-tetrahydro-7H-pyrano[2,3-g]quinoxalin-7-one scaffold has been synthesized and characterized. Probe L displays highly selective and sensitive recognition to H₂S over various anions and biological thiols with a large Stokes shift (125 nm) in THF/H₂O (6/4, v/v, Tris–HCl 10 mM, pH = 7.4). This probe exhibits turn-on fluorescence for H₂S through HS⁻ induced thiolysis of dinitrophenyl ether. Confocal laser scanning micrographs of MCF-7 cells incubated with L confirm that L is cell-permeable and can successfully detect H₂S in living cells.

A novel “off–on” fluorescent probe (L) for H₂S detection with NIR emission and imaging H₂S in living cells.