A new "on-off-on" fluorescent probe containing triarylimidazole chromophore to sequentially detect copper and sulfide ions

Activity-Based Fluorescent Probes for Hydrogen Sulfide and Related Reactive Sulfur Species

Hydrogen sulfide (H2S) is not only a well-established toxic gas but also an important small molecule bioregulator in all kingdoms of life. In contemporary biology, H2S is often classified as a "gasotransmitter," meaning that it is an endogenously produced membrane permeable gas that carries out essential cellular processes. Fluorescent probes for H2S and related reactive sulfur species (RSS) detection provide an important cornerstone for investigating the multifaceted roles of these important small molecules in complex biological systems. A now common approach to develop such tools is to develop "activity-based probes" that couple a specific H2S-mediated chemical reaction to a fluorescent output. This Review covers the different types of such probes and also highlights the chemical mechanisms by which each probe type is activated by specific RSS. Common examples include reduction of oxidized nitrogen motifs, disulfide exchange, electrophilic reactions, metal precipitation, and metal coordination. In addition, we also outline complementary activity-based probes for imaging reductant-labile and sulfane sulfur species, including persulfides and polysulfides. For probes highlighted in this Review, we focus on small molecule systems with demonstrated compatibility in cellular systems or related applications. Building from breadth of reported activity-based strategies and application, we also highlight key unmet challenges and future opportunities for advancing activity-based probes for H2S and related RSS.

A novel "on-off-on" near-infrared fluorescent probe for Cu2+ and S2- continuous detection based on dicyanoisoflurone derivatives, and its application in bacterial imaging

We have successfully synthesized a near-infrared fluorescent probe for the continuous detection of copper and sulfur ions. The probe has good selectivity and anti-interference ability against Cu2+ and S2-. The results show that after adding Cu2+ to the DL solution of the near-infrared fluorescent probe, Cu2+ forms a [DL + Cu2+] complex with the probe, which leads to fluorescence quenching due to the paramagnetism of Cu2+. The probe can be used for the quantitative detection of Cu2+ with a detection limit of 1.26 × 10-9 M. According to the Job's plot curve the binding stoichiometry between DL and Cu2+ is 1 : 1. Subsequently, S2- was added to the [DL + Cu2+] solution, because the precipitation dissolution equilibrium constant of CuS was Ksp = 1.27 × 10-36, so the binding capacity between Cu2+ and S2- was stronger, CuS precipitation was formed, and red fluorescence was re-released, and the quantitative detection of S2- was realized, and the detection limit was 3.50 × 10-8 M. Through bacterial imaging experiments, we found that the probe can accomplish the fluorescence imaging experiments of Staphylococcus aureus, indicating that the probe has good biopenetration and biocompatibility, and has application prospects in bioimaging and environmental monitoring. In addition, the probe DL has good suitability for Cu2+ and S2- detection in real samples.

Development in Fluorescent OFF-ON Probes Based on Cu2+ Promoted Hydrolysis Reaction of the Picolinate Moiety

Anions and cations have a key role in our normal life. Cu²⁺ ion is a crucial trace element accountable for the part of several cellular enzymes and proteins, including cytochrome c oxidase, dopamine monooxygenase, Cu/Zn superoxide dismutase, and ceruloplasmin. WHO has found the extreme acceptable level of Cu²⁺ ions in drinking water is up to 2.0 ppm. Excess use of Cu²⁺ ions is associated with various human genetic disorders. Thus, the visualization of Cu²⁺ ions to avoid its toxic effects in chemical and biological systems is significant. In this review we have summarized sensors based on catalytic hydrolysis of picolinate to detect Cu²⁺ ions. The sensors based on hydrolysis of picolinate are very selective as compared to the other sensors for Cu²⁺ ions detection. We have focused on describing the structure, spectral properties, detection limits, and bioimaging model of the sensors.

Synthesis of a novel triphenylamine-based multifunctional fluorescent probe for continuous recognition application

In this paper, a novel fluorescent probe, TPA-PAT, with continuous recognition based on triphenylamine was designed, synthesized, and characterized by NMR, IR, and fluorescence spectrophotometry techniques.

Carbazole-thiophene based fluorescent probe for selective detection of Cu2+ and its live cell imaging

Highly sensitive and specific imaging of copper ion (Cu²⁺) in living cells is essential for better understanding the physiological and metabolic processes. We develop a novel fluorescent probe based on carbazole-thiophene for specific Cu²⁺ detection in living cells. Job's plot and density functional theory (DFT) confirmed a stoichiometric ratio of 2:1 between the probe molecules and Cu²⁺. This probe exhibits strong fluorescence in aqueous media, while its fluorescence intensity significantly decreased in the presence of Cu²⁺. An in vitro assay shows that the fluorescent probe has rapid response within 5 s and high sensitivity for the detection of Cu²⁺ in the range from 1 to 10 μM with a detection limit of 0.29 μM. Live cell studies reveal that the fluorescent probe has good cell-membrane permeability and can successfully visualize the fluctuation of the intracellular Cu²⁺ concentration. In addition, the fluorescent probe has low cytotoxicity, which may provide a new tool for monitoring other analytes in living cells.

Progress of NiO-based anodes for high-performance Li-ion batteries

Rechargeable lithium-ion batteries (LIBs) are of great significance to the development of renewable energy. The traditional graphite anode is gradually unable to meet increasing demands for high energy density and power density due to its low theoretical capacity. NiO has gained considerable attention because of its high theoretical capacity, low toxicity, and stable chemical properties. This review summarizes the research progress of NiO-based nanomaterials in LIBs and centers on the electrochemical reaction mechanism, synthesis methods, and strategies for improving the electrochemical properties of NiO anodes. The results demonstrate that the electrochemical characteristics highly depend on the synthesis method, morphology, surface area, conductive substrate, etc. Compared with pure NiO, NiO-based composites including NiO/carbon-based materials and NiO/metal oxide often present higher capacity and cycle stability. Furthermore, challenges and future perspectives of NiO-based anodes are also discussed.

An IMPLICATION-logic-based fluorescent probe for sequential detection of Cu2+ and phosphates in living cells

In this manuscript, we developed an IMPLICATION logic fluorescent probe, HL, for the sequential detection of Cu2+ and phosphate anions in extracellular and intracellular environments.

Sensing mechanism of fluorogenic urea with fluoride in solvent media: A new fluorescence quenching mechanism

The interaction of 1-Phenyl-3-(pyren-1-yl) urea (LH) and fluoride anion (F^-) with a unique ON¹-OFF-ON² fluorescent response has been investigated by the density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations. The hydrogen-bonding dynamics and photophysical properties of the complex LH-F, as well as its isolated receptor LH and anion form L-H₁, have been studied in detail. We demonstrate that the intermolecular hydrogen bond (N-H…F) of the complex LH-F is greatly enhanced in the electronically excited state. The nonradiative deactivation via electron transfer and internal conversion rather than excited-state intramolecular proton transfer (ESIPT) can be facilitated by the excited state hydrogen bond strengthening. The results have been cross-validated by molecular structure, electronic spectra, frontier molecular orbitals, and infrared spectra as well as hydrogen bond binding energy. These results indicate that the current calculations completely reproduce the experimental results and provide compelling evidence for the sensing mechanism of LH for F^-.

A Heterocyclic-based Bifunctional Sensor for Detecting Cobalt and Zinc Ion

A new bifunctional chemosensor HBP ((E)-2-(2-((5-bromopyridin-2-yl)methylene)hydrazinyl) quinoline) based on heterocyclic compounds was designed and studied. The HBP showed successful detecting ability toward cobalt ion with a UV-visible red-shift and a color change of colorless to pink. Moreover, toward zinc ion, the HBP showed an obvious fluorescence turn-on response. The binding ratio of the HBP to cobalt and zinc was a 2 to 1 for both ions. The detection limits were found to be 10 nM for Co2+ and 18 nM for Zn2+. Based on UV-vis and fluorescent spectral variations, Job plots, ESI-MS, FT-IR and calculations, the binding mechanisms of the HBP toward cobalt and zinc ions were proposed.

Cu2+-selective NIR fluorescence sensor based on heptamethine cyanine in aqueous media and its application

A near-infrared (NIR) colorimetric fluorescence sensor, Cy7C3, based on heptamethine cyanine dye was synthesized for determining the presence of Cu²⁺ ions. The sensor showed highly sensitive fluorescence quenching toward Cu²⁺ ions in acetonitrile/buffer solution at physiological pH with long emission wavelength of 718 nm. Cy7C3 also provided an excellent selectivity to Cu²⁺ ions over other competing metal ions, with a low detection limit of 9 ppb, which was lower than the maximum concentration of Cu²⁺ ions in drinking water of U.S. EPA. Cy7C3 could achieve naked-eye detection of Cu²⁺ ions via the color change from blue to colorless, which allowed determination of Cu²⁺ ions in hydroponic fertilizers. Additionally, the sensor was developed to detect Cu²⁺ ions in HepG2 cancer cells via fluorescence imaging.

Direct and sensitive detection of sulfide ions based on one-step synthesis of ionic liquid functionalized fluorescent carbon nanoribbons

Despite widely reported fluorescence sensors for cations, direct detection of anions is nevertheless still rare. In this work, ionic liquid-functionalized fluorescent carbon nanoribbons (IL-CNRs) are one-step synthesized and serve as the fluorescent probes for direct and sensitive detection of sulfide ions (S²⁻). The IL-CNRs are synthesized based on electrochemical exfoliation of graphite rods in a water-IL biphasic system. The as-prepared IL-CNRs exhibit uniform structure, high crystallinity, strong blue fluorescence (absolute photoluminescence quantum yield of 11.4%), and unique selectivity towards S²⁻. Based on the fluorescence quenching of IL-CNRs by S²⁻, a fluorescence sensor is developed for direct, rapid and sensitive detection of S²⁻ in the range of 100 nM to 1 μM and 1–300 μM with a low detection limit (LOD, 85 nM). Moreover, detection of S²⁻ in a real sample (tap water) is also demonstrated.

Sensitive detection of sulfide ions is realized based on one-step synthesis of ionic liquid functionalized fluorescent carbon nanoribbons.

Diaminomaleonitrile-based Fluorophores as Highly Selective Sensing Platform for Cu2

A colorimetric and turn-on fluorescent chemodosimeter 1 based on diaminomaleonitrile was synthesized for Cu²⁺ detection. It showed high selectivity and sensitivity towards Cu²⁺ over the other tested metal ions. Probe 1 in acetonitrile exhibited a strong absorption band at 530 nm and weak fluorescence emission when excited at 480 nm, while the addition of Cu²⁺ could lead to a 30-nm blue shift of the absorption band and a remarkable fluorescence enhancement. Moreover, the detection limit of probe 1 for Cu²⁺ was calculated to be 28 nM. Quite different from the reported mechanism based on a metal-complexation induced fluorescence enhancement, the sensing mechanism was proved to be based on the Cu²⁺-promoted hydrolysis reaction, which was confirmed by ¹H NMR, ¹³C NMR and mass spectrum analysis. Studies on probe 2 were carried out to verify the universality of this sensing mechanism.

Synthesis of methionine methyl ester-modified coumarin as the fluorescent-colorimetric chemosensor for selective detection Cu2+ with application in molecular logic gate

A methionine methyl ester-modified coumarin derivative was designed and synthesized, which could discriminate Cu²⁺ from other metal ions in HEPES buffer (10 mM, pH 7.4)/CH₃CN (40:60, V/V). The detection limit of WM toward Cu²⁺ was 1.84 × 10^-7 M, which was lower than the concentration of Cu²⁺ in drinking water suggested by WHO and EPA. And the proposed coordination mode exhibiting the interaction between WM and Cu²⁺ was studied by UV-Vis, fluorescence spectrum, ESI-MS and FT-IR. Based on the fluorescent reversibility of WM, WM was considered as a molecular logic gate and molecular keypad lock. In addition, the test strips and the silica gel plates prepared from the solution of WM also demonstrate the favorable selectivity toward Cu²⁺.

A highly turn-on fluorescent CHEF-type chemosensor for selective detection of Cu2+ in aqueous media

An efficient "turn on" fluorescence chemosensor Schiff base LH based on the combination of 2-Hydroxy-5-(p-tolyldiazenyl)benzaldehyde and N-(3-Aminopropyl)imidazole was prepared and characterized then evaluated for its selective fluorescent sensing of Cu²⁺ amongst other metal ions. The CN isomerization inhibition process induced by the Cu²⁺ binding warrants the chelation-induced enhanced fluorescence (CHEF) effect. In addition, the detection limit sensing of LH for Cu²⁺ was found to be 1.8 × 10^-6 M that is below the WHO recommendation level (20 μM) for drinking water.

A chemosensor with a paddle structure based on a BODIPY chromophore for sequential recognition of Cu2+ and HSO3−

In this study, a highly selective chemosensor ML based on a BODIPY fluorescent chromophore was synthesized for sequential recognition of Cu²⁺ and HSO₃⁻ in a CH₃OH/H₂O (99 : 1 v/v) system, which contained three recognition sites and its structure characterized by ¹H NMR, ¹³C NMR and ESI-HR-MS. The sensor ML showed an obvious “on–off” fluorescence quenching response toward Cu²⁺ and the ML-Cu²⁺ complex showed an “off–on” fluorescence enhancement response toward HSO₃⁻. The detection limit of the sensor ML was 0.36 μM to Cu²⁺ and 1.4 μM to HSO₃⁻. In addition, the sensor ML showed a 1 : 3 binding stoichiometry to Cu²⁺ and the recovery rate of ML-Cu²⁺ complex identifying HSO₃⁻ could be over 70%. Sensor ML showed remarkable detection ability in a pH range of 4–8.

A highly selective chemosensor based on a BODIPY chromophore for sequential recognition of Cu²⁺ and HSO₃⁻.