An effective fluorescent sensor for ClO- in aqueous media based on thiophene-cyanostilbene Schiff-base

Engaging a highly fluorescent conjugated polymer network for probing endogenous hypochlorite in macrophage cells: improved sensitivity via signal amplification

We have employed a triazine-based conjugated polymer network (CPN) for the selective detection of hypochlorite in a semi-aqueous environment. CPNs have been widely employed in gas capture, separation, and adsorption, but the fluorescent properties of CPNs possessing extensive π-conjugated systems tend to be unexplored. Herein, we report the photophysical properties of the CPN and investigate its sensing capability towards hypochlorite. Spectroscopic investigations reveal that the CPN forms π-stacked aggregates in aqueous medium, while loose aggregates were observed to be formed in hydrophobic solvents. The fluorogenic CPN demonstrates remarkable selectivity via fluorescence quenching and a blueshift response towards hypochlorite in a semi-aqueous medium, accompanied by a color change under UV light. Such a turn-off fluorescence response, along with the blue shift upon hypochlorite sensing, was attributed to the oxidation of the sulfur atom of the thiophene functionality of the CPN, consequently resulting in suppression of Intramolecular Charge Transfer (ICT) in the corresponding oxidized adduct. The fluorescence intensity of the CPN exhibits a linear response to hypochlorite concentration, achieving a low detection limit of 1.2 nM. Furthermore, the practical applicability was demonstrated by the detection of hypochlorite in water samples and fluorescent test-paper strips. Additionally, the present system is utilized for bio-imaging of endogenous hypochlorite in RAW 264.7 cells.

Sulfur-based fluorescent probes for biological analysis: A review

The widespread adoption of small-molecule fluorescence detection methodologies in scientific research and industrial contexts can be ascribed to their inherent merits, including elevated sensitivity, exceptional selectivity, real-time detection capabilities, and non-destructive characteristics. In recent years, there has been a growing focus on small-molecule fluorescent probes engineered with sulfur elements, aiming to detect a diverse array of biologically active species. This review presents a comprehensive survey of sulfur-based fluorescent probes published from 2017 to 2023. The diverse repertoire of recognition sites, including but not limited to N, N-dimethylthiocarbamyl, disulfides, thioether, sulfonyls and sulfoxides, thiourea, thioester, thioacetal and thioketal, sulfhydryl, phenothiazine, thioamide, and others, inherent in these sulfur-based probes markedly amplifies their capacity for detecting a broad spectrum of analytes, such as metal ions, reactive oxygen species, reactive sulfur species, reactive nitrogen species, proteins, and beyond. Owing to the individual disparities in the molecular structures of the probes, analogous recognition units may be employed to discern diverse substrates. Subsequent to this classification, the review provides a concise summary and introduction to the design and biological applications of these probe molecules. Lastly, drawing upon a synthesis of published works, the review engages in a discussion regarding the merits and drawbacks of these fluorescent probes, offering guidance for future endeavors.

Optical Chemosensor as a Sensitive and Selective Tool for the Detection of Thiocyanate Ions Via Cu2+ Induced Sensor and Its Practical Application

In various fields, including analytical, environmental, and biochemistry, the detection of ions is significant. A simple probe, 3-(1-((4-aminophenyl)imino)ethyl)-4-hydroxy-6-methyl-2H-pyran-2-one (DPD), was designed for this study and used for the detection of Cu2+ ions in methanol, based on dehydroacetic acid and phenylenediamine moieties. Binding interactions studies were performed using UV-Vis measurements, which showed selective binding behaviour towards Cu2+ ions. The HRMS spectral data and Job's plot were used to check the stoichiometry ratio of 2:1 of a probe to Cu2+ ions. A detection limit of 1.38×10-7 M for Cu2+ ions was observed. Theoretical DFT calculations were used to determine the quantum parameters and the energy gap between frontier molecular orbitals. Interestingly, the DPD-Cu2+ complex acted as a probe for the detection of SCN- ions at a low LOD value, i.e., 1.97×10-7 M. A novel incidence of reversibility with SCN- ions was reported using the HRMS technique. Next, real water and blood samples were used, and the concentration of Cu2+ ions was calculated to further analyse the practical applicability of the probe. The DPD probe showed better selectivity and sensitivity than previously reported sensors, especially in complex matrices, where other sensors frequently experience interference and detection limit issues, indicating its potential as an advanced tool for ion detection in various applications.

Glowing discoveries: Schiff base-cyanostilbene probes illuminating metal ions and biological entities

Schiff bases featuring cyanostilbene units have emerged as versatile and highly effective probes for the selective detection of various metal ions as well as biologically important species. This review comprehensively highlights recent advances in the development and application of the probes, which exhibit remarkable Aggregation-Induced Emission (AIE), Twisted Intramolecular Charge Transfer (TICT), and Excited-State Intramolecular Proton Transfer (ESIPT) properties. These unique structural characteristics facilitate their potential applications in the detection of biologically important metal ions such as Zn2+, Fe3+, Cu2+, Hg2+ and Co2+ ions with high sensitivity and selectivity. Furthermore, these probes have demonstrated significant potential in the recognition of vital biological species, including arginine, hydrazine and hypochlorite (ClO-). The present review discusses the underlying detection mechanisms, emphasizing the role of the Schiff base and cyanostilbene moieties for the selective detection of particular biologically important entities. Moreover, this discussion highlights the practical applications, problems, and future directions in this fast-growing field, emphasizing the vital importance of these probes in both analytical chemistry and bioassays.

Ex Tenebris Lux: Illuminating Reactive Oxygen and Nitrogen Species with Small Molecule Probes

Reactive oxygen and nitrogen species are small reactive molecules derived from elements in the air─oxygen and nitrogen. They are produced in biological systems to mediate fundamental aspects of cellular signaling but must be very tightly balanced to prevent indiscriminate damage to biological molecules. Small molecule probes can transmute the specific nature of each reactive oxygen and nitrogen species into an observable luminescent signal (or even an acoustic wave) to offer sensitive and selective imaging in living cells and whole animals. This review focuses specifically on small molecule probes for superoxide, hydrogen peroxide, hypochlorite, nitric oxide, and peroxynitrite that provide a luminescent or photoacoustic signal. Important background information on general photophysical phenomena, common probe designs, mechanisms, and imaging modalities will be provided, and then, probes for each analyte will be thoroughly evaluated. A discussion of the successes of the field will be presented, followed by recommendations for improvement and a future outlook of emerging trends. Our objectives are to provide an informative, useful, and thorough field guide to small molecule probes for reactive oxygen and nitrogen species as well as important context to compare the ecosystem of chemistries and molecular scaffolds that has manifested within the field.

Wavelength-tunable AIEgens based on 6-methoxy-2-naphthaldehyde: AIE behavior and bioimaging performance

AIE-active dyes have lately received considerable attention due to their versatile applications, especially in bioimaging and theranostics. Herein, 6-methoxy-2-naphthaldehyde was used to construct fluorophores through Knoevenagel condensation with various active methylene compounds. All the obtained compounds showed varying degrees of AIE characteristics. It was worth mentioning that the condensation product of 6-methoxy-2-naphthaldehyde and malononitrile (MOP-e) exhibited a large redshift and a large Stokes shift when forming aggregates. Furthermore, it showed an ultra-wide AIE band which enabled it to be utilized for dual-channel bioimaging. The single crystal X-ray diffraction analysis showed that two different molecular arrangement modes, the monomolecular stacking and the discrete π-π dimeric stacking, existed in the aggregates of MOP-e. The discrete dimeric stacking leads to excimer-induced enhanced emission, which results in its unique AIE behavior. Moreover, MOP-e displayed an excellent bioimaging performance in living cells in green channel and in red channel respectively.

Synthesis, determination, and bio-application in cellular and biomass-bamboo imaging of natural cinnamaldehyde derivatives

Cinnamon essential oil (CEO) is the main ingredient in the renewable biomass of cinnamon, which contains natural cinnamaldehyde. To valorize the value of cinnamaldehyde, two simple and useful compounds (1 and 2) from CEO were synthesized using a Schiff-base reaction and characterized by infrared spectra (IR), nuclear magnetic resonance (NMR), and high-resolution mass spectrometry (HRMS). Compound 1 was used to confirm the presence of Fe³⁺ and ClO⁻ in solution, as well as compound 2. Using fluorescence enhancement phenomena, it offered practicable linear relationship of 1’s fluorescence intensity and Fe³⁺ concentrations: (0–8.0 × 10⁻⁵ mol/L), y = 36.232x + 45.054, R² = 0.9947, with a limit of detection (LOD) of 0.323 μM, as well as compound 2. With increasing fluorescence, F₄₀₄/F₄₂₆ of 1 and the ClO⁻ concentration (0–1.0 × 10⁻⁴ mol/L) also had a linear relationship: y = 0.0392x + 0.5545, R² = 0.9931, LOD = 0.165 μM. However, the fluorescence intensity of 2 (596 nm) was quenched by a reduced concentration of ClO⁻, resulting in a linear. In addition, compounds 1 and 2 were used to image human astrocytoma MG (U-251), brain neuroblastoma (LN-229) cells, and bamboo tissue by adding Fe³⁺ or ClO⁻, with clear intracellular fluorescence. Thus, the two compounds based on CEO could be used to dye cells and bamboo tissues by fluorescence technology.

An effective long-wavelength fluorescent sensor for Cu2+ based on dibenzylidenehydrazine-bridged biphenylacrylonitrile

Although numerous fluorescence sensors for Cu²⁺ have been presented, a long-wavelength sensor in aqueous media has rarely been reported as expected due to practical application requirements. In this work, a novel AIE molecule (DHBB) containing two biphenylacrylonitrile units bridged by dibenzylidenehydrazine was prepared. It possessed the merits of long-wavelength emission, good emission in aqueous media, and multiple functional groups for binding Cu²⁺. It exhibited good sensing selectivity for Cu²⁺ among all kinds of tested metal ions. The detection limit was as low as 1.08 × 10^-7 M. The sensing mechanism was clarified as 1:1 stoichiometric ratio based on the binding cooperation of O and N functional groups of DHBB. The selective sensing ability for Cu²⁺ remained stable at pH = 5-9 and was influenced little by other metal ions. The Cu²⁺ sensing ability of DHBB was applied in real samples with 96% recovery rate. The bio-imaging experiment of living cells suggested that DHBB possessed not only good bio-imaging performance but also sensing ability for Cu²⁺ in living environments. This work suggested the good application prospect of DHBB to sense Cu²⁺ in real samples and living environment.

An effective dual sensor for Cu2+ and Zn2+ with long-wavelength fluorescence in aqueous media based on biphenylacrylonitrile Schiff-base

Although some sensors for Cu²⁺ and Zn²⁺ had been reported, the sensor with long-wavelength emission in aqueous media for in-situ detecting Cu²⁺ and Zn²⁺ was always expected. Herein, a biphenylacrylonitrile Schiff-base (OPBS) with large aromatic conjugated system was designed and synthesized in yield of 82%. OPBS possessed excellent long-wavelength fluorescence at 550-750 nm in aqueous media, which selectively response to sense Cu²⁺ with quenched fluorescence and Zn²⁺ with chromotropic fluorescence from red to yellow. The detection of Cu²⁺ and Zn²⁺ were realized without mutual interference in their coexistence system by means of the assistance of ATP. The detection limits were 2.3 × 10^-7 M for Cu²⁺ and 1.8 × 10^-6 M for Zn²⁺, respectively. The sensing mechanism was elucidated by binding MS spectra, fluorescence Job's plot and ¹H NMR spectra. Moreover, OPBS exhibited good bioimaging performance and the in-situ sensing abilities for Cu²⁺ and Zn²⁺ in living cells, suggesting the application potential for detecting Cu²⁺ and Zn²⁺ in both vitro assay and vivo environment.