Search Results (1,718)

The precise determination of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels is critical for understanding the photophysical and photochemical properties of carbon dots (C-dots), which directly govern their performance in optoelectronic, catalytic, and sensing applications. However, the lack of distinct redox peaks in cyclic voltammetry (CV) curves of C-dots poses a major challenge to conventional energy level calculation methods. Herein, we propose a novel strategy to calculate the HOMO–LUMO energy levels of C-dots by combining electron transfer (ET) kinetics with Marcus theory. A series of quinones (electron acceptors, EAs) and ferrocene derivatives (electron donors, EDs) were employed to quench the fluorescence of C-dots, and the ET rate constants (K) were derived from fluorescence lifetime measurements. The CV curves of EAs and EDs provided their respective oxidation and reduction potentials, which were used as reference energy levels. The UV–Vis absorption spectra confirmed that the fluorescence quenching mechanism was dominated by ET rather than energy transfer. Based on Marcus theory, the free energy change (ΔG) of ET reactions was correlated with K, and the HOMO and LUMO energy levels of C-dots were calculated to be −1.84 V (vs. SCE) and +1.60 V (vs. SCE), respectively. This study not only provides a reliable method for determining the energy levels of C-dots without distinct redox peaks but also deepens the understanding of ET mechanisms between C-dots and small molecules. The proposed strategy is expected to be extended to other fluorescent nanomaterials with similar CV limitations. Full article

The damage caused by herbivores is generally measured as the amount of leaf tissue consumed, without accounting for the fate of the leftover tissue. As a result, the plant defense mechanisms that promote resistance to herbivore feeding by photosynthetically acclimating the rest of the plant to the feeding spot leaf area have not been well exploited. Plant-insect interactions are now becoming better defined with the development of visualization methods that permit spatial whole-leaf assessment of photosynthetic efficiency after herbivore attack. The purpose of our study was to evaluate the spatial heterogeneity of photosystem II (PSII) function at the whole-leaf level before and after herbivory by the Colorado potato beetles. Twenty minutes after Colorado potato beetle (Leptinotarsa decemlineata) feeding, the maximum efficiency of PSII photochemistry (Fv/Fm) decreased significantly, suggesting photoinhibition due to reduced efficiency of the oxygen-evolving complex (OEC). The decreased quantum yield of PSII photochemistry (Φ_PSII) after feeding, at the neighboring area of the feeding spot and at the rest of the leaf area, was attributed to the reduced efficiency of the open PSII reaction centers (Fv′/Fm′), since there was no change in the fraction of open PSII reaction centers (qp). Nevertheless, plant defense elicitation was activated by the photoprotective mechanism of non-photochemical quenching (NPQ) that reduced the singlet oxygen (¹O₂) formation in potato plants in the neighboring area of the feeding spot and at the rest of the leaf area. In addition, the increased production of hydrogen peroxide (H₂O₂) triggered by this increase suggests that it acted as a signaling molecule in the biotic stress defense response. Full article

Tyrosinase promotes excessive deposition of melanin, which may lead to severe skin diseases. Passiflora edulis f. edulis seeds have been reported to be rich in diverse bioactive constituents exhibiting potential tyrosinase inhibitory activity. However, the principal bioactive constituents responsible for tyrosinase inhibitory activity and its underlying mechanisms remain largely unclear. Therefore, this study aimed to: (1) optimize SC-CO₂ extraction of Passiflora edulis f. edulis seed oil (PFSO) for maximum yield and bioactive preservation; (2) comprehensively characterize its physicochemical and phytochemical profile; (3) elucidate the tyrosinase inhibition mechanism through kinetic, spectroscopic, and computational approaches; and (4) validate its safety, antioxidant, and anti-pigmentation efficacy in a zebrafish model. PFSO exhibited a yield of 24.96%, with a high content of unsaturated fatty acids (88.03%, mainly linoleic acid at 74.40%). The oil inhibited tyrosinase via a reversible mixed-type mechanism (IC₅₀ = 1.12 mg/mL). Fluorescence spectroscopy and molecular docking revealed that linoleic acid binds to LYS180 and β-sitosterol binds to TYR78, mainly driven by hydrogen bonding and hydrophobic interaction, which changed the microenvironment of tryptophan residues and indicated static quenching. Further validation experiments revealed that the major constituent, linoleic acid, exhibited only weak inhibitory activity against tyrosinase (IC₅₀ = 29.44 mg/mL), whereas the key component β-sitosterol markedly suppressed tyrosinase activity (IC₅₀ = 46.43 μg/mL). In vitro assays demonstrated PFSO’s significant efficacy in reducing the melanin content and tyrosinase activity in α-MSH-stimulated B16F10 murine melanoma cells. In vivo experiments in zebrafish that received dietary supplementation with PFSO confirmed that PFSO (≤5 mg/mL) reduced ROS production, suppressed melanin deposition, inhibited tyrosinase activity, and downregulated the expression of melanogenesis-related genes (TYR, TYRP1, TYRP2, MITF). This study provides, for the first time, a comprehensive elucidation of PFSO’s potential as a natural tyrosinase inhibitor, integrating extraction optimization, multicomponent characterization, multimodal inhibition analysis, and in vivo validation. Full article

The objective of this study was to design and evaluate π-extended 1,8-naphthalimide derivatives as photoinduced electron transfer (PET) optical sensors for protons and metal cations, with emphasis on the role of heterocyclic annulation and receptor–chromophore electronic matching. Benzofuran- and benzodioxin-annulated naphthalimides bearing either a dimethylaminoethyl receptor or a non-donating alkyl substituent at the imide nitrogen were synthesized using tailored synthetic strategies. Their photophysical properties were investigated by absorption and fluorescence spectroscopy, while sensing performance was evaluated by fluorescence titrations. Quantum chemistry calculations were employed to rationalize experimental observations. Benzofuran-annulated derivatives exhibit structured π–π* absorption bands and strong fluorescence, whereas introduction of the receptor induces efficient fluorescence quenching via reductive PET. Protonation or metal ion coordination suppresses PET and leads to pronounced fluorescence enhancement, particularly in the presence of Cu(II) and Sn(II). In contrast, benzodioxin-annulated derivatives display intramolecular charge-transfer absorption bands, large Stokes shifts, and low fluorescence quantum yields in polar media, resulting in a negligible sensing response. Computational results attribute this behavior to an unfavorable energy arrangement of the donor–acceptor orbitals. Overall, the study demonstrates that heterocyclic annulation critically governs the electronic structure and sensing performance of naphthalimide fluorophores, providing guidelines for the rational design of PET-based optical sensors. Full article

This paper proposes an innovative contact sponge–fluorescent tracer technique for the rapid, non-destructive detection of 1–100 μm microcracks in cementitious materials. The technique combines a porous sponge carrier with a moisture-sensitive fluorescent tracer: after the sponge adsorbs the aqueous dye solution, capillary action drives fluorescent molecules into microcracks upon contact with the wall, ensuring stable luminescence during a 30-day continuous observation period. This technique was applied to cement paste specimens with three different water-to-cement ratios, dried at 105 °C for varying durations to induce drying–shrinkage microcracks. Results demonstrate that the technique clearly characterizes microcrack networks with high resolution and excellent stability. Under the same drying duration, the average microcrack width decreases with an increasing water-to-cement ratio, while the total crack length and fractal dimension increase. Regression analysis reveals that the average crack width is the primary factor controlling capillary water absorption. This method enables the early detection of microcracks in critical infrastructure such as tunnels and bridges, facilitating timely maintenance and reducing deterioration risk. Full article

Biofouling remains a critical challenge in membrane bioreactors (MBR), which is primarily caused by the production of extracellular polymeric substances (EPS) as an initial step in biofilm formation. This still limits their widespread application in wastewater treatment. In the past decades, much research has been carried out to understand and consequently reduce biofouling in MBR. More recent studies have focused primarily on inhibiting the release of EPS by applying quorum quenching (QQ) to control biofouling in MBR. This study presents the first investigation of the QQ potential of Rubellimicrobium mesophilum and its effects on biofilm inhibition by EPS reduction, which is demonstrated for MBR operated with submerged flat sheet (PTFE, PS) and hollow fibre polyvinylidene fluoride (PVDF) membranes operated in parallel for 114 days. The QQ effect has a significant impact on the reduction in biofilm thickness on PTFE membranes by 45% and on PS membranes by about 47%, respectively. Additionally, the performance of PVDF was improved by 287.5%. Similarly, the total protein concentration on the PTFE membranes was reduced by 57%, while on the PS membranes, the reduction was 78%. In mixed liquor, protein reduction was 55%, indicating its effectiveness in controlling biofouling over extended operation. The biofilm formation was monitored by measuring the biofilm thickness via fluorescence microscopy and by analyzing the protein and sugar content of the developing biofilm and of the mixed liquor. All parameters indicated decreasing biofilm formation with increasing amounts of entrapped QQ bacteria, while the removal efficiency of organic compounds and ammonia remained similar between all MBRs. Full article

Background: Guanine-rich DNA regions can fold into G-quadruplex (G4) structures, which are prevalent in telomeres and oncogene promoters, making them attractive targets for anticancer therapeutics. Small molecules capable of selectively stabilizing G4 DNA can disrupt telomerase activity and oncogene expression, offering a promising strategy for cancer intervention. Methods: A rationally designed series of DPPZ–anhydride-conjugated ligands (1 and 2) and their corresponding quaternized derivatives (1-q and 2-q) were synthesized to investigate the combined effects of π-extension, bromine substitution, and cationic modification on DNA recognition. The synthetic strategy relied on the incorporation of a highly planar DPPZ–anhydride scaffold to enhance π-surface area, followed by selective quaternization to introduce permanent positive charge and reinforce electrostatic interactions with the DNA backbone. All compounds were fully characterized by NMR and spectroscopic methods. The DNA-binding properties of the ligands were systematically evaluated toward duplex (ds-DNA) and G-quadruplex (G4-DNA) structures using UV–Vis absorption titration, fluorescence intercalator displacement (FID) assays, and competitive dialysis experiments. Quaternization markedly enhanced intrinsic binding constants and significantly reduced DC₅₀ values, particularly for G4-DNA. While bromine substitution increased overall binding affinity, it did not substantially improve topology selectivity. Among the series, compound 1-q exhibited the most favorable balance between affinity and G4 selectivity. Results: The interaction of the compounds with BSA was quantified using Stern–Volmer quenching constants, which demonstrated a clear trend of enhanced quenching efficiency upon modification. The binding strength followed a descending order of 1-q > 2-q > 1 > 2, highlighting the superior performance of the first series over the second. These findings indicate that the structural features of 1-q facilitate a more robust interaction within the hydrophobic pockets of the protein. Conclusions: Overall, the results demonstrate that strategic π-conjugation combined with electrostatic reinforcement provides an effective approach for the development of topology-selective DNA-binding ligands. Full article

Hydrogen peroxide (H₂O₂) plays a very vital role in industrial and biological processes, but its high concentration may cause health hazards. Therefore, accurate detection of H₂O₂ is crucial for chemical and biological sensing applications. In this work, a ratiometric fluorescent probe was developed using a core–shell structural silica nanoparticle for the detection of H₂O₂. Firstly, a silica core structure with red fluorescence emission was constructed by encapsulating a Schiff base compound (SD). Afterwards, a mesoporous silica shell was fabricated, and the AIE featured fluorophore with a H₂O₂ response character was covalently linked on the surface of the mesoporous shell layer. As recognition sites on the shell, blue-emitting TB molecules specifically identified H₂O₂ through their phenylboronic acid ester group. The blue fluorescence of core–shell structural nanoprobes would be quenched in the presence of H₂O₂, while red fluorescence remained unchanged, ensuring the high sensitivity and specificity of the ratio sensing. This design has demonstrated significant potential for the reliable monitoring of hydrogen peroxide in biological and environmental applications. Full article

Curcumin, a natural polyphenol derived from Curcuma longa, is widely recognized for its therapeutic properties. However, its clinical utility is limited because of poor solubility, rapid degradation and hence low bioavailability. To overcome these issues, nanoformulation approaches, especially PEGylated liposomes, have been explored as advanced delivery systems. PEGylation, which involves attaching polyethylene glycol (PEG) to the liposomal surface, enhances circulation time by creating a steric shield that reduces protein interactions and clearance by the mononuclear phagocyte system (MPS). However, PEG can alter lipid membrane properties, which may in turn affect curcumin’s solubility and distribution within the liposomal bilayer, ultimately reducing its loading efficiency. To ensure that PEG-modified liposomes can be effectively loaded with curcumin, we investigated curcumin–membrane interactions in saturated (DMPC) and unsaturated (POPC) liposomes, both in the presence and absence of PEG. Based on dissociation constants (K_d) obtained from fluorescence spectroscopy measurements, we found that PEGylated DMPC liposomes exhibit the strongest binding affinity for curcumin. Fluorescence quenching experiments showed that curcumin adopts a transbilayer orientation in all membranes examined. Curcumin’s location within PEGylated and non-PEGylated liposomal membranes was further confirmed by examining its effects on membrane properties, including fluidity, polarity, and oxygen transport. These effects were investigated using electron paramagnetic resonance (EPR) spectroscopy with spin labels. The results indicate that PEG does not impose major changes on membrane properties. Curcumin, however, was found to reinforce the liposomal membranes, increase their polarity, and reduce oxygen availability. Overall, the findings suggest that liposomes, particularly those composed of PEGylated DMPC, are effective vehicles for curcumin delivery. Full article

Natural anthraquinones possess a wide range of biological activities, including antibacterial, antiviral, antitumor, and antioxidant effects. However, studies on their ability to inhibit amyloid protein aggregation remain relatively limited. In this study, we used insulin as a model protein to investigate the anti-amyloidogenic potential of several natural anthraquinones. Specifically, the inhibitory mechanisms of five anthraquinones (emodin, anthraflavin, aloe-emodin, alizarin, and purpurin) on insulin amyloid fibrillation were explored in both dilute and crowded environments (PEG 2000 and PEG 4000). Multidisciplinary analytical results demonstrated that all five anthraquinones could effectively inhibit insulin amyloid fibrillation in both dilute and crowded environments. Simultaneously, crowded agents themselves also exhibited inhibitory effects on insulin amyloid aggregation. However, the inhibitory efficacy of anthraquinones was weaker in crowded environments than in dilute solutions, indicating that although crowded agents themselves suppressed insulin aggregation, they may interfere with the regulatory roles of anthraquinones on insulin aggregation behavior. Interestingly, purpurin showed stronger inhibitory activity in crowded environments compared to dilute solutions. Furthermore, fluorescence spectral analysis suggested that the quenching mechanism of insulin by all these anthraquinones was identified as static quenching mode. Molecular simulation studies revealed that anthraquinones could bind to the aggregation-prone regions of insulin via hydrogen bonding and hydrophobic interactions, thereby inhibiting insulin amyloid aggregation. Notably, the inhibitory capacity of these compounds was correlated with their structural features and the binding affinities to insulin. Collectively, this study explored the anti-amyloid activity of anthraquinones, which held significant research value for the development of potential therapeutic agents for amyloid-associated proteinopathies. Full article

In order to achieve rapid and qualitative detection of soluble heavy metal ions, nitrogen-doped fluorescent carbon quantum dots (N-CQDs) were synthesized using chitin extracted from shrimp and crab shells as the carbon source. The structural, morphological, and optical properties of the synthesized N-CQDs were systematically characterized using transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FTIR), Raman, X-ray photoelectron spectroscopies (XPS), ultraviolet-visible (UV-Vis) absorption spectroscopy and fluorescence spectroscopy. The resulting N-CQDs exhibited a carbonization yield of 54.46% and a fluorescence quantum yield of 34.33%. Their morphology, structure and optical properties were thoroughly characterized using a range of analytical techniques. The synthesized N-CQDs exhibited excellent fluorescence properties, and remarkable stability. When applied for metal ion detection, the N-CQDs displayed a distinct and selective fluorescence quenching response exclusively toward Fe³⁺ ions. The detection limit for Fe³⁺ at room temperature was 4.04 μmol/L. Furthermore, due to the inherent nitrogen present in the acetyl amino groups of chitin, nitrogen doping was achieved without the need for external dopants during the hydrothermal synthesis process. Owing to their high stability, low cost and low toxicity, the N-CQDs synthesized in this study provide a promising fluorescence sensing platform with excellent selectivity for Fe³⁺ detection, achieved through precise control of surface functional groups. Full article

Fluorescent metal nanoclusters show great promise in heavy metal ion sensing. Herein, a bimetallic nanocluster (GSH-Au/Ag NCs) with orange fluorescence was synthesized through a facile one-pot method. The synthesized GSH-Au/Ag NCs displayed optimal excitation and emission peaks at 275 and 610 nm, respectively. The incorporation of silver can enhance the fluorescence of metal nanoclusters. The fluorescence of as-synthesized GSH-Au/Ag NCs can be significantly quenched by Hg²⁺ and Cu²⁺, and a “on–off” fluorescent probe was designed. The detection conditions, including pH and the concentration of the probe, were optimized. The respective detection limits for Hg²⁺ and Cu²⁺ ions under optimal detection conditions are estimated to be 40 nM and 33 nM, over the linear range of 100–1200 nM. Furthermore, a ratiometric fluorescent probe was prepared by mixing quinine sulfate and as-synthesized GSH-Au/Ag NCs. Hg²⁺ and Cu²⁺ can effectively quench the red fluorescence of GSH-Au/Ag NCs, whereas the blue fluorescence of quinine sulfate remains invariant. This leads to measurable changes in the RGB values of the resulting fluorescence images. The ratio (R/B) exhibits a linear relationship with the concentration of Hg²⁺ and Cu²⁺, enabling the determination of its concentration by analyzing RGB values in fluorescence images. This visual detection method significantly reduces both assay time and cost, making it suitable for on-site detection of heavy metal ions in water samples. Full article

The fluorescence properties of organic molecules are largely determined by molecular architecture, π-conjugation, and electronic substituent effects. In this study, three novel pyrene-chromone Schiff base derivatives were designed and synthesized to investigate substituent-driven modulation of photophysical behavior. The compounds were obtained via condensation of 1-aminopyrene with three different chromone-based aldehydes and fully characterized by FT-IR, ¹H-NMR, and mass spectrometry. The molecular design involves a donor-π-acceptor architecture: pyrene donates electrons, while the chromene moiety accepts them, enabling charge transfer upon excitation. UV-Vis and fluorescence spectroscopy revealed intense absorption in the 430–440 nm range and tunable emission in the 540–565 nm region, corresponding to large Stokes shifts (107–125 nm). Substituent effects significantly influenced optical band gaps and emission intensities, with the nitro-substituted derivative exhibiting a reduced band gap and pronounced fluorescence quenching due to enhanced intramolecular charge transfer. Concentration-dependent absorption studies demonstrated linear Beer–Lambert behavior, indicating the absence of aggregation within the investigated range. These results establish clear structure–property relationships in pyrene-chromene Schiff bases and highlight their potential as promising candidates for optoelectronic and fluorescence-based sensing applications. Full article

Detection of metal ions under complex and heterogeneous conditions is crucial for food safety, environmental monitoring, and cellular studies. Fluorescent proteins (FPs) are attractive biosensors due to their ease of expression, strong emission without external cofactors, and fluorescence quenching upon metal binding. tKeima features a large Stokes shift, pH sensitivity, and spectral stability, reducing background interference and enabling metal detection in complex samples. Here, we examined tKeima quenching toward biologically relevant metal ions (Fe²⁺, Fe³⁺, and Cu²⁺). Metal titration fitted to the Langmuir isotherm yielded dissociation constants (K_d) of 2710.7 ± 178.6 μM (Fe²⁺), 3112.0 ± 176.7 μM (Fe³⁺), and 881.9 ± 76.2 μM (Cu²⁺), with maximum quenching capacities (B_max) of 133.8 ± 2.4%, 128.3 ± 2.5%, and 109.2 ± 1.2%, respectively. Limits of detection were 396.0 μM (Fe²⁺), 428.6 μM (Fe³⁺), and 457.7 μM (Cu²⁺), and linear quenching responses were observed up to ~1000, 1500, and 1000 μM, respectively. Sphere-of-action combined with Stern–Volmer analysis indicated primarily dynamic quenching for Fe²⁺ and Cu²⁺, whereas Fe³⁺ showed a stronger static component. tKeima showed partial fluorescence restoration with ethylenediaminetetraacetic acid and moderate selectivity against interfering ions. These findings clarify tKeima’s metal-quenching mechanism and support its use as a platform for metal-responsive biosensors. Full article

Sentinel lymph node mapping is increasingly used in canine and feline oncology and often involves the combined use of visible dyes and fluorescent tracers. However, the effect of methylene blue on the fluorescence of indocyanine green during near-infrared imaging remains unclear. This explorative study aimed to quantitatively and qualitatively assess potential fluorescence quenching in solutions of methylene blue–indocyanine green at different ratios in three near-infrared imaging modalities (overlay, color map, contrast). Four solutions were prepared: 100%/0%, 75%/25%, 50%/50%, and 25%/75% indocyanine green/methylene blue. The fluorescence intensity of the four solutions was quantitatively measured in vitro using near-infrared imaging. Subsequently, four lymphographies, one for each solution, were performed from the metatarsal region of feline cadavers. Observers with varying levels of experience evaluated lymphographic images. Methylene blue caused a concentration-dependent reduction in fluorescence both at the quantitative evaluation and qualitative lymphography interpretation. Despite this reduction, fluorescence remained sufficient in cadavers for accurate identification of lymph nodes, and observer experience did not significantly affect interpretation, except for the color map mode. Because methylene blue-dominant solutions showed a greater quenching effect on indocyanine green fluorescence, clinicians should favor indocyanine green-dominant mixtures. This approach may preserve fluorescence performance, maintaining the surgical guidance benefits of methylene blue. Future confirmatory studies should include a substantially larger number of specimens to allow appropriate statistical comparisons and to better account for inter-individual variability. Full article