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Sulfur doped graphene quantum dots as a potential sensitive fluorescent probe for the detection of quercetin
摘要： In this work, a novel, selective and sensitive fluorescent probe (sulfur doped graphene quantum dots, SGQDs) was designed for real-time detection of quercetin in red wine samples. SGQDs were synthesized by pyrolyzing citric acid (CA) and 3-Mercaptopropionic acid (MPA) and characterized through advanced techniques. It was observed that fluorescence intensity of SGQDs could be substantially quenched by the addition of quercetin through inner filter effect (IFE) mechanism. Additionally, a visual color change (colorless to light yellow) was also noticed after addition of quercetin into a solution of SGQDs. The change in SGQDs fluorescence intensity with varying quercetin content revealed good linearity in the 0-50.0 μM range with regression coefficient of 0.9943 and a lowest detection limit of 0.006 μg/mL. To authenticate the real-time application of SGQDs as a potential fluorescent probe, red wine samples having different quercetin concentrations were used for quantitative analysis, after the optimization of several analytical parameters.
关键词： Sulfur doped graphene quantum dots,inner filter effect,pharmaceutical assay,fluorescent probe,quenching,quercetin
更新于2025-09-23 15:19:57
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MEH-PPV photophysics: insights from the influence of a nearby 2D quencher
摘要： The effect of 2D quenching on single chain photophysics was investigated by spin coating 13 nm thick films of polystyrene lightly doped with MEH-PPV onto CVD grown graphene and observing the changes in several photoluminescent (PL) observables. With 99% of the PL quenched, we found a 60% drop in the PL lifetime, along with a significant blue-shift of the PL emission due to the preferential quenching of emission at longer wavelengths. During photo-bleaching, the blue spectral shift observed for isolated polymers was eliminated in the presence of the quencher up until 70% of the polymer was photo-bleached. Results were interpreted using a static disorder induced conjugation length distribution model. The quencher, by opening up a new non-radiative decay channel, ensures that excitons do not have sufficient time to migrate to nearby lower energy chromophores. The reduction of energy transfer into the lowest-energy chromophores thus reduces their rate of photo-bleaching. Finally, the difference between the quenched and non-quenched spectra allows the rate of energy transfer along the polymer backbone to be estimated at ～2 ns?1.
关键词： fluorescence lifetime,photo-bleaching,photophysics,conjugated polymers,fluorescence quenching,single molecules,graphene
更新于2025-09-23 15:19:57
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Inclusion complex of Tramadol in β-cyclodextrin enhances fluorescence by preventing self-quenching
摘要： Fluorescence self-quenching occurs at high concentration. Inhibition of self-quenching by inclusion of fluorescence emitters inside the hydrophobic cavity of β-cyclodextrin (β-CD) has been addressed taking the example of the fluorescence behavior of Tramadol hydrochloride. Indeed complexation by β-CD enhanced fluorescence emission of Tramadol under conditions where self-quenching was operative. A quantitative account of self-quenching and its inhibition by β-CD was done through determination of complexation equilibrium by 1H NMR experiments and a detailed study of absorption and fluorescence properties. Tramadol and β-CD associate as a complex of 1:1 stoichiometry with a formation constant K11 = 260. Complexation of Tramadol by β-CD does not cause modification of its absorbance and fluorescence spectra. Fluorescence self-quenching of Tramadol above ～ 1 mmol·L?1 was characterized by a Stern–Volmer constant K = 810 L·mol?1. Inhibition of self-quenching by formation of an inclusion complex was manifested by lower Stern–Volmer constants in the presence of β-CD. Such study required a correct account of Inner Filter Effects on fluorescence, which is mandatory in all physicochemical studies using fluorescence where concentrations are rather high.
关键词： Quenching,β-Cyclodextrin,Tramadol,Fluorescence
更新于2025-09-23 15:19:57
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Propensity for spontaneous relaxor-ferroelectric transition in quenched (Na <sub/>1/2</sub> Bi <sub/>1/2</sub> )TiO <sub/>3</sub> -BaTiO <sub/>3</sub> compositions
摘要： Recently, quenching lead-free non-ergodic relaxor Na1/2Bi1/2TiO3-BaTiO3 (NBT-BT) materials has been reported to increase the thermal depolarization temperature and enhance the lattice distortion. Driven by the conjecture that enhanced lattice distortion is typically associated with the onset of ferroelectric order, two non-ergodic relaxor NBT-BT compositions at the morphotropic phase boundary were investigated. As evident from the temperature-dependent permittivity, both compositions exhibit a stabilization of ferroelectric order upon quenching. An increase in the depolarization temperature by 40–60 °C is observed. Moreover, the composition with higher tetragonality undergoes a spontaneous relaxor-ferroelectric transition upon quenching. Annealing in oxygen atmosphere is shown to revert back the quenching-induced ferroelectric order to the relaxor state.
关键词： relaxor-ferroelectric transition,NBT-BT,quenching,lattice distortion,depolarization temperature
更新于2025-09-23 15:19:57
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On the impact of competing intra- and intermolecular triplet-state quenching on photobleaching and photoswitching kinetics of organic fluorophores
摘要： While buffer cocktails remain the most commonly used method for photostabilization and photoswitching of fluorescent markers, intramolecular triplet-state quenchers emerge as an alternative strategy to impart fluorophores with 'self-healing' or even functional properties such as photoswitching. In this contribution, we evaluated combinations of both approaches and show that inter- and intramolecular triplet-state quenching processes compete with each other. We find that although the rate of triplet-state quenching is additive, the photostability is limited by the faster pathway. Often intramolecular processes dominate the photophysical situation for combinations of covalently-linked and solution-based photostabilizers and photoswitching agents. Furthermore we show that intramolecular photostabilizers can protect fluorophores from reversible off-switching events caused by solution-additives, which was previously misinterpreted as photobleaching. Our studies also provide practical guidance for usage of photostabilizer–dye conjugates for STORM-type super-resolution microscopy permitting the exploitation of their improved photophysics for increased spatio-temporal resolution. Finally, we provide evidence that the biochemical environment, e.g., proximity of aromatic amino-acids such as tryptophan, reduces the photostabilization efficiency of commonly used buffer cocktails. Not only have our results important implications for a deeper mechanistic understanding of self-healing dyes, but they will provide a general framework to select label positions for optimal and reproducible photostability or photoswitching kinetics in different biochemical environments.
关键词： photoswitching,intramolecular quenching,self-healing dyes,super-resolution microscopy,intermolecular quenching,photostabilization,fluorophores,triplet-state quenching,STORM
更新于2025-09-19 17:15:36
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Effect of pH on the interaction of hypoxanthine and guanine with colloidal ZnS nanoparticles: A spectroscopic approach
摘要： The purpose of the current research was to study the interaction between the DNA nucleobases (hypoxanthine and guanine) and the ZnS nanoparticles (NPs). A good understanding of such interactions could be beneficial to researchers working in the field of bionanotechnology. The ZnS NPs were synthesized by a reported method and characterized by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). The interaction between the DNA nucleobases and the ZnS NPs was investigated by using UV-visible, fluorescence and infrared spectroscopy. The experiments were performed at pH 6.0 and 10.0 to investigate the role of molecular charge on the interaction process. The UV-visible absorption studies revealed that the absorption bands of the DNA nucleobases were red shifted in the presence of the semiconductor NPs. The red shift was observed to be greater at pH 6.0. The steady-state fluorescence studies showed that the nucleobases quenched the fluorescence emission of ZnS. The quenching was found to depend on the pH of the solution. It was observed that hypoxanthine was more efficient in quenching the fluorescence of the ZnS NPs compared to guanine. The infrared spectroscopic measurements indicated that both hypoxanthine and guanine bonded to the semiconductor surface through their nitrogen atoms.
关键词： Semiconductor,Fluorescence,Interaction,Quenching,Absorption
更新于2025-09-19 17:15:36
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Passive Quenching Electronics for Geiger Mode 4H-SiC Avalanche Photodiodes
摘要： We design and fabricate 4H-SiC UV avalanche photodiodes (APDs) with positive beveled mesa, which exhibit low leakage current and high avalanche gain when working in the Geiger mode. The single photon counting performance of the SiC APDs is studied by using a passive-quenching circuit. A new method to determine the exact breakdown voltage of the APD is proposed based on the initial emergence of photon count pulses. The photon count rate and dark count rate of the APD are also evaluated as a function of quenching resistance.
关键词： 4H-SiC,single photon counting,passive quenching,Geiger mode,avalanche photodiodes,breakdown voltage
更新于2025-09-19 17:15:36
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New perspective on the fluorescence and sensing mechanism of TNP chemosensor 2-(4,5-bis(4-chlorophenyl)-1H-imidazol-2-yl)-4-chlorolphenol
摘要： For TNP chemosensor 2-(4,5-Bis(4-Chlorophenyl)-1H-Imidazol-2-yl)-4-Chlorolphenol (HPICI), previous thought with no theoretical basis was that excited-state intramolecular proton transfer (ESIPT) process and the ground-state HPICI-TNP complex are mainly responsible for its fluorescence emission and the detection of TNP. However, this interpretation has been proved to be wrong by the present theoretical DFT/TDDFT explorations. Actually, the strong fluorescence of HPICI is mainly induced by the local excitation of the enol form HPICI(E) without ESIPT, and the fluorescence quenching by TNP is due to the photo-induced electron transfer (PET) process together with the cooperative effect of hydrogen-bonding interaction and π-π stacking interaction coexisting in the HPICI-TNP complex. The strengthened excited-state hydrogen bond promotes the PET process, thus facilitates the fluorescence quenching. This mechanism is proposed on the basis of the theoretical analyses on molecule geometry, binding energy, Gibbs free energy, electronic transitions, and frontier molecular orbitals (FMOs).
关键词： Fluorescence emission,Fluorescence quenching,Photo-induced electron transfer,Hydrogen-bonding interaction,Dynamical sensing mechanism,π-π stacking interaction
更新于2025-09-19 17:15:36
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One-pot synthesis of carbon dots co-doped with N and S: high quantum yield governed by molecular state and fluorescence detection of Ag <sup>+</sup>
摘要： Fluorescent carbon-based nanoparticles, called chronically as carbon dots (CDs), were synthesised from citric acid (CA) and 2-Aminothiophenol (2AT) via an N and S co-doped hydrothermal method. After a series of micro-structural characterisation, N and S elements could be sufficiently doped by means of the heteroatom in the CDs solution. The as-prepared CDs solution showed blue colour fluorescence with the highest QY of 78.6%, and study on the UV–visible and PL spectra further revealed that the outstanding fluorescence of as-prepared CDs mainly originates from the generated molecular fluorophores instead of the surface state. Owing to the strong fluorescence, the as-prepared CDs can be used as a sensing probe for the detection of Ag+ with high sensitivity and selectivity. However, the changes of fluorescence intensity exhibited the complex nature of the quenching mechanism due to the –SH and –NH2 groups on the fringes of carbonaceous cores or molecular fluorophores to aggregate into another fluorescent cores with the assistance of Ag+ ions, which promises a new approach for efficient detection of Ag+ for the application in industrial pollutants.
关键词： Ag+,N-CDs,S,quenching mechanism,molecular fluorophores,higher QYs
更新于2025-09-19 17:15:36
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Energy transfer and luminescence quenching of Cr3+-doped LiGaW2O8
摘要： Luminescence properties of the Cr3+-doped LiGaW2O8 crystals are investigated by laser excitation spectroscopy. The powder samples for various Cr3+ concentration were prepared by high-temperature solid state reaction. The temperature behaviors of the emission intensity and the decay time of the self-activated LiGaW2O8 host are discussed. The emission spectra and decay times of LiGa1-xW2O8:xCr3+ are measured under UV excitation in the temperature range 10 - 300 K. The luminescence quenching of LiGaW2O8:Cr3+ as functions of temperature and Cr3+-concentration is explained by structural and spectral characteristics.
关键词： luminescence quenching,temperature dependence.,energy transfer
更新于2025-09-19 17:15:36