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Spatial Heterogeneity of Cadmium Effects on Salvia sclarea Leaves Revealed by Chlorophyll Fluorescence Imaging Analysis and Laser Ablation Inductively Coupled Plasma Mass Spectrometry
摘要： In this study, for a first time (according to our knowledge), we couple the methodologies of chlorophyll fluorescence imaging analysis (CF-IA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), in order to investigate the effects of cadmium (Cd) accumulation on photosystem II (PSII) photochemistry. We used as plant material Salvia sclarea that grew hydroponically with or without (control) 100 μM Cd for five days. The spatial heterogeneity of a decreased effective quantum yield of electron transport (ΦPSII) that was observed after exposure to Cd was linked to the spatial pattern of high Cd accumulation. However, the high increase of non-photochemical quenching (NPQ), at the leaf part with the high Cd accumulation, resulted in the decrease of the quantum yield of non-regulated energy loss (ΦNO) even more than that of control leaves. Thus, S. sclarea leaves exposed to 100 μM Cd exhibited lower reactive oxygen species (ROS) production as singlet oxygen (1O2). In addition, the increased photoprotective heat dissipation (NPQ) in the whole leaf under Cd exposure was sufficient enough to retain the same fraction of open reaction centers (qp) with control leaves. Our results demonstrated that CF-IA and LA-ICP-MS could be successfully combined to monitor heavy metal effects and plant tolerance mechanisms.
关键词： effective quantum yield (ΦPSII),non-photochemical quenching (NPQ),photoprotective mechanism,photochemical quenching (qp),photosynthetic heterogeneity,phytoremediation,reactive oxygen species (ROS),bioimaging,singlet oxygen (1O2),clary sage
更新于2025-09-11 14:15:04
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Study of alloyed quantum dots-porphyrazine interaction in solution
摘要： The core-shell quantum dots, namely, CdSxSe1-x/ZnS (QD), and free-base porphyrazine (1) undergoes spontaneous interaction in solution. Steady state fluorescence measurements reveal significant quenching of the photoluminescence of QD in presence of 1. The average value of lifetime of QD (16.10 ns) suffers negligible change in presence of 1 (15.55 ns). The value of bimolecular quenching constant, i.e., kq for QD-1 system (kq = 1.380 × 1011 litre·mol-1·sec-1) determined from time-resolved fluorescence experiment rules out the possibility of diffusion driven process in present work. The mechanism of binding interaction between QD and 1 is established following the evaluation of binding constant value, i.e., K = 12,720 litre·mol-1 for QD-1 system. The results emanating from present work would be very much helpful for employing QD-porphyrazine type system as possible binding unit in energy and/ electron transfer process.
关键词： binding interaction,CdSxSe1-x/ZnS (QD),static quenching,free-base porphyrazine,PL quenching
更新于2025-09-11 14:15:04
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Sensitivity Analysis of Laser Quenching Parameters of ASTM 1045 of Disk Laser Based on Response Surface Method
摘要： Laser hardening is an important branch of laser surface hardening technology, which is widely used in metallurgy, transportation, machinery manufacturing, aerospace and other fields. At present, relying entirely on experience or process trial-and-error method, it can not effectively reveal the transient mechanism of laser quenching of disk laser, which is not conducive to shortening the research and development cycle and saving costs. The numerical simulation provides an effective way to obtain the dynamic evolution law of multi-field coupling in laser quenching process. In this paper, a thermo-mechanical coupling model of ASTM 1045 laser quenching process by disk laser is established. In the model, the temperature-dependent physical parameters were calculated by CALPHAD method. The transient law of temperature and microstructural transformation during quenching was obtained by solving the model. The formation and transformation degree of martensite were characterized by the dynamic changes of the depth and width of quenched transformation layer. The quenching structure and transformation hardening law were observed by Axioskop 2 SEM and Zeiss-IGMA HD FE-SEM to verify the accuracy of the simulation results. On this basis, the process parameters of laser quenching were sampled by Monte-Carlo method based on response surface methodology. The sensitivity effects of different process parameters on the temperature field and phase change field of laser quenching were analyzed, which laid a theoretical foundation for the optimization of process parameters.
关键词： Laser quenching,Quenching,Disk laser,Microstructures,Sensitivity analysis
更新于2025-09-11 14:15:04
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Fluorometric determination of aflatoxin B1 using a labeled aptamer and gold nanoparticles modified with a complementary sequence acting as a quencher
摘要： A fluorometric aptamer based assay is described for rapid and sensitive detection of aflatoxin B1 (AFB1). It is making use of a fluorescein (FAM) labeled anti-AFB1 aptamer and complementary DNA-modified gold nanoparticles (GNPs). In the absence of AFB1, the FAM-labeled aptamers hybridize with complementary DNA strands that were covalently immobilized on GNPs. This results in quenching of the green fluorescence (with excitation/emission peaks at 485/525 nm). In the presence of AFB1, the aptamer probe binds AFB1 and is released from the GNPs. Hence, fluorescence is restored. Under optimized conditions, AFB1 in the concentration range from 61 pM to 4.0 μM can be detected, and the detection limit is 61 pM. This assay is highly selective for AFB1. It was applied to the determination of AFB1 spiked into 50-fold diluted wine and 20-fold diluted beer.
关键词： Mycotoxin,Food safety,Environmental analysis,Fluorescence quenching,Fluorophore,Fluorescent probe,Nanomaterials,Nanoprobe
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Evaluation of Plamsonic Enhancement and Quenching of Ag Nanoparticles in Organic Light-Emitting Diode
摘要： The utilization of localized surface plasmon (LSPR) to improve the yield of organic light emitting diode (OLED), has been subject of numerous publications and reports. Several enhancement mechanisms have been highlighted such as the increase of F?rster energy transfer, the enhancement of the OLED electroluminescence as well as the increase of the current I and the decrease of the turn-on voltage V [1,2]. Nevertheless, these mechanisms are still not completely studied and understood. One major problem of using metallic NPs is the inherent losses associated with their conductivity. Another important issue concerns the evaluation of their electrical and optical effects on the total yield enhancement. Besides, the LSPR wavelength and the distance of the metallic NPs from the OLED emitting layer (EML) are very important parameters for a maximum enhancement of the near-field-induced energy transfer between excitons and NPs LSPR. In fact, LSPR modifies the radiative and the non-radiative decay rates of adjacent emitters resulting in two competitive processes: the fluorophores radiation intensity enhancement and the non-radiative quenching of activated fluorophores on the NP metal surface. To obtain an overall enhancement, the resonance energy of the fluorophore and the LSPR should be carefully adjusted with an appropriate distance between the metal NPs and the emitter. In this work, we report a thorough investigation of Ag NPs randomly dispersed into a standard guest-host OLED (Alq3:DCM) by thermal evaporation during the OLED fabrication process. Mainly, we follow-up the interaction between the Ag-thin layer and the excitons by varying the position of Ag-NPs within the OLED stack (fig. 1). At each position of Ag-NPs, we compare the plasmonic-OLED performances to those of the reference one without NPs (zero line) and we bring a general analysis of the electroluminescence efficiency variation as a function of the position of Ag-NPs related to the excitons distribution within the OLED emitting layer. The experimental results allow us to draw the balance between the amplification and quenching due to the Ag-NPs. By considering the spatial distribution of the emission sites in the EML, we particularly, highlighted two competing effects: the LSPR amplification for large distances between the Ag-NPs and the emissive sites, and the quenching effect by metallic NPs for short distances between the Ag-NPs and the emissive sites. Nevertheless, other phenomena such as the influence of Ag-NPs on the charge carriers injection and transport as well as extraction effect should be also taken into account in order to thoroughly understand the effect of plasmonic nanoparticles on the OLED structure performance. Our study enable us to suggest a figure of merit giving the total yield as following (cid:75) (cid:97) σ. (cid:69)a. (cid:69)q. (cid:75)ex, where (cid:86) accounts for the electrical effects, (cid:69)a and (cid:69)b are LSPR amplification and plasmonic quenching, respectively and (cid:75)ex is related to the extraction effect. The weight of the previous parameters depends on the distance NPs-EML with three zones of interest: anode side, cathode side and nearby the EML. Two different physical phenomena are also to be considered on the side of the cathode and the anode (blue and green lines in fig.1), as well as the correlation between near and far field. These results are of a great interest in order to develop new generation of highly efficient OLED-based devices.
关键词： Ag nanoparticles,plasmonic enhancement,localized surface plasmon (LSPR),quenching,organic light emitting diode (OLED)
更新于2025-09-11 14:15:04
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Structural and luminescence properties of Dy3+-doped alkali fluoroborophosphate glasses for white LEDs applications
摘要： A new series of Dy3+-doped alkali fluoroborophosphate glasses were prepared by conventional melt quenching technique, and their structural and optical properties were investigated through XRD, FTIR, optical absorption, luminescence and decay measurements. The X-ray diffraction pattern reveals the amorphous nature of the prepared glasses. The fundamental stretching vibrations of various borate (BO3 and BO4) and phosphate (PO4) networks were identified through the FTIR analysis. The nature of the metal–ligand bonding and the electronic band structure has been investigated using the absorption spectra. The Judd–Ofelt (JO) intensity parameters (X2, X4 and X6) were evaluated, and the experimental oscillator strength values were also calculated. Using the JO intensity parameters, radiative properties like radiative transition probability (A), stimulated emission cross section (rE) and branching ratios (bR) for the emission transitions of the Dy3+ ions have been calculated. The luminescence spectra exhibit two visible bands of 4F9/2 → 6H15/2 (Blue) and 4F9/2 → 6H13/2 (Yellow). The decay time of the 4F9/2 level has been measured from the decay profiles and compared with the calculated lifetimes. The yellow-to-blue (Y/B) ratios and color coordinates have been calculated from the luminescence spectra and can be considered for white light emitting diodes applications.
关键词： Absorption,CIE diagram,Melt quenching technique,Rare-earth,Photoluminescence
更新于2025-09-11 14:15:04
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Interfacial Energy Transfer in Hollow Double-Shelled TiO <sub/>2</sub> : <i>x</i> %Eu <sup>3+</sup> @SiO <sub/>2</sub> : <i>y</i> %Tb <sup>3+</sup> Nanospheres for Tissue Imaging
摘要： In this paper, hollow double-shelled TiO2:x%Eu3+@SiO2:y%Tb3+ nanospheres (C1-Ti-x/Si-y) were fabricated using carbon spheres as hard template followed by a two-step sol-gel coating process. The results demonstrate that there is strong interaction between inner TiO2 layer and outer SiO2 layer, which can be characterized by the high surface content of Ti-O-Si bonds. The strong interaction makes it possible to achieve efficient energy transfer from Tb3+ to Eu3+ ions through crossing the double-shelled interface. The interfacial energy transfer (IET) efficiency from Tb3+ to Eu3+ions is strongly influenced by the doping concentration of Eu3+ ions whose maximum is determined to be 30.2%. Furthermore, the surface of inner TiO2 layer is modified by the outer SiO2 layer through this strong interaction, which significantly enhances the emission intensity and suppresses the concentration quenching of Eu3+ ions. Under 377 nm excitation, C1-Ti-x/Si-y simultaneously exhibits red and green emissions derived from Eu3+ and Tb3+ ions, respectively. Moreover, by varying doping concentration of Tb3+ and Eu3+ ions, the luminescence color of the samples can be tuned from green to orange and red. The characterization results show that our proposed phosphors may provide potential applications in tissue imaging.
关键词： Multicolor phosphors,Hollow double-shelled nanostructure,Interfacial energy transfer,Concentration quenching suppressed,Surface modification
更新于2025-09-11 14:15:04
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Novel Dicyano-Phenylenevinylene Fluorophores for Low-Doped Layers: A Highly Emissive Material for Red OLEDs
摘要： Two efficient deep red (DR)-emitting organic dicyano-phenylenevinylene derivatives with terminal withdrawing or donor groups were synthesized. The spectroscopic properties of the neat solids and the low-doped layers in polystyrene or polyvinylcarbazole host matrixes were analyzed, and the luminescence performance was explained using density functional theory (DFT) analysis. A noteworthy 89% fluorescence quantum yield was observed for the brightest red-emissive polyvinylcarbazole (PVK) blend. This result pushed us to successfully produce an emissive red organic light-emitting device (OLED) as a preliminary feasibility test.
关键词： dicyano-phenylenevinylene,fluorophore,aggregation-caused quenching (ACQ),OLED,DR
更新于2025-09-11 14:15:04
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A fluorescence quenching based gene assay for Escherichia coli O157:H7 using graphene quantum dots and gold nanoparticles
摘要： A fluorometric assay is described for highly sensitive quantification of Escherichia coli O157:H7. Reporter oligos were immobilized on graphene quantum dots (GQDs), and quencher oligos were immobilized on gold nanoparticles (AuNPs). Target DNA was co-hybridized with reporter oligos on the GQDs and quencher oligos on AuNPs. This triggers quenching of fluorescence (with excitation/emission peaks at 400 nm/530 nm). On introducing target into the system, fluorescence is quenched by up to 95% by 100 nM concentrations of target oligos having 20 bp. The response to the fliC gene of E. coli O157:H7 increases with the logarithm of the concentration in the range from 0.1 nM to 150 nM. The limit of detection is 1.1 ± 0.6 nM for n = 3. The selectivity and specificity of the assay was confirmed by evaluating the various oligos sequences and PCR product (fliC gene) amplified from genomic DNA of the food samples spiked with E. coli O157:H7.
关键词： Food pathogens,Static quenching,fliC gene,Selectivity,Fluorophore,Quencher,Real samples
更新于2025-09-11 14:15:04
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Compact quantum dot surface modification to enable emergent behaviors in quantum dot-DNA composites
摘要： Quantum dot (QD) biological imaging and sensing applications often require surface modification with single-stranded deoxyribonucleic acid (ssDNA) oligonucleotides. Furthermore, ssDNA conjugation can be leveraged for precision QD templating via higher-order DNA nanostructures to exploit emergent behaviors in photonic applications. Use of ssDNA-QDs across these platforms requires compact, controlled conjugation that engenders QD stability over a wide pH range and in solutions of high ionic strength. However, current ssDNA-QD conjugation approaches suffer from limitations, such as the requirement for thick coatings, low control over ssDNA labeling density, requirement of large amounts of ssDNA, or low colloidal or photostability, restraining implementation in many applications. Here, we combine thin, multidentate, phytochelatin-3 (PC3) QD passivation techniques with strain-promoted copper-free alkyne-azide click chemistry to yield functional ssDNA-QDs with high stability. This process was broadly applicable across QD sizes (i.e., λem = 540, 560, 600 nm), ssDNA lengths (i.e., 10–16 base pairs, bps), and sequences (poly thymine, mixed bps). The resulting compact ssDNA-QDs displayed a fluorescence quenching efficiency of up to 89% by hybridization with complementary ssDNA-AuNPs. Furthermore, ssDNA-QDs were successfully incorporated with higher-order DNA origami nanostructure templates. Thus, this approach, combining PC3 passivation with click chemistry, generates ssDNA-PC3-QDs that enable emergent QD properties in DNA-based devices and applications.
关键词： ssDNA,click chemistry,DNA origami,quantum dots,fluorescence quenching
更新于2025-09-11 14:15:04