Fluorescence Emission Research Articles

Rational design of long wavelength solid-state fluorescent carbon dots based on zirconium

As a new type of zero dimensional carbon based fluorescent nanomaterial, carbon dots (CDs) have been studied and developed for many years. Various methods have been explored to prepare multicolor CDs to achieve tunable fluorescence of CDs. However, synthesizing fluorescent CDs located in the long wavelength emission region remains a challenge. Here, through a simple one-step solvothermal method using anhydrous citric acid (CA) as the raw material, ZrCl4 as both a metal element dopant and an inorganic salt matrix, and NH3·H2O as nitrogen source, Zr-doped CDs (Zr-CDs) solution with long wavelength fluorescence emission and solid powders with blue fluorescence can be obtained simultaneously. By optimizing the usage of ZrCl4, the fluorescence emission of the prepared CDs red shifted from 596 nm to 650 nm. The introduction of Zr4+ can cause a significant redshift. In addition, based on the sensitivity of CDs to oxygen, they can be used for the detection of trace amounts of H2O2. When using metal-organic framework (MOF) to encapsulate the Zr-CDs which is in the solution, optically stable CD@MOF powders can be obtained, which can be used for the construction of red light-emitting diodes (LEDs), demonstrating its potential application in the field of solid-state lighting. The synthesis technology is expected to provide favorable technical support for the future development of CDs.

Genome size data for eight endemic plant species from the Nanda Devi Biosphere Reserve (Western Himalaya).

The Himalaya harbors a large number of plant endemics but information on their genome size is largely lacking. This study aims to fulfill this gap by reporting genome sizes for 8 endemic Himalayan plant species (Impatiens devendrae Pusalkar, Impatiens scabrida DC., Impatiens sulcata Wall., Geranium robertianum L., Geranium wallichianum D.Don ex Sweet, Thalictrum cultratum Wall., Thalictrum elegans Wall. ex Royle, Thalictrum foliolosum DC.) from the Western Indian Himalayan state of Uttarakhand. The study involved collecting leaf tissues from each of the 8 plant species, chopping, staining and estimating nuclear DNA content using CyFlow Cube 8 flow cytometer with 532 nm laser light source and an orange-red fluorescence emission (>590 nm). The CyFlow Cube 13 programme was utilised to obtain the median fluorescence value from PI-stained G0/G1 (quiescent phase/first growth phase) nuclei, devoid of cellular debris. The DNA 2C value of each sample was then estimated by comparing the median fluorescence intensity values of both sample and standard (Solanum lycopersicum L.) using the standard scientific formula. The highest DNA 2C-values were observed in Geranium, which ranged from 5.29 ± 0.02 pg to 2.49 ± 0.02 pg. The genome size of Impatiens species varied from 1.49 ± 0.08 pg to 3.14 ± 0.04 pg while the three species of genus Thalictrum had nearly similar genome sizes varying between 1.53 ± 0.01 pg to 1.96 ± 0.06 pg. The coefficient of variation among nuclei varied from 3.52 % to 5.38 % with 103 to 1811 numbers of stained nuclei. The results and framework presented in the current study can serve as a template for future studies that attempt to estimate the genome sizes of endemic plant species in the Himalaya, a global biodiversity epicentre and one of the least studied biodiversity hotspots of the world.

Fluorescence spectra as an indicator of the influence of environmental conditions on fruit trees

Molecular fluorescence spectra determine possible structural changes of these molecules and provide data (by comparing them with absorption ones) on the efficiency of solar energy utilization. Fluorescence emission spectra provide information on the functionality of the photosynthetic apparatus by means of two bands red F690 and beyond red F735. The objective of the study is to highlight possible changes in the organization and operation of the photosynthetic apparatus, induced by different radiations, in the leaves, for a variety of pear (Santa Maria), based on the characteristics of the two bands of emitted fluorescence. The Santa Maria variety was studied in the period of June.

A europium-based MOF fluorescent probe for efficiently detecting Co2+ and CrO42−

Cobalt is an essential trace element in the human body that is vital for metabolism in living organisms. Insufficient or excessive intake of cobalt can lead to adverse effects. We prepared a europium-based metal–organic framework (Eu-MOF), NH4[Eu(sal)4(phen)2] (abbreviated as Eu-sal, sal = salicylic acid group, phen = 1,10-phenanthroline). Fluorescence investigations revealed that Eu-sal can efficiently and selectively identify Co2+ through a fluorescence quenching effect, with a quenching efficiency K SV and limit of detection (LOD) of 2.7 × 104 M−1 and 0.37 μM, respectively. In addition, Eu-sal also shows highly selective for CrO42− (K SV: 3.6 × 104 M−1; LOD: 0.27 μM). The quenching of Eu-sal fluorescence emission by Co2+ and CrO42− ions may be caused by spectral overlap, energy transfer, and competition. Furthermore, Eu-sal has good thermal and chemical stability. These results indicate that Eu-sal is a promising fluorescence probe for highly selective detection of Co2+ and CrO42− ions.

Source of the Fe Kalpha emission in T Tauri stars. Radiation induced by relativistic electrons during flares. An application to RY Tau

T Tauri stars (TTSs) are magnetically active stars that accrete matter from the inner border of the surrounding accretion disk; plasma becomes trapped into the large-scale magnetic structures and falls onto the star, heating the surface through the so-called accretion shocks. The X-ray spectra of the TTSs show prominent Fe Kalpha fluorescence emission at 6.4 keV (hereafter, Fe Kalpha emission) that cannot be explained in a pure accretion scenario because its excitation requires significantly more energy than the maximum available through the well-constrained free-fall velocity. Neither can it be produced by the hot coronal plasma. TTSs display all signs of magnetic activity, and magnetic reconnection events are expected to occur frequently. In these events, electrons may become accelerated to relativistic speeds, and their interaction with the environmental matter may result in Fe Kalpha emission. It is the aim of this work to evaluate the expected Fe Kalpha emission in the context of the TTS research and compare it with the actual Fe Kalpha measurements obtained during the flare detected while monitoring RY Tau with the XMM-Newton satellite. The propagation of high-energy electrons in dense gas generates a cascade of secondary particles that results in an electron shower of random nature, whose evolution and radiative throughput was simulated in this work using the Monte Carlo code PENELOPE. A set of conditions representing the environment of the TTSs where these showers may impinge was taken into account to generate a grid of models that can aid the interpretation of the data. The simulations show that the electron beams produce a hot spot at the point of impact; strong Fe Kalpha emission and X-ray continuum radiation are produced by the spot. This emission is compatible with RY Tau observations. The Fe Kalpha emission observed in TTSs could be produced by beams of relativistic electrons accelerated in magnetic reconnection events during flares.

Extraction of Dual‐Switch Fluorescent Nanosheets from Asphaltenes under Ambient Conditions

AbstractAsphaltene, often regarded as an undesirable by‐product of petroleum processing, possesses abundant reserves but limited market value. In this study, a simple and environmentally friendly solvent extraction method is conducted under ambient conditions to convert low‐value asphaltene into high‐value asphaltene‐based fluorescent carbon nanosheets (a‐FCS). This approach yields dual‐switch a‐FCS capable of emitting orange‐red fluorescence in solid‐state or water environment and exhibiting blue‐to‐yellow fluorescence in organic solvents. Moreover, the redshift observed in the fluorescence emission wavelength in the solvent is attributed to its intrinsic self‐assembly behavior, which becomes more pronounced with increasing concentration. Upon introduction to water, hydrophobic interactions induce the aggregation of a‐FCS. This aggregation triggers the orange‐red fluorescence by restricting intramolecular rotation on the surface, a phenomenon facilitated by the entanglement of aliphatic chains from asphaltene molecules. This unique property makes them applicable in anti‐counterfeiting and determination of ethanol content in aqueous solution.

Tandem four-component reaction to access fused polycycles exhibiting aggregation-enhanced through-space charge transfer emission.

Rapid construction of new fluorescence emitters is essential in advancing synthetic luminescent materials. This study illustrated a piperidine-promoted reaction of chiral dialdehyde with benzoylacetonitrile and malonitrile, leading to the formation of the 6/6/7 fused cyclic product in good yield. The proposed reaction mechanism involves a dual condensation/cyclization process, achieving the formation of up to six bonds for fused polycycles. The single crystal structure analysis revealed that the fused cyclic skeleton contains face-to-face naphthyl and cyanoalkenyl motifs, which act as the electronic donor and acceptor, respectively, potentially resulting in through-space charge transfer (TSCT) emission. While the TSCT emissions were weak in solution, a notable increase in luminescence intensity was observed upon aggregation, indicating bright fluorescent light. A series of theoretical analyses further supported the possibility of spatial electronic communication based on frontier molecular orbitals, the distance of charge transfer, and reduced density gradient analysis. This work not only provides guidance for the one-step synthesis of complex polycycles, but also offers valuable insights into the design of aggregation-enhanced TSCT emission materials.

Blue emitting fluorescent Cs2ZnCl4 perovskite nanoprobe for the sensing and visual detection of bilirubin-a jaundice biomarker

Lead halide perovskites are an advanced class of materials with high photoluminescence and optoelectronic properties. However their instability towards moisture and lead toxicity hinders their applications especially in biological sensing. Hence the need for novel lead free perovskite nanocrystals are of utmost important. Herein we synthesized a lead free, highly efficient, stable, cost effective Cs2ZnCl4 perovskite nanocrystals (PNCs) and extends its application in biosensing. The PNCs exhibits bright blue fluorescence upon UV irradiation and was able to selectively detect bilirubin (BR) - a clinically important jaundice biomarker. The intense fluorescence emission of the sensor was completely quenched upon the addition of bilirubin. The sensor could detect bilirubin even in the presence of other interfering biomolecules with a good limit of detection of 26.10 nM. The sensor could successively detect BR in human serum samples. Furthermore, for the visual detection of bilirubin, a paper strip sensor was also designed making the sensor more economical and adaptable.

Preparation and Performance of a Fiber Optic Temperature Sensor with Multiple Fluorescence Mechanisms.

The tip of a piece of plastic fiber was dyed with thymol blue to form a temperature probe. The fiber optic sensor was calibrated on a heatboard by comparison with a K-type thermal couple. Fluorescence characteristics including fluorescence intensity, emission bandwidth, peak & barycenter wavelengths, and self-referenced intensity ratio were used to carry the information of environment temperature. Accordingly, more than five temperature sensing functions were retrieved from the fluorescent sensor. Among such functions, the emission band barycenter showed premium precision. Temperature-driven shift of the emission band barycenter has a sensitivity of 0.095nm/K, with a nonlinearity of 2.2%FS, resolution of 4K and repeatability of 1.8%FS. The sensor can find its applications in wearable devices and radiofrequency ablation. Finally in a verification experiment, the sensor was used to monitor the temperature of a microwave oven chamber in real time.

An All‐Rounder for NIR‐II Phototheranostics: Well‐Tailored 1064 nm‐Excitable Molecule for Photothermal Combating of Orthotopic Breast Cancer

AbstractThe second near‐infrared (NIR‐II, 1000–1700 nm) light‐activated organic photothermal agent that synchronously enables satisfying NIR‐II fluorescence imaging is highly warranted yet rather challenging on the basis of the overwhelming nonradiative decay. Herein, such an agent, namely TPABT‐TD, was tactfully designed and constructed via employing benzo[c]thiophene moiety as bulky electron donor/π‐bridge and tailoring the peripheral molecular rotors. Benefitting from its high electron donor–acceptor strength and finely modulated intramolecular motion, TPABT‐TD simultaneously exhibits ultralong absorption in NIR‐II region, intense fluorescence emission in the NIR‐IIa (1300–1500 nm) region as nanoaggregates, and high photothermal conversion upon 1064 nm laser irradiation. Those intrinsic advantages endow TPABT‐TD nanoparticles with prominent fluorescence/photoacoustic/photothermal trimodal imaging‐guided NIR‐II photothermal therapy against orthotopic 4T1 breast tumor with negligible adverse effect.

Computational Hyperspectral Microflow Cytometry.

Miniaturized flow cytometry has significant potential for portable applications, such as cell-based diagnostics and the monitoring of therapeutic cell manufacturing, however, the performance of current techniques is often limited by the inability to resolve spectrally-overlapping fluorescence labels. Here, the study presents a computational hyperspectral microflow cytometer (CHC) that enables accurate discrimination of spectrally-overlapping fluorophores labeling single cells. CHC employs a dispersive optical element and an optimization algorithm to detect the full fluorescence emission spectrum from flowing cells, with a high spectral resolution of ≈3nm in the range from 450 to 650nm. CHC also includes a dedicated microfluidic device that ensures in-focus imaging through viscoelastic sheathless focusing, thereby enhancing the accuracy and reliability of microflow cytometry analysis. The potential of CHC for analyzing T lymphocyte subpopulations and monitoring changes in cell composition during T cell expansion is demonstrated. Overall, CHC represents a major breakthrough in microflow cytometry and can facilitate its use for immune cell monitoring.

Synchronously Sensitive Immunoassay and Efficient Inactivation of Living Zika Virus via DNAzyme Catalytic Amplification and In Situ Aggregation-Induced Emission Photosensitizer Generation.

Sensitive identification and effective inactivation of the virus are paramount for the early diagnosis and treatment of viral infections to prevent the risk of secondary transmission of viruses in the environment. Herein, we developed a novel two-step fluorescence immunoassay using antibody/streptavidin dual-labeled polystyrene nanobeads and biotin-labeled G-quadruplex/hemin DNAzymes with peroxidase-mimicking activity for sensitive quantitation and efficient inactivation of living Zika virus (ZIKV). The dual-labeled nanobeads can specifically bind ZIKV through E protein targeting and simultaneously accumulate DNAzymes, leading to the catalytic oxidation of Amplex Red indicators and generation of intensified aggregation-induced emission fluorescence signals, with a detection limit down to 66.3 PFU/mL and 100% accuracy. Furthermore, robust reactive oxygen species generated in situ by oxidized Amplex Red upon irradiation can completely kill the virus. This sensitive and efficient detection-inactivation integrated system will expand the viral diagnostic tools and reduce the risk of virus transmission in the environment.

A novel tricyanofuran-based near-infrared fluorescent probe for rapid detection and discrimination of Cys/Hcy and GSH/H2S

A novel dual-emission responsive near-infrared fluorescent probe (2-OH-TCF-NBD) for the detection and discrimination of Cys/Hcy, GSH/H2S was developed on the basis of the conjugation of a tricyanofuran-based fluorophore (2-OH-TCF) and 4-chloro-7-nitrobenzofurazan (NBD-Cl). When the probe was added to the Cys/Hcy solution, it resulted in significant fluorescence enhancement at both 527 and 630 nm, while GSH/H2S induced major fluorescence emission only at 630 nm. The detection limits for Cys, Hcy, GSH, and H2S were determined to be 0.029, 0.020, 0.29, and 0.20 μM, respectively. Furthermore, the probe demonstrated some merits including easy preparation, rapid response time, and good anti-interference ability. The possible response mechanism was also proposed and validated by HPLC analysis of the reaction process. Therefore, the probe can be a potential tool for discriminating the detection of Cys/Hcy and GSH/H2S under physiological conditions.

Promotion and Detection of Cell-Cell Interactions through a Bioorthogonal Approach.

Manipulation of cell-cell interactions via cell surface modification is crucial in tissue engineering and cell-based therapy. To be able to monitor intercellular interactions, it can also provide useful information for understanding how the cells interact and communicate. We report herein a facile bioorthogonal strategy to promote and monitor cell-cell interactions. It involves the use of a maleimide-appended tetrazine-caged boron dipyrromethene (BODIPY)-based fluorescent probe and a maleimide-substituted bicyclo[6.1.0]non-4-yne (BCN) to modify the membrane of macrophage (RAW 264.7) and cancer (HT29, HeLa, and A431) cells, respectively, via maleimide-thiol conjugation. After modification, the two kinds of cells interact strongly through inverse electron-demand Diels-Alder reaction of the surface tetrazine and BCN moieties. The coupling also disrupts the tetrazine quenching unit, restoring the fluorescence emission of the BODIPY core on the cell-cell interface, and promotes phagocytosis. Hence, this approach can promote and facilitate the detection of intercellular interactions, rendering it potentially useful for macrophage-based immunotherapy.

Introducing Internal Host Component to Thermally Activated Delayed Fluorescence Emitter for Efficient NIR Nondoped Organic Light-Emitting Diodes.

Developing thermally activated delayed fluorescence (TADF) near-infrared (NIR) organic light-emitting diodes (OLEDs) based on nondoped emitting layers is intriguing yet challenging, limited by low exciton utilization and notorious concentration quenching. Herein, a facile strategy is proposed to address this issue by incorporating an internal host component onto a traditional donor (D)-acceptor (A)-type red TADF molecule. A proof-of-concept emitter with an internal host is accordingly developed as well as a control one without an internal host. In the case of their monomer states, both emitters exhibit similar emission spectra due to their identical D-A pairs. However, under nondoped conditions, significant improvement in exciton utilization and quenching-resistant features are observed for the molecule with the internal host. The corresponding nondoped OLED yielded a maximum external quantum efficiency of 2.4%, with NIR emission peaking at 765 nm, which was a nearly 10-fold improvement relative to the efficiency based on the control molecule without an internal host. To the best of our knowledge, this result is on par with those of state-of-the art nondoped NIR TADF OLEDs in a similar emission region. These results offer a feasible pathway for the design and development of high-efficiency NIR nondoped OLEDs.

Fluorescence lifetime of plant leaves with sub-nanosecond resolution

The study aimed to develop a measurement apparatus for in vivo chlorophyll-a (Chl-a) fluorescence decay measurements of plants by means of time correlated single photon counting. In this approach, sub-nanosecond laser pulses with a repetition rate of 10 MHz are applied to excite the sample, followed by the analysis of arrival times of the emitted fluorescence photons. Photon statistics are generated by iteratively fitting the sum of two exponential functions. The tool was tested on both plastid and in vivo leaf samples of Savoy cabbage (Brassica oleracea var. sabauda) with 3–4 subsequent leaves giving a complete sample coverage starting from the outermost. The Chl-a fluorescence lifetime exhibited a gradual increase in both the isolated plastid suspensions and the in vivo leaf samples towards the innermost leaf layers explained by an increase of natural absence of light (etiolation syndrome). Furthermore, cadmium stress and iron deficiency were investigated on treated sugar beet (Beta vulgaris) samples in vivo using TCSPS measurements. The reduced fluorescence quenching resulted in an increased fluorescence lifetime. Finally, a long-term (10 week) testing of the setup was carried out on Chl-retaining resurrection Haberlea rhodopensis plants protecting themselves by an elevated non-photochemical quenching yielding a decrease of fluorescence lifetime during their desiccation.

A versatile ratiometric fluorescence nanoprobe for the determination of clonazepam in patients' plasma samples.

Despite the necessity of the study of therapeutic drug monitoring of clonazepam (CLZ), there are only a few fast detection methods available for determining CLZ in biological media. This study aims to develop a cost-effective and ratiometric probe for the quantification of CLZ in plasma samples. Fluorescent polydopamine nanoparticles were produced through a self-polymerization process at a pH of 8.5. Rhodamine B molecules were employed as a fluorescent reference material, emitting stable fluorescence in the visible range. The fabricated probe exhibited a specific detection capability for CLZ. The fluorescence emission of the probe was enhanced in two concentration ranges: from 50 ng/mL to 1.0 μg/mL and from 1.0 to 15.0 μg/mL with a lower limit of quantification of 50 ng/mL, indicating the sensitivity of the probe for detecting CLZ plasma levels. The accuracy of the probe is favorable which could be recommended for CLZ monitoring in the biological media. Furthermore, this probe is highly specific towards CLZ in the presence of various interfering agents which is mainly caused by its ratiometric nature. The developed platform showed high reliability in quantifying CLZ concentrations in patients' plasma samples. Hence, the fabricated probe could be recommended as a reliable method for the routine detection of CLZ in clinical settings.

Dynamic Electrostatic Interfacial Engineering for Block Copolymer Microparticles with Reversible Structures.

Responsive nanoparticle surfactants (NPSs) can dynamically and reversibly modulate the interfacial interactions between incompatible components, which are essential in the interfacial catalysis, corrosion, and self-assembly of block copolymers (BCPs). However, NPSs with stimuli-responsive behavior often involve tedious chemical synthesis and surface modifications. Herein, we propose a strategy to in situ construct a kind of dynamic and reversible NPSs by the interfacial electrostatic interaction between the negatively charged nanoparticles (NPs) and the positively charged homopolymers. The NPSs assembled at the oil/water interface reduce the interfacial tension and direct the confined assembly of BCP. Meanwhile, the dynamic NPSs can be disassembled by increasing the pH value or introducing competitive electrostatic attractions, which can dynamically and reversibly change the interfacial properties as well as the alignment of polymer chains, enabling BCP microparticles with reversibly switchable lamellar and cylindrical structures. Furthermore, by the introduction of aggregation-induced emission luminogens as tails to the NPSs, the reversible transformation of BCP microparticles can be visualized by fluorescence emission, which is dependent on the nanostructures of microparticles. This work establishes a concept for dynamically manipulating interfacial interactions and reversibly switching BCP microparticles without time-consuming NPS synthesis, showing promising applications in the fabrication of smart materials with switchable structures and properties.

Achieving Deep‐Blue Through‐Space Charge‐Transfer Emitter by Designing the Donor‐π‐Donor‐σ‐Acceptor Molecular Structure

AbstractIn the realm of organic light‐emitting diode (OLED), through‐space charge transfer (TSCT) thermally activated delayed fluorescence (TADF) emitters have demonstrated remarkable achievements. Nevertheless, realizing both deep‐blue emission and high efficiency by the TSCT strategy remains a persistent challenge. Here, the novel donor‐π‐donor‐σ‐acceptor (D‐π‐D‐σ‐A) type deep‐blue TSCT emitter, namely D‐tCz‐BO, is formulated to investigate its performance in OLED. D‐tCz‐BO show a narrow deep‐blue emission and efficient TADF character (λPL = 448, FWHM = 54 nm, ΦPL = 82%, and ΔEST = 0.09 eV). More importantly, the OLED based on D‐tCz‐BO as the emitter showed a maximum external quantum efficiency (EQEmax) of 20.5%, with a Commission Internationale de l'Eclairage (CIE) coordinate of (0.14, 0.12). This represents one of the best deep‐blue TSCT‐TADF emitters to date.

Two-Photon Absorption Aggregation-Induced Emission Luminogen/Paclitaxel Nanoparticles for Cancer Theranostics.

Multifaceted nanoplatforms integrating fluorescence imaging and chemotherapy have garnered acknowledgment for their potential potency in cancer diagnosis and simultaneous in situ therapy. However, some drawbacks remain for traditional organic photosensitizers, such as poor photostability, short excitation wavelength, and shallow penetration depth, which will greatly lower the chemotherapy treatment efficiency. Herein, we present lipid-encapsulated two-photon active aggregation-induced emission (AIE) luminogen and paclitaxel (PTX) nanoparticles (AIE@PTX NPs) with bright red fluorescence emission, excellent photostability, and good biocompatibility. The AIE@PTX NPs exhibit dual functionality as two-photon probes for visualizing blood vessels and tumor structures, achieving penetration depth up to 186 and 120 μm, respectively. Furthermore, the tumor growth of the HeLa-xenograft model can be effectively prohibited after the fluorescence imaging-guided and PTX-induced chemotherapy, which shows great potential in the clinical application of two-photon cell and tumor fluorescence imaging and cancer treatment.