Long-wavelength Excitations Research Articles

Retrieving the in vivo Scopoletin Fluorescence Excitation Band Allows the Non-invasive Investigation of the Plant-Pathogen Early Events in Tobacco Leaves.

In this study, we developed and applied a new spectroscopic fluorescence method for the in vivo detection of the early events in the interaction between tobacco (Nicotiana tabacum L.) plants and pathogenic bacteria. The leaf disks were infiltrated with a bacterial suspension in sterile physiological solution (SPS), or with SPS alone as control. The virulent Pseudomonas syringae pv. tabaci strain ATCC 11528, its non-pathogenic ΔhrpA mutant, and the avirulent P. syringae pv. tomato strain DC3000 were used. At different post-infiltration time–points, the in vivo fluorescence spectra on leaf disks were acquired by a fiber bundle-spectrofluorimeter. The excitation spectra of the leaf blue emission at 460 nm, which is mainly due to the accumulation of coumarins following a bacterial infiltration, were processed by using a two-bands Gaussian fitting that enabled us to isolate the scopoletin (SCT) contribution. The pH-dependent fluorescence of SCT and scopolin (SCL), as determined by in vitro data and their intracellular localization, as determined by confocal microscopy, suggested the use of the longer wavelength excitation band at 385 nm of 460 nm emission (F385_460) to follow the metabolic evolution of SCT during the plant–bacteria interaction. It was found to be directly correlated (R2 = 0.84) to the leaf SCT content, but not to that of SCL, determined by HPLC analysis. The technique applied to the time-course monitoring of the bacteria–plant interaction clearly showed that the amount and the timing of SCT accumulation, estimated by F385_460, was correlated with the resistance to the pathogen. As expected, this host defense response was delayed after P. syringae pv. tabaci ATCC 11528 infiltration, in comparison to P. syringae pv. tomato DC3000. Furthermore, no significant increase of F385_460 (SCT) was observed when using the non-pathogenic ΔhrpA mutant of P. syringae pv. tabaci ATCC 11528, which lacks a functional Type Three Secretion System (TTSS). Our study showed the reliability of the developed fluorimetric method for a rapid and non-invasive monitoring of bacteria-induced first events related to the metabolite-based defense response in tobacco leaves. This technique could allow a fast selection of pathogen-resistant cultivars, as well as the on-site early diagnosis of tobacco plant diseases by using suitable fluorescence sensors.

Fast outdoor screening and discrimination of carotenoids of halophilic microorganisms using miniaturized Raman spectrometers

Eight miniaturized Raman spectrometers were used to perform a fast outdoor screening and discrimination of carotenoids of a series of halophilic and non-halophilic microorganisms on a set of eight lyophilized samples, each containing high concentrations of a specific dominant carotenoid pigment. Raman spectra were acquired using different excitations (532, 785, sequentially shifted excitation of 785 and 853, and 1064 nm), based on the model of each Raman spectrometer, in order to ascertain the feasibility of individual wavelengths. The wavenumber positions of diagnostic Raman bands of carotenoids were observed for the different carotenoid species. Characteristic carotenoid Raman bands of the pigment bacterioruberin were reported (using the 532 nm excitation) at 1504–1509 cm−1, salinixanthin at 1510–1513 cm−1, spirilloxanthin at 1509–1513 cm−1, decaprenoxanthin at 1519 cm−1, β–carotene at 1526 cm−1, and sarcinaxanthin at 1526–1528 cm−1. A 532 nm excitation consistently provided best results due to the significant resonance signal enhancement (both quantitative and qualitative carotenoid detection). Good results were also obtained using the sequentially shifted excitation combining two lasers in the near infrared spectral region, and similarly good results were acquired using a standard 1064 nm excitation. The least suitable was a 785 nm excitation, with the carotenoid Raman signal almost always weaker compared to major fluorescence signal arising from other types of pigments or biomolecules in the samples. A thorough light shielding was essential in order to acquire good quality data. This study shows that miniaturized Raman spectrometers, some even equipped with longer wavelength excitation, are able to detect different carotenoid pigments under non-laboratory conditions in a fast way, and discriminate between them, to a certain degree. The implications of this type of research are especially useful in astrobiology, where the searching, detection and discrimination of biomarkers such as carotenoids is receiving significant attention.

Direct excitation of tryptophan phosphorescence. A new method for triplet states investigation

We studied room temperature phosphorescence of tryptophan (TRP) embedded in poly (vinyl alcohol) films. With UV (285 nm) excitation, the phosphorescence spectrum of tryptophan appears at about 460 nm. We also observed the TRP phosphorescence with blue light excitation at 410 nm, well outside of the S0 →S1 absorption. This excitation reaches the triplet state of tryptophan directly without the involvement of the singlet excited state. The phosphorescence lifetime of tryptophan is in the sub-millisecond range. The long-wavelength direct excitation to the triplet state results in high phosphorescence anisotropy which can be useful in macromolecule dynamics study via time-resolved phosphorescence.

Domain Textures in the Fractional Quantum Hall Effect.

Impacts of domain textures on low-lying neutral excitations in the bulk of fractional quantum Hall effect (FQHE) systems are probed by resonant inelastic light scattering. We demonstrate that large domains of quantum fluids support long-wavelength neutral collective excitations with well-defined wave vector (momentum) dispersion that could be interpreted by theories for uniform phases. Access to dispersive low-lying neutral collective modes in large domains of FQHE fluids such as long wavelength magnetorotons at filling factor v=1/3 offer significant experimental access to strong electron correlation physics in the FQHE.

Understanding photolysis of CH3ONO2 with on-the-fly nonadiabatic dynamics simulation at the ADC(2) level

The nonadiabatic dynamics of methyl nitrate (CH3ONO2) is studied with the on-the-fly trajectory surface hopping dynamics at the ADC(2) level. The results confirmed the existence of the ultrafast nonadiabatic decay to the electronic ground state. When the dynamics starts from S1 and S2, the photoproducts are CH3O+NO2, consistent with previous results obtained from the experimental studies and theoretical dynamics simulations at more accurate XMS-CASPT2 level. The photolysis products are CH3O+NO2 at the ADC(2) level when the dynamics starts from S3, while different photolysis products were obtained in previous experimental and theoretical works. These results demonstrate that the ADC(2) method may still be useful for treating the photolysis mechanism of CH3ONO2 at the long-wavelength UV excitation, while great caution should be paid due to its inaccurate performance in the description of the photolysis dynamics at the short-wavelength UV excitation. This gives valuable information to access the accuracy when other alkyl nitrates are treated at the ADC(2) level.

Photocleavage-based Photoresponsive Drug Delivery.

Targeted drug delivery has been extensively studied in the last decade, whereas both passive and active targeting strategies still face many challenges, such as off-target drug release. Light-responsive drug delivery systems have been developed with high controllability and spatio-temporal resolution to improve drug efficacy and reduce off-target drug release. Photoremovable protecting groups are light-responsive moieties that undergo irreversible photocleavage reactions upon light irradiation. They can be covalently linked to the molecule of interest to control its structure and function with light. In this review, we will summarize recent applications of photocleavage technologies in nanoparticle-based drug delivery for precise targeting and controlled drug release, with a highlight of strategies to achieve long-wavelength light excitation. A greater understanding of these mechanisms and emerging studies will help design more efficient photocleavage-based nanosystems to advance photoresponsive drug delivery.

Hot-Band-Absorption-Induced Anti-Stokes Fluorescence of Aggregation-Induced Emission Dots and the Influence on the Nonlinear Optical Effect.

Hot-band absorption (HBA)-induced anti-Stokes fluorescence (ASF) with longer-wavelength excitation is one effective pathway to deep penetration and low autofluorescence in intravital fluorescence imaging, raising demands for fluorophores with broad spectra, high absorption, and strong emission. However, typical fluorescent dyes display some emission quenching when their concentration is increased in order to obtain brighter fluorescence. In this work, the HBA-induced ASF of aggregation-induced emission (AIE) dots is reported. BPN-BBTD dots were synthesized and confirmed with a fluorescence enhancement and a considerable ASF intensity. In addition, the mechanism of ASF and the HBA process of BPN-BBTD dots were carefully validated and discussed. To obtain the full advantages of the long-wavelength excitation and the short fluorescence lifetime in deep-tissue bioimaging, a large-depth ASF confocal microscopic imaging of in vivo cerebral vasculature was conducted under the excitation of a 980 nm continuous wave laser after intravenous injection of BPN-BBTD dots. Meanwhile, the 3D structure of the cerebrovascular network was successfully reconstructed.

High-frequency magnetotransport in a viscous electron fluid under a Stern-Gerlach force

We apply a hydrodynamic theory to study transverse magnetosonic resonances in a viscous two-dimensional electron fluid under an in-plane Stern-Gerlach force (SGF), a perpendicular magnetic field with cyclotron frequency ${\ensuremath{\omega}}_{c}$, and an alternating electric field with frequency $\ensuremath{\omega}$. The SGF leads to a splitting in the dispersion curve of the transverse magnetosound wave and hinders the long-wavelength plasmonic excitation. The effective diagonal viscosity coefficient can be enhanced by about one order of magnitude due to the SGF. The variation of absorption power $Y$ with ${\ensuremath{\omega}}_{c}$ exhibits a viscoelastic (VE) resonance at ${\ensuremath{\omega}}_{c}=\ensuremath{\omega}/2$ and transverse magnetosound resonances. The SGF can raise the heights of all resonant peaks and leave the peak positions almost completely unchanged. The most substantial magnetosonic resonant peak, much weaker than the VE peak in the absence of SGF, can be tuned by the SGF to be well above the VE peak. Our results indicate that the SGF can be used to tune the VE resonance and transverse magnetosound resonances, which is relevant to the manipulation of photoresistance and photovoltaic effects in viscous electron fluids.

Anti-Kasha Behavior of 3-Hydroxyflavone and Its Derivatives.

Excited state intramolecular proton transfer (ESIPT) in 3-hydroxyflavone (3HF) has been known for its dependence on excitation wavelength. Such a behavior violates Kasha’s rule, which states that the emission and photochemistry of a compound would only take place from its lowest excited state. The photochemistry of 3HF was studied using femtosecond transient absorption spectroscopy at a shorter wavelength excitation (266 nm), and these new experimental findings were interpreted with the aid of computational studies. These new results were compared with those from previous studies that were obtained with a longer wavelength excitation and show that there exists a pathway of proton transfer that bypasses the normal first excited state from the higher excited state to the tautomer from first excited state. The experimental data correlate with the electron density difference calculations such that the proton transfer process is faster on the longer excitation wavelength than compared to the shorter excitation wavelength.

Two-photon peak molecular brightness spectra reveal long-wavelength enhancements of multiplexed imaging depth and photostability.

The broad use of two-photon microscopy has been enabled in part by Ti:Sapphire femtosecond lasers, which offer a wavelength-tunable source of pulsed excitation. Action spectra have thus been primarily reported for the tunable range of Ti:Sapphire lasers (∼700-1000 nm). However, longer wavelengths offer deeper imaging in tissue via reduced scattering and spectral dips in water absorption, and new generations of pulsed lasers offer wider tunable ranges. We present the peak molecular brightness spectra for eight Alexa Fluor dyes between 700-1300 nm as a first-order surrogate for action spectra measured with an unmodified commercial microscope, which reveal overlapping long-wavelength excitation peaks with potential for multiplexed excitation. We demonstrate simultaneous single-wavelength excitation of six spectrally overlapping fluorophores using either short (∼790 nm) or long (∼1090 nm) wavelengths, and that the newly characterized excitation peaks measured past 1000 nm offer improved photostability and enhanced fidelity of linear spectral unmixing at depth compared to shorter wavelengths.

Chlorine Modulation Fluorescent Performance of Seaweed-Derived Graphene Quantum Dots for Long-Wavelength Excitation Cell-Imaging Application.

Biological imaging is an essential means of disease diagnosis. However, semiconductor quantum dots that are used in bioimaging applications comprise toxic metal elements that are nonbiodegradable, causing serious environmental problems. Herein, we developed a novel ecofriendly solvothermal method that uses ethanol as a solvent and doping with chlorine atoms to prepare highly fluorescent graphene quantum dots (GQDs) from seaweed. The GQDs doped with chlorine atoms exhibit high-intensity white fluorescence. Thus, their preliminary application in bioimaging has been confirmed. In addition, clear cell imaging could be performed at an excitation wavelength of 633 nm.

Perylene-Cy3 FRET System to Analyze Photoactive DNA Structures.

We report a new Förster resonance energy transfer (FRET) system for structural analyses of DNA duplexes using perylene and Cy3 as donor and acceptor, respectively, linked at the termini of a DNA duplex via D-threoninol. Experimentally obtained FRET efficiencies were in good agreement with theoretical values calculated based on canonical B-form DNA. Due to the relatively long Förster radius, this system can be used to analyze large DNA structures, and duplexes containing photo-reactive molecules can be analyzed since perylene can be excited with visible light. The system was used to analyze a DNA duplex containing stilbene, demonstrating that in the region of the stilbene cluster the duplex adopts a ladder-like structure rather than helical one. Upon photodimerization between stilbene residues, FRET efficiencies indicated the reaction does not disturb DNA duplex. This FRET system will be useful for analysis of photoreactions of nucleobases as well as a wide range of nucleic acid structures.

Upconversion-based dual-mode optical nanosensor for highly sensitive and colorimetric evaluation of heparin in serum

Heparin is an important anticoagulant in clinics, which requires regular detection and dose adjustment. Fluorimetry is a powerful tool considering the advantages of fast response and high sensitivity while most fluorescent sensors suffer from spontaneous fluorescence for excitation under short-wavelength light, the occurrence of false positives, complex and time-consuming preparation, as well as expensive detection instruments. Herein, we developed upconversion nanoparticles (UCNPs) based nanosensor for fluorescent and colorimetric detection of heparin. The nanosensor exhibited sensitive detection for heparin with the low limit of detection (LOD) of 0.1 nM in fluorescent mode and 0.3 nM in colorimetric mode. In addition, we used a smartphone-sensing platform for quantitative detection of heparin with the LOD of 2 nM. Depending on long-wavelength excitation and fluorescent-colorimetric dual-response detection signal, the designed nanosensor could eliminate the auto-fluorescence, which effectively increased the accuracy of the sensor, thus extending the applications for bed-side heparin assay and related medical safety.

Red emissive two-photon carbon dots: Photodynamic therapy in combination with real-time dynamic monitoring for the nucleolus

Treatment in combination with real-time monitoring of dynamic organelle changes is of great significance for evaluating therapeutic efficacy. However, it remains highly challenging to realize such specific treatment and monitoring in organelles. Herein, we developed one kind of red emissive two-photon carbon dots (TP-CDs) via an N doping strategy for nucleolus-targeted treatment combined with real-time monitoring of dynamic changes in the nucleolus. In the TP-CD system, N doping endows TP-CDs with intrinsic two-photon excitation, red emission at 605 nm, and singlet oxygen (1O2) production under 638 nm laser irradiation. More importantly, N heterocycles induced by doping offers significant affinity for TP-CDs toward RNA to realize specific self-targeting toward nucleolus and fluorescence variation during the photodynamic therapy (PDT) via the cleaving of RNA chain by 1O2 to dissociate TP-CDs@RNA complex. By combining 1O2 production, fluorescent variation during the PDT process, long-wavelength excitation and emission characteristics, as well as specific self-targetability of nucleolus, TP-CDs can be considered as a kind of “smart” CDs to realize treatment in combination of real-time dynamic changes in nucleolus for the first time.

Designing a sustainable fluorescent targeting probe for superselective nucleus imaging

Specific targeting of cell organelles is indispensable for bioimaging and diagnostics but remains a challenge due to the limitation of highly selective fluorescent targeting probes. Herein, we successfully designed a molecular fusion route to controllably synthesize bright orange fluorescent graphene quantum dots (GQDs). The relative nitrogen doping level of the GQDs reached 18.88 at%. The GQDs exhibited long-wavelength excitation fluorescence and photoluminescence (PL) stability. Femtosecond transient absorption spectroscopy elucidated that the sp2 cluster and the surface state's synergistic effect contributed to the PL. Furthermore, the most alluring discovery was that the GQDs had good biocompatibility and an unprecedented targeting capability for superselective nucleus imaging without staining cell organelles. Molecular dynamics simulations revealed that once the GQDs were transported across the plasma membrane, the higher the N-doping ratio of the GQDs was, and the easier the GQDs penetrated the membrane. The reason may stem from the compatibility of –NH2 with lipid molecules, which is higher than that of –OH. Enriched nitrogen doping in GQDs is beneficial for crossing the cell membrane to the target nucleus. Our findings could provide scientific theory and a technical basis to design nucleus-targeting probes in the future.

Optical signatures of shear collective modes in strongly interacting Fermi liquids

The concept of Fermi liquid lays a solid cornerstone to the understanding of electronic correlations in quantum matter. This ordered many-body state rigorously organizes electrons at zero temperature in progressively higher momentum states, up to the Fermi surface. As such, it displays rigidity against perturbations. Such rigidity generates Fermi-surface resonances which manifest as longitudinal and transverse collective modes. Although these Fermi-liquid collective modes have been analyzed and observed in electrically neutral liquid helium, they remain unexplored in charged solid-state systems up to date. In this paper I analyze the transverse shear response of charged three-dimensional Fermi liquids as a function of temperature, excitation frequency and momentum, for interactions expressed in terms of the first symmetric Landau parameter. I consider the effect of momentum-conserving quasiparticle collisions and momentum-relaxing scattering in relaxation-time approximation on the coupling between photons and Fermi-surface collective modes, thus deriving the Fermi-liquid optical conductivity and dielectric function. In the high-frequency, long-wavelength excitation regime the electrodynamic response entails two coherent and frequency-degenerate polaritons, and its spatial nonlocality is encoded by a frequency- and interaction-dependent generalized shear modulus; in the opposite high-momentum low-frequency regime anomalous skin effect takes place. I identify observable signatures of propagating shear collective modes in optical spectroscopy experiments, with applications to the surface impedance and the optical transmission of thin films.

Detection of Urinary Albumin Using a "Turn-on" Fluorescent Probe with Aggregation-Induced Emission Characteristics.

Human serum albumin (HSA) is a broadly used biomarker for the diagnosis of various diseases such as chronic kidney disease. Here, a fluorescent probe TC426 with aggregation-induced emission (AIE) characteristics is reported as a sensitive and specific probe for HSA. This probe is non-emissive in aqueous solution, meanwhile it shows bright fluorescence upon interacting with HSA, which makes it applicable in detecting HSA with a high signal to noise ratio. Besides, the fluorescence of TC426 exhibits a high linear correlation with the concentration of albumin in the range of microalbumin (20-200 mg/L), which has a significant importance for the early diagnosis of glomerulus related diseases. Compared with previously reported HSA probes TPE-4TA and BSPOTPE, TC426 shows comparable anti-interference ability towards creatinine and other major components in urine but is excited by a longer excitation wavelength at the visible light range. Finally, with the established assay, TC426 shows excellent performance in detecting HSA in real human urine, indicating its great potential in practical urinalysis.

Excitation-Dependent Triplet-Singlet Intensity from Organic Host-Guest Materials: Tunable Color, White-Light Emission, and Room-Temperature Phosphorescence.

A series of organic host-guest materials with multifunctional luminescence were constructed. Four isoquinoline derivatives were used as the guests, and benzophenone was used as the host. The doped system exhibited excellent dual emission with cyan fluorescence and orange-yellow room-temperature phosphorescence, and the dual emission could be combined into almost pure white-light emission. Importantly, the relative intensity of the fluorescence-phosphorescence could be adjusted by changing the excitation wavelength, with the phosphorescence intensity being significantly higher than the fluorescence intensity under shorter excitation wavelengths and vice versa under longer excitation wavelengths. Therefore, three-color emission switching among cyan, white, and orange could be achieved by simply adjusting the excitation wavelength. The results of experimental and theoretical calculations indicated that the excitation-dependent emission colors were caused by different transfer paths for excitons under different excitation wavelengths. These materials with multifunctional luminescence could be used as writable inks for advanced anticounterfeiting.

Polarizing the medium: Fermion-mediated interactions between bosons

We consider a homogeneous mixture of bosons and polarized fermions. We find that long-range and attractive fermion-mediated interactions between bosons have dramatic effects on the properties of the bosons. We construct the phase diagram spanned by boson-fermion mass ratio and boson-fermion scattering parameter. It consists of a stable region of mixing and unstable region toward phase separation. In the stable mixing phase, the collective long-wavelength excitations can either be well behaved with infinite lifetime or be finite in lifetime suffered from the Landau damping. We examine the effects of the induced interaction on the properties of weakly interacting bosons. It turns out that the induced interaction not only enhances the repulsion between the bosons against collapse but also enhances the stability of the superfluid state by suppressing quantum depletion.

Emergence of spin-active channels at a quantum Hall interface

We study the ground state of a system with an interface between $\ensuremath{\nu}=4$ and $\ensuremath{\nu}=3$ in the quantum Hall regime. Far from the interface, for a range of interaction strengths, the $\ensuremath{\nu}=3$ region is fully polarized but $\ensuremath{\nu}=4$ region is unpolarized. Upon varying the strength of the interactions and the width of the interface, the system chooses one of two distinct edge/interface phases. In phase $A$, stabilized for wide interfaces, spin is a good quantum number, and there are no gapless long-wavelength spin fluctuations. In phase $B$, stabilized for narrow interfaces, spin symmetry is spontaneously broken at the Hartree-Fock level. Going beyond Hartree-Fock, we argue that phase $B$ is distinguished by the emergence of gapless long-wavelength spin excitations bound to the interface, which can be detected by a measurement of the relaxation time ${T}_{2}$ in nuclear magnetic resonance.