Short-wavelength Emission Research Articles

Construction of Long‐Wavelength Emissive Organic Nanosonosensitizer Targeting Mitochondria for Precise and Efficient In Vivo Sonotherapy

AbstractAs a modern biomedical therapeutic modality, sonodynamic therapy (SDT) presents unique advantages, including superior tissue penetration capability, temporal–spatial controllability, and negligible side effects. However, the bottlenecks of most organic sonosensitizers are their short emission wavelengths, strong phototoxicity, and unsatisfactory SDT effect, which undermines the precise fluorescence imaging‐guided SDT in vivo. Here, a long‐wavelength emissive and mitochondria‐targeted organic nanosonosensitizer, named CCNU980 nanoparticles (NPs), is rationally designed, which possesses deep‐tissue optical penetration (up to 6 mm), depth‐activated ROS production (up to 8 cm), high photostability, and low phototoxicity. In vitro studies verify CCNU980 NPs selectively enriches in cancer cells with the ability to target the mitochondria and induce mitochondria‐mediated apoptosis using abundant 1O2 under US irradiation. Notably, CCNU980 NPs enables precise in vivo NIR‐II fluorescence imaging‐guided SDT, accompanied by the suppression of the bilateral 4T1 tumor growth with minimal side effects. The current work can inspire a general strategy for the design of organic nanosonosensitizers with long‐wavelength emission and new thoughts for precision medicine.

Exciton Dynamics in Colloidal CdS Quantum Dots with Intense and Stokes Shifted Photoluminescence in a Single Decay Channel.

CdS quantum dots (QDs), synthesized by a sol-gel method, exhibit significantly Stokes shifted bright photoluminescence (PL), predominantly from the trap states. Surprisingly, the PL decay at the emission maximum is single-exponential. This is an unusual observation for as-prepared QDs and indicates a narrow distribution in the nature of trap states. A closer look reveals an additional fast component for the decays at shorter emission wavelengths, presumably due to the band edge emission, which remains elusive in the steady-state spectra. Indeed, a significantly narrower and blue-shifted emission band is observed in the decay-associated spectra. The contribution of this component to the steady-state PL intensity is shown to be overwhelmed by that of the significantly stronger trap emission. Exciton dynamics in the quantum dots is elucidated using transient absorption spectra, in which the stimulated emission is observed even at low pump power.

Microdisk-Type Multicolor Semipolar Nitride-Based Light-Emitting Diodes

Recently, III-nitride semiconductors have gained immense attention for application in high-performance optoelectronic devices. However, in the device fabrication process, it is essential to develop a wet-etching process for conventional polar nitride-based devices to reduce the dry-etching damage. In this study, semipolar microdisk (MD)-type light-emitting diodes (LEDs) are fabricated using only a wet-etching process. The wet-etching rate of the n-type GaN film is the highest, followed by those of the undoped and p-type GaN films. The n- and p-type GaN films exhibit upward and downward surface-band-bending heights, respectively, because of which they can easily attract and repel OH– to form Ga2O3. In addition, the fully wet-etched MD-LED shows high light extraction efficiency from the etched nanofacets because of the increase in the escape cone angle with low etching damage. The smaller diameters of the MD-LEDs result in shorter emission wavelengths, allowing multicolor emission ranging from the violet (∼420 nm) to amber (∼620 nm) wavelengths to be achieved on a single LED wafer. Thus, monolithic multicolor emissions and increased light output power are achieved by fabricating parallel-connected MD-LED arrays using only a wet-etching process.

A lysosome-targeted near-infrared fluorescent probe for cell imaging of Cu2+

Cu2+ in lysosomes are closely related to some diseases such as Menke's syndrome, Wilson's diseases and Alzheimer's diseases. Although many fluorescent probes have been constructed for the detection of Cu2+ in lysosomes, the poor water solubility and short wavelength emission (λem < 600 nm) limit the application of these probes. To solve this problem, a fluorescent probe DHUCu-1 with near-infrared emission was designed and synthesized in this work. DHUCu-1 could detect Cu2+ in PBS solution (1% alcohol as co-solvent) with high sensitivity and good selectivity. Moreover, DHUCu-1 could target lysosomes and respond to Cu2+ in lysosomes. This probe thus can be used as a tool for the exploration of physiological functions of Cu2+ and the related diseases.

Solvent free synthesis and spectral analysis of 2,4-dimethyl-6-(1-phenyl-1H-benzimidazol-2-yl)phenol: on/off fluorescence, inter and intramolecular hydrogen bonding

2,4-dimethyl-6-(1-phenyl-1H-benzimidazol-2-yl)phenol (DPBP) has been prepared and characterized by 1H NMR, 13C NMR, mass spectral studies and elemental analysis. DPBP shows On/off fluorescence system (fluorescence enhancing and quenching) by tuning with Fe3+ metal ion and H3PO4. Addition of Fe3+ ions into DPBP results in quenching of fluorescence. Other cations, including Zn2+, Ni2+, Pb2+, Ca2+, Co2+, Cd2+ and Mg2+ had little effect in the fluorescence intensity. The addition of H3PO4 with Fe3+-DPBP complex results in the enhanced fluorescence due to the detachment of Fe3+-DPBP complex. Dual emission has been observed by DPBP in non-polar solvent medium whereas single emission was observed in polar solvents due to Intra and Intermolecular hydrogen bonding respectively. Shorter wavelength emission of DPBP is due to enol rotamer and longer wavelength emission of DPBP is due to keto rotamer.

Synthesis and intriguing single-component white-light emission from oxadiazole or thiadiazole integrated with coumarin luminescent core

There has been evidence of non-typical fluorescence activities in thiadiazole and oxadiazole derivatives. Also, some coumarin compounds with tunable luminescence properties via controlling the molecular structure and its aggregation have been recently reported. As a result, our effort concentrated on integrating these moieties in order to improve the applicability of the target compounds through easy synthetic schemes. All the synthesized derivatives underwent extensive spectrum analysis, including NMR, FT-IR, and mass spectroscopy. DFT calculations, UV–visible, and luminescence spectroscopy were used to study the photophysical characteristics of three compounds having coumarin luminescent core integrated with the thiadiazole, oxadiazole, or hydrazinecarbothioamide. We found that manipulating the packing of a compound under specific conditions (e.g., the solid state or moderate solution concentration of compounds containing the heterocyclic substituent “thiadiazole or oxadiazole”) can trigger processes related to the way the molecules interact, resulting in the appearance of dual or multiple fluorescence bands that cover the full visible range. Additionally, we deduced that the intriguing white emission from a single component might be generated by modifying the degree of molecular aggregation to balance the relative band intensities at short and long wavelengths. Long-wavelength emission arises from aggregated molecules whereas short-wavelength emission results from single molecules. It is evident that this balance is feasible in both the solid form of the thiadiazole derivative and 1 × 10–5 mol L–1 solution of the oxadiazole derivative. Hence, this research proposes an easy method for creating the intriguing white-light emission from a single component.

A new insights into multicolor emissive carbon dots using Trachelospermum jasminoides leaves for the application of WLEDs

Carbon dots (CDs) have recently emerged as a very encouraging family of materials with augmented performance in WLEDs. Facile synthesis of CDs with high optical tuning using sustainable green precursors is a great challenge in the applications of WLEDs. In this work, we prepare red, green, and blue-color emissive CDs (RGB CDs) using an extract of Star Jasmine leaves (Trachelospermum jasminoides). The red emission originates due to the presence of an extensive conjugated carbonic system with a few esters (-COOR) and amide (-CONR) moieties on their surface. And the shorter wavelength emission appears due to the presence of carboxylic (-COO) moieties. Specifically, in green emissive CDs, the formation of the OZnO bond causes the fluorescence shifting (>100 nm) and a higher lifetime as it restricts the making of the conjugated -COOR/-CONR groups. The detailed study revealed that an average lifetime of CDs has a linear relationship with the core state lifetime. These highly stable and effective naturally produced RGB CDs have been used as fabrication of WLEDs, which exhibited CCT and CIE coordinates of 4283 K and (0.36,0.32), respectively. Additionally, the red CDs detected water and chloroform visually and fluorometrically in a broad range. This work will open up a new route for developing high-performance WLEDs using natural precursors.

A novel precipitating-fluorochrome-based fluorescent probe for monitoring carbon monoxide during drug-induced liver injury

Carbon monoxide (CO), as one of significant gas transmitter, is closely associated with a variety of physiological and pathological processes. Although plenty of fluorescent probes have been prepared for detecting CO, most of them suffer from water-soluble fluorophores and short emission wavelength, which tends to diffuse and is limited to apply in vivo. Herein, a novel water-soluble fluorescent probe (HPQ-MQ-CO) is prepared to detect CO by releasing a precipitating fluorochrome (HPQ-MQ-OH), which is developed by introducing the 1-ethyl-2-methylquinoline group into HPQ to obtain long emission wavelength and good diffusion resistant ability. Allyl formate, as the identification unit of CO, has good water solubility and quenches the fluorescence of HPQ-MQ-CO. When the probe reacts with CO and Pd2+, an long-emission and solid-state fluorescence signal at 650 nm can be observed, which is based on excited-state intramolecular proton transfer (ESIPT) mechanism. When the concentration of CO is raised to 100.0 μM, the fluorescence is increased 29 times, indicating the sensitivity of the probe. Moreover, this probe shows prominent selectivity for CO compared with other interfering species. Given these advantages, HPQ-MQ-CO can be used for CO detection in HepG2 cells and zebrafish by in-situ and long-term fluorescence imaging. In addition, this probe can monitor the up-regulation of CO in HepG2 cells and zebrafish during drug-induced liver injury (DILI).

Multiphoton microscopy of mesoporous silicon

In this work, the behavior of the luminescence of mesoporous silicon under irradiation with a femtosecond IR laser is shown by the method of multiphoton microscopy. It was demonstrated that, along with the background photoluminescence of porous silicon, bright photoluminescence centers appear on the layer surface, and under certain conditions. Centers with a different, shorter-wavelength emission spectrum also appear.

Bioconjugates of photon-upconversion nanoparticles for cancer biomarker detection and imaging.

The detection of cancer biomarkers in histological samples and blood is of paramount importance for clinical diagnosis. Current methods are limited in terms of sensitivity, hindering early detection of disease. We have overcome the shortcomings of currently available staining and fluorescence labeling methods by taking an integrative approach to establish photon-upconversion nanoparticles (UCNP) as a powerful platform for cancer detection. These nanoparticles are readily synthesized in different sizes to yield efficient and tunable short-wavelength light emission under near-infrared excitation, which eliminates optical background interference of the specimen. Here we present a protocol for the synthesis of UCNPs by high-temperature co-precipitation or seed-mediated growth by thermal decomposition, surface modification by silica or poly(ethylene glycol) that renders the particles resistant to nonspecific binding, and the conjugation of streptavidin or antibodies for biological detection. To detect blood-based biomarkers, we present an upconversion-linked immunosorbent assay for the analog and digital detection of the cancer marker prostate-specific antigen. When applied to immunocytochemistry analysis, UCNPs enable the detection of the breast cancer marker human epidermal growth factor receptor 2 with a signal-to-background ratio 50-fold higher than conventional fluorescent labels. UCNP synthesis takes 4.5 d, the preparation of the antibody-silica-UCNP conjugate takes 3 d, the streptavidin-poly(ethylene glycol)-UCNP conjugate takes 2-3 weeks, upconversion-linked immunosorbent assay takes 2-4 d and immunocytochemistry takes 8-10 h. The procedures can be performed after standard laboratory training in nanomaterials research.

First-principles identification of VI + Cui defect cluster in cuprous iodide: origin of red light photoluminescence

The γ-phase cuprous iodide (CuI) emerges as a promising transparent p-type semiconductor for next-generation display technology because of its wide direct band gap, intrinsic p-type conductivity, and high carrier mobility. Two main peaks are observed in its photoluminescence (PL). One is short wavelength (410–430 nm) emission, which is well attributed to the electronic transitions at Cu vacancy, whereas the other long wavelength emission (680–720 nm) has not been fully understood. In this paper, through first-principles simulations, we investigate the formation energies and emission line shapes for various defects, and discover that the intrinsic point defect cluster is the source of the long wavelength emission. Our finding is further supported by the prediction that the defect concentration decreases dramatically as the chemical condition changes from Cu-rich to I-rich, explaining the significant reduction in the red light emission if CuI is annealed in abundant I environment.

Evaluating Street Lighting Quality in Residential Areas by Combining Remote Sensing Tools and a Survey on Pedestrians’ Perceptions of Safety and Visual Comfort

The perceived quality of street lighting influences pedestrians’ perceptions of safety and visual comfort, as well as outdoors activities at night. This study explores the association between street lighting attributes, such as illuminance and wavelength, and pedestrians’ feeling of safety (FoS) and perceived lighting quality (PLQ) in eight residential districts in Dalian, China. To achieve this goal, we combine remote sensing technology with ground investigation. The ground research includes physical measurements of lighting attributes, such as intensity, color temperature, and glare, as well as survey evaluations of pedestrians’ perceptions of safety and visual comfort. We also analyze the influence of several environmental factors, such as traffic volumes and vegetation, while accounting for personal characteristics of the observers, such as gender and age. Findings from the remote sensing reveal that Dalian’s residential districts differ substantially by their nighttime light emissions, with high concentration of strong red band (i.e., long wavelength) emissions occurring in Zhongshan and Jinzhou, and strong blue band (i.e., short wavelength) emissions found in central Zhongshan. Results from the ground surveys further indicate that a satisfactory level of FoS reaches at the illumination levels of 5–17 lx, and that people feel safer if nighttime light is warm and uniform. From a multiple regression analysis, it is also found that illuminance and uniformity are the main factors affecting PLQ under conditions of low or high illuminance, while glare and color temperature play a more significant role under high illuminance. In addition, a satisfactory level of PLQ is found at illuminance levels of 25–35 lx and light color temperature of 4000 K–5500 K.

High-Power Mid-Infrared (λ∼3-6 μm) Quantum Cascade Lasers

The performances of mid-infrared (IR) quantum cascade lasers (QCLs) are now reaching a maturity level that enables a variety of applications which require compact laser sources capable of watt-range output powers with high beam quality. We review the fundamental design issues and current performance limitations, focusing on InGaAs/AlInAs/InP QCLs with emission in the 3-6 μm wavelength range. Metamorphic materials broaden the available compositions for accessing short emission wavelengths (λ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ \leq $</tex-math></inline-formula> 3.5 μm) or for integration with GaAs- and Si-photonics platforms. Conduction-band engineering through the use of varying compositions throughout the active-region structure has been utilized to achieve the highest performance levels to date. Interface roughness scattering plays a dominant role in determining both the lower-laser-level lifetime as well as the carrier-leakage current. Numerous approaches have been implemented in attempts to control, scale, and stabilize the spatial mode to high output powers. Of all approaches photonic-crystal structures with high built-in index contrast, thus capable of maintaining modal properties under strong self-heating, are the most promising device configuration for achieving single-spatial-mode, single-lobe reliable CW operation to multiwatt-range power levels. Such devices have demonstrated to date >5W front-facet output powers with diffraction-limited beams in short-pulse operation.

A high absorption efficiency blue-emitting phosphor NaSrScSi2O7:Eu2+ for near-UV-pumped white light-emitting diodes

The Eu2+ ion is extensively used as an activator due to its wide excitation band and high efficiency emission spectrum. However, most Eu2+-activated blue-emitting phosphors have low absorption efficiency in the near-ultraviolet (n-UV) region or lack the short-wavelength blue light emission (<450 nm), resulting in UV light leakage or poor color rendering. Herein, we have successfully prepared a brand-new blue phosphor NaSrScSi2O7: Eu2+ by solid-state reaction method. The Rietveld refinement of the powder diffraction data, luminescent properties, decay lifetime, quantum efficiencyand thermal quenching have been investigated in detail. Under 345 nm excitation, the NaSrScSi2O7: 0.03Eu2+phosphor manifests an asymmetric emission spectrum centered at 427 nm, and notably, shows a high absorption efficiency of 84.35%. Finally, we encapsulated two white light-emitting diodes (WLEDs) devices using as-prepared blue-emitting phosphor and three commercial phosphors. At 80 mA drive current, both packaged devices demonstrate warm white light. Meanwhile, the WLED-2 with NaSrScSi2O7: 0.03Eu2+ blue-emitting phosphor has a lower correlated color temperature of 3726 K, its spectrum complements more short-wavelength spectrum, and the special color rendering index R6 and R7 increased from 95.2, 94.5 to 98.3, 96.5, respectively, compared with WLED-1 without present phosphor. These results demonstrate that NaSrScSi2O7: Eu2+ blue-emitting phosphor is a prospective novel luminescent material for WLEDs.

Scintillation and optical properties of xenon-doped liquid argon

Liquid argon (LAr) is a common choice as detection medium in particle physics and rare-event searches. Challenges of LAr scintillation light detection include its short emission wavelength, long scintillation time and short attenuation length. The addition of small amounts of xenon to LAr is known to improve the scintillation and optical properties. We present a characterization campaign on xenon-doped liquid argon (XeDLAr) with target xenon concentrations ranging from 0 to 300 ppm by mass encompassing the measurement of the photoelectron yield Y, effective triplet lifetime τ 3 and effective attenuation length λ att. The measurements were conducted in the Subterranean Cryogenic ARgon Facility, Scarf, a 1 t (XeD)LAr test stand in the shallow underground laboratory (UGL) of TU-Munich. These three scintillation and optical parameters were observed simultaneously with a single setup, the Legend Liquid Argon Monitoring Apparatus, Llama. The actual xenon concentrations in the liquid and gaseous phases were determined with the Impurity DEtector For Investigation of Xenon, Idefix, a mass spectrometer setup, and successful doping was confirmed. At the highest dopant concentration we find a doubling of Y, a tenfold reduction of τ 3 to ∼90 ns and a tenfold increase of λ att to over 6 m.

New dyes improve bioimaging in mice

Fluorescent dyes with emission wavelengths in the near-infrared region (NIR) can enable tissue imaging from deeper within the sample than dyes with shorter emission wavelengths. But dyes with emission wavelengths in the so-called NIR-II region, 1,000–1,700 nm, are often not as bright as researchers would like. Wen Shi and coworkers at the Chinese Academy of Sciences now report a family of xanthene-based dyes that fluoresce strongly in the NIR-II ( J. Am. Chem. Soc. 2021, DOI: 10.1021/jacs.1c07711 ). These dyes, which the researchers call VIXs, have a xanthene core that is modified with para-substituted styryls. VIXs with nitrogen-bearing styryls fluoresce at longer wavelengths than VIXs with oxygen-bearing styryls. VIX-4, which fluoresces at wavelengths longer than 1,200 nm, is modified with julolidinestyryl. To demonstrate the dyes’ performance, the researchers used VIX-4 encapsulated in liposomes to image blood circulation in mice. They injected VIX-4 into the tail vein of mice and were

Super-Resolution Imaging With Lanthanide Luminescent Nanocrystals: Progress and Prospect.

Stimulated emission depletion (STED) nanoscopy has overcome a serious diffraction barrier on the optical resolution and facilitated new discoveries on detailed nanostructures in cell biology. Traditional fluorescence probes employed in the super-resolution imaging approach include organic dyes and fluorescent proteins. However, some limitations of these probes, such as photobleaching, short emission wavelengths, and high saturation intensity, still hamper the promotion of optical resolution and bio-applications. Recently, lanthanide luminescent probes with unique optical properties of non-photobleaching and sharp emissions have been applied in super-resolution imaging. In this mini-review, we will introduce several different mechanisms for lanthanide ions to achieve super-resolution imaging based on an STED-like setup. Then, several lanthanide ions used in super-resolution imaging will be described in detail and discussed. Last but not least, we will emphasize the future challenges and outlooks in hope of advancing the next-generation lanthanide fluorescent probes for super-resolution optical imaging.

Perfecting and extending the near-infrared imaging window

In vivo fluorescence imaging in the second near-infrared window (NIR-II) has been considered as a promising technique for visualizing mammals. However, the definition of the NIR-II region and the mechanism accounting for the excellent performance still need to be perfected. Herein, we simulate the photon propagation in the NIR region (to 2340 nm), confirm the positive contribution of moderate light absorption by water in intravital imaging and perfect the NIR-II window as 900–1880 nm, where 1400–1500 and 1700–1880 nm are defined as NIR-IIx and NIR-IIc regions, respectively. Moreover, 2080–2340 nm is newly proposed as the third near-infrared (NIR-III) window, which is believed to provide the best imaging quality. The wide-field fluorescence microscopy in the brain is performed around the NIR-IIx region, with excellent optical sectioning strength and the largest imaging depth of intravital NIR-II fluorescence microscopy to date. We also propose 1400 nm long-pass detection in off-peak NIR-II imaging whose performance exceeds that of NIR-IIb imaging, using bright fluorophores with short emission wavelength.

Investigation of a Separated Short-Wavelength Peak in InGaN Red Light-Emitting Diodes

We fabricated indium gallium nitride (InGaN) red light-emitting diodes (LEDs) with a peak emission wavelength of 649 nm and investigated their electroluminescence (EL) properties. An additional separated peak in the EL spectrum of the red LEDs at 20 mA was observed at 465 nm. This additional peak also exhibits a blue-shift with increasing currents as does the main emission peak. Using high-resolution microscopy, we observed many point-like emission spots in the EL emission images at the currents below 1 mA. However, these emission spots cannot be identified at currents above 5 mA because the red emission from quantum wells (QWs) is much stronger than that emitted by these spots. Finally, we demonstrate that these emission spots are related to the defects generated in red QWs. The measured In content was lower at the vicinity of the defects, which was regarded as the reason for separated short-wavelength emission in red InGaN LEDs.

Benzothiazolium Derivative-Capped Silica Nanocomposites for β-Amyloid Imaging In Vivo

Alzheimer’s disease (AD) is a neurodegenerative disease, and β-amyloid (Aβ) is believed to be a causative factor in AD pathology. The abnormal deposition of Aβ is believed to be responsible for progression of AD. In order to facilitate the imaging of Aβ in vivo, suitable probe molecules with a near-infrared emission wavelength that can penetrate the blood–brain barrier (BBB) were utilized. The commercial fluorescent probe thioflavin-T (ThT) is used to image Aβ; however, because of its short emission wavelength and poor BBB penetration, ThT can only be used in vitro. With this research, based on ThT, we design three fluorescent probes (SZIs) having a longer emission wavelength in order to image Aβ aggregates. SZIs with different numbers of double bonds respond to Aβ aggregates. The SZIs have a structure similar to ThT, and as such, the SZIs are also unable to penetrate the BBB. To deal with the problem, we develop nanocomposites (MSN-Lf@SZIs) to deliver SZIs into the brain of AD mouse and image Aβ successfully. These new nanocomposites are able to deliver the dyes into the brain and facilitate Aβ imaging in vivo.