Large Stokes Shift Research Articles

A ratiometric fluorescent probe based on phenothiazine and quinazolinone for rapid detection of ClO− and its application

A novel fluorescent probe (BPQ-1) with large conjugated system (phenothiazine was conjugated with quinazolinone) was synthesized. BPQ-1 showed a remarkable ratiometric fluorescence response to ClO− within 10 s, and achieved large stokes shift (168 nm), high sensitivity (LOD = 16.7 nM) and excellent selectivity. Among the analytes to be detected, there is a significant change from bright yellow fluorescence to cyan fluorescence only when ClO− is added to BPQ-1. Through density functional theory calculation and mass spectrometry experiments, the fluorescence response mechanisms of the BPQ-1 are given. In addition, BPQ-1 has been successfully applied to the detection of ClO− in real water samples and test strips for detecting ClO− with different concentrations have been prepared. In particular, the probe has been successfully applied to the fluorescence imaging of exogenous ClO− in living cells.

A novel fluorescent probe for fast detection of sulfur dioxide derivatives in water, soil, food samples and its applications in biological imaging

Sulfur dioxide (SO2) has a wide range of applications in food additives and industrial production, and it is one of the main substances that form acid rain, causing serious harm to ecosystems and human health. Hence, it is necessary to construct an effective tool to quickly and accurately detect SO2 derivatives in environmental, food, and biological samples. In this study, fluorescent probe NPMQ was built to detect SO2 derivatives from nopinone with the merits of superior water solubility, high sensitivity (12nM), excellent specificity, large Stokes shift (180nm), and rapid response time (within 5s). NPMQ was used to qualitatively and quantitatively detect SO2 derivatives in environmental water, soil and food samples. In addition, an electrospinning film was prepared with the probe NPMQ to image SO2 derivatives, and test strips are capable of rapidly, sensitively, and selectively detecting SO2 derivatives with the naked eye. Moreover, the probe NPMQ was used to visualize endogenous SO2 derivatives in Arabidopsis thaliana under Cd2+ stress. Furthermore, the probe NPMQ was employed to image exogenous and endogenous SO2 derivatives in living Hela, HepG-2 cells, and zebrafish. This study develops an effective tool for monitoring SO2 derivatives in the environmental, food, and biological systems.

A near-infrared fluorescent probe with a large Stokes shift for the detection and imaging of biothiols in vitro and in vivo.

In this study, a new near-infrared (NIR) fluorescent turn-on probe featuring a large Stokes shift (198nm) was developed for the detection of biothiols. The probe was based on a dicyanoisophorone derivative serving as the fluorophore and a 2,4-dinitrobenzenesulfonyl (DNBS) group functioning as both a recognition site and a fluorescence quencher. In the absence of biothiols, the fluorescence of the probe was low due to the photoinduced electron transfer (PET) effect between the fluorophore and DNBS. Upon the presence of biothiols, the DNBS group underwent a nucleophilic aromatic substitution reaction with the sulfhydryl group of biothiols, leading to the release of the fluorophore and a notable emission peak at 668nm. This developed probe exhibited exceptional selectivity and sensitivity to biothiols in solution, with an impressive detection limit of 28nM for cysteine (Cys), 22nM for homocysteine (Hcy), and 24nM for glutathione (GSH). Furthermore, the probe demonstrated its applicability by successfully visualizing both endogenous and exogenous biothiols in living systems.

Quantum Dot Reporters Designed for CRISPR-Based Detection of Viral Nucleic Acids.

Diagnostic methods based on CRISPR technology have shown great potential due to their highly specific, efficient, and sensitive detection capabilities. Although the majority of the current studies rely on fluorescent dye-quencher reporters, the limitations of fluorescent dyes, such as poor photostability and small Stokes shifts, urgently necessitate the optimization of reporters. In this study, we developed innovative quantum dot (QD) reporters for the CRISPR/Cas systems, which not only leveraged the advantages of high photoluminescence quantum yield and large Stokes shifts of QDs but were also easily synthesized through a simple one-step hydrothermal method. Based on the trans-cleavage characteristics of Cas12a and Cas13a, two types of QD reporters were designed, the short DNA strand and the hybridization-based QD reporters, achieving the detection of DNA and RNA at the pM level, respectively, and validating the performance in the analysis of clinical samples. Furthermore, based on the unique property of QDs that allowed multicolor emission under one excitation, the application potential for simultaneous detection of diseases was further investigated. Taken together, this work proposed novel QD reporters that could be applied to the various CRISPR/Cas systems, providing a new toolbox to expand the diagnosis of bioanalytical and biomedical fields.

Ethynylbenzaldehydes as novel reaction-based “turn-on” fluorescent probes for primary amine detection in solution, vapor, food, proteins, and live cells

Amine detection is of great importance as excess volatile amine exposure and increased concentration of biogenic amines in human body can cause adverse effects to human health. Thus, the development of easy-accessible and efficient fluorescent probes for amine detection is of great importance. In this study, we are the first to establish a cascade reaction sequence featuring imine formation followed by 6-endo-dig cyclization reaction for the development of sensitive and selective “turn-on” fluorescent probes toward primary amines by using the ortho-ethynylbenzaldehydes (EBAs) as the reaction site. The corresponding isoquinolinium products generated give a significant red-shifted absorbance change and highly intense “turn-on” fluorescence. Nine EBAs (EBA-1a-1e, EBA-2–5) were designed and synthesized to study the structure-photophysical property relationship (SPPR) for selective primary amine sensing. Our EBAs possessed a highly sensitive response toward primary amines in aqueous conditions within 30 min (LOD as low as 0.45 µM) with tunable absorption (338–430 nm) and emission (410–535 nm), large Stokes shift (up to 115 nm), and high fluorescence quantum yield (up to 0.86). EBA-loaded paper strips were prepared as a portable low cost tool for amine detection in solution, vapor, and food. Fluorogenic protein labelling and in-gel fluorescent imaging were efficiently achieved by using EBAs in which the fluorescence signal was obviously observed by naked eyes under 365 nm UV lamp. Moreover, the favorable membrane permeabilization, low to moderate cytotoxicity, and “turn-on” fluorescent response of EBA-1a-1e and EBA-4–5 allow wash-free live cell imaging. Interestingly, EBA-1a-1e and EBA-4 showed high selectivity to fluorescent imaging of mitochondria.

Discovery of a novel near-infrared triphenylamine-dicyanoisophorone fluorescent probe with a large Stokes shift for long-term tracking of lysosomes in live cells

Fluorescent probes are powerful tools for real-time tracking of lysosomal movements and spatial distribution, which appears to be essential for understanding the biology of lysosomes. However, the commercially used lysosomal trackers exhibited some limitations, such as narrow Stokes shifts, poor photostability, and green to red instead of near-infrared (NIR) emission. In this study, we have developed a fluorescent probe by incorporating the triphenylamine fragment into the dicyanoisophorone fluorophore. This probe displayed impressive NIR emission (centered at 755 nm) and remarkable Stokes shift (235 nm), which was then demonstrated to be insensitive to lysosomal pH as well as viscosity, and expressed long-term lysosomal tracking ability with little cytotoxicity in live cells. Altogether, this study provided an ideal NIR fluorescent probe for lysosomal tracking.

Dithieno[3,2-b; 2',3'-f]phosphepinium-Based Near-Infrared Fluorophores: px-π* Conjugation Inherent to Seven-Membered Phosphacycles.

Positively charged phosphorus-containing heterocycles are characteristic core skeletons for functional molecules. While various phosphonium-containing five- or six-membered-ring compounds have been reported, the seven-membered-ring phosphepinium have not been fully studied yet. In this study, dithieno[3,2-b; 2',3'-f]phosphepinium ions containing electron-donating aminophenyl groups were synthesized. An X-ray crystallographic analysis of the resulting donor-acceptor-donor dyes revealed a bent conformation of the central seven-membered ring. These compounds exhibit fluorescence in the near-infrared region with a bathochromic shift of ca. 70 nm compared to a phosphepine oxide congener and a large Stokes shift. High fluorescence quantum yields were obtained even in polar solvents due to the suppression of the nonradiative decay process. A theoretical study revealed that the phosphepinium skeleton is highly electron-accepting owing to the orbital interaction between a px orbital of the phosphonium moiety and a π* orbital of the 1,3,5-hexatriene moiety. Due to the lower-lying px orbital in the phosphonium moiety compared to that of the phosphine oxide and the bent conformation of the seven-membered ring, the phosphepinium ring permits effective px-π* conjugation. A large structural relaxation with a contribution of a quinoidal resonance structure is suggested in the excited state, which should be responsible for the bright emission with a large Stokes shift.

Sb3+ dopant triggered highly efficient emission in zero-dimensional organic-inorganic hybrid metal halides.

Hybrid luminescent metal halides have attracted considerable attention for their structural diversity and versatility in photonic applications. Herein, we fabricate Sb3+ doped organic-inorganic hybrid metal halides (DMA)2CsInCl6 (DMA = [CH3NH2CH3]+) single crystal. Under ultraviolet light excitation, the crystals yield bright green emission at 550 nm with near-unity photoluminescence quantum efficiency (PLQY), which is attributed to the strong electronegativity and ns2 lone pairs of Sb3+ dopants. Given the slender rod-shaped semblance, bright green emission, near-unity PLQY, and large Stokes shift, Sb3+-doped (DMA)2CsInCl6 allows the potential optical waveguide applications.

Recent advances of lipid droplet-targeted AIE-active materials for imaging, diagnosis and therapy

Lipid droplets (LDs) are cellular organelles specialized in the storage and regulating the release of lipids critical for energy metabolism. As investigation on LDs deepens, the complex biological functions of LDs are revealed and their relationships with various diseases such as atherosclerosis, fatty liver, obesity, and cancer are uncovered. Fluorescence-based techniques with simple operations, visible results and high non-invasiveness are ideal tools for investigating LD-related biological processes and diseases. Materials with aggregation-induced emission (AIE) characteristics have emerged as promising candidates for investigating LDs due to their high signal-to-noise ratio (S/N), strong photostability, and large Stokes shift. This review discusses the principles and advantages of LD-targeting AIE probes for imaging LDs, diagnosis of LD-associated diseases including atherosclerotic plaques, liver diseases, acute kidney diseases and cancer, therapies with LD-targeting AIE-active photosensitizers and other relevant fields in the past five years. Through typical examples, we illustrate the status of investigating LD-related imaging, diagnosis of diseases and therapy with AIE materials. This review is expected to attract attentions from scientists with different research backgrounds and contribute to the further development of LD-targeting AIE materials.

Highly selective peptide-based fluorescent turn-on probe with large Stokes shift for the detection of Cd(II) and its applications in bio-imaging and smartphone-assisted recognition

Cadmium ions (Cd2+) is a ubiquitous environmental pollutant that endangers all forms of life, and it has become critical to develop simple and highly selective detection methods for monitoring Cd2+. Herein, a new fluorescent turn-on probe DPGC with dansyl fluorophore labelled tripeptide (ProGlyCys-NH2) was successfully synthesized using solid-phase peptide synthesis technology with Fmoc chemistry. Interestingly, DPGC showed high specificity and fluorescence “turn on” response towards Cd2+ in 100% aqueous solution. In addition, the limit of detection (LOD) for Cd2+ recognition by DPGC was calculated to be 12.4 nM. The pH test showed that DPGC had a wide detection range of 7–11 for Cd2+, and the response time was also less than 30 s. Notably, the DPGC-Cd2+ complex forms a 2:1 binding stoichiometry was determined using fluorescence titration, Job's plot, ESI-HRMS and DFT calculations. Additionally, the binding of DPGC with Cd2+ was found fluorescence reversible on addition of EDTA. Meanwhile, DPGC has excellent membrane permeability and low cytotoxicity, and was successfully employed for detecting Cd2+in living cells and zebrafish. More importantly, the colour change of Cd2+ solution with different concentrations under 365 nm UV light was detected by a smartphone App to achieve semi-quantitative visual analysis of Cd2+ ions.

A Dicyanoisophorone-based Fluorescent Turn-on Probe for Rapid Detecting Thiophenol in Aqueous Medium and Living Cell Imaging

A novel colorimetric and fluorescent thiophenol probe based on dicyanoisophorone has been successfully achieved, which has low-cost, easy operation, high selectivity, sensitivity and stability. The chemosensor shows a large Stokes shift and approximately 170 nm when excited at 510 nm. ISO-DiNO2 could be utilized as “Turn-on” and a naked-eyes chemosensor to detect PhSH, which is accompanied by a distinct color shift from red to dark purple with strong red fluorescence at 365 nm UV-light. Its limit of detection was determined to be 1.15 μM. More importantly, ISO-DiNO2 can react instantaneously (<10 s) with PhS−. In addition, ISO-DiNO2 has been utilized in test paper strips, water sample together with imaging of PhS− in living Raw264.7 cells, demonstrating that ISO-DiNO2 has excellent and promising applications.

Multi-color emission composites of white carbon dots and dyes through inner filter effect

A series of multi-color carbon dot composites were obtained by transforming white carbon dots (WCDs) into three primary colors using the dyes' inner filter effect (IFE). WCDs were combined with three distinct dyes (methyl red, bromocresol green, and methylene blue), and three fluorescence colors (red, yellow, and blue) were obtained. The colors of the emitting light excited by the same UV light were similar to the colors of the respective dyes, and have a large Stokes shift. The presence of the IFE between WCDs and dyes was proved through a variety of methods, the analysis of the relationship between the UV of dyes and fluorescence spectra of WCDs, the excitation-emission matrix, as well as the comparison PL decay profiles of WCDs before and after dye addition. The Stern-Volmer quenching constant KSV exhibited no temperature dependence during the IFE process with increasing concentrations of dyes. The UV spectra of the mixture of WCDs and dyes were simply the sum of two individual components, which implies that there is no chemical interaction between WCDs and dyes. Since methyl red and bromocresol green are acid-base indicators, the fluorescence color of the carbon dot composite also changed continuously during the dilute NaOH solution titration process. In furtherment, distributing the binary system of “WCDs + dye” within poly (vinyl alcohol) (PVA), three colors fluorescent composite films of “WCDs / Dye / PVA” were produced successfully.

A glutathione-activatable near-infrared fluorescent probe with a large Stokes shift for imaging 4T1 tumor and its ferroptosis

Some tumor cells have higher concentrations of glutathione (GSH) compared to normal cells, and ferroptosis can result in a significant decrease of GSH level in tumor cells. Thus, GSH can be employed as the biomarker for imaging some tumors and their ferroptosis. In this article, a GSH-activatable near-infrared fluorescent probe (QL-NF) with a large Stokes shift (110 nm) was developed for imaging 4T1 tumor and its ferroptosis. QL-NF employs the quinolinium-xanthene dye as the fluorophore and the 2-fluoro-4-nitrobenzene-1-sulfonate group as the response unit for GSH. QL-NF has a high selectivity and an applicable linear response range (0.50 mM–10.00 mM) for physiological GSH. Moreover, QL-NF was successfully used for imaging GSH in cancer cells and monitoring the concentration fluctuations of GSH during ferroptosis of cancer cells. Finally, QL-NF was further successfully employed for imaging 4T1 tumor and its ferroptosis in mice. All these results demonstrate that QL-NF is a useful tool for detecting GSH in vivo and imaging tumor ferroptosis, which is helpful for understanding tumor ferroptosis and further promoting the treatment of tumor.

Smart sensing property of Eu3+-induced polyelectrolyte nanoaggregates on nitrofuran antibiotics in aqueous environments

Pollution of water with antibiotics is a very serious global issue. So, simple, fast, and ecofriendly detection of such pollutants in aqueous environments has aroused great attention. Several intriguing properties such as narrow emission band, large stokes shift, long luminescence decay time and resistance to photobleaching distinguishes europium-based materials from commonly used fluorophores in biology as a superior optical smart material for applications in diverse fields. Herein, strongly luminescent Eu3+-induced polyelectrolyte nanoaggregates (EINAP) were synthesized and successfully characterized. The biocompatible polysaccharides hyaluronic acid and chitosan are used to disperse organic europium complexes resulting in formation of hybrid nanoaggregates. As synthesized EINAP demonstrated excellent quantum yield (89.29 %) and luminescence lifetime (656 µs). The EINAP also have high sensitivity and low limit of detection with good analytical precision for nitrofuran antibiotics in aqueous environments. The luminescent nano sensor developed in this work could be a novel tool for assessment of antibiotic pollution in the environment. The overall sensing mechanisms for detection of nitrofurans in aqueous environments were found to be the combination of inner filter effect and photoinduced electron transfer respectively.

A dual-response ratiometric near-infrared fluorescence probe based on cyanine platform for Cu2+ detection and its imaging in vitro and vivo

A near-infrared fluorescent probe (NUST-Cy-1) was disclosed here, which displays ratiometric and dual-channel response for Cu2+ (λex1 = 450 nm, λex2 = 750 nm) with large Stokes shifts (143 nm, 375 nm, 75 nm respectively). This probe demonstrates high sensitivity with low detection limit (1.4 μM) and selectivity for Cu2+ detection. Furthermore, fluorescent imaging of Cu2+ in vitro and vivo were successfully achieved.

A dual sensitive fluorescence probe for the simultaneous visualization of hypochlorite and viscosity in living cells and zebrafish

As vital microenvironmental indicators, hypochlorite and viscosity levels can be applied to diagnose diseases. Thus, real time and in situ monitoring of hypochlorite and viscosity has gained increasing attentions. A fluorescence probe named JDK was developed by using a novel acceptor of 2-(2-(5-(dimethylamino)thiophen-2-yl)vinyl)-1,3,3-trimethyl-3H-indol-1-ium fluorophore basing on FRET and TICT system. JDK possessed large Stokes shift, broad emission peak gap, prominent photostability and biocompatibility. JDK could track hypochlorite with rapid response time (within 1 min) and low detection limit (28.5 nM). Meaningfully, JDK was favor to append on mitochondria where physiological processes can be disrupted deriving from the abnormal concentrations of hypochlorite and viscosity. Successfully, JDK could visualize endogenous hypochlorite and viscosity in living cells and zebrafish.

Discovery of Fluorescent Naturally-Occurring Inhibitor of SARS-CoV-2 Main Protease by AIE Fluorescent Probe.

Target-based high-throughput screening (HTS) is an efficient way to identify potent drugs. However, the accuracy of HTS could be affected by Pan-Assay Interference Compounds (PAINS). One reason for the generation of PAINS is that the inherent photophysical property of screened compounds could interfere with typically used assay signals including absorption and fluorescence. Our previous studies indicate that the fluorescent probe based on the fluorophore with characteristics of aggregation-induced emission (AIE) could provide high accuracy of HTS, especially for the fluorescent natural products. Herein, we report an AIE-based fluorescent probe for the main protease (Mpro) of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We designed and synthesized an AIE fluorescent probe ZLHG5, which has a site that can be specifically cleaved by Mpro to produce a light-up fluorescence. Thanks to the large Stokes shift of AIE fluorophore (~200 nm), the probe could be effectively used for HTS of Mpro inhibitors. After screening a library of fluorescent natural products with ZLHG5, we obtained two coumarin-originated natural compounds with potent inhibitory activity towards Mpro protease. This study provides both useful fluorescent HTS probe and potent inhibitors for Mpro protease.

NIR fluorescence of phenol-π-malononitrile derivatives achieved by extending π-bridge and unexpected intermolecular deprotonation

NIR fluorescent phenol-π-malononitrile derivatives were achieved by extending vinylene π-bridge through Wittig reaction and following Knoevenagel condensation. In addition to regular D-A effect, unexpected intermolecular deprotonation of phenol group triggered by an electron-withdrawing group on phenyl ring pushed emissions to 762 nm with a large Stokes shift up to 323 nm. The extending of π-bridge and unexpected intermolecular deprotonation of phenol group promised a feasible strategy for construction of low-molecular weight NIR fluorophores.

Luminescent Solar Concentrators for Greenhouse Applications Based on Highly Luminescent Carbon Quantum Dots

Carbon quantum dots (CQDs) are promising luminophores for luminescent solar concentrators (LSCs) in transparent photovoltaic greenhouse covers due to their high ultraviolet (UV)‐light absorption coefficient, which is vital for plant growth. Herein, high quantum yield (75%) and large Stokes shift (0.706 eV) CQDs are synthesized by a simple, fast, cheap, and mass scalable method. A comprehensive study on the LSC engineering is carried out. Thin layers of CQDs with different concentrations of 1, 3, and 5 wt% and different number of layers (1–5) are coated on glass and poly(methyl methacrylate) (PMMA) waveguides, sized 5 × 5 × 0.6 and 15 × 15 × 0.6 cm3. The best performing single‐layer LCS exhibits power conversion efficiency (PCE) and optical efficiency as high as 1.6% and 6.5%, respectively (LSC size 5 × 5 × 0.6 cm3), and 1.19% and 3.27% (LSC size of 15 × 15 × 0.6 cm3), respectively. Over 90 days, stability tests show a 2% PCE decrease. Tests on a small‐scale greenhouse model demonstrate that transparent photovoltaic LSC roofs not only produce electricity but also control temperature inside the greenhouse. Hence, CQD‐based LSCs synthesized by the scalable method can be used in commercialization of transparent greenhouses photovoltaic covers.

Reversible pH-switchable NIR-II nano-photosensitizer for precise imaging and photodynamic therapy of tumors

Photodynamic therapy (PDT) has attracted widespread attention from researchers as an emerging cancer treatment method. There have been many reports on various types of NIR-II photosensitizers for imaging and treatment of tumor sites. However, there are few reports on the development of NIR-II organic small molecule photosensitizers that have intelligent response to the tumor microenvironment, precise imaging, real-time treatment, and high biocompatibility. In this work, we developed a series of NIR-II photosensitizers (RBTs) with near-infrared excitation, good photostability, and large Stokes shift. Among them, RBT-Br exhibited higher reactive oxygen species (ROS) generation efficiency due to the introduction of halogen heavy atoms to enhance intersystem crossing (ISC). It is noteworthy that RBT-Br can generate singlet oxygen (1O2) and superoxide anion radicals (•O2−) simultaneously under 730 nm laser. Subsequently, we used molecular engineering technology to construct three pH-responsive NIR-II photosensitizers (RBT-pHs) by utilizing the closure of the lactam ring, among which RBT-pH-1 (pKa = 6.78) is able to be directionally activated under the stimulation of tumor micro-acid environment, with its fluorescence emission window reaching 933 nm. Subsequently, RBT-pH-1 NPs encapsulated in DSPE-mPEG5k were applied for PDT treatment of mouse tumors. The results showed that RBT-pH-1 NPs were activated by the acidic tumor microenvironment and generated ROS under laser excitation, exhibiting precise tumor imaging and significant tumor growth inhibition. We look forward to these multifunctional NIR-II organic small molecule photosensitizers providing a more efficient approach for clinical treatment of tumors. Statement of significanceA reversible pH-switchable NIR-II nano-photosensitizer RBT-pH-1 NPs (pKa = 6.76) is developed for precise imaging and PDT therapy of mouse tumors, which can be effectively used for targeted enrichment and activation of tumor micro-acid environments. The results show that this NIR-II photosensitizer generates ROS through tumor micro-acid environment stimulation and laser triggering, showing precise tumor imaging guidance and significant tumor growth inhibition.