Endoplasmic reticulum-targeting fluorescence turn-on probe for nitric oxide detection in living cells and serum samples

Nitric oxide (NO) is an important gas signaling molecule, and endoplasmic reticulum (ER) stress induced by NO may be related to the pathogenesis of many diseases. Therefore, the development of ER-targeted fluorescent probes for NO is of great significance to investigate the relationship between ER stress and NO concentration changes in related diseases. Herein, an ER-targeted fluorescent probe (ER-Np) for sensing NO was constructed. ER-Np was served as an excellent tool for detection NO with high selectivity, sensitivity and ER-targetable ability. Moreover, fluorescence imaging experiments indicated that ER-Np is capable of imaging NO in living cells. Impressively, visualization of endogenous NO production during dithiothreitol (DTT)-induced ER stress in living cells was successfully observed. In addition, we found that serum NO levels were upregulated in epilepsy children, which opens up a new avenue for further understanding the relationship between the diagnostic of epilepsy.

A series of fluorescent dyes based on 4-phenylacetylene-1,8-naphthalimide: Synthesis, theoretical calculations, photophysical properties and application in two-color imaging and dynamic behavior monitoring of lipid droplets and lysosomes

A series of fluorescent dyes (NapPAs) based on 4-phenylacetylene-1,8-naphthalimide were synthesized and characterized, whose conjugated structures were extended by the introduction of phenylethynyl. Furthermore, changes in the photophysical properties of the dyes when substituents with varying electron richness were introduced at the p-position of phenylacetylene were studied. The theoretical calculation of the dye molecules was carried out by B3LYP functional and 6-31G(d,p) basis set, and the effects of different substituents at the p-position of phenylacetylene on the electronic structure and photophysical properties of the dyes were studied by theoretical calculation results. Theoretical calculations provided a reliable means of predicting the properties of dyes, which could help in the design of more efficient and novel dyes. To verify the practicability of the dyes, two dyes with excellent photophysical properties (large Stokes shift, high polarity-viscosity sensitivity, good biocompatibility) were selected as fluorescent probes for visualization of LDs and two-color imaging of LDs and lysosomes. Cell imaging showed that NapPA-LDs and NapPA-LDs-Lyso serve as excellent imaging tools to monitor the dynamic changes, movements, and behaviors of LDs and lysosomes in real time. Notably, NapPA-LDs-Lyso held promise as a potential tool to study the interaction between LDs and lysosomes.

Molecular engineering and bioimaging applications of C2-alkenyl indole dyes with tunable emission wavelengths covering visible to NIR light

As an important member of dyes, small-molecule fluorescent dyes show indispensable value in biomedical fields. Although various molecular dyes have been developed, full-color dyes covering blue to red region derived from a single chromophore are still in urgent demand. In this work, a series of dyes based on C2-alkenyl indole skeleton were synthesized, namely AI dyes, and their photophysical properties, cytotoxicity, and imaging capacity were verified to be satisfactory. Particularly, the maximal emission wavelengths of these dyes could cover a wide range from visible to NIR light with large Stokes shifts. Besides, the optical and structural discrepancies between the C2- and C3- alkenyl AI dyes were discussed in detail, and the theoretical calculations were conducted to provide insights on such structure-activity relationship. Finally, as a proof-of-concept, a fluorescent probe AI-Py-B capable of imaging endogenous ONOO- was presented, demonstrating the bioimaging potentials of these alkenyl indole dyes. This work is anticipated to open up new possibilities for developing dye engineering and bio-applications of natural indole framework.

The how and why of naphthalimide/heterocycle-fused hybrid dyes: an overview of the latest developments in the quest for dyes with innovative optical properties

In this review, a variety of hybrid structures fusing aromatic heterocycles of different natures to a naphthalimide backbone are discussed. This strategy constitutes an efficient approach to generate original structures displaying singular photophysical properties and thus offering new perspectives in the fields of fluorogenic detection, optoelectronics, and photodynamic therapy. In this review, different synthetic approaches and structures reported in the literature are discussed. A critical look at the design and the applications of these new fused hybrids allows us to evaluate the benefits and drawbacks of a fused hybrid strategy applied to naphthalimides.

Design and synthesis of photostable triphenylamine based neutral AIE nano luminogens: specific and long-term tracking of mitochondria in cells

With the increasing dependence on fluorescence bioimaging, luminogens with aggregation-induced emission (AIE) properties have gained significant attention due to their excellent photostabilization, minimal photobleaching, high reliability, and superior biocompatibility. Since mitochondria are crucial subcellular organelles in eukaryotic cells with important biological functions, organelle-specific AIE emitters with distinct functions have been highly sought after, but with limited success using simple synthetic methods. Here, we describe a strategy for synthesizing two triphenylamine (TPA) based acrylonitriles, tethered to different donor groups, TPA and phenothiazine (PTZ), respectively, with superior AIE properties using Suzuki coupling. We conducted a systematic and detailed experimental analysis of the structural characteristics of both AIE luminogens, which exhibited excellent photostability, a large Stokes shift, and bright solid-state emission. A cell viability study carried out with F1 and F2 dyes revealed that both luminogens exhibited excellent biocompatibility. Based on fluorescence experiments, F2 displayed excellent AIE characteristics, permeability, biocompatibility, and photostability compared to rhodamine 123, allowing it to selectively stain and track mitochondria in cancer cells over an extended period of time. The Pearson correlation coefficient of F2 and rhodamine 123 was estimated to have an r-value of 0.99. Our findings are expected to provide insight into the synthesis of an extensive archive of AIE-based acrylonitriles with fascinating properties for mitochondrial staining.

Engineering of a novel D-A type fluorophore with hydrogen bond-induced enhanced emission property for sensitively detecting endogenous HOCl in living cells and tissues

Fluorescence imaging has been widely employed for biomedical research and clinical diagnostics. With ease of synthesis and excellent photophysical properties, D-A type fluorophores are widely designed for fluorescence imaging. However, traditional D-A type fluorophores are solvatochromic which reduces the fluorescence brightness in the biological system. To solve this problem and build on our previous work, we devised a novel HIEE fluorophore MTC with typical anti-solvatochromic fluorescence. Furthermore, the activated fluorescent probe designed based on MTC showed excellent imaging performance. We believe that the strategy based on the fluorophores with typical anti-solvatohromic fluorescence can be a useful platform for designing fluorescent probes for high-brightness imaging in the biological system.

Distinguishing normal and inflammatory models by viscosity changes with sensitively mitochondrial-trackable fluorescent probe

Biological microenvironment plays a momentous role in the regulation of various vital activities, and its abnormal changes are often closely related to some diseases. Viscosity, as an indispensable part of microenvironment parameters, has always been one of the research hotspots of investigators. Herein, we constructed a new red-emitting fluorescent probe (HVM) to identify the abnormal situation of mitochondria through viscosity changes in the biological microenvironment. Interestingly, HVM has excellent optical properties such as large stokes shift (160 nm), viscosity sensitivity (195-fold), high photostability, and biochemical properties with low cytotoxicity and excellent biocompatibility. For these reasons, the novel probe could successfully be used to identify the normal and inflammatory models via viscosity changes in biological experiments. Therefore, we provided a convenient synthetic route to obtain viscosity sensor HVM with excellent application properties.

Recent advances in the targeted delivery of paclitaxel nanomedicine for cancer therapy

Cancer cases have reached an all-time high in the current era.

Synthesis and Visualization of a Novel Fluorescent-Tagged Polymeric Antiscalant during Gypsum Crystallization in Combination with Bisphosphonate Fluorophore

An attempt to reveal the mechanisms of scale inhibition with the use of two different fluorescent-tagged antiscalants at once is undertaken. To reach the goal, a novel 1,8-naphthalimide-tagged polyacrylate (PAA-F2) is synthesized and tested separately and jointly with 1,8-naphthalimide-tagged bisphosphonate (HEDP-F) as a gypsum scale inhibitor within the frames of NACE Standard TM0374-2007. Here, it is found that at a dosage of 10 mg·dm−3 it provides a much higher inhibition efficiency (96%) than HEDP-F (32%). A PAA-F2 and HEDP-F blend (1:1 mass) has an intermediate efficacy (66%) and exhibits no synergism relative to its individual components. The visualization of PAA-F2 revealed a paradoxical effect: an antiscalant causes modification of the CaSO4·2H2O crystals habit, but does not interact with them, forming particles of its own solid complex [Ca-PAA-F2]. This paradox is interpreted in terms of the “nano/microdust” concept, prioritizing the bulk heterogeneous nucleation step, while an ability of the scale inhibitor to block the nucleus growth at the next steps is proven to be of secondary importance. At the same time, HEDP-F does not change the gypsum crystals morphology, although this antiscalant is completely located on the surface of the scale phase. The PAA-F2 and HEDP-F blend revealed an accumulation of both antiscalants in their own [Ca-PAA-F2/Ca-HEDP-F] phase with some traces of HEDP-F and PAA-F2 on the CaSO4·2H2O crystals surface. Thus, the visualization of two different antiscalants separately and jointly applied to gypsum deposition demonstrates differences in phosphonic and polymeric inhibitors location, and a lack of causal relationship between antiscalant efficiency and scale particle habit modification. Finally, it is shown that the confocal microscopy of several fluorescent antiscalant blends is capable of providing unique information on their interrelationships during scale deposition.

Simultaneously Enhanced Singlet Oxygen and Fluorescence Production of Nanoplatform by Surface Plasmon Resonance Coupling for Biomedical Applications

Photodynamic therapy (PDT) and fluorescence imaging offer the possibility of precise and personalized treatment of cancer, but low singlet oxygen production of a commercial photosensitizer and the quenching effect of fluorescent dyes limit the further application of PDT treatment and fluorescence imaging. In addition, the single nanoplatform that simultaneously achieved singlet oxygen and fluorescence enhancement is rare. In this paper, a novel simultaneously enhanced singlet oxygen and fluorescence production nanoplatform of AuNR@mSiO₂-Ce6-Cy5.5 has been successfully designed and synthesized by surface plasmon resonance coupling. The as-synthesized nanoplatform achieved a 1.8-fold enhancement of the singlet oxygen production of Ce6 and a 5.0-fold enhancement of the fluorescence production of Cy5.5 by surface plasmon resonance coupling. The as-synthesized nanoplatform simultaneously enhances the photodynamic therapy and fluorescence imaging of cancer, which will have great potential in biomedical applications.

Tissue Imaging of Glutathione-Specific Naphthalimide-Cyanine Dye with Two-Photon and Near-Infrared Manners

Molecular probes suitable for different fluorescence imaging technologies can meet the requirements of different scientific research in biological applications. In this work, a naphthalimide-cyanine-based sulfonamide was used to specifically visualize the glutathione of mouse tissues with a two-photon manner for the naphthalimide moiety and a near-infrared manner for the cyanine moiety, respectively. The results showed that this probe served as a dual-model tissue-imaging agent for visualization of glutathione with around 200 μm imaging depth in a two-photon manner and 120 μm imaging depth in a near-infrared manner, which provided a model for tissue imaging in the visible and near-infrared channels.

Tuning the π-bridge of quadrupolar triarylborane chromophores for one- and two-photon excited fluorescence imaging of lysosomes in live cells

A series of tetracationic quadrupolar chromophores containing three-coordinate boron π-acceptors linked by different π-bridges, namely 4,4'-biphenyl, 2,7-pyrene, 2,7-fluorene, 3,6-carbazole and 5,5'-di(thien-2-yl)-3,6-diketopyrrolopyrrole, were synthesized. While their neutral precursors 1-5 displayed highly solvatochromic fluorescence, the water-soluble tetracationic target molecules 1M-5M, did not, but their emission colour could be tuned from blue to pink by changing the π-bridge. Compound 5M, containing the diketopyrrolopyrrole bridge, exhibits the most red-shifted absorption and emission maxima and the largest two-photon absorption cross-section (4560 GM at 740 nm in MeCN). Confocal laser scanning fluorescence microscopy studies in live cells confirm localization of the dye at the lysosome. Moreover, the low cytotoxicity, and high photostability of 5M combined with two-photon excited fluorescence imaging studies demonstrate its excellent potential for lysosomal imaging in live cells.

Aggregation-Induced Emission Luminogens with the Capability of Wide Color Tuning, Mitochondrial and Bacterial Imaging, and Photodynamic Anticancer and Antibacterial Therapy

Recently, luminogens with the aggregation-induced emission characteristic (AIEgens) have received much attention in the field of bioimaging and therapeutic applications. However, the development of AIEgens that are derived from the simple core skeleton with emission color tuning for imaging and therapy is still a formidable challenge. To address this constraint, we present a series of cationic AIEgens based on cyanopyridinium salts (CP1-CP5). The AIEgens can be facilely prepared by varying the aromatic electron donor while fixing the cyanopyridinium group as the electron acceptor within a single benzene ring. The obtained AIEgens possess wide color tunability, large Stokes shifts, and bright emission in the condensed state. Due to their good biocompatibility and cationic nature, these AIEgens can be utilized for multiple-color imaging of intracellular mitochondria as well as Gram-negative and Gram-positive bacteria. Importantly, these AIEgens exhibit remarkable structure-dependent singlet-oxygen generation ability under white light illumination (25 mW cm^-2), and CP4 was optimized to serve as an excellent photosensitizer for photodynamic anticancer and antibacterial therapy.

A chromenoquinoline-based two-photon fluorescent probe for the highly specific and fast visualization of sulfur dioxide derivatives in living cells and zebrafish

Sulfur dioxide (SO₂) derivatives play critical roles in various biological processes. Therefore, effective methods for monitoring SO₂ are of vital importance in bisulfite/sulfite biology. In this study, a two-photon (TP) imaging probe (CQ-SO₂) for detecting SO₂ derivatives was designed and constructed, based on the chromenoquinoline (CQ) fluorophore and a β-chlorovinyl aldehyde sensing moiety. The TP properties of the CQ derivatives were revealed for the first time in this study. This study enriched the biological application range of CQ derivatives and also provided a new choice for the development of TP dyes. In particular, the CQ-SO₂ probe exhibited a fast response time (about 5 s), low detection limit (16 nM) and ultrahigh specificity towards SO₂ derivatives. Furthermore, the probe was successfully applied to the highly specific TP bioimaging of SO₂ derivatives in living cells and zebrafish.

A naphthalimide-indole fused chromophore-based fluorescent probe for the detection of biothiol with red emission and a large Stokes shift

This probe exhibited red emission (λ_max = 590 nm) and a large Stokes shift (143 nm) for the detection of biothiols.

Unusual fluorescence of o-phenylazonaphthol derivatives with aggregation-induced emission and their use in two-photon cell imaging

Unusual fluorescence of o-phenylazonaphthol derivatives with aggregated-induced emission (AIE) is reported for the first time, which can be used in two-photon cell imaging applications.

Two-photon fluorescent polydopamine nanodots for CAR-T cell function verification and tumor cell/tissue detection

Chimeric antigen receptor T-Cell (CAR-T) immunotherapy has been regarded as one of the most promising methods for cancer therapy. How to verify CAR-T cell function and efficiency is very significant for clinical applications. Meanwhile, the identification of tumor cells/tissues is very important for tumor diagnosis and operation. In this study, biocompatible and mass-produced polydopamine (PDA) nanodots have been prepared by a facile method. Oxidized polydopamine (OPDA) can be synthesized by the reaction between PDA and hydrogen peroxide at atmospheric pressure and temperature, and it possesses both one-photon and two-photon fluorescence properties. OPDA nanodots can image living cells for long time periods without mitosis and proliferation inhibition. After ingestion of OPDA nanodots, Raji cells can be used to verify CAR-T cell lethality and efficiency by visualization through fluorescence. The fluorescence intensity change originating from the conversion of PDA into OPDA can function as a signal to identify the tumor and normal cells/tissues because of the different concentration of ROS in tumor cells (high) and normal cells (low). Therefore, the facile synthesis of mass-produced novel organic nanodots with two-photon fluorescence properties will have wide applications in long time living cell imaging without mitosis and proliferation inhibition, CAR-T cell function verification and tumor cell/tissue detection.

Acquiring High-Performance Deep-Blue OLED Emitters through an Unexpected Blueshift Color-Tuning Effect Induced by Electron-Donating -OMe Substituents

A series of blue-emissive 7-(diphenylamino)-4-phenoxycoumarin derivatives bearing -CF₃ , -OMe, or -N(Me)₂ substituents on the phenoxy subunit were synthesized. Although both the -CF₃ and -N(Me)₂ modifications were found to trigger redshifted fluorescence, the -OMe substitution was demonstrated to exert an unexpected blueshift color-tuning effect toward the deep-blue region. The reason is that the moderate electron-donating -OMe group can endow coumarins with unaltered HOMO but elevated LUMO energy levels. Moreover, the -OMe substitution was found to be beneficial to the thermal stability of these coumarins. Therefore, the trimethoxy-substituted objective compound can act as a high-performance deep-blue organic light-emitting diode (OLED) emitter, and OLED based on it emits deep-blue light with CIE coordinates of (0.148, 0.084), maximum luminance of 7800 cd m^-2 , and maximum external quantum efficiency of 5.1 %. These results not only shed light on the molecular design strategy for high-performance deep-blue OLED emitters through color-tuning, but also show the perspective of coumarin derivatives as deep-blue OLED emitters.

Diarylmaleimide-based branched oligomers: strong full-color emission in both solution and solid films

An effective design method is presented to construct highly efficient fluorescent materials in both solution and solid films, by non-conjugately linking fluorophores into branched oligomers. Surface aryl groups are changed to tune the luminescent color from blue (λ_em = 480 nm) to red (λ_em = 651 nm), and realize full-color emission.

Amino-Si-rhodamines: A new class of two-photon fluorescent dyes with intrinsic targeting ability for lysosomes

Noninvasive and specific visualization of lysosomes by fluorescence technology is critical for studying lysosomal trafficking in health and disease and for evaluating new cancer therapeutics that target tumor cell lysosomes. To date, there are two basic types of lysosomal probes whose lysosomal localization correlates with lysosomal acidity and endocytosis pathway, respectively. However, the former may suffer from pH-sensitive lysosomal localization and alkalization-induced lysosomal enzyme inactivation, and the latter need long incubation time to penetrate cell membrane due to the energy-dependency of endocytosis process. In this work, a new class of two-photon fluorescent dyes, termed amino-Si-rhodamines (ASiRs), were developed, which possess the intrinsic lysosome-targeted ability that is independent of lysosomal acidity and endocytosis pathway. As a result, ASiRs show not only the stable lysosomal localization against lysosomal pH changes and negligible interference to lysosomal function, but also excellent cell-membrane-permeability due to the energy-independent passive diffusion pathway. These merits, coupled with their excellent two-photon photophysical properties, long-term retention ability in lysosomes, and negligible cytotoxicity, make ASiRs very suitable for real-time and long-term tracking of lysosomes in living cells or tissues without interference to normal cellular processes. Moreover, the easy functionalization via amino linker further allows the construction of various fluorescent probes for biological targets of interest based on ASiR skeleton, as indicated by the cancer-targeted fluorescent probe ASiR6 as well as a fluorescent peroxynitrite probe ASiR-P.

Near-Infrared Fluorescent Probe for Sensitive Detection of Pb(II) Ions in Living Cells

A new near-infrared fluorescent probe (NIR-PbP) for sensitive detection of Pb(II) ions in solution and living cells has been rationally designed and synthesized. The NIR-PbP is inherently non-fluorescent and gains fluorescence in the presence Pb(II) ions. The ion detection is based on Pb(II)-induced unmasking the fluorophore through the opening of the spyrocycle, with more than 500-fold fluorescence for sub-micromolar Pb(II) concentration. The NIR-PbP has high sensitivity, good photo-stability, low detection limit, and reversible response to Pb(II) ions.