Ingenious fluorescent probes for biogenic amine and their applications in bioimaging and food spoilage detection.

Food safety issues have received much attention. Biogenic amines are considered important markers of food spoilage. Accurate detection of biogenic amines is important for food quality monitoring. Herein, we developed two coumarin-difluoroboron ß-diketonate hybrid probes, 1 and 2, for detection of amines. Both probes possess large conjugated structures and donor-acceptor-donor configuration, exhibiting solvatochromic effects due to intramolecular charge transfer mechanism. Upon reaction with amines, the boron atom in difluoroboron unit can interact with lone pair electrons of nitrogen atom, thus resulting in significant changes in absorption and fluorescence properties. These probes were successfully utilized to image amine in live cells and liver tissues. Moreover, by photographing probe-loaded food extract supernatant, we establish the relationship between color parameters and food storage time, which can easily indicate food spoilage process. This work and its findings hold promise for providing potential strategies for real-time and convenient detection of food freshness.

Et4NCl-Promoted Electrochemical Atherton-Todd Type Reaction to Construct P(O)-F Bonds.

An electrochemical synthetic strategy to construct P(O)-F bonds was developed via the Atherton-Todd reaction. Promoted by Et4NCl, a series of biologically active phosphoric fluorides were synthesized by use of commercially available P(O)-H feedstocks and Et3N·3HF as the F-source. With this protocol, some potentially functional P(O)-OR and P(O)-SR motifs could also be smoothly forged. This sustainable fluorination approach features step-economy, is chemical-oxidant- and metal-catalyst-free, and offers low cost and mild conditions. Additionally, cyclic voltammetry and control experiments were conducted to propose a reasonable mechanism.

A colorimetric and fluorescent sensor for non-destructive screening of the freshness of shrimp and fish.

The freshness of fish and shrimp is closely associated with food safety, hence it is a wide concern to develop a facile and effective method for fast, non-destructive and visual screening the freshness of fish and shrimp. Herein, we developed a chromogenic and fluorogenic sensor (RFCC) based on resorufin for sensing of biogenic amines including cadaverine and putrescine. RFCC underwent aminolysis with cadaverine or putrescine, displaying a remarkable fluorescence turn on response at 593 nm along with obvious color change from colorless to pink. RFCC was fabricated into test strips to sense cadaverine vapor, and the RGB value of test strips showed a good linear relationship with the concentration of cadaverine (0.5 - 8.2 × 103 ppm). The RFCC tag was used to in situ screen the freshness of fish and shrimp according to obvious fluorescence change, and satisfactory results were achieved. Furthermore, this test strip was validated by total volatile base nitrogen (TVBN), providing a simple, low cost and portable tool to screen the freshness of fish and shrimp for consumers and suppliers without expensive instrumentation.

A novel 1,8-naphthalimide-based fluorescent chemosensor for the detection of HSA in living cells.

Human serum albumin (HSA) is an essential protein for maintaining human health. Accurate detection and quantification of HSA are of great significance for disease diagnosis and biochemical research. Here, a new HSA fluorescent probe BNPE based on the 1,8-naphthalimide fluorophore was designed and synthesized. The probe could recognize HSA through a twisted intramolecular charge transfer mechanism, effectively avoid the interference of most substances, and realize HSA fluorescence imaging in living cells.

Early diagnostic imaging of pneumonia with an ultra-sensitive two-photon near-infrared fluorescent probe.

The mortality rate of pneumonia increases significantly with the prolongation of illness. In the pursuit of a tool to accurately diagnose pneumonia in its early stages, we designed and synthesized a two-photon near-infrared fluorescent probe (DCQN) to identify increased concentrations of the inflammation marker SO2. The probe was found to specifically react with SO2 by undergoing a 1,4-addition reaction to generate near-infrared fluorescence with good sensitivity (6 s), a large Stokes shift (110 nm) and low detection limit (1.49 nM). DCQN has near-infrared emission as well as good two-photon performance, which can image exogenous and endogenous SO2 in cells and avoid interference from background fluorescence from cells. Furthermore, this study achieved accurate imaging of a pneumonia lesion site in deep tissues to provide a tool for the fluorescence diagnostic imaging of pneumonia in situ.

An ultrasensitive lipid droplet-targeted NIR emission fluorescent probe for polarity detection and its application in liver disease diagnosis.

Compared to normal cells, cancer cells require more energy supply during proliferation and metabolism. In living cells, in addition to mitochondria, lipid droplets are also an important organelle for providing energy. Studies have shown that the number and distribution of lipid droplets change significantly during the production of lesions in cells. At this stage, the predisposing factors for the development of cellular lesions are not clear, thus leading to limitations in the early diagnosis and treatment of diseases such as liver injury, fatty liver, and hepatitis. To meet the urgent challenge, we used a near-infrared emission fluorescent probe SSR-LDs based on the intramolecular charge transfer effect (ICT) to detect polarity changes within intracellular lipid droplets. The probe SSR-LDs has ultra-sensitive polarity sensitivity, excellent chemical stability and photo-stability. In addition, by comparing normal and cancer cells through cell imaging experiments, we found that the robust probe has the ability to sensitively monitor the changes in lipid droplet polarity in the living cells. More importantly, using the constructed fluorescent probe, we have achieved an in vitro fluorescence detection of liver injury and fatty liver, and the detection of hepatitis at the in vivo level. The unique fluorescent probe SSR-LDs is expected to serve as a powerful tool for the medical diagnosis of diseases related to lipid droplet polarity.

A molecular recognition platform for the simultaneous sensing of diverse chemical weapons.

Chemical warfare agents (CWAs) such as phosgene and nerve agents pose serious threats to our lives and public security, but no tools can simultaneously screen multiple CWAs in seconds. Here, we rationally designed a robust sensing platform based on 8-cyclohexanyldiamino-BODIPY (BODIPY-DCH) to monitor diverse CWAs in different emission channels. Trans-cyclohexanyldiamine as the reactive site provides optimal geometry and high reactivity, allowing trans-BODIPY-DCH to detect CWAs with a quick response and high sensitivity, while cis-BODIPY-DCH has much weaker reactivity to CWAs due to intramolecular H-bonding. Upon reaction with phosgene, trans-BODIPY-DCH was rapidly converted to imidazolone BODIPY (<3 s), triggering green fluorescence with good sensitivity (LOD = 0.52 nM). trans-BODIPY-DCH coupled with nerve agent mimics, affording a blue fluorescent 8-amino-BODIPY tautomer. Furthermore, a portable test kit using trans-BODIPY-DCH displayed an instant response and low detection limits for multiple CWAs. This platform enables rapid and highly sensitive visual screening of various CWAs.

A new NIR emission mitochondrial targetable fluorescent probe and its application in detecting viscosity changes in mouse liver and kidney injury.

As important organs of the human body, the liver and kidneys ensure the stability of the internal environment of the body and allow the body to carry out normal metabolism. The lack of effective methods for early diagnosis of liver and kidneys diseases is an important reason for delaying the treatment of kidney diseases. Therefore, the development of a simple, non-invasive and effective test is essential for the early diagnosis of liver and kidneys disease. Herein, a new viscosity fluorescent probe, Mito-ND, is rationally designed and synthesized in order to solve the practical problem of realizing the diagnosis of liver and kidneys diseases. The constructed fluorescent probe Mito-ND has the advantages of near-infrared emission, mitochondrial localization, high chemical and photo-stable properties, and sensitive viscosity detection performance, etc. Using this fluorescent probe, besides in vitro cell viscosity fluorescence imaging, the viscosity fluorescence imaging of mouse liver and kidney injury are also achieved for the first time. Mito-ND provides more accurate tools for the non-invasive diagnosis of viscosity-related diseases such as liver injury and kidney injury. Therefore, Mito-ND provides more accurate detection techniques for the early diagnosis of liver and kidney diseases such as liver injury and kidney injury.

Low-frequency ultrasound and nitrogen limitation induced enhancement in biomass production and lipid accumulation of Tetradesmus obliquus FACHB-12.

The two-stage cultivation strategy was optimized in this study to simultaneously promote the growth and lipid accumulation of Tetradesmus obliquus. Results showed that the optimal dual-stress conditions were nitrogen concentration at 25 mg N·L-1 and low-frequency ultrasound at 200 Watt, 1 min, and 8 h interval. The biomass and lipid content of Tetradesmus obliquus were increased by 32.1% and 44.5%, respectively, comparing to the control, and the lipid productivity reached 86.97 mg-1·L-1·d-1 at the end of the cultivation period. The protein and photosynthetic pigment contents of microalgae decreased by 22.4% and 14.0% under dual stress comparing to the control environment. In addition, dual stress cultivation of microalgae presented higher level of antioxidant capacity to balance to oxidation level in microalgal cells. This study provides a new insight for microalgae growth and lipid accumulation with dual stress stimulation.

A novel fluorescent probe with large Stokes shift for the detection of viscosity changes and its imaging in living cells.

As an important cellular microenvironmental parameter, viscosity could reflect the status of living cells. Small molecular fluorescent probes are a vital tool to measure the change of viscosity in living cells. A novel fluorescence probe ZL-1 with a large Stokes shift (in methanol it reached to 153 nm and in glycerol it reached to 125 nm) and excellent sensitivity toward viscosity was developed. The sharp enhancement of the emission intensity for the probe ZL-1 from low viscous methanol to high viscous glycerol indicated that the probe ZL-1 could respond to the viscosity variations. Moreover, the probe ZL-1 has been successfully utilized to detect of the viscosity variations in living cells.

A novel cysteine fluorescent probe with large stokes shift for imaging in living cells, zebrafish and living mice.

The small molecule biological thiols, such as Cysteine (Cys), homocysteine (Hcy), and glutathione (GSH), play crucial roles in maintaining various cellular vital activities. In the organism, abnormal levels of small-molecule biological thiols have been associated with a variety of diseases. Therefore, quantitative determination of biological thiols, especially Cys, is significant for understanding their functions in various biological processes. Thus, in this work we designed a new fluorescent probe Ty-Cys1 with a large Stokes shift of 207 nm to monitor Cysteine. The maximum absorption wavelength of Ty-Cys1 was 418 nm, and the maximum emission wavelength was 625 nm. Significantly, the novel probe Ty-Cys1 was effectively in detecting of Cys changes in living cells, zebrafishes, and living mice.

[Exploration of active components and mechanism of Scutellariae Radix-Phellodendri Chinensis Cortex drug pair in treatment of psoriasis based on network pharmacology and molecular docking].

This paper aims to explore active components and mechanism of Scutellariae Radix(SR)-Phellodendri Chinensis Cortex(PCC) drug pair in treatment of psoriasis by network pharmacology and molecular docking. Specifically, the chemical components of SR and PCC were retrieved from literature and TCMSP, as well as targets of these components from PharmMapper and UniProt, and the targets related to psoriasis from OMIM, TTD, PharmGkb, and DrugBank. Then the chemical component-medicinal target, protein-protein interaction(PPI), and chemical component-psoriasis target networks were constructed by Cytoscape. Gene ontology(GO) term enrichment analysis and Kyoto encyclopedia of genes and genomes(KEGG) pathway enrichment analysis were performed based on Metascape. Finally, molecular docking of the chemical components(high degree) with core therapeutic targets was carried out by AutoDock vina. The results showed 88 compounds of SR and PCC(including baicalin, wogonoside, berberine and phellodendrine) and 30 targets of the pair in the treatment of psoriasis. The 30 targets mainly involved the biological processes such as neutrophil mediated immunity(GO: 0002446) and T cell activation(GO: 0042110), and the signaling pathways such as metabolism of xenobiotics by cytochrome P450(hsa00980), apoptosis(hsa04210), and PI3 K-Akt signaling pathway(hsa04151). The results of molecular docking demonstrated that the main active components can spontaneously bind to the targets and the binding energy of 46 components with epidermal growth factor receptor(EGFR) was less than-8 kcal·mol~(-1). According to the PPI analysis, EGFR may be a key target for the treatment of psoriasis. Active components such as baicalin and berberine had high binding affinity with EGFR. This study preliminarily revealed the multi-component, multi-target and multi-pathway mechanism of SR-PCC drug pair in the treatment of psoriasis, which provided theoretical basis for the research on the mechanism of the drug pair in the treatment of psoriasis.

Carrier-free nanoparticles of camptothecin prodrug for chemo-photothermal therapy: the making, in vitro and in vivo testing.

BACKGROUND: Nanoscale drug delivery systems have emerged as broadly applicable approach for chemo-photothermal therapy. However, these nanoscale drug delivery systems suffer from carrier-induced toxicity, uncontrolled drug release and low drug carrying capacity issues. Thus, to develop carrier-free nanoparticles self-assembled from amphiphilic drug molecules, containing photothermal agent and anticancer drug, are very attractive. RESULTS: In this study, we conjugated camptothecin (CPT) with a photothermal agent new indocyanine green (IR820) via a redox-responsive disulfide linker. The resulting amphiphilic drug-drug conjugate (IR820-SS-CPT) can self-assemble into nanoparticles (IR820-SS-CPT NPs) in aqueous solution, thus remarkably improving the membrane permeability of IR820 and the aqueous solubility of CPT. The disulfide bond in the IR820-SS-CPT NPs could be cleaved in GSH rich tumor microenvironment, leading to the on demand release of the conjugated drug. Importantly, the IR820-SS-CPT NPs displayed an extremely high therapeutic agent loading efficiency (approaching 100%). Besides, in vitro experimental results indicated that IR820-SS-CPT NPs displayed remarkable tumor cell killing efficiency. Especially, the IR820-SS-CPT NPs exhibited excellent anti-tumor effects in vivo. Both in vitro and in vivo experiments were conducted, which have indicated that the design of IR820-SS-CPT NPs can provide an efficient nanotherapeutics for chemo-photothermal therapy. CONCLUSION: A novel activatable amphiphilic small molecular prodrug IR820-SS-CPT has been developed in this study, which integrated multiple advantages of GSH-triggered drug release, high therapeutic agent content, and combined chemo-photothermal therapy into one drug delivery system.

An endoplasmic reticulum targetable turn-on fluorescence probe for imaging application of carbon monoxide in living cells.

Carbon monoxide (CO) is a significant mediator in regulating endoplasmic reticulum (ER) stress, and its level may play a potential role in the treatment of vascular diseases combined with ER stress. In-situ visualization of CO in the ER helps to elucidate its physiological and pathological mechanistic behavior. Herein, a novel CO fluorescent probe (Na-CM-ER) with ER-targeting characteristics was structured. Na-CM-ER with naphthalimide as a fluorescent group, under the trigger of CO, an ICT (Intramolecular Charge Transfer) mechanism was constructed by converting a nitro group to an amino group and showed dazzling green fluorescence. Na-CM-ER exhibited satisfactory response speed, selectivity, photo-stability and sensitivity to CO in vitro. Furthermore, biological imaging experiments demonstrated that Na-CM-ER could monitor the changes of exogenous/endogenous CO in living cells and possess an ER-targeting property. To sum up, we hope that Na-CM-ER can be as a serviceable molecular tool for imaging CO in cellular ER.

Preparation of robust fluorescent probes for tracking endogenous formaldehyde in living cells and mouse tissue slices.

Formaldehyde (FA) is the simplest active carbonyl species that can be spontaneously produced in the body and plays important roles in human cognitive ability and spatial memory. However, excessive intake of FA may cause a series of diseases, including cancer, diabetes, heart and liver diseases and various neuropathies. Hence, the exploration of sensitive and fast detection methods for FA is crucial to understand and diagnose these diseases. Recently, fluorescent probes have been increasingly employed as powerful tools for detecting a broad range of different small molecules due to their high selectivity, rapid response, convenient operation and relatively non-invasive nature. Thus, we have developed two naphthalimide-based fluorescent probes for detecting FA in cells and in lysosomes. Compared with other FA fluorescent probes, these two probes have several advantages, including high sensitivity and selectivity, excellent two-photon properties and high signal-to-noise ratio. In this protocol, we provide detailed procedures for the synthesis of the two probes; characterization of their sensitivity, selectivity and stability in solution; and representative application procedures for detecting FA in living cells and mouse liver tissue slices. The protocol requires ~88 h to synthesize the probes, ~24 h to characterize the probes in solution and ~25 h to carry out the biological fluorescence imaging experiments in cells and liver tissue slices.

Erratum: Publisher Correction: Endogenous formaldehyde is a memory-related molecule in mice and humans.

[This corrects the article DOI: 10.1038/s42003-019-0694-x.].

Endogenous formaldehyde is a memory-related molecule in mice and humans.

Gaseous formaldehyde is an organic small molecule formed in the early stages of earth's evolution. Although toxic in high concentrations, formaldehyde plays an important role in cellular metabolism and, unexpectedly, is found even in the healthy brain. However, its pathophysiological functions in the brain are unknown. Here, we report that under physiological conditions, spatial learning activity elicits rapid formaldehyde generation from mitochondrial sarcosine dehydrogenase (SARDH). We find that elevated formaldehyde levels facilitate spatial memory formation by enhancing N-methyl-D-aspartate (NMDA) currents, but that high formaldehyde concentrations gradually inactivate the NMDA receptor by cross-linking NR1 subunits to NR2B via the C232 residue. We also report that in mice with aldehyde dehydrogenase-2 (ALDH2) knockout, formaldehyde accumulation due to hypofunctional ALDH2 impairs memory, consistent with observations of Alzheimer's disease patients. We also find that formaldehyde deficiency caused by mutation of the mitochondrial SARDH gene in children with sarcosinemia or in mice with Sardh deletion leads to cognitive deficits. Hence, we conclude that endogenous formaldehyde regulates learning and memory via the NMDA receptor.

A novel mitochondria-targeted near-infrared (NIR) probe for detection of viscosity changes in living cell, zebra fishes and living mice.

Viscosity is a key factor that determines the diffusion-controlled processes in biological systems. The matrix of mitochondria contains various enzymes and other proteins with high density, and the diffusion of which are severely restricted by the cristae, making it the most crowded place in the cells. Herein, we reported a new near-infrared probe NV-1 with increased Stokes shift for monitoring viscosity changes in mitochondria. A remarkable increase of the fluorescence was observed in glycerol compared with which was observed in methanol at 744 nm. The probe was applied for measuring viscosity changes not only in mitochondria, but also in vivo (in zebra fishes and mice).

Rational Design of a Reversible Fluorescent Probe for Sensing Sulfur Dioxide/Formaldehyde in Living Cells, Zebrafish, and Living Mice.

Living systems contain a diverse array of molecules and ions undergoing dynamic changes by a web of interacting chemical reactions. Sulfur dioxide (SO2) and formaldehyde (FA) can be generated endogenously in living organisms to maintain their homeostasis, but aberrant production of these species is implicated with some critical diseases. The dynamic interaction between SO2 and FA on the overall health and disease of living organisms remains challenging to elucidate owing to a dearth of methods for monitoring dynamic fluctuation of these transient species. Herein, we present the rational design, synthesis, and photophysical property studies of the probe (CaP), the first reversible fluorescent probe for investigating the dynamics changes of SO2 and FA. Importantly, the highly desirable attributes of the robust probe CaP (such as ultrafast response to SO2 in less than 5 s, swift restoration by FA in less than 1 min) make it possible to reversibly monitor the dynamic fluctuation of endogenous SO2 and FA in real-time in living cells for the first time. Moreover, we demonstrate the utility of this unique probe to detect the fluctuations of SO2 and FA in living zebrafish and murine species. This work provides a powerful chemical tool for monitoring the dynamic interaction of endogenous SO2 and FA, which will pave an avenue for interrogating the intersecting correlation between SO2 and FA in health and disease states.

Strategies for designing organic fluorescent probes for biological imaging of reactive carbonyl species.

Reactive carbonyl species (RCS) are involved not only in diverse physiological pathways but also in various pathological processes, including Alzheimer's disease, diabetes, cardiovascular disease, and other malignant diseases. Therefore, it is essential to develop a simple and sensitive technology which can be employed to selectively monitor RCS in living biological samples, such as living cells, tissues, and animals. The subtle changes in the concentration of RCS in organisms can be detected by this technique. In this review, the design strategies of the typical examples of RCS fluorescent probes are highlighted and discussed. These advanced RCS probes may set the foundation for biomedical research on dynamic real-time monitoring of RCS in living systems.