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Multicolor fluorescent probes based on small organic molecules have the advantages of low cost, good biocompatibility, easily modifiable molecular structures and adjustable fluorescence performance. In addition, small molecule multicolor fluorescent probes generally undergo multi-site or multi-step reactions, which means that they can be used for the specific detection of structurally similar substances in complex bio-systems. In this review, we focus on the design and application of multicolor fluorescent probes based on small organic molecules: single fluorophores with multiple reaction sites, multiple fluorophores with single reaction sites, or multiple fluorophores with multiple reaction sites. Moreover, a design strategy for multicolor fluorescent probes and its application in biological imaging are also summarized, providing a systematic plan for future research on fluorescent probes functionalized by small organic molecules. It will also play an important role in the development of additional functions for small organic molecule fluorescent probes.

To enhance the advantage of a long-term stability and low-toxicity active packaging system, two biodegradable covalent immobilized antibacterial packaging films were developed and applied to fresh beef preservation in this study. A polylactic acid (PLA) film was prepared by the extrusion-casting method. The surface of the PLA film was modified with plasma treatment to generate carboxylic acid groups, and then antibacterial agent nisin or e-poly lysine (e-PL) was covalently attached to the modified film surface. Physical, chemical, and antimicrobial properties of films were then characterized. Scanning electron microscopy and water contact angle images confirmed that nisin or e-PL was successfully grafted onto the film surface. The values of protein loading on the nisin-g-PLA film and e-PL-g-PLA film were 5.34 ± 0.26 and 3.04 ± 0.25 μg of protein/cm2 on the surface. Microbial analysis indicated that the grafted films effectively inhibit the growth of bacteria. Finally, the effects of the nisin-g-PLA film or e-PL-g-PLA film on physicochemical changes and microbiological counts of fresh beef during cold storage at 4 °C were investigated. The total viable count of the control sample exceeded 7 logarithms of the number of colony forming units per gram (log CFU/g) after 11 days of cold storage (7.01 ± 0.14 log CFU/g) versus 15 days for the e-PL-g-PLA film (7.37 ± 0.06 log CFU/g) and the nisin-g-PLA film (6.83 ± 0.10 log CFU/g). The results showed that covalent immobilized antibacterial packaging films had positive impacts on the shelf life and quality of fresh beef. Therefore, a covalent immobilized antibacterial packaging system could be a novel preservative method for foods.

Chronic hepatitis C (CHC) is a major liver disease caused by the hepatitis C virus. The current standard of care for CHC can achieve cure rates above 95%; however, the drugs in current use are administered for a period of 8-16 weeks. A combination of safe and effective drugs with a shorter treatment period is highly desirable. We report synthesis and biological evaluation of a series of 2',3'- and 2',4'-substituted guanosine nucleotide analogues. Their triphosphates exhibited potent inhibition of the HCV NS5B polymerase with IC50 as low as 0.13 μM. In the HCV replicon assay, the phosphoramidate prodrugs of these analogues demonstrated excellent activity with EC50 values as low as 5 nM. A lead compound AL-611 showed high levels of the nucleoside 5'-triphosphate in vitro in primary human hepatocytes and in vivo in dog liver following oral administration.

The reactive oxygen species (ROS) including hypochlorous acid (HOCl), on the one hand they can regulate physiological function in our living organisms, on the other hand abnormal concentration of ROS would induce a series of biomacromolecules damage and further endanger virtually all aspects of human health. Especially it can be directly related to cancer. Thus to elucidate and visualize their concentration is very imminent. Before many fluorescent probes were used to detect HOCl. In recent years, near-infrared or ratiometric fluorescent developed prosperously. The strategy of combining near-infrared and ratiometric fluorescent probe is overwhelming in the design of fluorescent probes. In this work, we successfully designed and obtained a near-infrared and ratiometric fluorescent probe with large stokes by reacting isophorone with coumarin, which can monitor HOCl high efficiently with quick response and low detection limit. In addition, cell imaging experiments show that the probe can identify endogenous and exogenous ClO− successfully, and nude mouse imaging experiments show that the probe can detect exogenous ClO−. It is possible that the probe can be applied in early clinical diagnosis.

In recent years, it has become a trend to employ organic molecular fluorescent probes with multireaction sites for the distinguishable detection and biological imaging of similar substances. However, the introduction of multireaction sites brought great challenges to organic synthesis, and at the same time, often destroyed the conjugated structure of the molecules, leading to an unsatisfactory fluorescence emission wavelength not conducive to practical application. As the eternal theme of life, metabolism goes on all the time. Metabolism is a series of ordered chemical reactions that occurs in the organism to maintain life. Chemical reactions in metabolism can be summarized as metabolic pathways. Simultaneous monitoring of different metabolic pathways of the same substance poses a lofty challenge to the probe. Here, we developed a new strategy: to construct new sites through the preliminary reactions between probes and some targets, which can be used to further distinguish among targets or detect their metabolites, so as to realize the simultaneous visualization tracer of multiple metabolic pathways. By intravenous injection, it revealed that the probe containing benzopyrylium ion can target tumors efficiently, and thiols are highly expressed in tumors compared to other tissues (heart, lung, kidney, liver, etc.). The consumption of thiols by the probe could not prevent tumor growth, suggesting that the tumor cure was not correlated with thiol concentration. The construction of new sites in the reaction process is a novel idea in the pursuit of multiple reaction sites, which will provide more effective tools for solving practical problems.

Chronic hepatitis C (CHC) is a major liver disease caused by the hepatitis C virus. The current standard of care for CHC can achieve cure rates above 95%; however, the drugs in current use are administered for a period of 8-16 weeks. A combination of safe and effective drugs with a shorter treatment period is highly desirable. We report synthesis and biological evaluation of a series of 2',3'- and 2',4'-substituted guanosine nucleotide analogues. Their triphosphates exhibited potent inhibition of the HCV NS5B polymerase with IC

Sulfur dioxide (SO2), as the main member of reactive sulfur species (RSS), it is mainly produced in mitochondria and involved in a variety of activities at the cellular level. Excessive inhalation of SO2 could cause respiratory tract damage, cardiovascular disease and even cancer. The mitochondrial and lysosomal as two important organelles, their interactions (fusion and contact) are important for maintaining eukaryotic homeostasis. Some study indicated that SO2 is active in the above interaction process. In this work, benzopyranium salt unit was constructed as fluorophore I, where O+ was the mitochondrial target site, and naphthalimide was linked to morpholine to construct fluorophore II, where morpholine was the lysosomal target group. Studies have shown that the probe has a good performance in targeting both mitochondria and lysosomes. And after the reaction with SO2, FRET was broken, resulting in red quenching, and green emitting, which made it can detect SO2 with a ratiometric response. Cells cultured with nystatin showed decreased red and green fluorescence increased, indicating that the autophagy of mitochondria produced SO2. In addition, synthesized control reagents (targeting lysosomes alone and responding to SO2) from no signal to gradually enhanced blue fluorescence, indicating that SO2 produced by mitochondria is transferred to lysosomes. What's more, it could monitor the changes of SO2 concentration under heat stroke. More importantly, it could quantitatively detect sulfite concentration in Yuba and crystal sugar.

Because of the high toxicity of hydrazine, the development of ultrasensitive fluorescent probes for hydrazine has been challenging. In this work, an ultrasensitive fluorescent probe based on o-phthalaldehyde has been exploited for hydrazine. The probe was designed based on creating an efficient fluorophore by incorporating hydrazine into o-phthalaldehyde framework via an intermolecular condensation-cyclization reaction. The probe could quickly detect hydrazine and displayed a high sensitivity for hydrazine with a LOD of 1.9 nM (0.06 ppb), which is far below the U.S. Environmental Protection Agency standard (10 ppb). Moreover, the probe was successfully applied to the detection of hydrazine in real water samples and hydrazine vapor.

Through-wall imaging radar (TWIR) usually transmits ultra-wideband (UWB) signals to obtain high-range resolution and penetrate walls to image the concealed human targets. Because of the round-trip high attenuation of walls and low reflectivity of human target, the received human target echoes are extremely weak, and consequently it is necessary to enhance the human target echoes and improve the low signal-to-noise ratio (SNR) before image formation. However, directly applying the conventional moving target detection (MTD) is faced with the range migration issue due to the high-range resolution of UWB TWIR. In this paper, we introduce the radon-Fourier transform (RFT) into the UWB TWIR to enhance the human target echo in the velocity domain, which can overcome the range migration. Simulation results show that noise can be effectively suppressed and target echoes can be significantly enhanced.

We report the synthesis and biological evaluation of a series of 4'-fluoro-2'- C-substituted uridines. Triphosphates of the uridine analogues exhibited a potent inhibition of hepatitis C virus (HCV) NS5B polymerase with IC50 values as low as 27 nM. In an HCV subgenomic replicon assay, the phosphoramidate prodrugs of these uridine analogues demonstrated a very potent activity with EC50 values as low as 20 nM. A lead compound AL-335 (53) demonstrated high levels of the nucleoside triphosphate in vitro in primary human hepatocytes and Huh-7 cells as well as in dog liver following a single oral dose. Compound 53 was selected for the clinical development where it showed promising results in phase 1 and 2 trials.

In recent years, coumarin fluorescent probes have been widely used in the detection of environmental pollutants, disease diagnosis and drug development due to their excellent optical properties, good water solubility and easy structure modification. Most coumarin fluorescent probes are modified at 3 and 7 positions mainly by introducing substituents, while at 4 and 8 positions are relatively less modified. Herein, compound 2 and 3 were prepared by introducing electron-donating group (EDG) and electron-withdrawing group (EWG) into the 4 position of 7-diethylamino-3-acetyl coumarin, respectively, and their properties were studied by theoretical calculation and spectral test. Then, we successfully prepared Probe 1 and Probe 2 by introducing pyrazoline ring at 7 position. Probe 2 exhibited high quantum yield and rapid response to ClO− in pure PBS. We speculated that it is a synergistic action of –OH and pyrazoline rings. In addition, Probe 2 could effectively detect ClO− in HeLa cells and zebrafish. Modification of substituents in different positions is a novel concept for the construction and optimization of fluorescent probes, which will provide a more effective tool for solving practical problems.

Forster resonance energy transfer (FRET) is a relatively new strategy for constructing ratiometric fluorescent probes and increasing the Stokes shift. Fluorescent probes based on FRET require spectral overlap between the energy donor emission spectrum and the acceptor absorption spectrum, while providing high energy transfer efficiency. In addition, systems exhibiting FRET typically exhibit intense dual fluorescence, thereby improving the resolution of biological imaging and detection. Herein, on the union of a benzopyrylium salt with a coumarin carboxylic acid, a novel near-infrared fluorescent probe CM-P-DP with FRET regulation strategy was designed and synthesized for the detection of sulfite (SO32−). CM-P-DP showed large Stokes shift (230 nm) and fast response to SO32− in pure PBS buffer (15 s). When SO32− was added, the fluorescence intensity at 455 nm gradually increased, and the fluorescence intensity at 635 nm decreased rapidly. Moreover, CM-P-DP could effectively target mitochondria and imaging SO32− in biological systems.

Thiophenols are an important class of raw material and intermediate to prepare pesticides, medicines and polymers in chemical industry. However, they are highly toxic and harmful to the organisms and the environment, evaluated as No. P014 acute hazardous waste by USEPA (the environmental protection agency in US). Despite establishing the permittable discharge standards, thiophenols still bring about a threat to the environment primarily due to the absence of reliable and convenient detection methods. In this study, 2,4-dinitrobenzenesulfonyl (DNPS) was introduced to enhance SNAr, then ESIPT of the fluorophore was triggered quickly by ‘enhanced SNAr’ between the probe and strongly nucleophilic thiophenols, thus NIR ultrafast thiophenols detection was realized. The probe was able to detect the 4-methyl thiophenol (MTP) within 13 s with the limit of detection (LOD) of 13.3 nM (below the exposure limit of 0.5 ppm provided by the National Institute for Occupational Safety and Health (NIOSH)). More, the probe was successfully applied to monitor the levels of the thiophenols in environmental water samples and Hela cells.

Hypochlorous acid (HClO) as a reactive oxygen species (ROS) played an important role in many pathological and physiological processes. HClO could kill invading pathogens and bacteria in the immune system. But excessive concentrations of HClO may cause many diseases. Near-infrared fluorescent probes have strong tissue penetrating ability, low autofluorescence interference, and broad application prospects in the field of fluorescence imaging research. In this work, we synthesized a new near-infrared (670 nm) “dual-mode” fluorescent dye NSSN based on the benzothiazole framework for the visual detection of HClO. The NSSN had a large Stokes shift (220 nm), good selectivity, ratiometric near-infrared and low detection limit (0.13 μM). In addition, NSSN could achieve mitochondrial target detection of HClO in HeLa cells, also HClO could be visually detected in nude mice by NSSN. Thus NSSN is expected to be used in the early diagnosis of HClO.

Cysteine (Cys), Glutathione (GSH) can resist the reactive oxygen species due to adversity and aging in plants. Thus, the specific detection of individual thiol in plants is very important. However, just a few have been used to discrimination of Cys/Hcy and GSH in vivo. Not to mention the discrimination detection for them in plants. In this work, we synthesized a potential promoting tandem reaction type fluorescent probe based on benzene-conjugated benzopylium ion and NBD-Cl. The probe could detect Cys/Hcy and GSH with high selectivity and low detection limit. More interesting, firstly we employed the probe to successfully detect Cys/Hcy and GSH in arabidopsis thaliana. Our research is useful for studying the conversion and metabolic pathways of thiols in plants.