Diagnosis of Bacterial Plant Diseases via a Nitroreductase-Activated Fluorescent Sensor

A Dual-Channel Fluorescent Probe for Accurate Diagnosis and Precise Photodynamic Killing of Bacterial Infections by Employing Dual-Mechanism Responses

Bacterial infections pose a huge challenge to global public health, exacerbated by the growing threat of antibiotic resistance due to overuse of antibiotics, and there is an urgent need to develop epidemiological control methods that enable accurate detection and precise treatment. In this study, we present an innovative dual-response integrated probe, Nap-CefTTPy, which is capable of dual-channel fluorescence imaging, synergizing with photodynamic therapy for the accurate diagnosis and precise treatment of bacterial infections. The probe has excellent selectivity for bacteria and can produce two independent spectral responses to bacteria through two different response mechanisms under a single laser excitation, achieving accurate diagnosis of dual-channel bacterial infections. At the same time, it can also produce reactive oxygen species for synergistic photodynamic therapy, which ensures the accuracy of diagnosis and treatment. In a mouse bacterial infection model, it largely promoted the wound healing of S. aureus-infected mice. This platform represents a significant advancement in the field, providing a novel approach for the dual-code mutual correction diagnosis and photodynamic therapy of bacterial infections.

Fabrication of Multifunctional Three-Component Supramolecular Nano-Biscuits via Two Macrocycles-Involved Self-Assembly for Rice, Citrus and Kiwifruit Protections

Bacterial plant diseases, worsened by biofilm-mediated resistance, are increasingly threatening global food security. Numerous attempts have been made to develop agrochemicals that inhibit biofilms, however, their ineffective foliar deposition and difficulty in removing mature biofilms remain major challenges. Herein, multifunctional three-component supramolecular nano-biscuits (NI6R@CB[7]@β-CD) are successfully engineered via ordered self-assembly between two macrocycles [cucurbit[7]uril (CB[7]), β-cyclodextrin (β-CD)] and (R)-2-naphthol-based bis-imidazolium bromide salt (NI6R). This macrocycles-involved bactericidal material combines many advantages. 1) Alleviate the off-target movement of droplets on hydrophobic blade surfaces. 2) Enhance the biofilm-disrupting ability. At a low-dose of 4.44 µg mL-1, the inhibition rate of biofilm formation reached 78.3%. At 35.5 µg mL-1, the potency to remove mature biofilms reached 77.6%. 3) Efficiently hinder bacterial reproduction, swimming, extracellular polysaccharide production, extracellular enzyme secretion, and virulence to plants. These superior characteristics are undoubtedly transmitted to the in vivo control effect. At 200 µg mL-1, this smart material exhibits superior control efficiencies of 49.6%/65.0%/85.4% against three kinds of bacterial diseases (rice leaf blight, citrus canker, and kiwifruit canker), respectively, surpassing the commercial bactericide-thiodiazole-copper-20%SC (33.6%/41.5%/43.2%) and NI6R (40.3%/51.2%/71.2%). Furthermore, NI6R@CB[7]@β-CD is biosafe to non-target organisms. This study is instructive for constructing multifunctional agrochemicals in sustainable crop protection.

Fluorescence imaging opens a new window for the diagnosis of early-stage Alzheimer's disease

As the global population ages, the incidence and prevalence of Alzheimer's disease (AD) continues to rise, posing a serious threat to human health. Butyrylcholinesterase (BChE), which is overexpressed in the brains of patients with AD, is a potential drug target and biomarker. However, the molecular mechanism underlying BChE's role in the AD process remains unclear. Therefore, the development of tools for BChE detection can aid in the diagnosis of AD and deepen our understanding of BChE's contribution to disease progression. Motivated by a bioinspired strategy based on the natural substrate of BChE, we designed a BChE fluorescent probe (HCYO) with a novel recognition group for BChE detection to assist in the early diagnosis of AD. This probe can selectively detect endogenous BChE with an excellent detection limit of 28.9 ng/mL. Using HCYO, we successfully imaged four-week-old mice with an ultraearly AD model, the early diagnosis of the disease. Furthermore, using this HCYO probe, we confirmed that BChE influences the inflammation-induced upregulation the levels of phosphorylated tau and Trigger Receptor Expressed on Myeloid Cells 2, impacting AD progression. These findings provide a crucial theoretical basis for the development of BChE inhibitors for AD treatment.

Discovery of Novel Antibacterial Agents against Plant Pathogens: Design, Synthesis, Antibacterial Activity, and Mechanism of Action of 1,2,4-Thiadiazole Derivatives Containing a Sulfone Moiety

1,2,4-Thiadiazole derivatives containing a sulfone moiety were designed and synthesized via scaffold hopping to facilitate the discovery of novel antibacterial agents. Most of the compounds exhibited excellent activity against three plant pathogenic bacteria. The half-maximal effective concentrations (EC50) of compound B7 for Xanthomonas oryzae pv oryzae (Xoo) and X. oryzae pv oryzicola (Xoc) concentrations were 0.4 and 1.0 mg/L, respectively. In addition, the EC50 values of compounds B1 and B24 for Xoo, Xoc, and Pseudomonas syringae pv actinidiae (Psa) were less than 5 mg/L and significantly better than those of the positive control agents thiodiazole copper (121.8, 119.5, and 142.0 mg/L, respectively) and bismerthiazol (73.3, 65.6, and 128.8 mg/L, respectively). Compound B7 exhibited protective and curative activities of 48.1 and 46.7%, respectively, against bacterial leaf blight, which were higher than those of bismerthiazol (35.5 and 36.9%, respectively) and thiodiazole copper (39.3 and 39.5%, respectively). Additionally, compound B7 exerted an effect on the virulence factors of Xoo (production of exopolysaccharides and extracellular enzymes, biofilm formation, and motility), membrane permeability, cell surface morphology, and intracellular content of reactive oxygen species. Transcriptome analysis showed that compound B7 improved the resistance of rice plants to external stress by influencing the metabolic process, biological regulation, catalytic activity of enzymes, and plant-pathogen interaction. Compound B7 can therefore be considered as a potential candidate antibacterial agent and warrants an in-depth investigation in the future.

Colorimetric aptasensor based on self-screened aptamers and cascaded catalytic reaction for the detection of quarantine plant bacteria

Quarantine plant bacteria (QPB) are significant component of invasive alien species that result in substantial economic losses and serious environmental damage. Herein, a colorimetric aptasensor has been proposed based on the sandwich structure and the cascaded catalytic strategy for on-site detecting Xanthomonas hyacinthi, a type of QPB, in natural environments. The self-screened aptamer obtained through SELEX can bind to specific sites on the surface of viable organism with high affinity and specificity, which guarantees the selectivity of aptasensor. As an important part of the aptasensor, MIL-88-NH2(Fe) not only acts as a multifunctional carrier for both aptamers and glucose oxidase, but also catalyzes enzyme-like reaction because of specific surface area, amino and peroxidase-like activity. The present of Xanthomonas hyacinthi can trigger the formation of a sandwich structure and the occurrence of cascade catalytic reaction, enabling the detection with UV-Vis spectra and naked eyes. The proposed aptasensor presents a low detection limit of 2 cfu/mL and a wide linear range of 10 -107 cfu/mL. Compared to traditional detection methods for QPB, the reasonable design, high selectivity and convenience significantly improve the detection efficiency and contribute to environmental protection.

High-throughput fluorescence sensing array based on tetraphenylethylene derivatives for detecting and distinguishing pathogenic microbes

Infections induced by pathogenic microorganisms will bring negative effects such as diseases that damage health and result in heavy economic burden. Therefore, it is very important to detect and identify the pathogens in time. Moreover, traditional clinical diagnosis or food testing often faces the problem of dealing with a large number of samples. Here, we designed a high-throughput fluorescent sensor array based on the different binding ability of five tetraphenylethylene derivatives (TPEs) with various side chains to different kinds of pathogenic microbes, which is used to detect and distinguish various species, so as to realize rapid mass diagnosis, and hopefully provide guidance for further determination of microbial infections and clinical treatment.

A near-infrared fluorescence probe with large Stokes shift for selectively monitoring nitroreductase in living cells and mouse tumor models

Hypoxia is commonly regarded as a typical feature of solid tumors, which originates from the insufficient supply of oxygen. Herein, the development of an efficient method for assessing hypoxia levels in tumors is strongly desirable. Nitroreductase (NTR) is an overexpressed reductase in the solid tumors, has been served as a potential biomarker to evaluate the degrees of hypoxia. In this work, we elaborately synthesized a new near-infrared (NIR) fluorescence probe (MR) to monitor NTR activity for assessment of hypoxia levels in living cells and in tumors. Upon exposure of NTR, the nitro-unit of MR could be selectively reduced to amino-moiety with the help of nicotinamide adenine dinucleotide. Moreover, the obtained fluorophore emitted a prominent NIR fluorescence, because it possessed a classical "push-pull" structure. The MR displayed several distinguished characters toward NTR, including intense NIR fluorescent signals, large Stokes shift, high selectivity and low limit of detection (46 ng/mL). Furthermore, cellular confocal fluorescence imaging results validated that the MR had potential of detecting NTR levels in hypoxic cells. Significantly, using the MR, the elevated of NTR levels were successfully visualized in the tumor-bearing mouse models. Therefore, this detecting platform based on this probe may be tactfully constructed for monitoring the variations of NTR and estimating the degrees of hypoxia in tumors.

Non-invasive diagnosis of bacterial and non-bacterial inflammations using a dual-enzyme-responsive fluorescent indicator

Bacterial infections, as the second leading cause of global death, are commonly treated with antibiotics. However, the improper use of antibiotics contributes to the development of bacterial resistance. Therefore, the accurate differentiation between bacterial and non-bacterial inflammations is of utmost importance in the judicious administration of clinical antibiotics and the prevention of bacterial resistance. However, as of now, no fluorescent probes have yet been designed for the relevant assessments. To this end, the present study reports the development of a novel fluorescence probe (CyQ) that exhibits dual-enzyme responsiveness. The designed probe demonstrated excellent sensitivity in detecting NTR and NAD(P)H, which served as critical indicators for bacterial and non-bacterial inflammations. The utilization of CyQ enabled the efficient detection of NTR and NAD(P)H in distinct channels, exhibiting impressive detection limits of 0.26 μg mL-1 for NTR and 5.54 μM for NAD(P)H, respectively. Experimental trials conducted on living cells demonstrated CyQ's ability to differentiate the variations in NTR and NAD(P)H levels between A. baumannii, S. aureus, E. faecium, and P. aeruginosa-infected as well as LPS-stimulated HUVEC cells. Furthermore, in vivo zebrafish experiments demonstrated the efficacy of CyQ in accurately discerning variations in NTR and NAD(P)H levels resulting from bacterial infection or LPS stimulation, thereby facilitating non-invasive detection of both bacterial and non-bacterial inflammations. The outstanding discriminatory ability of CyQ between bacterial and non-bacterial inflammation positions it as a promising clinical diagnostic tool for acute inflammations.

Nitroreductase-Responsive Photosensitizers for Selective Imaging and Photo-Inactivation of Intracellular Bacteria

Intracellular Staphylococcus aureus (S. aureus), especially the methicillin resistant staphylococcus aureus (MRSA), are difficult to detect and eradicate due to the protection by the host cells. Antibacterial photodynamic therapy (aPDT) offers promise in treating intracellular bacteria, provided that selective damage to the bacteria ranther than host cells can be realized. According to the different nitroreductase (NTR) levels in mammalian cells and S. aureus, herein NTR-responsive photosensitizers (PSs) (T)CyI-NO2 were designed and synthesized. The emission and 1O2 generation of (T)CyI-NO2 are quenched by the 4-nitrobenzyl group, but can be specifically switched on by bacterial NTR. Therefore, selective imaging and photo-inactivation of intracellular S. aureus and MRSA were achieved. Our findings may pave the way for the development of more efficient and selective aPDT agents to combat intractable intracellular infections.

Carbon Monoxide: A Second Biomarker to Couple with Viscosity for the Construction of "Dual-Locked" Near-Infrared Fluorescent Probes for Accurately Diagnosing Non-Alcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) can progress to cirrhosis and liver cancer if left untreated. Therefore, it is of great importance to develop useful tools for the noninvasive and accurate diagnosis of NAFLD. Increased microenvironmental viscosity was considered as a biomarker of NAFLD, but the occurrence of increased viscosity in other liver diseases highly reduces the diagnosis accuracy of NAFLD by a single detection of viscosity. Hence, it is very necessary to seek a second biomarker of NAFLD. It has been innovatively proposed that the overexpressed heme oxygenase-1 enzyme in NAFLD would produce abnormally high concentrations of CO in hepatocytes and that CO could serve as a potential biomarker. In this work, we screened nine lactam Changsha dyes (HCO-1-HCO-9) with delicate structures to obtain near-infrared (NIR), metal-free, and "dual-locked" fluorescent probes for the simultaneous detection of CO and viscosity. Changsha dyes with a 2-pyridinyl hydrazone substituent could sense CO, and the 5-position substituents on the 2-pyridinyl moiety had a great electron effect on the reaction rate. The double bond in these dyes served as the sensing group for viscosity. Probe HCO-9 was utilized for precise diagnosis of NAFLD by simultaneous detection of CO and viscosity. Upon reacting with CO in a high-viscosity microenvironment, strong fluorescence at 745 nm of probe HCO-9 was turned on with NIR excitation at 700 nm. Probe HCO-9 was proven to be an effective tool for imaging CO and viscosity. Due to the advantages of NIR absorption and low toxicity, probe HCO-9 was successfully applied to image NAFLD in a mouse model.

Rational design of a ratiometric fluorescent probe for imaging lysosomal nitroreductase activity

Overexpressed nitroreductase (NTR) is often utilized to evaluate the hypoxic degree in tumor tissues, thus it is of great importance to develop high selective and efficient optical method to detect NTR. The dynamic fusion and function of lysosome promoted us to explore the possible appearance of NTR inside this organelle and to probe its behavior in a cellular context. In this work, a ratiometric fluorescent probe based on an extended π-π conjugation of a triphenylamine unit was designed for NTR detection and lysosomes imaging. The dual-emission mechanism of the probe in the presence of catalytic NTR was confirmed by theoretical study. The structure-function relationship between probe and NTR was revealed by docking calculations, suggesting a suitable structural and spatial match of them. The photophysical studies showed the probe had high selectivity, rapid response and a wide pH range towards NTR. MTT assay indicated the probe had low cytotoxicity in both normal (HUVEC) and tumor (MCF-7) cells. Furthermore, the inverse fluorescent imaging results confirmed the probe was NTR-active and exhibited time- and concentration-dependent fluorescence signals. In addition, the relatively high Pearson's correlation coefficient (0.99 in HepG2 and 0.97 in MCF-7 cells, compared to Lyso-Tracker Red) demonstrated the probe had excellent lysosomes colocalization. This study illustrates a ratiometric detection of NTR agent for lysosomes fluorescent imaging, which may provide a novel insight in molecular design.

A fluorescent probe for imaging nitroreductase with signal amplification in high-viscosity environments

Herein, we developed a fluorescent probe ENBT for in vitro detection of nitroreductase (NTR) as well as imaging intracellular NTR. ENBT itself is non-fluorescent and it could be catalyzed by NTR to generate a viscosity-sensitive fluorophore EBT. The fluorescence intensity of EBT could be further enhanced in cancer cells with relatively high viscosity due to the inhibition of the twisted intramolecular charge transfer effect. The probe ENBT has a good response to NTR with a detection limit of 36.8 ng mL-1, and EBT has a good response to viscosity. Furthermore, different concentrations of NTR (0-1.4 μg mL-1) were used to react with the probe and the reaction systems were subjected to different viscosity solutions, and the fluorescence signals of the products in the viscosity range of 45.86-163.60 cP were increased up to 1.69-fold. ENBT was successfully used to image NTR in cells under different hypoxic conditions as well as in Staphylococcus aureus. Finally, lipopolysaccharide was added to stimulate an increase in cellular viscosity after ENBT was catalyzed by intracellular NTR into EBT, and the fluorescence signals were observed to increase by 1.72-fold. The signal amplification capability gives ENBT higher sensitivity and immunity to interference. Moreover, it has the advantages of mitochondrial targeting, large Stokes shift (190 nm), high selectivity, and can be easily synthesized.

Photocontrolled Release of Carbendazim from Photocaged Molecule

Carbendazim (MBC) is a high-efficient and broad-spectrum fungicide, but excessive residues caused by its improper use have caused health toxicity and environmental pollution. It is an irresistible trend to find green, safe, accurate and controllable release technology of MBC. To achieve the purpose of safe and efficient use of MBC, photolabile protecting group was used to realize the controllable release. This study aimed to covalently link MBC and 6-nitropiperonyl alcohol (NP) to synthesize photocaged molecule NP-MBC. The photodegradation test showed that NP-MBC could effectively release MBC under ultraviolet light. The antifungal activity of NP-MBC showed significant difference against Rhizoctonia solani, Sclerotinia sclerotiorum and Fusarium graminearum before and after irradiation, and the effects on mycelial morphology are different. The hyphae morphology of R. solani and F. graminearum changed significantly, and mycelia were severely damaged. The hyphae surface of former was swollen and broken, and the latter was collapsed and shriveled after NP-MBC light treatment. NP-MBC could realize the light-controlled release of MBC, and the antifungal activity before and after irradiation was significantly different, which provides an effective way to release MBC.

Pattern Recognition and Visual Detection of Aldehydes Using a Single ESIPT Dye

The accurate discrimination and quantification of aldehydes is a worthy objective made challenging by their similar chemical reactivities. Considering the nucleophilic reaction mechanism between an aldehyde and a primary amine, it is reasonable to vary the reaction pH to manipulate the reactivity of aldehydes and the stability of the resulting Schiff base for analytical purposes. We have designed and synthesized three benzothiazole-based fluorescent molecules (BS1-BS3) containing an amino group substituted at the ortho-, meta-, and para-positions for aldehyde sensing. It was determined that only BS1 having an amino group at the ortho-position exhibits a significant fluorescence response in the presence of formaldehyde at a particular pH, whereas BS2 and BS3 gave negligible responses, indicating that the ESIPT process in BS1 should be responsible for the changes in its fluorescence. Accordingly, a pH-mediated sensor array BS1SA was constructed by dissolving BS1 in aqueous solvents with different pH values. BS1SA was found to be reliable for the discrimination of seven different aldehydes and identification of unknown aldehyde samples. Moreover, BS1 was successfully applied to prepare a fluorescent test paper for the visual detection of formaldehyde vapor.

Supramolecular Host-Guest Strategy for the Accelerating Detection of Nitroreductase

Identifying nitroreductase (NTR) with fluorescent techniques has become a research hotspot, due to its good sensitivity and selectivity toward the early-stage cancer diagnosis and monitoring. Herein, a host-guest reporter (NAQA⊂Zn-MPPB) is successfully achieved by encapsulating the NTR probe NAQA into a new NADH-functioned metal-organic cage Zn-MPPB, which makes the reporter for ultrafast detection of NTR within dozens of seconds in solution. The host-guest strategy fuses the Zn-MPPB and NAQA to form a pseudomolecule material, which changes the reaction process of NTR and NAQA from a double substrates mechanism to a single substrate one, and accelerates the reduction efficiency of NAQA. This advantage make the new host-guest reporter exhibit a linear relationship between emission changes and NTR concentration, and it shows better sensitively toward NTR than that of NAQA. Additionally, the positively charged water-soluble metal-organic cage can encapsulate NAQA in the cavity, promote it to dissolve in an aqueous environment, and facilitate their accumulation into tumor cells. As expected, such host-guest reporter displays a fast and high efficiently imaging capability toward NTR in tumor cells and tumor-bearing mice, and flow cytometry assay is conducted to corroborate the capability as well, implying the considerably potential of host-guest strategy for early tumor diagnosis and treatment.