Increase In Fluorescence Emission Research Articles

Probing Alzheimer's pathology: Exploring the next generation of FDDNP analogues for amyloid β detection

Fluorescent probes are a powerful tool for imaging amyloid β (Aβ) plaques, the hallmark of Alzheimer’s disease (AD). Herein, we report the synthesis and comprehensive characterization of 21 novel probes as well as their optical properties and binding affinities to Aβ fibrils. One of these dyes, 1Ae, exhibited several improvements over FDDNP, an established biomarker for Aβ- and Tau-aggregates. First, 1Ae had large Stokes shifts (138–213 nm) in various solvents, thereby reducing self-absorption. With a high quantum yield ratio (φ(dichloromethane/methanol) = 104), 1Ae also ensures minimal background emission in aqueous environments and high sensitivity. In addition, compound 1Ae exhibited low micromolar binding affinity to Aβ fibrils in vitro (Kd = 1.603 µM), while increasing fluorescence emission (106-fold) compared to emission in buffer alone. Importantly, the selective binding of 1Ae to Aβ1–42 fibrils was confirmed by an in cellulo assay, supported by ex vivo fluorescence microscopy of 1Ae on postmortem AD brain sections, allowing unequivocal identification of Aβ plaques. The intermolecular interactions of fluorophores with Aβ were elucidated by docking studies and molecular dynamics simulations. Density functional theory calculations revealed the unique photophysics of these rod-shaped fluorophores, with a twisted intramolecular charge transfer (TICT) excited state. These results provide valuable insights into the future application of such probes as potential diagnostic tools for AD in vitro and ex vivo such as determination of Aβ1–42 in cerebrospinal fluid or blood.

Liposomal nanoformulations with trans-caryophyllene and caryophyllene oxide: do they have an inhibitory action on the efflux pumps NorA, Tet(K), MsrA, and MepA?

This study aimed to evaluate the antibacterial and inhibitory action of NorA, Tet(K), MsrA and MepA efflux pumps in S. aureus strains using the sesquiterpenes named trans-caryophyllene and caryophyllene oxide, both isolated and encapsulated in liposomes. The antibacterial and inhibitory action of these efflux pumps was evaluated through the serial microdilution test in 96-well microplates. Each sesquiterpene and liposome/sesquiterpene was combined with antibiotics and ethidium bromide (EtBr). The antibiotics named norfloxacin, tetracycline and erythromycin were used. The 1199 B, IS-58, RN4220 and K2068 S. aureus strains carrying NorA, Tet(K), MsrA and MepA, respectively, were tested. In the fluorescence measurement test, K2068 S. aureus was incubated with the sesquiterpenes and EtBr, and the fluorescence emission by EtBr was measured. The tested substances did not show direct antibacterial activity, with MIC >1024 μg/mL. Nonetheless, the isolated trans-caryophyllene and caryophyllene oxide reduced the MIC of antibiotics and EtBr, indicating inhibition of NorA, Tet(K) and MsrA. In the fluorescence test, these same sesquiterpenes increased fluorescence emission, indicating inhibition of MepA. Therefore, the sesquiterpenes named trans-caryophyllene and caryophyllene oxide did not show direct antibacterial action; however, in their isolated form, they showed possible inhibitory action on NorA, Tet(K), MsrA and MepA efflux pumps. They may also act in antibiotic potentiation. Further studies are needed to identify the mechanisms involved in antibiotic potentiation and efflux pump inhibitory action.

Polydopamine functionalized dendritic fibrous silica nanoparticles as a generic platform for nucleic acid-based biosensing

Accurate and rapid detection of nucleic acid sequences is of utmost importance in various fields, including disease monitoring, clinical treatment, gene analysis and drug discovery. In this study, we developed a "turn-on" fluorescence biosensor that enables simple and highly efficient detection of nucleic acid biomarkers. Our approach involves the utilization of 6-carboxyfluorescein modified single-stranded DNA (FAM-ssDNA) as molecular recognition element, along with polydopamine-functionalized dendritic fibrous nanosilica (DFNS). FAM-ssDNA serves as both specific molecular recognition element for the target analyte and reporter capable of transducing a detectable signal through Watson–Crick base pairing. The polydopamine-functionalized DFNS (DFNS@DA) exhibits strong binding to FAM-ssDNA via polyvalent metal mediated coordination leading to effective quenching by fluorescence resonance energy transfer. In the presence of a complementary target sequence, FAM-ssDNA forms hybridized structure and detaches from DFNS@DA, which causes an increased fluorescence emission. The analytical system based on FAM-ssDNA and DFNS@DA demonstrates exceptional sensitivity, selectivity, and rapid response for the detection of nucleic acid sequences, leveraging the high adsorption and quenching properties of DFNS@DA. For the first proof of concept, we demonstrated the successful detection of microRNA (miR-21) in cancer cells using the FAM-ssDNA/DFNS@DA system. Our results highlight the promising capabilities of DFNS@DA and nucleic acid-based biosensors, offering a generic and cost-effective solution for the detection of nucleic acid-related biomarkers.Graphical abstract

Supramolecular complex of tetracationic porphyrin with acyclic cucurbituril-like container induces quantitative singlet oxygen generation. Phototoxicity studies in vitro in MCF-7 human breast cancer cells

Singlet oxygen generation by porphyrin-based photosensitizers is one of the main strategies used in the photodynamic therapy of cancerous lesions. In this work, we report that the complexation of tetracationic 5,10,15,20-tetrakis(N-methylpiridinium-4-yl)porphyrin (TMPyP) with an acyclic cucurbituril-like container denominated M2C4 achieves quantitative generation of singlet oxygen. The complexation was studied by isothermal titration calorimetry, revealing a highly favored binding event controlled by enthalpic contributions, a stoichiometry of 1:1 and a high binding constant (K = (1.7 ± 0.2) × 107 M−1). Photophysical studies of the complex showed bathochromic shifts in the absorption bands, increased fluorescence emission quantum yield and lengthened fluorescence lifetime. Nonetheless, fluorescence emission was minor, being intersystem crossing with the consequent generation of singlet oxygen the main deactivation pathway for the excited state. All these properties were compared with the previously reported TMPyP and cucurbit[7]uril (CB[7]) complex, which showed a superiority of the acyclic complex in terms of quantum efficiencies. Phototoxicity studies in a breast cancer cell line (MCF-7) cultured in vitro, showed that the TMPyP@M2C4 complex is unable to enter the cells even after a 24 h incubation period. However, this issue could be circumvented by encapsulating the complex into liposomes which delivered the complex to the cells efficiently. Overall, this strategy showed good potential for a highly efficient photodynamic treatment using the TMPyP@M2C4 complex in liposomal formulations.

A new lysosome-targeted fluorescent probe for hydrogen peroxide based on a benzothiazole derivative.

As an important member of reactive oxygen species, hydrogen peroxide (H2O2) plays a key role in oxidative stress and cell signaling. Abnormal levels of H2O2 in lysosomes can induce damage or even loss of lysosomal function, leading to certain diseases. Therefore, real-time monitoring of H2O2 in lysosomes is very important. In this work, we designed and synthesized a novel lysosome-targeted fluorescent probe for H2O2-specific detection based on a benzothiazole derivative. A morpholine group was used as a lysosome-targeted unit and a boric acid ester was chosen as the reaction site. In the absence of H2O2, the probe exhibited very weak fluorescence. In the presence of H2O2, the probe showed an increased fluorescence emission. The fluorescence intensity of the probe for H2O2 displayed a good linear relationship in the concentration range of H2O2 from 8.0×10-7 to 2.0×10-4 mol·L-1. The detection limit was estimated to be 4.6×10-7 mol·L-1 for H2O2. The probe possessed high selectivity, good sensitivity and short response time for the detection of H2O2. Moreover, the probe had almost no cytotoxicity and had been successfully applied to confocal imaging of H2O2 in lysosomes of A549 cells. These results illustrated that the developed fluorescent probe in this study could provide a good tool for the determination of H2O2 in lysosomes.

Hg(II) immobilization and detection using gel formation with tetra-(4-pyridylphenyl)ethylene and an aggregation-induced luminescence effect

Tetra-(4-pyridylphenyl)ethylene (TPPE), featuring an aggregation-induced luminescence effect (AIE), has been synthesized and used for selective detection of Hg2+ in DMF/H2O (3:7, v/v) binary solutions. There was a color change from colorless to yellow in the detection of the Hg2+ ions, in addition to an increased fluorescence emission. This shows that TPPE will function as an excellent “turn-on” fluorescence probe in the detection Hg2+. Moreover, the interference of Al3+, Ba2+, Mn2+, Ca2+, Fe3+, Cu2+, Ag+, Cd2+, Co2+, Ni2+, Mg2+, Pb2+, Zn2+, and Cr3+ ions was found to be negligible under optimized solvent conditions. Cysteine and EDTA were also found to form TPPE-based fluorescent switches with the Hg2+ ions. The practical use of the TPPE sensor was also demonstrated by using a specific test kit. Characterization using FT-IR, NMR titration, UV titration, EDS, and HR-MS techniques showed that Hg2+ will form a 1:1 complex with TPPE. Also, the observation of a Tyndall effect, in addition to UV absorption and fluorescence spectra, did clearly demonstrate the presence of an AIE. More noteworthy, TPPE and Hg2+ were found to form a metal–organic gel (MOG) in the DMF solution. The SEM, TEM, ICP, and Zeta potential analyses confirmed that the fluorescent MOG could further adsorb an excess of Hg2+ ions. The BET analyses revealed that the MOG showed a type IV-H3 hysteresis loop according to the International Union of Pure and Applied Chemistry classification. The results of the XRD analysis and of the spectroscopic titrations show that a π–π stacking may be the auxiliary driving force for the gel formation, after that a coordination has taken place. These results indicate that further research on structurally simple metal ion fluorescent probes, which are based on the AIE, is promising for the achievement of a simultaneous fluorescent detection and adsorption of heavy metal pollutants.

An Inorganic Fluorescent Chemosensor: Rational Design and Selective Mg2+ Detection.

A Zn2+ based complex, 3, displays greatly increased fluorescence emission in the presence of Mg2+. Fluorescent and computational studies suggest that 3 selectively interacts with Mg2+ due to optimal cavity size formation between two uncoordinated pyrazole side arms. This work thus represents a new approach to the development of fluorescent chemosensors.

Terpyridine-Grafted Nitrogen-Terminal Endowing Cyanine with Metal-Ion-Regulated Photophysical Properties for Cancer Theranostics.

Heptamethine cyanines (Cy7) are one of the most important dyes in bioimaging and phototherapy, but they often suffer from poor photostability or limited photothermal conversion efficiency. Here, a facile molecular engineering approach to regulating the photophysical properties of Cy7 by metal ions is demonstrated. By innovatively modifying the nitrogen with functional groups, a novel terpyridine-grafted nitrogen-terminated Cy7 scaffold (denoted as CydtPy) was synthesized and exhibited tunable photophysical properties when chelating with various metal ions (Mn2+, Fe2+, etc.). In comparison with metal-ion-free PEGylated CydtPy (LET-11), Mn2+-chelated LET-11 (namely, LET-11-Mn) exhibited the increased fluorescence emission intensity, and Fe2+-chelated LET-11 (namely, LET-11-Fe) showed the enhanced photostability with ~2-fold increase in photothermal conversion efficiency. By simply switching the chelated metal ion species, LET-11-Mn or LET-11-Fe could be used for near-infrared fluorescence imaging, magnetic resonance imaging, or photoacoustic imaging. Furthermore, LET-11-Fe displayed superior synergistic efficacy of photothermal therapy and chemodynamic therapy both in vitro and in vivo. This work not only provides a new strategy for regulating the photophysical properties of cyanine dyes but also establishes a versatile nanoplatform for cancer theranostics.

Non-Invasive Quantification of Layer-Specific Intrinsic Fluorescence From Mucosa of the Uterine Cervix Using Monte-Carlo-Based Models

Fluorescence spectroscopy has been demonstrated to non-invasively detect changes related to precursors of epithelial cancers, which include decreased fluorescence emission from collagen crosslinks in the connective tissue and increased fluorescence emission from reduced nicotinamide adenine dinucleotide (NADH) in the epithelial tissue. We implemented two-layer forward Monte Carlo models to predict diffuse reflectance and fluorescence intensities at the surface of cervical mucosa given tissue absorption, scattering, and fluorescence properties. The absorption and scattering coefficients of the upper epithelial layer and underlying connective tissue, as well as the epithelial thickness, were estimated from diffuse reflectance spectra using iterative curve fitting. The estimated parameters were used by the fluorescence forward model to obtain quantities needed to relate the intrinsic fluorescence of tissue fluorophores to measured fluorescence intensity. The emission spectra of tissue fluorophores were modeled by skew normal functions, and together with the efficiency of the fluorophores were extracted by fitting the modeled fluorescence spectra to measured spectra using the genetic algorithm. Compared to conventional one-layer forward models, the proposed two-layer models showed significantly smaller errors both in tissue properties estimated from simulated spectra, and in spectral errors of fitting to in-vivo data. Results of a preliminary in-vivo study showed that in seven of eight subjects with histopathologically confirmed dysplasia, the NADH-to-collagen intrinsic fluorescence ratio estimated from the biopsied site was at least two times greater than that estimated from the normal site on the same subject. The ability to more accurately estimate layer-specific intrinsic fluorescence from cervical mucosa could aid the detection of precancers in the cervix as well as other sites including oral and esophageal mucosae.

The Evolution of 5-Aminolevulinic Acid Fluorescence Visualization: Time for a Headlamp/Loupe Combination

The use of 5-aminolevulinic acid (5-ALA) for intraoperative protoporphyrin IX fluorescent imaging in the resection of malignant gliomas has been demonstrated to improve tumor visualization, increase the extent of resection, and extend progression-free survival. The current technique for visualization of 5-ALA consists of excitation and emission filters built into the operating microscope. However, there are notable limitations to this process, including low quantum yield, expense, and masking of surrounding anatomy. We present 3 cases in which 3 separate methods were employed for visualizing fluorescence. The devices reported are 1) a low-cost blue light flashlight, 2) a low-cost headlamp, and 3) the first reported case of the new Designs for Vision REVEAL Fluorescence-Guided Surgery (FGS) 5-ALA fluorescent headlight and loupes. The aim of the study is to provide confirmation that tumor fluorescence can be observed using commercially available products other than the microscope. We demonstrate through 3 intraoperative cases that a variety of devices can produce visible fluorescence of the high-grade tumor and allow for simultaneous real-time visualization of the adjacent brain parenchyma and vasculature. The REVEAL FGS system appears to offer increased fluorescence emission compared with all other methods, including the microscope. Our study demonstrates the feasibility of using blue/ultraviolet light supplied by a commercially available, inexpensive flashlight or headlamp to visualize 5-ALA fluorescence in high-grade gliomas. We also provide the first documentation of the intraoperative use of the new Designs for Vision REVEAL FGS 5-ALA fluorescent headlight and loupes and report on the experience. Lack of an operative microscope capable of fluorescent illumination should not be a limiting factor in performing fluorescent-guided glioma resection.

Enhanced fluorescent sensing probe via PbS quantum dots functionalized with gelatin for sensitive determination of toxic bentazon in water samples

Fluorescent chemical sensors to detect materials, by increasing fluorescence emission and absorption or by shutting down, because they are nondestructive, the ability to show decomposed concentrations, fast response, high accuracy have been considered and used. In this research, a chemical sensor was synthesized PbS functionalized with gelatin quantum dots for the determination of toxic bentazon (BTZN) one of the most problematic pesticides polluting in water samples, and extremely harmful to humans and animals even at low concentrations. The calibration curve was linear in the range of (0.05 to 200.0 ng mL−1). The current response was linearly proportional to the BTZN concentration with a R2∼ 0.999. The standard deviation of less than (3%), and detection limits (3S/m) of the method (0.5 ng mL−1, in time 50 s, 325 nm) were obtained for sensor level response PbS Quantum Dot–Gelatin nanocomposites sensor with (99%) which is below the U.S. Health Advisory level. The observed outcomes confirmed the suitability recovery and a very low detection limit for measuring the BTZN. The method fluorometric introduced to measure BTZN in water samples was used and can be used for in different intricate matrices, the chemical PbS Quantum Dot–Gelatin nanocomposites sensor made it possible as an excellent sensor with good reproducibility.

Relationships between the Physicochemical Properties of Dissolved Organic Matter and Its Reaction with Sodium Borohydride.

The reaction of dissolved organic matter (DOM) with sodium borohydride has been used to understand the geographic origin of DOM and investigate the photophysical model underlying DOM's optical properties. However, the physicochemical properties of DOM (e.g., molecular size and charge) that influence the kinetics and ultimate reducibility of DOM by borohydride remain poorly characterized. Herein, we studied the kinetics of DOM-borohydride reactions by recording absorbance and fluorescence spectra at a high temporal frequency (every ∼10 min for 24 h) for a diverse set of DOM isolates of aquatic and soil origin. The reducibility of DOM by sodium borohydride (as judged by relative removal of initial absorbance) varied appreciably among the DOM samples studied, with soil humic substances being less reducible than aquatic humic substances and natural organic matter. While statistically significant correlations were found between the reducibility of DOM and descriptors of molecular size, these descriptors were not able to differentiate the reducibility of soil versus aquatic DOM isolates that had similar bulk properties. Thus, it appears that the extent of absorbance removal by borohydride is largely driven by the origin of the humic substance isolate (aquatic vs soil) instead of molecular size or charge. Borohydride reduction resulted in increased fluorescence emission across UV and visible excitation wavelengths. However, the enhanced emission at visible excitation decreased over a time period of hours to days, suggesting that reduction of an important subset of DOM chromophores is reversible. This reversibility in fluorescence emission is consistent with the small role of quinones in the absorbance of DOM but suggests a more important role for quinone-containing charge-transfer contacts in the fluorescence of DOM, particularly at visible excitation wavelengths.

(Invited) Photoluminescence Study of Carbon Nanomaterial Interactions with the Immune System

Carbon nanomaterials such as graphene and carbon nanotubes have attracted tremendous attention for various applications in science and technology. However, increasing use of carbon nanomaterials also necessitates careful scrutiny of their impact on human health. Understanding their interactions with different components of the innate immune system is of particular importance.Myeloperoxidase (MPO), a key enzyme released by neutrophils during inflammation, has been shown to catalyze the biodegradation of carbon nanomaterials. We investigated the changes in photoluminescence (PL) properties of graphene oxide (GO) and single-walled carbon nanotubes (SWCNT) during MPO degradation. Increased fluorescence emission was observed with the progression of enzymatic oxidation of GO as a result of the formation of graphene quantum dots (GQDs). In contrast, the fluorescence of surfactant-coated SWCNT was either quenched or remained almost unchanged (depending on the surfactant used) during 5-day degradation. The two different PL systems were combined as SWCNT/GO nanoscrolls into ratiometric fluorescence sensors to monitor MPO activity.Lipid metabolites play an important role in the immune response. We demonstrated a photo-induced cycloaddition reaction between oxygenated lipid metabolites containing enone functional group and SWCNTs. By creating covalent and tunable sp3 defects in the sp2 carbon lattice of SWCNTs, this photochemical reaction results in the gradual appearance of the bright red-shifted near-IR photoluminescence in SWCNTs.

Visual detection of viscosity through activatable molecular rotor with aggregation-induced emission

Food safety has become one of the urgent affairs in the global public health studies, and irregular viscosity is closely associated with the food spoilage extent. In this study, one kind of activatable molecular rotor (TPA-PBZ) based on triphenylamine derivates has been synthesized via the Schiff base condensation reaction. This rotor is comprised by donor-accepter conjugated structure, with aggregation induced-emission feature and a large Stokes shift of 160 nm in water. The rotation of aromatic rings in TPA-PBZ is restricted in high-viscosity microenvironment, with the gradually increasing fluorescence emission signal at 568 nm. Significantly, this rotor TPA-PBZ has successfully been applied not only in the determination of thickening effects of food gum, but also in the detection of viscosity enhancement during the liquid food spoilage process. This molecular rotor can be utilized as an intelligent monitor platform for food quality and safety inspection in viscosity-related conditions.

α-Amylase assay with starch–iodine–sodium fluorescein-based fluorometric method in human serum samples

A new fluorometric method was developed for the determination of α-amylase activity in human serum samples. Firstly, a saturated starch–iodine complex (SI) was prepared. The SI complex was combined with sodium fluorescein to form a starch–iodine–sodium fluorescein complex (SIF). As the SIF complex decomposes with the α-amylase enzymatic hydrolysis of starch, the intensity of its fluorescence emission increases. The α-amylase activity is determined using the increased fluorescence emission intensity following hydrolysis of the SIF complex by α-amylase. The optimum pH, optimum buffer concentration, optimum temperature, and interference effect were identified for the developed fluorometric measurement method. Under the optimum conditions, a linear calibration curve was obtained between 0.18 and 9.00 U/L for α-amylase. The α-amylase activity in the human serum sample was also determined by our prepared measurement system and compared with the result from a medical center. Both methods are in good agreement with each other. Because this newly developed fluorometric method for α-amylase activity in serum samples is inexpensive, easy to use, and carried out to detect a very low amount of human serum α-amylase with sensitivity, it can be proposed this method for alpha-amylase activity assay in all other biological samples.

Physicochemical and structural properties of lunasin revealed by spectroscopic, chromatographic and molecular dynamics approaches

Lunasin is a 43-amino acid peptide from seeds and grains with bioavailability in humans and potent chemotherapeutic action against several cancer cell lines. Here, we investigate new information about the physicochemical and structural properties of lunasin using circular dichroism (CD), fluorescence spectroscopy, electrospray ionization-ion mobility spectrometry-mass spectrometry (ESI-IMS-MS), size exclusion chromatography (SEC), molecular dynamics (MD), and bioinformatics. CD analysis and disorder prediction obtained by PONDR indicate that lunasin has a mostly unordered structure. Double wavelength [θ]222nm x [θ]200nm plot data suggests that lunasin is an intrinsically disordered peptide (IDP) in a pre-molten globule-like (PMG-like) state, while CD spectrum deconvolution and MD simulation indicate small β-strand content. The presence of residual structure was supported by loss of CD signal at 222 nm after treatment with urea and by increasing fluorescence emission upon bis-ANS binding. Lunasin also demonstrated stability to heating up to the temperature of 100 °C, as verified by CD. MD and CD analyses in the presence of TFE and MoRFpred prediction indicated the helix propensity of lunasin. ESI-IMS-MS data revealed that lunasin shows a propensity to form disulfide bonds at the conditions used. MD data also indicated that disulfide bond formation affects the adopted structure, showing a possible role of aspartyl-end in structure stabilization and compaction. In conclusion, our data support a characterization of lunasin as a peptide with an intrinsic disorder in a PMG-like state and reveal new aspects about its structural stability and plasticity, as well as the effects of disulfide bond formation and electrostatic attractions.

Quantifying the Thermodynamic Stability of Amyloid Fibrils

Amyloid fibrils are a pathological hallmark for several neurodegenerative disorders, including Alzheimer's and Parkinson's diseases. Whilst there has been extensive research into the formation and structural attributes of amyloid fibrils, attempts to develop pharmaceutical strategies to combat the affiliated diseases have thus far lacked success. An improved understanding of the fibril equilibrium and how it contributes to the formation of toxic species is hence required. Therefore, to try and better design potential therapeutics, further insights into the nature and origin of amyloid fibril stability is necessary. This work aims to increase our ability to quantify the thermodynamic stability of amyloid fibrils and extend the analysis to investigate the enthalpy and entropy of these systems. Standard protocols involve a laborious centrifugation-based assay using a monomer concentration readout to obtain fibril denaturation curves and generate stability approximations. Here we have focused on developing a novel assay for quantifying thermodynamic stability over multiple temperatures, in a high-throughput, sustainable and accessible manner. Our assay can be performed in a standard multi-well plate reader and utilises thioflavin-T emission as a readout as this dye is well-known to have increased fluorescence emission when bound to amyloid fibrils. The readout is non-destructive, allowing the plate to be equilibrated at each temperature of interest and read again, to obtain data at multiple temperature points. We have used this assay to analyse the stability of fibrils from three different proteins, including human lysozyme, insulin and α-synuclein, under physiological temperatures and demonstrate that very little temperature dependence is observed. This assay offers a facile, high-throughput method to quantify the stability of amyloid fibrils and has the added versatility that it can be extended to different amyloid species and can use various probes to monitor a range of species within the amyloid equilibrium.

Whole cell FRET immunosensor based on graphene oxide and graphene dot for Campylobacter jejuni detection

In this work a new fluorescence immunosensor with use of graphene oxide and graphene quantum dot for detection Campylobacter jejuni whole cell in food samples was designed. This biosensor was designed based on interaction of poly clonal antibody conjugated with graphene quantum dot with surface protein in Campylobacter jejuni cell membrane. Specific binding of graphene quantum dot with Campylobacter jejuni membrane leads to generate a distance among graphene dot and graphene oxide and fluorescence is ON. In lack of Campylobacter jejuni or in existence of other bacterial cells, distance between of graphene dot and graphene oxide is very low and graphene quantum dot fluorescence emission was OFF. Experiment revealed that step by step increase in bacterial target cells caused to gradually increased fluorescence emission and this process was linear. Limit of detection for this bacterial sensor was 10 CFU/ml and ability of this FRET immunosensor for Campylobacter jejuni sensing in comparison with other bacterial cells was significant. Also, this method for monitoring Campylobacter jejuni in poultry liver was applied and results revealed that this immunosensor could be used for analysis bacterial cell in food samples.

Photoinduced electron and energy transfer in an amphiphilic perylenetetracarboxylic diimide derivative/CdS self-assembled hybrid film

An amphiphilic perylenetetracarboxylic diimide derivative with four 4-tert-butylphenoxy substituents at the bay positions (named as TPDI) has been used as not only the functional organic materials but also the organic template for growth of CdS nanoparticles. The highly ordered TPDI/CdS hybrid film was obtained where the petals-like CdS nanocrystals with a uniform size (about 50 nm) grown on the surface of TPDI film successfully. The crystalline regions for CdS were identified to be hexagonal wurtzite. Examination by spectroscopic methods revealed TPDI molecules in both pure film and hybrid film all adopt a typical J-aggregation mode with a slight declining orientation angle with respect to the substrate from 24.8° to 21.9° after incorporation of CdS nanoparticles into the TPDI matrix. In particular, energy transfer from CdS to TPDI is established by both increased fluorescence emission intensity and fluorescence quantum yield of TPDI in the hybrid film. Furthermore, the enhanced conductivity and electron mobility are obtained for the hybrid film relative to those of the pure film based on current-voltage (I-V), field-effect transistor (FET) and photocurrent measurements. Unexpectedly, photo-induced electron-transfer from TPDI molecules to CdS nanocrystals is revealed through much more enhanced conductivity and electron mobility for the TPDI/CdS hybrid film relative to pure TPDI film upon 365 nm UV light irradiation. In only one TPDI/CdS hybrid system, the energy band alignment of TPDI and CdS nanoparticles makes evident possibility for electron transfer, while their electronic absorption and fluorescence emission features provide reasonability for both electron and energy transfer.

Synthesis, DNA binding and cytotoxic activity of pyrimido[4′,5′:4,5]thieno(2,3-b)quinoline with 9-hydroxy-4-(3-diethylaminopropylamino) and 8-methoxy-4-(3-diethylaminopropylamino) substitutions

Two new derivatives of pyrimido[4′,5′;4,5]thieno(2,3-b)quinoline (PTQ), 9-hydroxy-4-(3-diethylaminopropylamino)pyrimido[4′,5′;4,5]thieno(2,3-b)quinoline (Hydroxy-DPTQ) and 8-methoxy-4-(3-diethylaminopropylamino)pyrimido[4′,5′;4,5]thieno(2,3-b)quinoline (Methoxy-DPTQ) were synthesized and their DNA binding ability was analyzed using spectroscopy (UV–visible, fluorescence and circular dichroism), ethidium bromide dye displacement assay, melting temperature (Tm) analysis and computational docking studies. The hypochromism in UV–visible spectrum and increased fluorescence emission of Hydroxy-DPTQ and Methoxy-DPTQ in the presence of DNA suggested the molecule-DNA interaction. The association constants calculated from UV–visible and spectral titrations were of the order 104 to 106M−1. Circular dichroism studies corroborated the induced conformational changes in DNA upon addition of molecules. The change in the ellipticity was observed both in negative and positive peak of DNA, thus, suggesting the intercalation of molecules. The observed displacement of ethidium bromide from the DNA and increased Tm, upon addition of DNA confirmed the intercalative mode of binding. This was further validated by computational docking, which showed clear intercalation of molecules into the d(GpC)-d(CpG) site of the receptor DNA. Anticancer activities of these molecules are evaluated by using MTT assay. Both molecules showed antiproliferative activity against all the three cancer cells studied, with Hydroxy-DPTQ being more potential molecule among the two. IC50 value of Hydroxy-DPTQ and Methoxy-DPTQ were in the range of 3–5μM and 130–250μM, respectively.