Novel triphenylamine-based fluorescent probe for specific detection and bioimaging of OCl−

Hypochlorite (OCl^?) plays important roles both in physiological and pathological processes, the detection of which is of great significance. Herein, a novel fluorescent probe based on the triphenylamine-type schiff base derivative (TPAD) was developed to detect OCl^?. Probe TPAD exhibited specific fluorescence response toward ClO^? with the fluorescence quenching rate up to 80%, and the detection limit was estimated to be 0.8?μM. The sensing mechanism study demonstrated that TPAD reacted with ClO^?via an oxidation process, which was evidenced by MS and NMR characterization. Moreover, owing to the excellent sensing properties and negligible cytotoxicity, TPAD was successfully applied in the bioimaging of OCl^? in living A549?cells.     

Properties of Dendrimer‐Encapsulated Pt Nanoparticles Doped Polypyrrole Composite Films and Their Electrocatalytic Activity for Glucose Oxidation

A type of novel electroanalytical sensing nanobiocomposite material was prepared by electropolymerization of pyrrole containing poly(amidoamine) dendrimers‐encapsulated platinum nanoparticles (Pt‐PAMAM), and glucose oxidase (GOx). The Pt nanoparticles encapsulated in PAMAM are nearly monodisperse with an average diameter of 3 nm, and they provide electrical conductivity. Polypyrrole acts as a polymer backbone to give stable and homogeneous cast thin films, and it also defines the electrical conductivity. Both Polypyrrole and PAMAM can provide a favorable microenvironment to keep the bioactivity of enzymes such as glucose oxidase. The homogeneity of GOx/Pt‐PAMAM‐PPy nanobiocomposite films was characterized by atomic force microscopy (AFM). Amperometric biosensors fabricated with these materials were characterized electrochemically using cyclic voltammetry (CV), electrochemical impedance spectra (EIS) and amperometric measurements in the presence of hydrogen peroxide or glucose. All those show the resultant biosensor sensitivity was strongly enhanced within the nanobiocomposite film. The optimized glucose biosensor displayed a sensitivity of 164 μA mM^?1 cm^?1, a linear range of 0.2 to 600 μM, a detection limit of 10 nM, and a response time of <3 s.     

High Sensitive Detection of Prostate Specific Antigen by Using Ferrocene Cored Asymmetric PAMAM Dendrimer Interface Screen Printed Electrodes

In this study, electrochemical immunosensors were developed for the detection of prostate specific antigen (PSA) using ferrocene (Fc) and polyamidoamine dendrimer (PAMAM) constructs. The biosensor fabrication was designed by modifying the screen‐printed gold electrode (Au) with ferrocene cored dendrimers (FcPAMAM) synthesized in three different generations. The self‐assembled monolayer principle was followed, to obtain sensitive, selective and disposable electrodes. Therefore, the Au electrodes were modified with cysteamine (Cys) to obtain a functional surface for FcPAMAM dendrimers to bind. Dendrimer generations were attached to this surface using a cross‐linker (glutaraldehyde) so that a suitable surface was obtained for binding of biological components. The Monoclonal PSA antibody (anti‐PSA) was immobilized on the Au electrode surface which coated with dendrimer, and (Au/Cys/FcPAMAM/anti‐PSA) biosensing electrode was obtained. The PSA detection performances of electrochemical impedance spectroscopy (EIS) and Amperometry based immunosensors exhibited very low detection limits; 0.001 ng mL^?1 and 0.1 pg mL^?1, respectively. In addition, EIS and Amperometry based biosensors using Au/Cys/FcPAMAM/anti‐PSA sensing electrode were represented excellent linear ranges of 0.01 ng mL^?1 to 100 ng mL^?1 and 0.001 ng mL^?1 to 100 ng mL^?1. In order to determine the applicability recovery and selectivity tests were performed using three different proteins in human serum.     

A fluorescence ratiometric sensor for hypochlorite based on a novel dual-fluorophore response approach

A fluorescence ratiometric sensor for OCl⁻ has been developed based on a novel dual fluorophore response approach. The sensor molecule contains a coumarin fluorophore and a rhodamine fluorophore, and the two fluorophores are directly linked to an OCl⁻ recognition group. The structure of the sensor was characterized by ESI-MS, NMR, and X-ray crystallographic analysis. Upon treatment with OCl⁻, both fluorophores in the sensor responded simultaneously at two separate optical windows, with large enhancement of the fluorescence ratio (I₅₇₈/I₅₀₁) from 0.01 to 39.55. The fluorescence ratios for the sensor showed a good linearity with the concentration of OCl⁻ in the range of 0.2–40 μM and the detection limits is 0.024 μM (S N⁻¹ = 3). Investigation of reaction products indicated that the sensor reaction with OCl⁻ produced two new fluorescent molecules, which were responsible for the fluorescence changes in two optical windows. In addition, the sensor showed high selectivity to OCl⁻ over other reactive oxygen species, reactive nitrogen species, cations, and anions. The sensor has also been successfully applied to detection of OCl⁻ in natural water samples with satisfactory recovery.     

A Triphenyl Amine‐Based Solvatofluorochromic Dye for the Selective and Ratiometric Sensing of OCl− in Human Blood Cells

A new visible‐light‐excitable fluorescence ratiometric probe for OCl^? has been developed based on a triphenylamine‐diamiomaleonitrile (TAM) moiety. The structure of the dye was confirmed by single‐crystal X‐ray analysis. It behaves as a highly selective and sensitive probe for OCl^? over other analytes with a fast response time (～100 s). OCl^? reacts with the probe leading to the formation of the corresponding aldehyde in a mixed‐aqueous system. The detection limit of the probe is in the 10^?8 M range. The probe (TAM) also exhibits solvatofluorochromism. Changing the solvent from non‐polar to polar, the emission band of TAM largely red‐shifted. Moreover, the probe shows an excellent performance in real‐life application in detecting OCl^? in human blood cells. The experimentally observed changes in the structure and electronic properties of the probe after reaction with OCl^? were studied by DFT and TDDFT computational calculations.     

Hypochlorite‐Mediated Modulation of Photoinduced Electron Transfer in a Phenothiazine–Boron dipyrromethene Electron Donor–Acceptor Dyad: A Highly Water Soluble “Turn‐On” Fluorescent Probe for Hypochlorite

A highly water‐soluble phenothiazine (PTZ)–boron dipyrromethene (BODIPY)‐based electron donor–acceptor dyad ( WS‐Probe ), which contains BODIPY as the signaling antennae and PTZ as the OCl^? reactive group, was designed and used as a fluorescent chemosensor for the detection of OCl^?. Upon addition of incremental amounts of NaOCl, the quenched fluorescence of WS‐Probe was enhanced drastically, which indicated the inhibition of reductive photoinduced electron transfer (PET) from PTZ to ¹BODIPY*; the detection limit was calculated to be 26.7 nm . Selectivity studies with various reactive oxygen species, cations, and anions revealed that WS‐Probe was able to detect OCl^? selectively. Steady‐state fluorescence studies performed at varied pH suggested that WS‐Probe can detect NaOCl and exhibits maximum fluorescence in the pH range of 7 to 8, similar to physiological conditions. ESI‐MS analysis and ¹H NMR spectroscopy titrations showed the formation of sulfoxide as the major oxidized product upon addition of hypochlorite. More interestingly, when WS‐Probe was treated with real water samples, the fluorescence response was clearly visible with tap water and disinfectant, which indicated the presence of OCl^? in these samples. The in vitro cell viability assay performed with human embryonic kidney 293 (HEK 293) cells suggested that WS‐probe is non‐toxic up to 10 μm and implicates the use of the probe for biological applications.     

Fluorophore-labeled Polyamidoamine (PAMAM) Dendritic Architectures: Synthesis and Fluorescence Sensing Properties

Novel polyamidoamine (PAMAM) dendrimers (G=0.5–2.5) with a naphthalene core unit have been prepared. They were found to display acid as well as metal ion sensitive fluorescence signal amplification, making them of potential use as chemosensing materials. PAMAM dendritic wedges as well as naphthalene-centered PAMAM dendrimers were characterized by FT-IR, ¹H and ¹³C NMR spectroscopic methods and elemental analysis.     

Dependence of Property of Silver Nanoparticles within Dendrimer-template on Molar Ratios of Ag+ to PAMAM Dendrimers

G5.0‐OH PAMAM dendrimers were used to prepare fluorescent silver clusters with weaker ultraviolet irradiation reduction method, in which the molar ratio of Ag⁺ to PAMAM dendrimers was the key factor to determine the geometry and properties of silver nanoparticles. The results showed that because of G5.0‐OH PAMAM dendrimers as strong encapsulatores, when the molar ratios of Ag⁺ to PAMAM dendrimers was smaller than 5, the obtained Ag_n clusters (n<5) had line structures and "molecular‐like" properties, which were highly fluorescent and quite stable in aqueous solution. Whereas when the molar ratios were between 5 and 8, the obtained Ag_n clusters were 2D structures and their fluorescence was weaker. When the molar ratio was larger than 8, the structure of silver nanoparticles was 3D and no fluorescence was observed from the obtained silver nanoparticles.     

Qualitative and quantitative analysis of poly(amidoamine) dendrimers in an aqueous matrix by liquid chromatography–electrospray ionization-hybrid quadrupole/time-of-flight mass spectrometry (LC-ESI-QTOF-MS)

This work introduces a liquid chromatography–electrospray ionization-hybrid quadrupole/time-of-flight mass spectrometry (LC-ESI-QTOF-MS)-based method for qualitative and quantitative analysis of poly(amidoamine) (PAMAM) dendrimers of generations 0 to 3 in an aqueous matrix. The multiple charging of PAMAM dendrimers generated by means of ESI has provided key advantages in dendrimer identification by assignation of charge state through high resolution of isotopic clusters. Isotopic distribution in function of abundance of isotopes ¹²C and ¹³C yielded valuable and complementarity data for confident characterization. A mass accuracy below 3.8 ppm for the most abundant isotopes (diagnostic ions) provided unambiguous identification of PAMAM dendrimers. Validation of the LC-ESI-QTOF-MS method and matrix effect evaluation enabled reliable and reproducible quantification. The validation parameters, limits of quantification in the range of 0.012 to 1.73 μM, depending on the generation, good linear range (R?>?0.996), repeatability (RSD?<?13.4 %), and reproducibility (RSD?<?10.9 %) demonstrated the suitability of the method for the quantification of dendrimers in aqueous matrices (water and wastewater). The added selectivity, achieved by multicharge phenomena, represents a clear advantage in screening aqueous mixtures due to the fact that the matrix had no significant effect on ionization, with what is evidenced by an absence of sensitivity loss in most generations of PAMAM dendrimers.

Amperometric Detection and Quantification of 8‐Hydroxy‐2′‐deoxyguanosine (8‐OHdG) Using Dendrimer Modified Electrodes

8‐Hydroxy‐2′‐deoxyguanosine (8‐OHdG) detection by high performance liquid chromatography (HPLC) with amperometric detection was studied using a Au electrode modified with different dendrimer based thin films. Gold electrode is thiol‐modified, forming self‐assembled monolayers on which different generation PAMAM dendrimers with terminal functional groups ? COOH and ? NH₂ have been attached using peptidic bonds. Results obtained in synthetic samples show low limits of detection and quantification for 8‐OHdG (1.2×10^?9 and 3.7×10^?9 M respectively), with matrix interference elimination, thus avoiding sample pretreatment. Best results are obtained with electrodes modified with aliphatic amino thiols and 3.5 and 4.5 generation carboxylated dendrimers (Au/AET/DG^3.5 and Au/AET/DG^4.5), demonstrating that these materials constitute a good alternative for 8‐OHdG determination in biological fluids.     

Cationic poly(amidoamine) dendrimers as additives for capillary electroseparation and detection of proteins

We examine the influence of cationic poly(amidoamine) (PAMAM) dendrimers on capillary electroseparation–UV analysis of proteins. PAMAMs adsorbing to the capillary surface suppressed the wall‐adsorption of proteins; meanwhile, PAMAMs added to the buffer exhibited selectivity toward proteins. Presence of 3×10^?4 g/mL PAMAM generation one (G 1.0) in 30 mM phosphate, at pH 2.6, rendered significant enhancement in separation efficiency; the merged peaks of myoglobin and trypsin inhibitor were separated. Moreover, the protein–dendrimer interactions changed the inherent UV absorbance profiles of proteins. UV–Vis study showed that the absorbance of cytochrome C and transferrin increased at the detection wavelength of 214 nm; their detection sensitivity enhanced by 2.44 and 2.01‐folds, respectively, with addition of 5×10^?4 g/mL PAMAM G 1.0.     

Cinnamoyl shell‐modified poly(amidoamine) dendrimers

Poly(amidoamine)(PAMAM) dendrimers with a cinnamoyl shell were prepared by reacting full generation PAMAM dendrimers (G=3.0) with 2‐chloroethanol and cinnamoyl chloride, which resulted in densely packed polymerizable unsaturated groups on the periphery. The cinnamoyl shell of the dendrimers dimerized when irradiated under a UV light by using 5‐nitroacenaphthylene as an initiator in dilute dimethylformamide (DMF). FTIR, ¹H NMR, UV‐Vis, SEC, and a viscosity test certified that the photocycloaddition of the cinnamoyl shell of the dendrimers took place within the molecules with the disappearance of double bond signals in the FTIR. ¹H NMR spectra as well as the intrinsic viscosity and polydispersity value of the products both before and after irradiation showed no difference. It was further found that the cinnamoyl shell‐modified dendrimers possessed fluorescence property, and the fluorescence intensity became stronger when the shell was photocyclized under UV‐ irradiation. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4147–4153, 2000     

Synthesis and photoresponsive study of azobenzene centered polyamidoamine dendrimers

A new series of novel polyamidoamine (PAMAM) dendrimers 4, 5 and 6 possessing azobenzene units specifically at the core were prepared and their reversible trans/cis photoisomerization properties were studied. PAMAM dendritic wedges as well as azo-based PAMAM dendrimers were fully characterized by means of FT-IR, NMR (¹H and ¹³C), mass spectrometry (MALDI-MS), thermogravimetric and elemental analysis.     

Ultrasensitive electrochemiluminescent immunoassay for morphine using a gold electrode modified with CdS quantum dots, polyamidoamine, and gold nanoparticles

We report on a novel electrochemiluminescent (ECL) immunoassay for the ultrasensitive determination of morphine by making use of a gold electrode which was modified with a nanocomposite film containing self-assembled polyamidoamine (PAMAM) CdS quantum dots and electrodeposited gold nanoparticles (Au-NPs). The highly uniform and well-dispersed quantum dots were capped with PAMAM dendrimers. Due to the synergistic effect of the modified quantum dots and the electrodeposited Au-NPs, the ECL response is dramatically enhanced. Under optimal experimental conditions, the immunoreaction between morphine and anti-morphine antibody resulted in a decrease of the ECL signal because of steric hindrance. The calibration plot is linear in the morphine concentration range from 0.2 to 180 ng?mL^?1, with a detection limit as low as 67 pg?mL^?1. The sensor was successfully applied to the determination of morphine in blood plasma. This kind of assay is expected to pave new avenues in label-free drug assays.

Synthesis of conjugates of β-cyclodextrin with polyamidoamine dendrimers and their molecular inclusion interaction with levofloxacin lactate

Polyamidoamine (PAMAM) dendrimers of different generations (G2 and G4) conjugated with β-cyclodextrin (β-CD), PAMAM (G2, G4)-CD, were synthesized using substitution reaction from mono-6-iodine-β-cyclodextrin and PAMAM dendrimers. The resulting molecular structures were characterized by NMR, IR. The molecular interaction between various dendrimers and levofloxacin lactate (LFL) were investigated by monitoring the fluorescence of LFL in the presence of dendrimers in buffer solution (pH 7.4) at 25?°C. It was found that the PAMAM (G2, G4)-CD possesses higher sensitizing ability than that of the corresponding parent dendrimers and natural β-CD, and increases concomitantly with the increases of generation and content of β-CD, suggesting that the PAMAM (G2, G4)-CD possesses stronger inclusion ability with LFL. The possible interaction mechanism between PAMAM-CD and LFL was proposed by ¹H NMR analysis and theoretical calculation. The results show that the LFL molecule is located at the amine end of dendrimer molecule and along the side of cyclodextrin cavities to form supramolecular complexes. Furthermore, results indicate that the main driving force of the complex could be attributed to the electrostatic interactions and hydrogen bonding between LFL and PAMAM-CD, as well as the synergistic effect of intermolecular forces.     

In Situ Synthesis of Imidazolium‐Crosslinked Ionogels via Debus–Radziszewski Reaction Based on PAMAM Dendrimers in Imidazolium Ionic liquid

This study reports a remarkably facile method to synthesize novel ionogels with imidazolium cycle crosslinks based on polyamidoamine (PAMAM) dendrimers via one‐pot, modified Debus–Radziszewski reaction in ionic liquid 1‐ethyl‐3‐methylimidazolium acetate ([EMIM][OAc]). High room temperature ionic conductivity (up to 6.8 mS cm⁻¹) is achieved, and more remarkably, it can still exceed 1 mS cm⁻¹ when the dendrimer content reached 70% because PAMAM dendrimers are completely amorphous with many cavities and the newly formed imidazolium crosslinks contains ions. The elastic modulus of these ionogels can exceed 10⁶ Pa due to the newly‐formed rigid imidazolium crosslinks. Crucially, these ionogels are robust gels even at temperatures up to 160 °C. Such novel ionogels with high ionic conductivity, tunable modulus, and flexibility are desirable for use in high‐temperature flexible electrochemical devices.     

Improvement of Selectivity and Stability of Amperometric Detection of Hydrogen Peroxide Using Prussian Blue‐PAMAM Supramolecular Complex Membrane as a Catalytic Layer

A novel hydrogen peroxide (H₂O₂) sensor was fabricated by using a submonolayer of 3‐mercaptopropionic acid (3‐MPA) adsorbed on a polycrystalline gold electrode further reacted with poly(amidoamine) (PAMAM) dendrimer (generation 4.0) to obtain a film on which Prussian Blue (PB) was later coordinated to afford a mixed and stable electrocatalytic layer for H₂O₂ reduction. On the basis of the electrochemical behaviors, atomic force microscopy (AFM) and X‐ray photoelectron spectra (XPS), it is suggested that the PB molecules are located within the dendritic structure of the surface attached PAMAM dendrimers. It was found that the PB/PAMAM/3‐MPA/Au modified electrode showed an excellent electrocatalytic activity for H₂O₂ reduction. The effects of applied potential and pH of solution upon the response of the modified electrode were investigated for an optimum analytical performance. Even in the presence of dissolved oxygen, the sensor exhibited highly sensitive and rapid response to H₂O₂. The steady‐state cathodic current responses of the modified electrode obtained at ?0.20 V (vs. SCE) in air‐saturated 0.1 mol L^?1 phosphate buffer solution (PBS, pH 6.50) showed a linear relationship to H₂O₂ concentration ranging from 1.2×10^?6 mol L^?1 to 6.5×10^?4 mol L^?1 with a detection limit of 3.1×10^?7 mol L^?1. Performance of the electrode was evaluated with respected to possible interferences such as ascorbic acid and uric acid etc. The selectivity, stability, and reproducibility of the modified electrode were satisfactory.     

Improved GFP gene transfection mediated by polyamidoamine dendrimer-functionalized multi-walled carbon nanotubes with high biocompatibility

The multi-walled carbon nanotubes (MWCNTs)-polyamidoamine (PAMAM) hybrid was prepared by covalent linkage approach, and characterized by transmission electron microscopy, Fourier transform infrared spectroscopy and ultraviolet-visible spectrometry. The PAMAM dendrimers were present on the surface of MWCNTs in high density, and the MWCNT-PAMAM hybrid exhibited good dispersibility and stability in aqueous solution. The interaction between MWCNT-PAMAM with plasmid DNA of enhanced green fluorescence protein (pEGFP-N1), intracellular trafficking of the hybrid, transfection performance and cytotoxicity to HeLa cells were evaluated in detail. We found that the MWCNT-PAMAM hybrid possessed good pEGFP-N1 immobilization ability and could efficiently delivery GFP gene into cultured HeLa cells. The surface modification of MWCNTs with PAMAM improved the transfection efficiency 2.4 and 0.9 times, and simultaneously decreased cytotoxicity by about 38%, as compared with mixed acid-treated MWCNTs and pure PAMAM dendrimers. The MWCNT-PAMAM hybrid can be considered as a new carrier for the delivery of biomolecules into mammalian cells. Therefore, this novel system may have good potential applications in biology and therapy, including gene delivery systems.     

Development of a new fluorescence ratiometric switch for endogenous hypochlorite detection in monocytes of diabetic subjects by dye release method

Increased oxidative stress in metabolic complications like type 2 diabetes, dyslipidemia and cardiovascular disorders exerts potential health hazards in many facets. Enhanced production of reactive oxygen species (ROS) due to increased oxidative stress promotes the damage of many biologically important macromolecules. Hypochlorous acid (HOCl), a microbicidal agent is also known to be an important ROS sub-species. An enhanced generation of endogenous HOCl due to diseased condition therefore can be detrimental to health. In present work, a new quinoline-diaminomaleonitrile based probe (HQMN) has been designed for the selective detection of hypochlorite. The probe in hand shows a selective ratiometric emission change towards OCl^?. The probe behaves as a highly selective and sensitive tool for the detection of OCl^? over other analytes with a fast response time (within 100 s). Bioimaging study revealed that HQMN can detect endogenous OCl^? in human monocytes and an increase in endogenous HOCl concentration has been witnessed in diabetic condition compared to healthy control. Thus HQMN can be used as an excellent fluorescent probe for dynamic tracking of hypochorite in living biological cells especially to identify diabetic conditions.     

Reaction‐Based Fluorescent Probe for Detection of Endogenous Cyanide in Real Biological Samples

Herein, two compounds ( 1 a and 1 b ) were rationally constructed as novel reaction‐based fluorescent probes for CN^? by making use of the electron‐withdrawing ability of the cyano group that was formed from the sensing reaction. Notably, this design strategy was first employed for the development of fluorescent CN^? probes. The experimental details showed that probe 1 a exhibited a fluorescence turn‐on response to CN^?, whereas other anions, biological thiols, and hydrogen sulfide gave almost no interference. The detection limit of probe 1 a for CN^? was found to be 0.12 μM . The sensing reaction product of 1 a with CN^? was characterized by NMR spectroscopy and mass spectrometry. TD‐DFT calculations demonstrated that the formed cyano group drives the intramolecular charge transfer (ICT) process from coumarin dye to the cyano group and thus the original strong ICT from the coumarin dye to the 3‐position pyridyl vinyl ketone substituent is weakened, which results in recovery of coumarin fluorescence. The practical utility of 1 a was also examined. By fabricating paper strips, probe 1 a can be used as a simple tool to detect CN^? in field measurements. Moreover, probe 1 a has been successfully applied for quantitative detection of endogenous CN^? from cassava root.