Surface Amine Groups Research Articles

Preparation and In Vitro Characterization of Dendrimer-based Contrast Agents for Magnetic Resonance Imaging.

Paramagnetic complexes of gadolinium(III) with acyclic or macrocyclic chelates are the most commonly used contrast agents (CAs) for magnetic resonance imaging (MRI). Their purpose is to enhance the relaxation rate of water protons in tissue, thus increasing the MR image contrast and the specificity of the MRI measurements. Current clinically approved contrast agents are low molecular weight molecules that are rapidly cleared from the body. The use of dendrimers as carriers of paramagnetic chelators can play an important role in the future development of more efficient MRI contrast agents. Specifically, the increase in local concentration of the paramagnetic species results in a higher signal contrast. Furthermore, this CA provides a longer tissue retention time due to its high molecular weight and size. Here, we demonstrate a convenient procedure for the preparation of macromolecular MRI contrast agents based on poly(amidoamine) (PAMAM) dendrimers with monomacrocyclic DOTA-type chelators (DOTA - 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate). The chelating unit was appended by exploiting the reactivity of the isothiocyanate (NCS) group towards the amine surface groups of the PAMAM dendrimer to form thiourea bridges. Dendrimeric products were purified and analyzed by means of nuclear magnetic resonance spectroscopy, mass spectrometry, and elemental analysis. Finally, high resolution MR images were recorded and the signal contrasts obtained from the prepared dendrimeric and the commercially available monomeric agents were compared.

Palladium-containing graphene-like material: Synthesis and catalytic activity

A graphene-like material with surface amine groups is obtained by graphite oxide reduction with ethylenediamine. A catalyst for the hydrogenation of nitrocompounds and unsaturated hydrocarbons is created by depositing Pd nanoparticles on the graphene material. The aliphatic chain is found to prevent agglomeration of the graphene sheets, while the amine groups form the growth centers of palladium nanoparticles, allowing their uniform distribution and small size.

Amine hybrid aerogel for high-efficiency CO2 capture: Effect of amine loading and CO2 concentration

The objective of this research was to develop a high-performance CO2 adsorbent by a simple, cost-effective and environmental-friendly route based on amine hybrid aerogel. A new amine hybrid titania/silsesquioxane composite aerogel (AHTSA) was prepared by a one-pot sol-gel process followed by supercritical drying (SCD). The wet gel was obtained by orderly mixing all the reactants in a container without adding any catalyst. SCD was conducted without contaminant emission. Effects of amine loading and CO2 concentration on pores structure and CO2 adsorption performance of AHTSA were investigated. Higher amine loading leads to lower specific surface area and mesopore volume of AHTSA, due to the increase of large pores and diminishment of mesopores when increasing the amine loading. Resulting from the sharp decrease of the surface area, overdosing of the amine precursor negatively affects the surface amine content of AHTSA and thus reduces its CO2 adsorption capacity. High CO2 concentration favors the CO2 adsorption capacity and rate as concentrated CO2 favors the CO2 diffusion in the pore space of the adsorbent, enhances the interaction between CO2 and surface amine groups. The dry CO2 adsorption capacity of AHTSA increases from 1.64, 4.19 to 6.66mmol/g when the CO2 concentration of the mixture gas varies from ∼400ppm (air), 1% to 10%. Short adsorption halftime and high amine efficiency of AHTSA with different CO2 concentrations reveal that AHTSA is a dynamic and effective adsorbent for CO2 capture, even direct air capture.

Nanocomposites of nanosilica-immobilized-nanopolyaniline and crosslinked nanopolyaniline for removal of heavy metals

Two novel nanocomposites have been designed and synthesized using simple and green functionalization of nanosilica sorbent with nanopolyaniline and crosslinked nanopolyaniline, [Sil-Phy-NPANI] and [Sil-Phy-CrossNPANI]. The images of scanning electron microscopy (SEM) and high resolution transmission electron microscope (HR-TEM) confirmed the immobilization process and particle size in the range of 7.14–23.91nm. The two novel nano-structured silica composites have been further confirmed and evaluated by determination of surface area, Fourier transform-infrared (FT-IR) study and thermal gravimetric analysis (TGA). The sorption characteristics of [Sil-Phy-NPANI] and [Sil-Phy-CrossNPANI] versus nanosilica were compared toward Cu(II), Cd(II), Hg(II) and Pb(II) ions and investigated by the batch technique in presence of different pH values, contact times, composite dosages, initial metal ion concentrations and interfering ions. The optimum sorption conditions of these metal ions were identified in pH 6.0 or 7.0 as a result of complexation or ion exchange of the metal ions by surface amine and/or hydroxyl groups. The highest metal capacity values of Cu(II), Pb(II), Hg(II) and Cd(II) were characterized in the ranges 1650–1700, 900–1450, 800–1050 and 600–1350μmolg−1, respectively. Fast equilibrium time was obtained (15–20min) for sorption of the target metal ions. The sorption behaviors of metal ions by [Sil-Phy-NPANI] and [Sil-Phy-CrossNPANI] were reflected by Langmuir and Freundlich isotherm models. The designed nanocomposites were successfully applied for adsorptive removal of Cu(II), Cd(II), Hg(II) and Pb(II) from drinking tap water, sea water and wastewater samples with excellent recovery values.

Hydrothermally treated chitosan spontaneously forms water-soluble spherical particles stable at a wide pH range

ABSTRACTThe authors report the spontaneous formation of water-soluble chitosan-tartaric acid (CS-TA) spherical particles. Particles are formed by heating chitosan in the presence of tartaric acid under hydrothermal conditions. Tartaric acid serves as an ionic cross-linker, a depolymerizing agent, and a particle stabilizer in aqueous phase. The CS-TA particles exhibit superior colloidal stability at a wide pH range due to their surface charge tunability, which is due to the colocalization of surface hydroxyl, amine, and carboxyl groups. At physiological pH condition, particles have zwitterionic structure as determined by the zeta potential measurements. Still, CS-TA maintains colloidal stability at neutral pH due to the abundance of surface hydroxyl groups. As a proof-of-concept study, the CS-TA particles were labeled with a model insoluble cargo (fluorescein isothiocyanate [FITC]) to demonstrate their capacity for solubilizing hydrophobic drugs. The CS-TA/FITC conjugates were found to remain well dispersed at neutral pH, while maintaining FITC fluorescence properties.

Magnetic Nanoparticles in Medical Diagnostic Applications: Synthesis, Characterization and Proteins Conjugation

Background: Magnetic nanoparticles (NPs) used in biomedical applications should be discrete with small particle sizes, narrow size distribution and superparamagnetic. NPs can be tailored to target, through chemical bonds, specific organs, cells, or even molecular markers of different diseases in vivo, with suitable surface chemistry modification. Methods: Nanoparticles are synthesized by a low cost coprecipitation reaction of ferrous and ferric salts with alkaline solution. The characteristics of the NPs are modified by varying the addition rate of the alkaline solution. NPs surface is silica coated using a modified Stöbe method. The conversion of the surface hydroxyl groups into amino-groups is performed by two different alkoxysilanes and the silanization reaction is conducted either in Methanol – Glycerol environment at elevated temperature, or in water at room temperature. The surface amine groups of the NPs are further converted, either to aldehyde groups by glutaraldehyde, or to carboxyl groups using glutaric anhydride. Bovine Serum Albumin and Vena human natural immunoglobulin are used in order to study the protein conjugation capacity of the functionalized NPs. The amount of protein attached to the nanoparticles is determined by UV–Vis spectroscopy of the supernatant. Conjugation of synthesized nanoparticles to protein BSA is examined by FTIR spectroscopy. SDS-PAGE electrophoresis followed by protein immunoblotting is used to test the effect of nano-conjugation to the antibodies. Results: Superparamagnetic Fe3O4 nanoparticles with saturation magnetization 60emu/g, a mean diameter 8-12 nm and BET surface areas between 100-250 m2/gr are obtained with total time of addition of the base between 1-5 minutes. They are coated with a thin and nearly uniform silica (SiO2) layer with thickness 1-2 nm. The most appropriate source for surface functionalization with amino groups is 3-aminopropyltriethoxysilane (APTES), while the two silanization methods used, proved to be equally efficient. NPs with surface aldehyde groups display better conjugation capacity than NPs functionalized with carboxyl groups. The FTIR spectra of the protein conjugated NPs samples, contain the two main peaks, at 1529 cm-1 and 1661 cm-1, attributed to the amide bond of the protein, which confirms the conjugation of the protein to the NPs. During a SDS-PAGE electrophoresis - protein immunoblotting experiment, the antibodies, after being conjugated to the nanoparticles, are selectively attached to their antigen, which indicates of lack of significant conformation changes secondary to the conjugation process. Conclusion: The conjugation capacity of the optimized nanoparticles is higher for Ig antibody than for BSA protein, under similar reaction conditions. The conjugational efficacy and conformational stability and the effect on electrophoretic mobility of the antibodies conjugated to the nanoparticles are verified by protein immunoblotting. Keywords: Conjugation, magnetite, nanoparticles, proteins, silica coating, superparamagnetic.

Elastic Light Tunable Tissue Adhesive Dendrimers.

Development of bioadhesive formulations for tissue fixation remains a challenge. The major drawbacks of available bioadhesives are low adhesion strength, toxic byproducts, and complexity of application onto affected tissues. In order to address these problems, this study has developed a hydrogel bioadhesive system based on poly amido amine (PAMAM) dendrimer, grafted (conjugated) with UV-sensitive, 4-[3-(trifluoromethyl)-3H-diazirin-3-yl] benzyl bromide (PAMAM-g-diazirine). This particular diazirine molecule can be grafted to the surface amine groups of PAMAM in a one-pot synthesis. Diazirine functionalities are carbene precursors that form covalent crosslinks with hydrated tissues after low-power UV activation without necessity of free-radical initiators. The rheological properties and adhesion strength to ex vivo tissues are highly controllable depending on diazirine grafting, hydrogel concentration, and UV dose intensity fitting variety types of tissues. Covalent bonds at the tissue/bioadhesive interface provide robust adhesive and mechanical strength in a highly hydrated environment. The free flowing hydrogel conversion to elastic adhesive after UV activation allows intimate contact with the ex vivo swine tissue surfaces with low in vitro cytotoxicity observed, making it a promising bioadhesive formulation toward clinical applications.

Novel pH-responsive swing gate system for adsorption and controlled release of BTB and MG dyes using amine functionalized mesoporous SBA-15 silica

Adsorption of anionic bromothymol blue (BTB) and cationic malachite green (MG) dyes on mono-, di- and triamine/ammonium functionalized mesoporous SBA-15 silica was investigated. The adsorbents were prepared via a post-synthesis grafting method of SBA-15 material using 3-aminopropyltrimethoxysilane, [1-(2-aminoethyl)-3aminopropyl]trimethoxysilane and 1-[3-(trimethoxysilyl)-propyl]-diethylenetriamine, followed by acidification in HCl solution to convert the attached surface amine groups to positively charged ammonium moieties. The release of BTB and MG species from free amine or ammonium functionalized adsorbents was controlled by adjusting the pH of solution. This system is proposed to be used as delivery modulation design system in which an ionically controlled molecular gate is created by using free amine/ammonium functionalized mesoporous materials with pH-responsive groups at the pore outlets. Results showed that the functionalized amine/ammonium SBA-15 materials act as a swing gate system and allow controlled selective adsorption–release of BTB and MG adsorbents and resulted in clean separation between them.

Synthesis and Characterization of Chitosan-Coated Near-Infrared (NIR) Layered Double Hydroxide-Indocyanine Green Nanocomposites for Potential Applications in Photodynamic Therapy.

We designed a study for photodynamic therapy (PDT) using chitosan coated Mg–Al layered double hydroxide (LDH) nanoparticles as the delivery system. A Food and Drug Administration (FDA) approved near-infrared (NIR) fluorescent dye, indocyanine green (ICG) with photoactive properties was intercalated into amine modified LDH interlayers by ion-exchange. The efficient positively charged polymer (chitosan (CS)) coating was achieved by the cross linkage using surface amine groups modified on the LDH nanoparticle surface with glutaraldehyde as a spacer. The unique hybridization of organic-inorganic nanocomposites rendered more effective and successful photodynamic therapy due to the photosensitizer stabilization in the interlayer of LDH, which prevents the leaching and metabolization of the photosensitizer in the physiological conditions. The results indicated that the polymer coating and the number of polymer coats have a significant impact on the photo-toxicity of the nano-composites. The double layer chitosan coated LDH–NH2–ICG nanoparticles exhibited enhanced photo therapeutic effect compared with uncoated LDH–NH2–ICG and single layer chitosan-coated LDH–NH2–ICG due to the enhanced protection to photosensitizers against photo and thermal degradations. This new class of organic-inorganic hybrid nanocomposites can potentially serve as a platform for future non-invasive cancer diagnosis and therapy.

P-Hydroxy benzoic acid-conjugated dendrimer nanotherapeutics as potential carriers for targeted drug delivery to brain: an in vitro and in vivo evaluation

Dendrimers which are discrete nanostructures/nanoparticles are emerging as promising candidates for many nanomedicine applications. Ligand-conjugated dendrimer facilitate the delivery of therapeutics in a targeted manner. Small molecules such as p-hydroxyl benzoic acid (pHBA) were found to have high affinity for sigma receptors which are prominent in most parts of central nervous system and tumors. The aim of this study was to synthesize pHBA-dendrimer conjugates as colloidal carrier for site-specific delivery of practically water insoluble drug, docetaxel (DTX) to brain tumors and to determine its targeting efficiency. pHBA, a small molecule ligand was coupled to the surface amine groups of generation 4-PAMAM dendrimer via a carbodiimide reaction and loaded with DTX. The conjugation was confirmed by 1HNMR and FT-IR spectroscopy. In vitro release of drug from DTX-loaded pHBA-conjugated dendrimer was found to be less as compared to unconjugated dendrimers. The prepared drug delivery system exhibited good physico-chemical stability and decrease in hemolytic toxicity. Cell viability and cell uptake studies were performed against U87MG human glioblastoma cells and formulations exerted considerable anticancer effect than plain drug. Conjugation of dendrimer with pHBA significantly enhanced the brain uptake of DTX which was shown by the recovery of a higher percentage of the dose from the brain following administration of pHBA-conjugated dendrimers compared with unconjugated dendrimer or formulation in clinical use (Taxotere®). Therefore, pHBA conjugated dendrimers could be an efficient delivery vehicle for the targeting of anticancer drugs to brain tumors.

Sorption Characteristics of Mixed Molecules of Glutaraldehyde from Water on Mesoporous Acid-Amine Modified Low-Cost Activated Carbon: Mechanism, Isotherm, and Kinetics

The environmental discharge of inefficiently treated waste solutions of the strong biocide glutaraldehyde (GA) from hospitals has potential toxic impact on aquatic organisms. The adsorption characteristics of mixed polarized monomeric and polymeric molecules of GA from water on mesoporous acid-amine modified low-cost activated carbon (AC) were investigated. It was found that the adsorption strongly depended on pH and surface chemistry. In acidic pH, the adsorption mechanism was elaborated to involve chemical sorption of mainly hydroxyl GA monomeric molecules on acidic surface groups, while in alkaline pH, the adsorption was elaborated to involve both chemical and physical sorption of GA polymeric forms having mixed functional groups (aldehyde, carboxyl, and hydroxyl) on acidic and amine surface groups. The optimum pH of adsorption was about 12 with significant contribution by cooperative adsorption, elucidated in terms of hydrogen bonding and aldol condensation. Freundlich and Dubinin-Radushkevich models were fitted to isotherm data. The adsorption kinetics was dependent on initial concentration and temperature and described by the Elovich model. The adsorption was endothermic, while the intraparticle diffusion model suggested significant contribution by film diffusion. The developed low-cost AC could be used to supplement the GA alkaline deactivation process for efficient removal of residual GA aquatic toxicity.

Phosphate modulated permeability of mesoporous silica spheres: a biomimetic ion channel decorated compartment model.

Due to their high loading capacity, permeability modulation, and biological compatibility, mesoporous silica spheres provide a suitable system for mimicking cellular compartments. Herein, a surface amine group functionalized mesoporous silica sphere was developed as a biomimetic compartment model, in which the ion permeability could be well modulated through the external phosphate ion. The amine group was selectively modified on the surface of the mesoporous silica sphere in the presence of a template molecule (CTAB) in the mesochannel. The surface amine group was employed as a gatekeeper shell and the specific binding of the anionic phosphate with the amine groups reversed the surface charge from positive to negative and gated the permeability of the model cationic Ru(bipy)3 2+. Ion channel decorated compartment is one of the key architectual principles of the cell, which maintains a high local reagent concentration inside it via the high surface area interior, and its permeability is tuned by a collection of ligand-gated ion channels outside to ensure a metabolic balance. The permeability modulation in the mesoporous silica sphere closely resembles that observed in a biological ion channel decorated compartment in vivo. This protocol provides the possibility of simulating the process of ion permeability in biological compartments based on mesoporous silica spheres, and it also contributes to the design of artificial cells and bio-inspired responsive nanoreactors.

Surface Modification and Spectroscopic Characterization of TiO2Nanoparticles with 2-Aminoethyl Dihydrogen Phosphate

A common strategy for the surface modification of nano TiO2 and other metal oxide nanoparticles is based on anchor groups using chelating ligands that can carry additional functionalities. This would allow the exploration of further applications of these materials. In the present work, we report the modification of TiO2 nanoparticles from nano TiO2 (Degussa P-25) dispersion in distilled water in the presence of 2-aminoethyl dihydrogen phosphate, followed by removing the excess of the capping agent through washing with water. The surface functionalization and the kind of surface interaction were analyzed applying different characterization methods like CHN elemental analysis, thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), attenuated total reflectance (ATR-FTIR), X-ray powder diffraction (XRD) and 1H, 13C, 31P magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR), confirming the presence of modifying agent on the surface. In the study of modified nano TiO2 by MAS NMR spectroscopy, a distinct downfield shift for 31P signal has been seen comparing to the pure cappping agent due to P-O-Ti bond formation. The phosphate groups interact with the surface via quite strong covalent interaction, while according the analyses results, the surface amine groups remained uncoordinated.

Thermal luminescence quenching of amine-functionalized silicon quantum dots: a pH and wavelength-dependent study.

Understanding and resolving the mechanisms that affect the photoluminescence (PL) of Si QDs are of great importance because of their strong potential for optoelectronic and solar cell materials. In this article, the intrinsic exciton dynamics of water-dispersed allylamine-functionalized silicon quantum dots (Si QDs) have been explored as a function of temperature by means of steady-state and time-resolved PL spectroscopy. Significant PL quenching of Si QDs has been observed with increase in temperature from 278 K to 348 K. This thermal quenching is found to be a reversible process. The mechanism involves nonradiative reversible relaxation of conduction band electrons through the thermally-created temporary trap states. These temporary trap states arise due to the displacement of surface atoms from their regular positions at elevated temperature. Upon cooling, these surface irregularities relax back to their equilibrium positions with retrieval of the original PL intensity. It has been observed that the quenching mechanism is strongly influenced by the pH and excitation wavelength (λex). At pH 3.5, the quenching mechanism involves nonradiative relaxation of conduction band electrons through the thermally-created temporary trap states. However, at pH 7.4, the unprotonated surface amine groups introduce permanent nitrogen-related surface defects inside the bandgap of Si QDs. At elevated temperature, the conduction band electrons get trapped in these nitrogen-related surface defects through the involvement of thermally-created temporary trap states. Subsequent exciton recombination of these nitrogen-related defect states results in red-shifted green color luminescence. By using the Arrhenius equation we have estimated the activation energy of this nonradiative thermal relaxation process and it was found to be 138 and 139 meV at pH 3.5 and pH 7.4, respectively.

Functional PEG-PAMAM-tetraphosphonate capped NaLnF₄ nanoparticles and their colloidal stability in phosphate buffer.

Developing surface coatings for NaLnF4 nanoparticles (NPs) that provide long-term stability in solutions containing competitive ions such as phosphate remains challenging. An amine-functional polyamidoamine tetraphosphonate (NH2-PAMAM-4P) as a multidentate ligand for these NPs has been synthesized and characterized as a ligand for the surface of NaGdF4 and NaTbF4 nanoparticles. A two-step ligand exchange protocol was developed for introduction of the NH2-PAMAM-4P ligand on oleate-capped NaLnF4 NPs. The NPs were first treated with methoxy-poly(ethylene glycol)-monophosphoric acid (Mn = 750) in tetrahydrofuran. The mPEG750-OPO3-capped NPs were stable colloidal solutions in water, where they could be ligand-exchanged with NH2-PAMAM-4P. The surface amine groups on the NPs were available for derivatization to attach methoxy-PEG (Mn = 2000) and biotin-terminated PEG (Mn = 2000) chains. The surface coverage of ligands on the NPs was examined by thermal gravimetric analysis, and by a HABA analysis for biotin-containing NPs. Colloidal stability of the NPs was examined by dynamic light scattering. NaGdF4 and NaTbF4 NPs capped with mPEG2000–PAMAM-4P showed colloidal stability in DI water and in phosphate buffer (10 mM, pH 7.4). A direct comparison with NaTbF4 NPs capped with a mPEG2000-lysine-based tetradentate ligand that we reported previously (Langmuir2012, 28, 12861−1287022906305) showed that both ligands provided long-term stability in phosphate buffer, but that the lysine-based ligand provided better stability in phosphate-buffered saline.

Determination of surface amine groups on amorphous carbon nitride thin films using a one step covalent grafting of a redox probe

A fluorocarbonyl terminated ferrocene based redox probe was synthesized and characterized using infrared spectroscopy and nuclear magnetic resonance. It was then successfully grafted on various amorphous carbon nitride (a-CNx) samples (0.12≤x≤0.27) via the formation of a -CO-NH- type linkage with surface amine groups, whose spontaneous formation on the surface of a-CNx materials was thus proved and exploited. Cyclic voltammetry experiments were carried out in an acidic aqueous solution in the presence of this freely diffusing redox probe, in order to identify its electrochemical behavior. By comparison, CV experiments carried out on the modified a-CNx electrodes in the same blank electrolytic solution undoubtedly confirmed the presence of electroactive sub-monolayers, in spite of distortions of the resulting voltammograms. These latter were shown to reflect the influence of bulk atomic nitrogen content on the electrochemical reactivity of a-CNx materials. The grafted surface amine percentage deduced from the charge passed during oxidation of grafted ferrocene moieties was found to decrease from 6.5% for a-CN0.12 down to 1.1% for a-CN0.27. This trend is expected to reflect the trend in surface concentration of reactive amine groups as a function of bulk atomic nitrogen content.

Poly(amidoamine) and Poly(propyleneimine) Dendrimers Show Distinct Binding Behaviors with Sodium Dodecyl Sulfate: Insights from SAXS and NMR Analysis

We investigate the interactions of generation 3 (G3) poly(amidoamine) (PAMAM) and G3 poly(propylenimine) (PPI) dendrimers with sodium dodecyl sulfate (SDS) in aqueous solution. Size and structure of the dendrimer-SDS aggregates as a function of SDS/dendrimer molar ratio were revealed by SAXS and NMR. G3 PAMAM has a relatively open and dense-core structure, while G3 PPI with the same number of surface amine groups possesses a compact and uniform structure. Upon addition of SDS, much more SDS monomers were encapsulated in the interior of PPI rather than in PAMAM. More significant size increase in PAMAM-SDS aggregate is observed at low SDS concentrations, due to the binding of SDS on PAMAM surface and further assembly into larger supramolecular structures. Both noncooperative and cooperative binding of SDS on G3 PPI surface are observed, while only noncooperative binding is proposed on G3 PAMAM, due to its open surface and large surface group distance. The size of the PPI-SDS complex is larger than that of PAMAM-SDS at higher SDS concentrations. Within the investigated SDS concentrations, SDS exhibits much stronger interactions with G3 PPI than with G3 PAMAM. These results provide new insights into dendrimer-surfactant interactions and explain why PPI is much more cytotoxic than PAMAM.

Fluorescence “Turn On” Detection of Mercuric Ion Based on Bis(dithiocarbamato)copper(II) Complex Functionalized Carbon Nanodots

A new "turn on" fluorescence nanosensor for selective Hg(2+) determination is reported based on bis(dithiocarbamato)copper(II) functionalized carbon nanodots (CuDTC2-CDs). The CuDTC2 complex was conjugated to the prepared amine-coated CDs by the condensation of carbon disulfide onto the nitrogen atoms in the surface amine groups, followed by the coordination of copper(II) to the resulting dithiocarbamate groups (DTC) and finally by the additional coordination of ammonium N-(dithicarbaxy) sarcosine (DTCS) to form the CuDTC2-complexing CDs. The CuDTC2 complex at surface strongly quenched the bright-blue fluorescence of the CDs by a combination of electron transfer and energy transfer mechanism. Hg(2+) could immediately switch on the fluorescence of the CuDTC2-CDs by promptly displacing the Cu(2+) in the CuDTC2 complex and thus shutting down the energy transfer pathway, in which the sensitive limit for Hg(2+) as low as 4 ppb was reached. Moreover, a paper-based sensor has been fabricated by printing the CuDTC2-CDs probe ink on a piece of cellulose acetate paper using a commercial inkjet printer. The fluorescence "turn on" on the paper provided the most conveniently visual detection of aqueous Hg(2+) ions by the observation with naked eye. The very simple and effective strategy reported here facilitates the development of portable and reliable fluorescence nanosensors for the determination of Hg(2+) in real samples.

Monte-Carlo simulations of PAMAM dendrimer-DNA interactions.

We use Monte Carlo simulations to determine the influence of poly(amido amine) (PAMAM) dendrimer size and charge on its interactions with double-stranded DNA conformation and interaction strength. To achieve a compromise between simulation speed and molecular detail, we combine the coarse-grained DNA model of de Pablo et al. which resolves each DNA base using three beads - and thereby retains the double-helix structure - with a dendrimer model with resolution similar to that of the DNA. The resulting predictions of the effects of dendrimer generation, dendrimer surface charge density, and salt concentration on dendrimer-DNA complexes are in agreement with both experiments and all-atom MD simulations. The model predicts that DNA wraps a fully charged G5 or G6 dendrimer at low salt concentration (10 mM) similarly to a histone octamer, and for the G5 dendrimer, DNA super helices with both handednesses occur. At salt concentrations above 50 mM, or when a high fraction of dendrimer surface charges are neutralized by acetylation, DNA adheres but does not compactly wrap the dendrimer, in agreement with experimental findings. We are also able to simulate pairs of dendrimers binding to the same DNA strand. Thus, our mesoscale simulation not only elucidates dendrimer-DNA interactions, but also provides a methodology for efficiently simulating chromatin formation and other cationic macroion-DNA complexes.

One-step synthesis of uniform and biocompatible amine functionalized cobalt ferrite nanoparticles: a potential carrier for biomedical applications

For the first time a simple one step method has been developed for the synthesis of uniform, water dispersible, amine functionalized nanoparticles of size about 7 nm. The synthesis process was accomplished by refluxing Fe(acac)3 and Co(acac)2 in diethylene glycol and ethanolamine. The synthesized particles show superparamagnetism at room temperature. Amine functionalized nanoparticles exhibit good cell viability, which is above 94% at a concentration of 80 μg mL−1 in MCF7 and L929 cell lines. The bare and functionalized cobalt ferrite nanoparticles were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) techniques. Their magnetic properties were also studied by using a superconducting quantum interference device (SQUID) technique. The presence of surface amine groups, good aqueous dispersion stability and excellent biocompatibility make them a suitable candidate for biomedical applications.