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1.
The aim of this study was to investigate the interactions between poly(propylene imine) (PPI) dendrimers and 2′-/3′-O-(N′-methylanthraniloyl)-ATP (Mant-ATP). Mant-ATP was used as a model molecule. Purine and pyrimidine nucleoside analogues are antimetabolites commonly used in therapy for cancer. Drug molecules can complex with dendrimers in two ways: therapeutic agents may be attached in dendrimer interior or bind to functional groups on the surface. Drugs attached to nanoparticles are characterized by improved solubility, pharmacokinetics and stability. Here, we have used poly(propylene imine) dendrimers of the 4th and 5th generations (PPI G4 and PPI G5) with primary amino surface groups partially modified with maltose (PPI-m) or without modification (PPI). We assessed the efficiency of complex formation in relation to dendrimer generation, pH of solution and the type of dendrimer used. A double fluorimetric titration method was used to estimate the binding constant (K b ) and the number of binding centers per molecule of the binding agent (n). 相似文献
2.
Zhao J Tian S Wang Q Liu X Jiang S Ji X An L Jiang B 《The European physical journal. E, Soft matter》2005,16(1):49-56
The surface topography of thin diblock copolymer films is studied by atomic
force microscopy (AFM). With AFM an island-to-ribbon transition is observed
for symmetric polystyrene-b-poly (4-vinylpyridine) (PS-b-P4VP) on mica with
increasing solution concentration. Our study also demonstrates how the
formation of the pattern strongly depends on the copolymer composition based
on the volume fraction. The substrate and solvent used both have great
effects on the morphology of the thin films. Only by using highly polar
substrate (mica), can we gain regular pattern. The reason why the regular
islands cannot be obtained with symmetric PS-b-P4VP on graphite is also
explained. On mica using nonselective and selective solvents, a rather
regular pattern can be obtained. The difference is only in the solution
concentration for forming regular patterns. 相似文献
3.
Silva L.P. Lacava Z.G.M. Buske N. Morais P.C. Azevedo R.B. 《Journal of nanoparticle research》2004,6(2):209-213
The present study provides a comparative analysis of the size dispersity of magnetic nanoparticles (MNPs) within magnetic fluids as obtained from atomic force microscopy (AFM) and transmission electron microscopy (TEM). Whereas the mean particle diameter obtained from the AFM data presented a reduction of about 34% as compared to the value obtained from the TEM data, the standard deviation obtained from the AFM data is twice the value found from the TEM data. Similarities and differences in the size dispersity parameters are discussed in terms of sample preparation and tip characteristics. A two-dimensional mode for the deposition of the MNPs on top of the mica substrate is discussed as well. 相似文献
4.
Erker W Scheumann V Möller M Knoll W Rühe J Decker H 《Micron (Oxford, England : 1993)》2006,37(8):735-741
The high molecular mass respiratory protein of the tarantula Eurypelma californicum, a 4 × 6-mer hemocyanin, was investigated by atomic force microscopy (AFM). Various substrates and methods were evaluated for immobilization of individual hemocyanin molecules on a solid surface. Samples were imaged after physisorption on mica and self-assembled monolayers, and after chemisorption on Au(111) and N-hydroxy-succinimide (NHS) functionalized surfaces. AFM measurements were carried out preferable in solution and contact mode, but also in Tapping mode and on air-dried samples. Adsorption of the protein on mica followed by drying and carrying out the measurements in Tapping mode gave the best results. In the AFM images the four hexamers of the native 4 × 6-mer hemocyanin have been defined. The results were compared with independent available structural data and represent a validation case for this technique applied for the first time on such giant and complex molecules. As observable in images taken by transmission electron microscopy and also proposed from SAXS data, 4 × 6-mers could be found where the half-molecules are tilted against each other. This study is a step in resolving conformational heterogeneities, involved in oxygen binding of hemocyanins, at the single-molecule level by AFM. 相似文献
5.
When mixed together, DNA and polyaminoamide dendrimers form fibers that condense into a compact structure. We use optical tweezers to pull condensed fibers and investigate the decondensation transition by measuring force-extension curves (FECs). A characteristic force plateau (around 10 pN) and hysteresis between the pulling and relaxation cycles are observed for different dendrimer sizes, indicating the existence of a first-order transition between two phases (condensed and extended) of the fiber. Upon salt variation FECs change noticeably confirming that electrostatic forces drive the condensation transition. We propose a simple model for the decondensing transition that qualitatively reproduces the FECs and which is confirmed by atomic force microscopy images. 相似文献
6.
The poly(propylene imine) dendrimer DAB-dendr- (NH2)8 was hydrophobically modified with dodecanoyl end groups. The modified dendrimer was deposited onto mica by adsorption from solution and observed by atomic force microscopy. With the decrease of adsorption time, the modified dendrimer varied from continuous film to scattered islands. For the adsorption time of 20s the dendrimer formed a sub-monolayer thin film that contained many fractal aggregates of fractal dimension 1.80 that were > 1 microm in diameter and no more than 0.8nm thick. After 5 months at 1#1 , the initial fractal aggregates transformed into disks and other less-branched shapes with average heights of the domains of 0.6nm and 0.4nm, respectively. Formation of the fractal aggregates is explained by diffusion-limited aggregation. The slow reorganization of dendrimer molecules in the fractal aggregates occurs at a temperature well above the Tg of the dendrimer. 相似文献
7.
Polystyrene latex (PSL) nanoparticle (NP) sample is one of the most widely used standard materials. It is used for calibration of particle counters and particle size measurement tools. It has been reported that the measured NP sizes by various methods, such as Differential Mobility Analysis, dynamic light scattering (DLS), optical microscopy (OM), scanning electron microscopy (SEM) and atomic force microscopy (AFM), differ from each other. Deformation of PSL NPs on mica substrate has been reported in AFM measurements: the lateral width of PSL NPs is smaller than their vertical height. To provide a reliable calibration standard, the deformation must be measured by a method that can reliably visualize the entire three dimensional (3D) shape of the PSL NPs. Here we present a method for detailed measurement of PSL NP 3D shape by means of electron tomography in a transmission electron microscope. The observed shape of the PSL NPs with 100 nm and 50 nm diameter were not spherical, but squished in direction perpendicular to the support substrate by about 7.4% and 12.1%, respectively. The high difference in surface energy of the PSL NPs and that of substrate together with their low Young modulus appear to explain the squishing of the NPs without presence of water film. 相似文献
8.
Yonghai Song 《Applied Surface Science》2008,254(11):3306-3312
The structure of n-hexadecanoic acid (HA) multilayers formed by spreading an ethanol solution containing this molecule onto a freshly cleaved mica surface has been studied by atomic force microscopy (AFM). AFM images of multilayers obtained with different coating time showed that HA molecules first formed some sporadic domains on mica surface. With the proceeding of the coating process, these domains gradually enlarged and coalesced, until formed a continuous film finally. It was observed that HA molecules were always adsorbed on mica surface with tilted even-numbered layers structure. The height of the repeated tilted bilayer film was measured to be approximately 3.8 ± 0.2 nm, which implied a ∼60° tilt molecular conformation of the HA bilayers on mica surface. Phase image confirmed that the HA multilayers terminated with the hydrophilic carboxylic acid groups. The formation mechanism of the HA multilayers was discussed in detail. Thus, resulted hydrophilic surfaces are of special interest for further study in biological or man-made member systems. 相似文献
9.
Mesoporous SBA-15 was synthesized using rice husk ash (RHA) as the silica source and their defective Si-OH groups were grafted with tris(2-aminoethyl) amine (TREN) dendrimers generation through step-wise growth technique. The X-ray diffraction (XRD) and nitrogen adsorption/desorption results of parent SBA-15 obtained from RHA, suggests its resemblance with SBA-15 synthesized using conventional silica sources. Furthermore, the nitrogen adsorption/desorption results of SBA-15/TREN dendrimer generations (G1-G3) illustrates the growth of dendrimer inside the mesopores of SBA-15 and their CO2 adsorption capacity was determined at 25 °C. The maximum CO2 adsorption capacity of 5-6 and 7-8 wt% over second and third dendrimer generation was observed which is discernibly higher than the reported melamine and PAMAM dendrimers. The experimental CO2 adsorption capacity was found to be less than theoretically calculated CO2 adsorption capacity due to inter and intra molecular amidation as result of steric hindrance during the dendrimer growth. These SBA-15/TREN dendrimer generations also exhibit thermal stability up to 350 °C and CO2 adsorption capacity remains unaltered upon seven consecutive runs. 相似文献
10.
H. Klein W. Blanc R. Pierrisnard C. Fauquet Ph. Dumas 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(2):371-376
We report here a preparation for thin gold films on mica substrates. We have investigated the influence of the substrate temperature
and the evaporation rate on the morphology of the films. After careful outgasing of the substrate, 100 nm of Au is evaporated
onto the mica surface maintained at high temperature. After slow cooling, ex situ characterizations are performed using AFM and STM. For our purposes, the best compromise between roughness and grain size
is found to occur for an evaporation rate of 2 ?s-1 onto a mica substrate maintained at 460 C. We have used these substrates for STM and AFM study of decanethiol self-assembled monolayers (SAMs). We present results
for gold samples immersed for a few seconds in decanethiol solutions, revealing an incomplete organization of the films. The
organization process is discussed through comparison between AFM and STM data recorded on the SAMs. Then we present molecular
resolution STM pictures of ordered SAMs for longer immersion times.
Received 25 May 1999 相似文献
11.
Yangzhe Wu Yi Hu Jiye Cai Shuyuan Ma Xiaoping Wang Yong Chen Yunlong Pan 《Micron (Oxford, England : 1993)》2009,40(3):359-364
Atomic force microscopy (AFM) is a rapidly developing tool recently introduced into the evaluation of the age of bloodstains, potentially providing legal medical experts useful information for forensic investigation. In this study, the time-dependent, morphological changes of red blood cells (RBC) under three different conditions (including controlled, room-temperature condition, uncontrolled, outdoor-environmental condition, and controlled, low-temperature condition) were observed by AFM, as well as the cellular viscoelasticity via force-vs-distance curve measurements. Firstly, the data indicate that substrate types have different effects on cellular morphology of RBC. RBC presented the typical biconcave shape on mica, whereas either the biconcave shape or flattened shape was evident on glass. The mean volume of RBCs on mica was significantly larger than that of cells on glass. Surprisingly, the adhesive property of RBC membrane surfaces was substrate type-independent (the adhesive forces were statistically similar on glass and mica). With time lapse, the changes in cell volume and adhesive force of RBC under the controlled room-temperature condition were similar to those under the uncontrolled outdoor-environmental condition. Under the controlled low-temperature condition, however, the changes in cell volume occurred mainly due to the collapse of RBCs, and the curves of adhesive force showed the dramatic alternations in viscoelasticity of RBC. Taken together, the AFM detections on the time-dependent, substrate type-dependent, environment (temperature/humidity)-dependent changes in morphology and surface viscoelasticity of RBC imply a potential application of AFM in forensic medicine or investigations, e.g., estimating age of bloodstain or death time. 相似文献
12.
J. D. Wei I. Knittel C. Lang D. Schüler U. Hartmann 《Journal of nanoparticle research》2011,13(8):3345-3352
Biogenic magnetite nanoparticles (MNP) extracted from the magnetotactic bacterium Magnetospirillum gryphiswaldense MSR-1 have been systematically studied by atomic force microscopy (AFM) and magnetic force microscopy (MFM). Isolated single
MNP and chains of MNP were obtained from diluted MNP aqueous suspension dried on mica surfaces in a homogeneous in-plane magnetic
field. The size of the MNP was determined by employing AFM tip deconvolution procedures. The obtained result has been confirmed
by scanning electronic microscopy. Magnetic properties of isolated single MNP and chains of MNP in remanence and in the presence
of external magnetic fields were investigated by MFM. In particular, the magnetization reversal of a two-particle chain has
been revealed and the dipolar interaction between the MNP is estimated. The change in the magnetic contrast on application
of an external magnetic field is consistent with the hysteresis curve obtained by cantilever magnetometry. 相似文献
13.
Poly(amidoamine) (PAMAM) dendrimers are a novel class of spherical, well-designed branching polymers with interior cavities and abundant terminal groups on the surface which can form stable complexes with drugs, plasmid DNA, oligonucleotides, and antibodies. Amine‐terminated PAMAM dendrimers are able to solubilize different families of hydrophobic drugs, but the cationic charges on dendrimer surface may disturb the cell membrane. Therefore, surface modification by PEGylation, acetylation, glycosylation, and amino acid functionalization is a convenient strategy to neutralize the peripheral amine groups and improve dendrimer biocompatibility. Anticancer agents can be either encapsulated in or conjugated to dendrimer and be delivered to the tumor via enhanced permeability and retention (EPR) effect of the nanoparticle and/or with the help of a targeting moiety such as antibody, peptides, vitamins, and hormones. Biodegradability, non-toxicity, non-immunogenicity, and multifunctionality of PAMAM dendrimer are the key factors which facilitate steady increase of its application in drug delivery, gene transfection, tumor therapy, and diagnostics applications with precision and selectivity. This review deals with the major topics of PAMAM dendrimers including structure, synthesis, toxicity, surface modification, and also possible new applications of these spherical polymers in biomedical fields as dendrimer-based nanomedicine. 相似文献
14.
《Current Applied Physics》2020,20(12):1391-1395
Muscovite mica is a widely accepted substrate for scanning probe microscopy (SPM) investigations. However, mica has intrinsic properties that alter samples and obstruct their analysis due to free charges build-up, ionic exchange and water adsorption taking place at the surface. In addition to interfacial phenomena, there is a growing interest in electrostatic charges on insulators as they are crucial in diverse applications. Despite the high demand for studies of this nature, experimental set-ups capable of resolving charge build-up at the micro-scale are still scarce and technically limited. Here, we report the imaging of surface charge dissipation on freshly cleaved mica by Kelvin-probe Force Microscopy (KPFM). A local electrostatic charge micro-domain was generated by friction between an atomic force microscope (AFM) tip and mica, and its decay was tracked by two-dimensional mapping using KPFM. We found time-dependent charge dissipation, which is attributed to the adsorption of water molecules on mica surface. 相似文献
15.
Somsubhra Saha Manash Ghosh Bipan Dutta Joydeep Chowdhury 《Journal of Raman spectroscopy : JRS》2016,47(2):168-176
Highly sensitive surface‐enhanced Raman scattering active substrate obtained by self‐assembly of silver nanocolloids (AgNCs) in the bilayer Langmuir–Blodgett (LB) film of stearic acid (SA) has been reported. Rhodamine 6G (R6G) has been used as the probe molecule to test the efficacy of the as prepared substrate. Gigantic enhancement factors ~1012 orders of magnitude have been estimated from the surface‐enhanced resonance Raman scattering [SER(R) S] spectrum of R6G, which proves that the as prepared substrate is superior or comparable with silver nanoparticle as dried AgNC solutions on microscopic slides. The optical properties of the as prepared substrates have been envisaged by ultraviolet‐visible absorption spectra, while their morphological features are mapped through field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) images. A correlation has been drawn between the SER(R) S efficacy and the corresponding FESEM and AFM images of the as prepared substrates. Electric field distributions around the aggregated AgNCs have been estimated with the aid of three‐dimensional finite difference time domain simulation studies. Localized surface plasmon coupling between the nanoaggregated geometries may be altered by lifting the LB film of SA at various surface pressures. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
16.
Pedziwiatr E Shcharbin D Chonco L Ortega P de la Mata FJ Gómez R Klajnert B Bryszewska M Muñoz-Fernandez MA 《Journal of fluorescence》2009,19(2):267-275
Dendrimers have been proposed as new carriers for drug delivery. They have distinctive characteristics, such as uniform and
controlled size, monodispersity and modifiable surface group functionality, which make them extremely useful for biomedical
applications. In this study, the binding capacity of water-soluble carbosilane dendrimers was examined. A double fluorimetric
titration method with 1-anilinonaphthalene-8-sulphonic acid (ANS) was used to estimate the binding constant and the number
of binding centers per dendrimer molecule. The data obtained suggest that ANS interacts non-covalently with the dendrimers.
Second generation dendrimers have an open, asymmetric structure that allows them to encapsulate ANS. The ability of the polymers
to interact with DNA was assessed by an ethidium bromide (EB) displacement assay. All the dendrimers studied bound to DNA
in competition with EB, though the strength of binding varied. Dendrimer interactions with a protein (BSA) were tested using
fluorescence quenchers. The dendrimers caused no conformation change in the protein, indicating that interactions between
carbosilane dendrimers and BSA are weak and occur preferentially at the protein surface. 相似文献
17.
Ge S Pu Y Zhang W Rafailovich M Sokolov J Buenviaje C Buckmaster R Overney RM 《Physical review letters》2000,85(11):2340-2343
We report results of glass transition (T(g)) measurements for polymer thin films using atomic force microscopy (AFM). The AFM mode, shear modulation force microscopy (SMFM), involves measuring the temperature-dependent shear force on a tip modulated parallel to the sample surface. Using this method we have measured the surface T(g) of thin (17-500 nm) polymer films and found that T(g) is independent of film thickness (t>17 nm), strength of substrate interactions, or even presence of substrate. 相似文献
18.
The formation of Ag nanoparticles synthesized by homogeneous nucleation, stabilized by polymers (PVA and PVP) was monitored
by UV–Vis spectrophotometry and transmission electron microscopy. Our aim was to differentiate between the two main phases
of particle formation, i.e. nucleation and growth and to characterize their rates with the help of appropriate kinetic equations.
Time resolved spectrophotometric measurements revealed that particle formation is an autocatalytic process: a slow, continuous
nucleation phase (3–5 min) is followed by a rapid, autocatalytic growth phase where the maximal particle size is 5–7 nm. By
freezing the reaction mixture, the process of particle growth can be followed from 5 to 40 min on TEM pictures. The first
order rate constants were calculated and they are strongly depend on the polymer concentration. If the growing particles are
attached by PEI to the surface of a solid support, the formation of silver nanoparticles can also be followed by atomic force
microscopy (AFM) and we can control the particle growth on mica surface. The cross section analysis of the pictures show,
that the particle growing process can be also monitored at solid–liquid interface. 相似文献
19.
Dendrimers are a promising class of polymeric nanoparticles for delivery of therapeutics and diagnostics. Polyamidoamine (PAMAM) dendrimers have shown significant efficacy in many animal models, with performance dependent on surface functionalities. Understanding the effects of end groups on biological interactions is critical for rational design of dendrimer-mediated therapies. In this study, we quantify the cellular trafficking kinetics (endocytosis and exocytosis) of generation 4 neutral (D4-OH), cationic (D4-NH2), anionic (D3.5-COOH), and generation 6 neutral (D6-OH) PAMAM dendrimers to investigate the nanoscale effects of surface functionality and size on cellular interactions. Resting and LPS-activated microglia were studied due to their central roles in dendrimer therapies for central nervous system disorders. D4-OH exhibits greater cellular uptake and lower retention than the larger D6-OH. D4-OH and D3.5-COOH exhibit similar trafficking kinetics, while D4-NH2 exhibits significant membrane interactions, resulting in faster cell association but lower internalization. Cationic charge may also enhance vesicular escape for greater cellular retention and preferential partitioning to nuclei. LPS activation further improves uptake of dendrimers, with smaller and cationic dendrimers experiencing the greatest increases in uptake compared to resting microglia. These studies have implications for the dependence of trafficking pathway on dendrimer properties and inform the design of dendrimer constructs tailored to specific therapeutic needs. Cationic dendrimers are ideal for delivering genetic materials to nuclei, but toxicity may be a limiting factor. Smaller, neutral dendrimers are best suited for delivering high levels of therapeutics in acute neuroinflammation, while larger or cationic dendrimers provide robust retention for sustained release of therapeutics in longer-term diseases. 相似文献