14 results on '"Guangzhao Mao"'
Search Results
2. Influence of Nanoscale Surface Roughness on Colloidal Force Measurements
- Author
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Charles W. Manke, Yi Zou, Sunil Jayasuriya, and Guangzhao Mao
- Subjects
chemistry.chemical_classification ,Work (thermodynamics) ,Materials science ,Nanostructure ,Molecular Structure ,Surface Properties ,digestive, oral, and skin physiology ,Nanotechnology ,Surfaces and Interfaces ,Substrate (electronics) ,Polymer ,Condensed Matter Physics ,Nanostructures ,Surface-Active Agents ,Colloid ,chemistry ,Electrochemistry ,Surface roughness ,General Materials Science ,Colloids ,Particle size ,Particle Size ,Composite material ,Nanoscopic scale ,Spectroscopy - Abstract
Forces between colloidal particles determine the performances of many industrial processes and products. Colloidal force measurements conducted between a colloidal particle AFM probe and particles immobilized on a flat substrate are valuable in selecting appropriate surfactants for colloidal stabilization. One of the features of inorganic fillers and extenders is the prevalence of rough surfaces-even the polymer latex particles, often used as model colloidal systems including the current study, have rough surfaces albeit at a much smaller scale. Surface roughness is frequently cited as the reason for disparity between experimental observations and theoretical treatment but seldom verified by direct evidence. This work reports the effect of nanoscale surface roughness on colloidal force measurements carried out in the presence of surfactants. We applied a heating method to reduce the mean surface roughness of commercial latex particles from 30 to 1 nm. We conducted force measurements using the two types of particles at various salt and surfactant concentrations. The surfactants used were pentaethylene glycol monododecyl ether, Pluronic F108, and a styrene/acrylic copolymer, Joncryl 60. In the absence of the surfactant, nanometer surface roughness affects colloidal forces only in high salt conditions when the Debye length becomes smaller than the surface roughness. The adhesion is stronger between colloids with higher surface roughness and requires a higher surfactant concentration to be eliminated. The effect of surface roughness on colloidal forces was also investigated as a function of the adsorbed surfactant layer structure characterized by AFM indentation and dynamic light scattering. We found that when the layer thickness exceeds the surface roughness, the colloidal adhesion is less influenced by surfactant concentration variation. This study demonstrates that surface roughness at the nanoscale can influence colloidal forces significantly and should be taken into account in colloidal dispersion formulations.
- Published
- 2015
3. Immobilization and Molecular Interactions between Bacteriophage and Lipopolysaccharide Bilayers
- Author
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M P Jackson, Hitesh Handa, Guangzhao Mao, and Stephen J. Gurczynski
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Kinetics ,Microscopy, Atomic Force ,Bacteriophage ,Viral Proteins ,Electrochemistry ,General Materials Science ,Bacteriophage P22 ,Spectroscopy ,biology ,Liaison ,Chemistry ,Bilayer ,Temperature ,Force spectroscopy ,O Antigens ,Surfaces and Interfaces ,Condensed Matter Physics ,biology.organism_classification ,Immobilized Proteins ,Membrane ,Biochemistry ,Biophysics ,Adsorption ,Bacterial outer membrane ,Biosensor - Abstract
The paper describes immobilization methods of bacteriophage P22 and tailspike gp9 proteins isolated from P22 on atomic force microscope (AFM) probes. The paper also reports single molecule force spectroscopy (SMFS) using AFM of the immobilized P22 (or gp9) interactions with substrate-supported O-antigenic lipopolysaccharides (LPS) bilayers. LPS covers the outer membrane of gram-negative bacteria, such as Salmonella typhimurium. Evidence from AFM imaging and SMFS shows that immobilized P22 (or gp9) are capable of strong and multivalent binding to supported LPS. The most common rupture forces between P22 and LPS were identified to be 72, 130, 206, and 279 pN at force loading rate of 12,000 pN/s. The quantized unbinding force was found to decrease with decreasing force loading rate as predicted by the Bell model. By fitting the force data with the Bell model, an energy barrier of 55 kJ/mol was obtained. Evidence is also provided that demonstrates the resilience of phage to pH and temperature fluctuation as well as dehydration/rehydration cycles. The biospecific interactions between P22 and the LPS are relevant to cell infection, inflammation, cancer progression and metastasis, food safety, pharmaceuticals, and biosensor development.
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- 2010
4. DNA Release Dynamics from Reducible Polyplexes by Atomic Force Microscopy
- Author
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David Oupický, Lei Wan, Devika S. Manickam, and Guangzhao Mao
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chemistry.chemical_classification ,Bioconjugation ,Chemistry ,Stereochemistry ,Peptide ,Surfaces and Interfaces ,Gene delivery ,Condensed Matter Physics ,Polyelectrolyte ,chemistry.chemical_compound ,Plasmid ,Electrochemistry ,Biophysics ,NLS ,General Materials Science ,Spectroscopy ,DNA ,Nuclear localization sequence - Abstract
Controlled intracellular disassembly of polyelectrolyte complexes of polycations and DNA (polyplexes) is a crucial step for the success of nonviral gene delivery. Motivated by our previous observation of different gene delivery performances among multiblock reducible copolypeptide vectors (Manickam, D. S., and Oupický, D. Bioconjugate Chem. 2006, 17, 1395−1403), atomic force microscopy is used to visualize plasmid DNA in various decondensed states from reducible polypeptide polyplexes under simulated physiological reducing conditions. DNA decondensation is triggered by reductive degradation of disulfide-containing cationic polypeptides. Striking differences in DNA release dynamics between polyplexes based on polypeptides of histidine-rich peptide (HRP, CKHHHKHHHKC) and nuclear localization signal (NLS, CGAGPKKKRKVC) peptide are presented. The HRP and NLS polyplexes are similar to each other in their initial morphology with a majority of them containing only one DNA plasmid. Upon reductive degradation by d...
- Published
- 2008
5. Fibronectin Adsorption onto Polyelectrolyte Multilayer Films
- Author
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Guangzhao Mao, A. Pascal Ngankam, and Paul R. Van Tassel
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Materials science ,Microscopy, Atomic Force ,Allylamine ,Electrolytes ,Mice ,chemistry.chemical_compound ,Adsorption ,Electrochemistry ,Animals ,Humans ,Organic chemistry ,General Materials Science ,Thin film ,Spectroscopy ,Deposition (law) ,Cationic polymerization ,Antibodies, Monoclonal ,Surfaces and Interfaces ,Condensed Matter Physics ,Polyelectrolyte ,Fibronectins ,chemistry ,Chemical engineering ,Immunoglobulin G ,Layer (electronics) ,Macromolecule - Abstract
The Layer-by-layer deposition of positively and negatively charged macromolecular species is an ideal method for constructing thin films incorporating biological molecules. We investigate the adsorption of fibronectin onto polyelectrolyte multilayer (PEM) films using optical waveguide lightmode spectroscopy (OWLS) and atomic force microscopy (AFM). PEM films are formed by adsorption onto Si(Ti)O2 from alternately introduced flowing solutions of anionic poly(sodium 4-styrenesulfonate) (PSS) and cationic poly(allylamine hydrochloride) (PAH). Using OWLS, we find the initial rate and overall extent offibronectin adsorption to be greatest on PEM films terminated with a PAH layer. The polarizability density of the adsorbed protein layer, as measured by its refractive index, is virtually identical on both PAH- and PSS-terminated films; the higher adsorbed density on the PAH-terminated film is due to an adsorbed layer of roughly twice the thickness. The binding of monoclonal antibodies specific to the protein's cell binding site is considerably enhanced to fibronectin adsorbed to the PSS layer, indicating a more accessible adsorbed layer. With increased salt concentration, we find thicker PEM films but considerably thinner adsorbed fibronectin layers, owing to increased electrostatic screening. Using AFM, we find adsorbed fibronectin layers to contain clusters; these are more numerous and symmetric on the PSS-terminated film. By considering the electrostatic binding of a segmental model fibronectin molecule, we propose a picture of fibronectin adsorbed primarily in an end-on-oriented monolayer on a PAH-terminated film and as clusters plus side-on-oriented isolated molecules onto a PSS-terminated film.
- Published
- 2004
6. Nanoscale Aggregate Structures of Trisiloxane Surfactants at the Solid−Liquid Interface
- Author
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Randal M. Hill, Guangzhao Mao, and Jinping Dong
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Models, Molecular ,Materials science ,Aggregate (composite) ,Siloxanes ,Surface Properties ,Interface (Java) ,Nanotechnology ,Surfaces and Interfaces ,Microscopy, Atomic Force ,Silicon Dioxide ,Condensed Matter Physics ,Phase Transition ,Surface-Active Agents ,Electrochemistry ,Aluminum Silicates ,Graphite ,General Materials Science ,Hydrophobic and Hydrophilic Interactions ,Nanoscopic scale ,Spectroscopy ,Solid liquid - Abstract
The self-associating structures at the solid-liquid interface of three nonionic trisiloxane surfactants ((CH3)3SiO)2Si(CH3)(CH2)3(OCH2CH2)n OH (n = 6, 8, and 12), or BEn, are studied as a function of substrate properties by atomic force microscopy (AFM) imaging and force measurement. These trisiloxane surfactants are known as superwetters, which promote rapid spreading of dilute aqueous solutions on low-energy surfaces. This study also attempts to relate the BEn surface aggregate structures at the solid-liquid interface to their superwetting behavior. Four substrates are used in the study: muscovite mica, highly oriented pyrolytic graphite, and oxidized silicon wafer with and without a full monolayer of self-assembled n-octadecyltrichlorosilane (OTS). The concentration of BEn is fixed at 2 times the critical aggregation concentration (CAC). The BEn surfactants are only weakly attracted to hydrophilic surfaces, more on oxidized silicon than on mica. All three form ordinary planar monolayers on HOPG and OTS-covered oxidized silicon. The significance of surfactant adsorption on the AFM tip is investigated by comparing the force curves obtained by tips with and without thiol modification. The surface aggregate structures of the BEn surfactants correlate with their bulk structures and do not exhibit anomalous adsorption behavior. The adsorption behavior of the BEn superwetters is similar to that of the CmEn surfactants. Thus, our results confirm previous work showing that superwetting shares its main features with other classes of surfactants.
- Published
- 2004
7. Direct Study of C12E5 Aggregation on Mica by Atomic Force Microscopy Imaging and Force Measurements
- Author
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Guangzhao Mao and Jinping Dong and
- Subjects
Kelvin probe force microscope ,Chemistry ,Electrostatic force microscope ,Surface force ,Kinetics ,Analytical chemistry ,Surfaces and Interfaces ,Conductive atomic force microscopy ,Condensed Matter Physics ,Adsorption ,Pulmonary surfactant ,Electrochemistry ,General Materials Science ,Mica ,Spectroscopy - Abstract
Atomic force microscopy (AFM) was used to study the aggregation structure and kinetics of nonionic surfactant penta(oxyethylene) dodecyl ether (C12E5) on mica as a function of temperature. Surface forces and topographical images of surfactant aggregates at the liquid/solid interface were captured in the vicinity of 21 °C. The surfactant molecular aggregates were imaged by choosing an imaging force in the steric repulsion region so that the AFM tip was just outside the surface of the aggregates. At below 21 °C, C12E5 adsorbed as fragments of tens of nanometers in size. The fragments consist of 1−2 nm thick strongly adsorbed species and weakly adsorbed species extending as far as 15 nm from the substrate surface. The fragments gradually increased in number and attached to each other to form clusters connected in one dimension (strings) and two dimensions (networks). With increasing surface coverage, the surface force changed from a purely attractive one to one showing a repulsive force barrier. At above 21 ...
- Published
- 2000
8. Interactions, Structure, and Stability of Photoreactive Bolaform Amphiphile Multilayers
- Author
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H. Ted Davis, Helmut Ringsdorf, Yi-hua Tsao, Volker Hessel, Matthew Tirrell, and Guangzhao Mao
- Subjects
Double layer (biology) ,Chemistry ,Surface force ,Surfaces and Interfaces ,Condensed Matter Physics ,Polyelectrolyte ,Photopolymer ,Chemical engineering ,Monolayer ,Amphiphile ,Electrochemistry ,Surface roughness ,Organic chemistry ,General Materials Science ,Layer (electronics) ,Spectroscopy - Abstract
Ultrathin organic multilayer films are appealing to scientists not only because they serve as molecular level models but also because they can be transformed into superlattices through successive deposition of alternating layers of different materials. Cationic bolaform amphiphile and anionic polyelectrolyte multilayers were self-assembled from their aqueous solutions via electrostatic attraction. The bolaform amphiphile layers are photopolymerizable by UV irradiation. The mechanical and surface electrical properties of the multilayer film were studied by surface force measurements, and the surface topography was studied by atomic force microscopy. We observed an average increase in film thickness of 75 with each amphiphile and polyelectrolyte double layer deposition, a molecularly smooth first anchoring amphiphile layer, and nonuniform polyelectrolyte layers with a surface roughness of 30 A. The surface roughness was preserved in the multilayer deposition process and was reduced by adding salt to the polyelectrolyte solution. Photopolymerization increases the integrity of the first anchoring layer as well as the subsequent multilayers. It took less than 5 min to dissolve a monomeric amphiphile film in chloroform, but immersion of the UV-irradiated film in chloroform for 2 h only resulted in partial removal of film materials. The multilayer film is quite fragile especially for the first few layers. Controlling of the monolayer structure by selective variation of the amphiphile chemical structure may help to optimize the photopolymerization process.
- Published
- 1995
9. Monolayers of Bolaform Amphiphiles: Influence of Alkyl Chain Length and Counterions
- Author
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Volker Hessel, Matthew Tirrell, Yi Hua Tsao, Guangzhao Mao, H. Ted Davis, Jan Van Esch, and Helmut Ringsdorf
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chemistry.chemical_classification ,Stereochemistry ,Surface force ,Surfaces and Interfaces ,Condensed Matter Physics ,Surface tension ,chemistry ,Chemical physics ,Amphiphile ,Lyotropic ,Monolayer ,Electrochemistry ,Molecule ,General Materials Science ,Surface charge ,Spectroscopy ,Alkyl - Abstract
We have prepared self-assembled monolayers of novel cationic bolaform amphiphiles on negatively charged substrates. Most of these amphiphiles form smooth, defect-free monolayers which can be used to reverse the substrate surface charge and thus allow subsequent adsorption of anionic molecules and construction of multilayers. Atomic force microscopy, surface force measurement, and surface plasmon spectroscopy were combined to probe the molecular orientation and ordering, mechanical properties, and surface electrical properties of the monolayers. In addition, the amphiphile aggregation behavior at an air-water interface was studied by surface tension measurement, and lyotropic phase behavior was studied by polarization microscopy. Our study suggests that monolayer interfacial and bulk properties can be controlled to a certain degree by selective variation of amphiphile chemical structure, in particular, the alkyl chain length and the type of counterions. A n increase in alkyl chain length assists close-packing at the liquid-solid interface and self-assembly in a liquid medium due to a favorable hydrophobic free energy change. Exchange of halide ions with the strongly associating salicylate ions reduces electrostatic repulsion between head groups and also favors self-assembly and close-packing. Our study suggests that it is possible to overcome the dominance and limitation of the substrate electrostatic effect on monolayer structure by using amphiphiles with a strong inherent tendency for close-packing. Our observations contribute to the understanding of two-dimensional topochemical photopolymerization, multilayer deposition of alternating surface charges, modification of hydrophilic surface electrical properties, and in general, the dependence of monolayer architecture on molecular chemical structure and intermolecular forces.
- Published
- 1994
10. Self-assembly of photopolymerizable bolaform amphiphile mono- and multilayers
- Author
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Guangzhao Mao, Matthew Tirrell, Helmut Ringsdorf, H. Ted Davis, Volker Hessel, and Yi-hua Tsao
- Subjects
Stereochemistry ,Chemistry ,Bilayer ,Surface force ,Surface forces apparatus ,Surfaces and Interfaces ,Condensed Matter Physics ,Polyelectrolyte ,Surface tension ,Chemical engineering ,Amphiphile ,Monolayer ,Electrochemistry ,General Materials Science ,Self-assembly ,Spectroscopy - Abstract
Monoand multilayers of photopolymerizable bolaform amphiphiles and polyelectrolytes self-assembled onto mica from aqueous solution were studied by surface force measurement and atomic force microscopy. Multiple layers of positively charged amphiphiles self-assemble if a negatively charged polyelectrolyte is inserted between them. The layers can be photopolymerized with a high-pressure UV lamp. The atomic force microscopy images indicate that the photopolymerized amphiphile monolayer has a higher degree of order than the unpolymerized monolayer, although the latter possesses some long-range order. Mechanical properties of the system measured by the surface force apparatus indicate that a photopolymerized layer is more robust and demonstrate that the rigidity and integrity of the first anchoring layer greatly influence the stability of the multilayer. The interaction between polyelectrolyte layers in water can be either attractive or repulsive depending on the coverage of the polyelectrolyte on the amphiphile layer. The mica separation of a pair of opposed monolayers in contact in the presence of water is surprisingly small (25 A) compared to the thickness (78 A) of a bilayer composed of fully extended amphiphiles.
- Published
- 1993
11. Influence of Nanoscale Surface Roughness on ColloidalForce Measurements.
- Author
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Yi Zou, Sunil Jayasuriya, CharlesW. Manke, and Guangzhao Mao
- Published
- 2015
- Full Text
- View/download PDF
12. DNA Release Dynamics from Bioreducible Layer-by-Layer Films.
- Author
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Jenifer Blacklock, Guangzhao Mao, David OupickyÌ, and Helmuth MoÌhwald
- Subjects
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THIN films , *DNA , *CONDENSATION , *POLYAMINES , *SULFIDES , *CHEMICAL bonds , *POLYELECTROLYTES , *SOLUTION (Chemistry) - Abstract
DNA release dynamics from layer-by-layer (LbL) films is an important aspect to consider with regards to localized gene delivery systems. The rate of DNA release and the condensation state of DNA during release are of particular interest in the field of gene delivery. A hyperbranched poly(amido amine) (RHB) containing bioreducible disulfide bonds is used to form interpolyelectrolyte complexes with DNA during LbL film assembly. During film disassembly, DNA is released in physiologic conditions due to the reducing nature of the RHB. Uncondensed DNA deposited on the surface was compared to DNA condensed by RHB in polyplex form by using two types of LbL films, RHB/DNA/RHB and polyplex terminated films, RHB/DNA/polyplex. LbL films with up to three layers are used in order to facilitate high-resolution atomic force microscopy (AFM) imaging. X-ray reflectivity, ellipsometry, and Fourier transform infrared spectroscopy are also used. The film disassembly, rearrangement, and release of molecules from the surface due to thiolâdisulfide exchange is conducted in reducing dithiothreitol (DTT) solutions. Salt is found to accelerate the overall rate of film disassembly. Additionally, it was found that the polyplex layer disassembles faster than the DNA layer. The predominant intermediate structure is the toroid structure for the polyplex layer and the fiber bundle structure for the DNA layer during film disassembly. This study offers a simple means to modulate DNA release from LbL films by utilizing both condensed and uncondensed DNA in different layers. The study highlights nanostructures, toroids, and bundles as dominant intermediate DNA structures during DNA release from LbL films. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
13. DNA Release Dynamics from Reducible Polyplexes by Atomic Force Microscopy.
- Author
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Lei Wan, Devika S. Manickam, David Oupický, and Guangzhao Mao
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- 2008
- Full Text
- View/download PDF
14. Temperature-Reversible Ultrathin Films of N-Isopropylacrylamide Terpolymer Adsorbed at the Solid−Liquid Interface.
- Author
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Lei Wan, Harender S. Bisht, Ye-Zi You, David Oupicky, and Guangzhao Mao
- Published
- 2007
- Full Text
- View/download PDF
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