COLL 1 Molecular sieve immobilized enzymes Kenneth J. Balkus Jr.1, Thomas J. Pisklak2, and Minedys Macias-Guzman1. (1) Department of Chemistry and the UTD NanoTech Institute, University of Texas at Dallas, Richardson, TX 75083-0688, Fax: 972-883-2925, balkus@utdallas.edu, (2) Department of Chemistry, The University of Texas at Dallas
Mesoporous Molecular Sieves have been employed as host materials for small proteins and enzymes. The uniform pore size and architectures as well as the compositional variance available within this family of porous materials makes them attrative supports for enzyme catalysts. We have now extended the types of molecular sieve hosts for enzymes to include mesoporous titania and the hybrid framework mesoporous benzene silica, where the pore walls are defined by alternating silica and benzene rings. Additionally, a metal organic framework has also been employed for the first time as a support for enzyme catalysts. The potential for these molecular sieves to bahve in a synergistic fashion with the enzyme will be discussed. Examples using microperoxidase (MP-11) in various oxidation reactions will also be presented where both enhancment in catalyst stability and activity was observed.
COLL 2 New strategy for enzyme stabilization involving molecular evolution and immobilization in mesoporous materials Haruo Takahashi and Chie Miyazaki-Imamura, Biotchnology Lab, Toyota Central R&D Labs., Inc, 41-1 Yokomichi, Nagakute, Aichi-Gun, Aichi, Japan, Fax: +81-561-63-6498, e1092@mosk.tytlabs.co.jp
In recent years, mesoporous materials (FSM) with uniform pore diameters of 2-30nm have been synthesized. We showed that the surface characteristics of FSM and matching of the size of protein molecule to the pore diameter of FSM are essential for the stabilization of proteins. On the other hand, we increased the H2O2 stability of heme containing enzyme, manganese peroxidase (MnP), using the SIMPLEX (single-molecule-PCR-linked in vitro expression) system in the presence of hemin and chaperones. Stabilized MnP mutant was immobilized in FSM. Unstable amino acids located in outer surface region would be protected by immobilization in suitable FSM. But unstable amino acids around the H2O2 binding pocket were not protected by FSM. Mutant MnP showed the excellent H2O2 stability by immobilization, because the unstable amino acids around the H2O2 binding pocket were evolved to stable amino acids. The combination of molecular evolution and immobilization in suitable mesoporous materials would be important for the best stability of enzymes.
COLL 3 Applications of ultra-large pore sized mesoporous silica and carbon materials to asymmetric catalysis, bio-catalysis and biosensors Taeghwan Hyeon1, Jinwoo Lee1, Jungbae Kim2, Jaeyun Kim1, Hongfei Jia3, Moon-Il Kim4, Ja Hun Kwak2, Sunmi Jin1, Hyun-Gyu Park4, Ping Wang3, and Jay W. Grate2. (1) School of Chemical Engineering, Seoul National University, San 56-1, Shilim-dong, Kwanak-gu, Seoul 151-744, South Korea, Fax: 82-2-888-1604, thyeon@plaza.snu.ac.kr, (2) Pacific Northwest National Laboratory, (3) Department of Chemical Engineering, The University of Akron, (4) Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology
Hierarchically ordered mesocellular mesoporous silica materials (HMMS) were synthesized using a single structure-directing agent under a neutral condition. The mesocellular pores are synthesized without adding any pore expander, and the walls of cellular pores in HMMS are composed of SBA-15 type mesopores. HMMS were used as a host of enzyme immobilization. To improve the retention of enzymes in HMMS, we employed adsorption of enzymes followed by cross-linking using glutaraldehyde (GA) treatment. The resulting crosslinked enzyme aggregates (CLEAs) in HMMS show an impressive stability with an extremely high loading of enzymes. The activity of crosslinked CT aggregates in HMMS was 10 times higher than that of the adsorbed CT, which represents 74 time higher activity per weight of HMMS due to higher CT loading of CLEA-CT. Mesocellular carbon foam (MSU-F-C) possessing two different sized pores was employed as a host matrix for enzyme immobilization. Due to its unique structure, the MSU-F-C enabled high enzyme loading without serious mass transfer limitation, resulting in high catalytic efficiency. We used this enzyme immobilized MSU-F-C for glucose biosensor. We demonstrate the utility and efficacy of the mesoporous carbon foam by investigating the performance of the constructed glucose biosensor in terms of enzyme loading and sensitivity of the biosensor. We synthesized magnetic nanoparticle-grafted hierarchically ordered mesocellular mesoporous silica (HMMS), and used the material to magnetically-separable heterogeneous support system for homogeneous chiral ligands. The cinchona alkaloid-anchored on the magnetic hierarchically ordered mesocellular mesoporous silica (M-MMS) system was successfully applied to the repetitive use in catalytic asymmetric dihydroxylation. The immobilized ligand for asymmetric dihydroxylation exhibited almost the same activity and enantioselectivity for the reactions of several olefins as those obtained in the homogeneous reaction. Magnetically recovered ligand could be recycled eight times without any significant loss of yields or enantioselectivities through the use of an external magnet.
COLL 4 Enabling multienzyme biocatalysis using nanostructures Ping Wang, Chemical Engineering, The University of Akron, 200 E. Buchtel Commons, Akron, OH 44325, wangp@uakron.edu
Synergizing with materials chemistry, nanostructures have manifested a great potential in enabling unique biocatalysis beyond the scope of traditional immobilized enzymes. In addition to enzyme stabilization and activation, nanostructures were also proven powerful in manipulating protein-protein and protein-environment interactions, and thus effected unique multienzyme biotransformations. Specifically, we demonstrate that nano-sized pores can confine multienzyme systems in a molecular vicinity, and thus allow the co-immobilized cofactor shuttle between enzymes and realize multistep reactions. We also show that collision between nanoparticles can provide another mechanism to enable enzyme-cofactor-enzyme interactions and thus achieve multienzyme catalysis with immobilized enzymes. We expect that further advances in this area will eventually allow people to compose multienzyme reaction pathways at will to perform with greatly improved efficiency complicated biotransformations that are currently only possible with specific microbes.
COLL 5 Magnetic enzymes Ansyl Dyal, Department of Chemical and Biological Science and Engineering, Polytechnic University, New York, NY 11201, aulman@duke.poly.edu, and Abraham Ulman, Othmer Department of Chemical and Biological Sciences and Engineering, Polytechnic University, Six Metrotech Center, Brooklyn, NY 11201, aulman@duke.poly.edu
The stability and enzymatic activity of two magnetic enzymes is reported. Recoverable and reusable enzymes were prepared by immobilizing Candida rugosa -Fe2O3 nanoparticles. ThegLipase (E.C.3.1.1.3) on 20 ± 10 nm in diameter enzymatic activity of the immobilized lipase was determined by following the ester cleavage of p-nitrophenol butyrate. The covalently immobilized enzyme was stabile and active over 30 days. Four restriction endonucleases, Apa I (ATCC 9432), Sac I (ATCC 12767), Xba I (ATCC 11672) and Xho I (ATCC 13461), were -Fe2O3 nanoparticles through a hydrophilic spacer. Thesegfunctionalized on magnetic enzymes were tested for seven days, using the endonucleic reaction of the enzyme with pBluescript II KS/SK (+) phagemid vector DNA, and were found active. It is concluded that while placing a hydrophilic spacer between the enzyme and the nanoparticle is critical, the position of attachment to the enzyme probably defines its activity.
COLL 6 One-pot encapsulation of enzymes and nanoparticles using silica precipitating peptides Melanie M. Tomczak, Maneesh K. Gupta, and Rajesh R. Naik, Materials and Manufacturing Directorate, MLPJ Biotechnology Group, Air Force Research Laboratory, 3005 Hobson Way, Wright-Patterson Air Force Base, Dayton, OH 45433, rajesh.naik@wpafb.af.mil
The successful use of enzymes for applications in catalysis and sensors is dependent on the host material used for immobilization of the enzymes. One of the most widely used method for immobilizing enzymes is sol-gel silica encapsulation. Here we describe an alternative method that mimics the diatom biosilicification process for the entrapment of enzymes in a silica matrix using silica precipitating peptides. The entrapment process is a one-pot procedure wherein the silica matrix is synthesized using a peptide, in the presence of the enzyme to be immobilized. Larger macromolecules and nanoparticles were also found to be encapsulated using this approach. The encapsulated enzymes were found to be stable and also exhibited heat stability compared to the free enzyme.
COLL 7 Concerted enzyme immobilization within polycation-templated silica Joseph C. McAuliffe1, Wyatt C. Smith1, Donald E. Ward1, Karl Sanford1, and Thomas H. Lane2. (1) Genencor International Inc, 925 Page Mill Road, Palo Alto, CA 94304, jmcauliffe@genencor.com, (2) Dow Corning Corporation
We have developed a concerted and economical method for the immobilization of a variety of enzymes within a polycation-templated silicate matrix. The method, termed silicate coprecipitation, was developed during studies into the mechanisms through which diatoms and other marine organisms produce biosilicates under ambient conditions. The procedure involves the addition of enzyme/polycation solutions to buffered silicate solutions and produces a colloidal precipitate within seconds that can be collected and further processed into a variety of forms. We will present both the basic properties of enzymes immobilized by the silicate coprecipitation method, the nanostructure of the resulting materials and strategies for the optimization and scaled up synthesis of such biocatalysts.
COLL 8 Encapsulating enzymes using nanoparticle-assembled microcapsules Michael S. Wong, Department of Chemical and Biomolecular Engineering and Department of Chemistry, Rice University, 6100 Main St., MS-362, Houston, TX 77251-1892, mswong@rice.edu, and Vinit Murthy, Department of Chemical Engineering, Rice University
The immobilization of enzyme biocatalysts can be carried out through a number of established techniques, such as physical adsorption or covalent binding to a solid, porous matrix, entrapment, and encapsulation. In this talk, I will describe a new encapsulation method based on nanoparticle self-assembly chemistry. We found that, under specific solution conditions, polyelectrolytes (e.g., polyallylamine) form aggregates under the crosslinking action of a multivalent salt (e.g., EDTA), and these metastable aggregates act as templates around which NPs (e.g., tin oxide) deposit to form a multilayer-thick shell (Rana et al., Adv. Mater., in press). Enzymes are encapsulated by incorporating them within the polymer aggregates prior to shell formation. The synthesis conditions (room temperature, atmospheric pressure, near-neutral pH, water solvent, rapid formation) are highly suitable for the encapsulation of water-soluble compounds, as the method is easy to carry out, scalable, and non-damaging.
COLL 9 Controlling nano-scale chemical, structural, biological and tribological properties of surfaces via self-assembled monolayers Shaoyi Jiang, Department of Chemical Engineering, University of Washington, Seattle, WA 98195, Fax: 206-685-3451, sjiang@u.washington.edu
Self-assembled monolayers (SAMs) of various terminal groups will be presented for their preparation, characterization, and applications. Charged SAMs of N+(CH3)3, SO3-, NH2, and COOH are used to control protein orientation while SAMs of oligo(ethylene glycol) (OEG) and phosphorylcholine (PC) to control surface resistance to protein adsorption and bacterial adhesion/biofilm formation. Results show that protein adsorption is sensitive to nano-scale chemical and structural properties of a surface. Mixed ssDNA and OEG SAMs are used to create protein arrays. Results show that the DNA-based platform provides a simple, but yet robust method to create multiple functional spots on a sensor chip with high sensitivity and specificity. Furthermore, SAMs are used to control the formation of fibrin and collagen thin films, which in turn affect cell behavior. In addition, SAMs are also used to study adhesion and friction in bioMEMS.
COLL 10 Study of protein (Ferritin) binding kinetics onto the PEGylated Langmuir monolayers David W. Britt, Biological Engineering, Utah State University, 4105 Old Mail Hill, Utah State University, Logan, UT 84322-4105, dbritt@cc.usu.edu, and Revathi Pepalla, Biological Engineering Department, Utah State University
Surface (in-plane) imprinting of proteins onto fluid multi-component lipid monolayers is investigated at the air-water interface. Protein adsorption and patterning of Langmuir monolayers of pure and mixed, cationic dioctadecyldimethylammonium bromide (DOMA), nonionic methylstearate (SME), and poly(ethylene glycol) (PEG) bearing phospholipids is presented. Our earlier studies of protein patterning on SME-DOMA binary lipid monolayers demonstrated an increase in adsorption of negatively charged ferritin to the monolayers with increasing neutral SME content. However, desorption of protein from the monolayer to regenerate the protein induced lipid pattern was difficult due to protein-protein interactions on the monolayer template. The incorporation of poly (ethylene glycol) bearing lipids reduces the protein-protein interactions. A protein induced mushroom to brush transition of PEG results in more specific and well controlled distribution of binding pockets for ferritin, improving the binding site affinity and homogeneity. The number, size and distribution of binding sites or pockets for the protein can thus be tuned by controlling the molar ratios, miscibility and lateral mobility of the lipids.
COLL 11 Optimization of self-assembled PEG-based films using SPR imaging for drug-DNA binding studies Lauren K. Wolf, Dominic E. Fullenkamp, and Rosina M. Georgiadis, Department of Chemistry, Boston University, 590 Commonwealth Avenue, Boston, MA 02215, Fax: 617-353-6466, lkwolf@bu.edu
Assays for screening drug - target interactions are currently in widespread use and development. However, secondary screening techniques that measure kinetics and thermodynamics of drug-target binding are relatively limited. Surface plasmon resonance (SPR) spectroscopy, an in-situ, label-free technique, is ideal for such measurements, having the sensitivity to monitor drug binding to surface-immobilized probes in an array format. Here, we demonstrate that array SPR imaging can be used to monitor drug-DNA interaction kinetics and thermodynamics for a model intercalating drug (Actinomycin-D). The development of a sensor molecular film, which blocks non-specific drug-surface interactions, was vital to these kinetic measurements. SPR imaging was an invaluable technique for fabricating such rationally designed surfaces. Here, it was used to rapidly optimize DNA probe attachment to a self-assembled poly-ethylene glycol (PEG)-based monolayer. Carbodiimide chemistry was employed to produce optimized DNA probe coverages of ~4 x 1012 molecules/cm2. Optimized conditions were then applied to the production of array surfaces presenting multiple DNA sequences containing different binding sites. Actinomycin-D binding to these sites was measured simultaneously with SPR imaging and compared to solution-phase measurements.
COLL 12 Controlled grafting of sulfobetaine polymers on gold surfaces via atom transfer radical polymerization (ATRP) to prevent protein adsorption Zheng Zhang, Shengfu Chen, Yung Chang, and Shaoyi Jiang, Deptartment of Chemical Engineering, University of Washington, Seattle, WA 98195, Fax: 206-685-3451, zhangzh@u.washington.edu
Sulfobetaine polymers with different initiator densities, molecular weights or thicknesses were grafted onto gold surfaces using atom transfer radical polymerization (ATRP). Two approaches were evaluated to bind initiators on gold surfaces: the first is to react bromoisobutyryl bromide with hydroxyl terminated self-assembled monolayers (SAMs) to achieve higher initiator densities, while the second is to prepare ω-mercaptoundecyl bromoisobutyrate to form SAMs on the surfaces. The initiator density and packing of the SAMs were characterized using electron spectroscopy for chemical analysis (ESCA), atomic force microscopy (AFM) and ellipsometry. It was demonstrated from surface plasmon resonance (SPR) experiments that the density and preparation method of the initiator, and the molecular weight and thickness of the polymers have effects on the amount of fibrinogen adsorption.
COLL 13 Thin films of self-assembled collagen fibrils: Effect of mechanical properties on cell response Anne L. Plant, John T. Elliottt, Kurt Langenbach, Dennis McDaniel, and John T. Woodward, Biotechnology, National Institute of Standards and Technology, 100 Bureau Drive, stop 8313, Gaithersburg, MD 20899-8313, Fax: 301-330-3447, anne.plant@nist.gov
Self assembled monolayers provide a spatially and chemical homogeneous surface onto which the extracellular matrix protein, collagen, can be adsorbed and assembled. The resulting thin films are highly reproducible and structurally stable. Collagen assembles into supramolecular fibrillar structures on hydrophobic alkanethiol monolayers, but not on hydrophilic surfaces. These fibrillar structures can be tens to hundreds of nanometers in diameter, and larger fibrils appear to grow out of smaller fibrils. Compared to thick collagen hydrogels, thin films of collagen fibrils appear to provide an identical environment to cells, as determined by morphological and biochemical characterization of vascular smooth muscle cells. The concentration of collagen in solution determines the size of fibrils that will form at the surface. By controlling the relative density of larger and smaller fibrils, and by dehydrating fibrillar collagen films, we can study of the effect of nano-scale mechanical properties of collagen fibrils on cellular response.
COLL 14 Limits to surface sensitivity using electrochemical labels on DNA self-assembled monolayers Nathan S Swami, Department of Electrical Engineering, University of Virginia, 351 McCormick Road, PO Box 400743, Charlottesville, VA VA 22904, nswami@virginia.edu
Electroanalysis schemes with monolayer arrays in microfluidics systems, are well-suited to sample pre-concentration methods for high-sensitivity lab-on-chip applications. Using a two-potential electrochemical labeling method to simultaneously and independently detect the immobilization of DNA capture probe monolayers and its hybridization to complementary target molecules in real-time and in-situ, this study examines the limits to surface sensitivity for this electro-analysis method. Capture probe DNA molecules were immobilized at a saturation surface coverage of ~2E13 molecules/cm2, where hybridization rates are maximum. Microchips with monolayers immobilized in this manner were contacted in microfluidic chambers with successively reduced concentrations of target DNA (1 micromolar to 1 pM), and electrochemical analysis was performed to quantitatively assess the number of bound target molecules. In the concentration ranges of 1 micromolar to 10 nM of target DNA in solution, saturation signals suggest that all capture probe DNA were bound to target molecules. For target concentrations below 10 nM, signal from bound target molecules dropped in a linear manner with concentration, since hybridization kinetics were limited by its diffusion to the surface. At the detection limit in current sensitivity of ~250 fA, electrochemical signal from ~ 1E9-1E8 bound target molecules/cm2 could be discerned (~500 molecules on a 20 um electrode).
COLL 15 Self-assembled DNA monolayers: From fundamental properties to applications Rastislav Levicky, Gang Shen, Maria Francis A Gaspar, and Youlei Weng, Department of Chemical Engineering, Columbia University, RM 801 Mudd BLDG, 500 W. 120th ST. MC4721, New York, NY 10027, RL268@columbia.edu
Heterogeneous hybridization, in which nucleic acid strands tethered to a solid support bind complementary nucleic acid molecules from solution, underpins a variety of diagnostic technologies. We investigate self-assembled DNA monolayers on metal and dielectric supports. Chains ranging in size from oligonucleotides to gene-sized polymers have been site-specifically attached without detectable side reactions in an end-tethered, "polymer brush" geometry. On metal supports, polythiol-mediated anchoring can be used to provide highly permanent immobilization of the nucleic acid. The interfacial capacitance of end-tethered films of DNA chains has been investigated using electrochemical methods and the results interpreted within a polyelectrolyte film model. The observed trends with ionic strength and strand surface coverage generally agree with physical expectations for a polyelectrolyte brush, with the exception of an increase in capacitance with decrease in ionic strength observed for densest monolayers. X-ray photoelectron spectroscopy and dynamic light scattering serve as auxiliary characterization methods.
COLL 16 Mutifunctional protective self-assembled monolayers of modified silanes on oriented growth of ZnO nanorods on cotton fabrics R. H. Wang, J. H. Xin, and X. M. Tao, Nanotechnology Center for Functional and Intelligent Textiles and Apparel, Institute of Textiles & Clothing, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, Fax: 852-2773-1432, tcroger.rhwang@polyu.edu.hk
Oriented ZnO nanorods were synthesized on cotton fabrics and consequently modified silanes were self-assembled onto the treated substrates. The as-prepared ZnO nanorods were wurtzite structure and characterized using various techniques. The UV protective, water-repellent, and antibacterial properties were evaluated in this paper. It can be shown that the as-treated fabrics have excellent UV protection factors with 700 plus, superhydrophobicity, and completely antibacterial. This surface-finishing process might successfully be used to produce environmentally friendly self-cleaning surfaces.
COLL 17 Direct measurement of interactions in colloidal suspensions Clemens Bechinger, Physikalisches Institut, University of Stuttgart, Pfaffenwaldring 57, D-70550 Stuttgart, Germany, C.Bechinger@physik.uni-stuttgart.de
A controversial debate in colloidal science has been launched about ten years ago when several groups reported an unusual long-range attractive component in the pair potential of charge stabilized colloidal particles. This so-called like-charge attraction (LCA) was only observed in thin sample cells while the pair-interaction in unconfined suspensions has been experimentally confirmed to be entirely repulsive. Despite additional theoretical attempts to understand this phenomenon, however, LCA remains a persistent mystery. We reinvestigate the pair-potential U(r) of charged colloidal particles in confined and unconfined geometries. In contrast to previous experiments, we obtain U(r) directly between two silica spheres exposed to an extended optical trap. We demonstrate that optical artifacts caused by the imaging process can lead to minute distortions in the particle distances as obtained by digital video microscopy. Those distortions result in an apparent minimum in U(r) which agrees with respect to its position and depth with the features observed in LCA. After correction of these distortions we find - independent of the confinement conditions - entirely repulsive pair interactions which show good agreement with linearized mean field theories.
COLL 18 Structure, miscibility and slow dynamics in suspensions of colloids and polymers Kenneth S. Schweizer, Department of Materials Science and Engineering, University of Illinois, 1304 West Green Street, Urbana, IL 61801, Fax: 217-333-2736, kschweiz@uiuc.edu
Microscopic statistical mechanical theories have been developed and quantitatively applied to describe in a unified fashion the structure, thermodynamics, phase separation, gelation and viscoelasticity of hard sphere-nonadsorbing coil polymer suspensions. Demixing boundaries depend sensitively on (nano)particle-polymer size ratio and solvent quality. Short range depletion attractions induce large modifications of colloidal organization over multiple length scales. The nonequilibrium gelation boundary, elastic modulus and localization length exhibit power law dependences on size ratio and concentrations. Novel theories has been developed for activated barrier hopping, and deformation induced gel softening, yielding and shear thinning. Generalization to treat weak polymer-particle adsorption and interparticle DVLO interactions results in a complex competition between depletion aggregation, steric stabilization and bridging attraction. The equilibrium theory has been extended to treat nonadsorbing polymer rods and a qualitatively different shift of the demixing boundaries with size ratio is predicted.
COLL 19 Protein-protein interactions in polymer solutions: An experimental study of depletion forces André C. Dumetz, Eric W Kaler, and Abraham M. Lenhoff, Department of Chemical Engineering, University of Delaware, Colburn Laboratory, 150 Academy Street, Newark, DE 19716, Fax: 3028311048, dumetz@che.udel.edu
Polyethylene glycol (PEG) is commonly added to protein solutions to drive crystallization. The effects of PEG on protein-protein interactions in these systems are often interpreted in terms of a depletion mechanism following the Asakura-Oosawa (AO) depletion potential, despite significant deviations of the experimental conditions from those assumed by AO. These include use of semi-dilute PEG solutions and PEG molecules larger than the protein molecules. We have used self-interaction chromatography (SIC) to measure the second osmotic virial coefficient for three different proteins (ovalbumin, myoglobin, ribonuclease A) in PEG solutions of different molecular weights (400, 1000, 3350, 8000). The effect of PEG on the protein-protein interactions is modeled using both the AO and the more complete PRISM potentials. The AO potential is found to overpredict the effect of depletion interactions, whereas the PRISM potential agrees well with the experimental values.
COLL 20 Phase behavior of mixtures of oppositely charged proteinaceous nanoparticles Martien A. Cohen Stuart, Laboratory for Physical & Colloid Science, Wageningen University, Dreijenplein 6, Wageningen 6703HB, Netherlands, Martien.CohenStuart@wur.nl, Saskia Lindhoud, Laboratory for Physical Chemistry and Colloid Science, Wageningen University, P. Maarten Biesheuvel, Shell Global Solutions International b.v, and Renko de Vries, Chemical Engineering Department, University of Delaware
Solutions of colloidal spheres, with sizes from hundreds of nm down to a few nm have been used extensively as models for simple liquids. Vice versa, theories of simple liquids have been used to interpret experiments on dispersions of colloidal spheres, including solutions of globular proteins. Colloidal analogues of A+B mixtures, in which A-A and B-B interactions are repulsive but A-B interactions attractive have not been studied so much. In colloidal terms, this is the domain of heterocoagulation; in terms of simple liquids, this is the area of electrolyte fluids. We here present experimental data on the phase behavior of aqueous mixtures of oppositely charged globular proteins. In order to have a pair of oppositely charged particles which is as closely matched as possible, we used the positively charged protein lysozym, and its succinylated counterpart which is negative at neutral pH. In contrast to common heterocoagulation cases, this system is entirely reversible, and we interpret the experimental phase diagram with help of a thermodynamic model with one single adjustable parameter.
COLL 21 Interaction potentials between lipid membrane coated colloidal particles Jay T. Groves, Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720, Fax: 510-642-8821, JTGroves@lbl.gov
Fluid lipid bilayer membranes can be assembled onto the surface of silica particles by spontaneous fusion of unilamellar vesicles. In addition to providing a convenient way of controllably modifying the surface chemistry of colloids, the behavior of colloidal dispersions of these particles provides a sensitive probe of the membrane surface. We have recently developed bioanalytical assays for protein binding on membrane surfaces using the colloidal distribution as an observable readout (Nature 2004, 427, p. 139). In efforts to reveal the underlying mechanism of these structural transitions, we have measured the pair interaction potential between particles by inverting the pair distribution function at low monolayer area fractions. Using automated image acquisition systems, high-precision lateral position measurements were compiled for more than 100,000 individual particles for each distribution. We observe a long-range attractive potential between similarly charged particles; disruption of this interaction by protein binding leads to the aforementioned assay.
COLL 22 Colloidal particles coated and stabilized by DNA-wrapped carbon nanotubes Erik K. Hobbie and Barry J. Bauer, Polymers Division, National Institute of Standards and Technology, Stop 8542, 100 Bureau Drive, Gaithersburg, MD 20899-8542, erik.hobbie@nist.gov
Single-walled carbon nanotubes (SWNTs) are made hydrophyllic through coating and wrapping with short segments of single-stranded DNA (ssDNA) containing alternating guanine (G) and thymine (T) units. Small-angle neutron scattering (SANS) measurements on dilute to semi-dilute aqueous suspensions of these colloidal SWNTs raise interesting questions about the degree of nanotube dispersion, with power-law exponents suggestive of weak attractive interactions. The SWNT-ssDNA complexes also act as nanoparticle surfactant, stabilizing the interface between water and toluene, for example. We exploit this to make hydrophillic cross-linked polymer particles coated and stabilized by the ssDNA wrapped SWNTs. Near-infrared fluorescence microscopy demonstrates the band-gap fluorescence of these SWNT-coated particles, suggesting potential routes to novel platforms and applications. Light scattering and optical microscopy from index-matched suspensions of the SWNT-coated colloids are compared with similar measurements on colloids made with conventional surfactants.
COLL 23 Solvent and solute effects on aqueous solution properties of associating polymers Eleftheria Antoniou, Marina Tsianou, and Paschalis Alexandridis, Department of Chemical and Biological Engineering, University at Buffalo - The State University of New York, 304 Furnas Hall, Buffalo, NY 14260-4200, Fax: 716-645-3822
Polymers are widely used in aqueous media to provide structure, solubilization domains, and/or colloidal stability. Underlying these functions are inter- and intra-molecular interactions which depend on (i) the nature of the polymers, (ii) solution conditions (e.g., salinity, pH), and (iii) external stimuli (e.g., temperature, shear). The solution behavior and interactions of associating polymers can be profoundly affected by the presence in water of polar organic solvents and/or solutes which are ubiquitous in pharmaceutical and coating formulations. This presentation will highlight our ongoing phase behavior and rheological investigation of solvent and solute effects on polysaccharide polymers. The observed effects on the polymer conformation are correlated with the solubility parameter of the solvent/solute.
COLL 24 Temperature and pH dependent micellization of novel triblock copolymers Beth L. Caba1, Anita Y. Carmichael-Baranauskas1, Judy S. Riffle2, and Richey M. Davis3. (1) Macromolecular Science and Engineering Program, Virginia Tech, Blacksburg, VA 24061-0211, bcaba@vt.edu, (2) Department of Chemistry, Virginia Tech, (3) Department of Chemical Engineering, Virginia Tech
Novel PEO triblock copolymers composed of poly(ethylene oxide) (PEO) end blocks and a center block containing urethane and carboxylic acid groups form tunable micelles in water. As observed by dynamic light scattering, micellization is controllable using pH and temperature, with ionic strength playing a lesser role. At pH 7 and 25°C, the copolymers are fully soluble unimers (hydrodynamic radius RH~2 nm). At pH 2-3, protonation of the core carboxylic acid groups drives assembly of micelles with RH~10 nm over a range of temperatures (5-40°C). At pH 7, micellization is induced upon decreasing the temperature to below 10°C, which is consistent with micellization driven by hydrogen bonding. Increasing ionic strength screens repulsion in the core and favors micellization. We propose a simple model to describe micellization of these unique polymers as a balance between hydrogen bonding and electrostatic repulsion in the core and repulsion between PEO chains in the corona.
COLL 25 Fast dissolution of nonionic diblock copolymer assemblies by nonionic surfactants, and formation of Y-micelles with short arms Dganit Danino, Department of Biotechnology and Food Engineering, Technion - Israel Institute of technology, Haifa, Israel, Fax: 972 4 829 3399, dganitd@tx.technion.ac.il, Karin Shimoni, Department of Biotechnology and Food Engineering, Technion - Israel Institute of Technology, and Nily Dan, Department of Chemical and Biological Engineering, Drexel University
The self-assembly of block copolymers in solution have attracted much attention in recent years. The multiple morphologies they form as well as their special characteristics (greater rigidity and stability in comparison with small amphiphiles), led to the growing interest in using them in diverse applications. In order to further advance their use in diverse applications, it is important to study their self-assembly behavior and dynamics in the presence of small amphiphilic molecules.
Two commercial polybutadiene-co-ethylene oxide (PBd-PEO) diblock copolymers were investigated here, a vesicle-forming compound (P2903-BdEO) and a micelle-forming compound (P3017-BdEO), and their dissolution upon interaction with the small-molecule detergent Triton X-100. Using only uncharged compounds allowed us to focus on the structural and dynamic effects resulting exclusively from geometrical considerations. We employed various methods to systematically characterize the block copolymer/detergent interactions and to follow the morphological changes as a function of time. Coexistence of vesicles, threadlike micelles, and spherical micelles is seen in the P2903-BdEO/Triton X-100 system, until vesicles dissolution is completed, and spherical micelles are exclusively observed. In the P3017-BdEO/Triton X-100 system large spherical polymer micelles transform directly into smaller mixed micelles of uniform size. In both systems, addition of detergent into the polymeric assemblies results in the formation of structures of higher curvature. Interestingly, we found over a large range of compositions, coexistence of end-caps and branch points in the form of Y branched micelles with short arms. We show that this novel structure is due to inhomogeneous mixing, and may appear in a variety of mixed amphiphilic systems. Furthermore, we show that mixing between large block copolymers and small-molecule detergent is instantaneous, and the assemblies seen within seconds after mixing are identical to those observed after long periods of time (weeks and months), indicating that equilibrium is reached quickly.
COLL 26 (CdSe)ZnS and CdSe quantum dots: Surface chemistry comparative study Roger M Leblanc, Kerim M. Gattás-Asfura, and Xiaojun Ji, Department of Chemistry, University of Miami, 1301 Memorial Drive, Miami, FL 33124, Fax: 305-284-1880, rml@miami.edu
UV-Vis spectroscopy, Langmuir film properties, and imaging of Langmuir-Blodgett (LB) films by transmission electron microscopy (TEM) established an alternate approach for the determination of molar absorptivity of nanoparticles. A nearly quadratic dependence between molar absorptivity and nanoparticle size was determined for CdSe quantum dots (QDs). Limiting nanoparticle areas of the two different type of QDs were derived from the surface pressure-area (π-A) isotherms. The data revealed that trioctylphosphine oxide (TOPO) forms close-packed monolayers on the surface of the CdSe QDs, and that 1-octadecanethiol-capped CdSe undergo alkyl chains interdigitation. The photoluminescence (PL) intensity of the LB film of (CdSe)ZnS QDs at the first emission maximum was found to increase linearly with the number of layers deposited. It was also found that the 2D packing arrangement of the QDs could be engineered at the air-water interface. The factors studied included nature of surfactant, nanoparticle size, surface pressure, and mixed monolayers.
COLL 27 "Tandem self-assembly" of nanoparticles and charged polymer Michael S. Wong1, Rohit K. Rana2, Vinit Murthy2, and Jie Yu2. (1) Department of Chemical and Biomolecular Engineering and Department of Chemistry, Rice University, 6100 Main St., MS-362, Houston, TX 77251-1892, mswong@rice.edu, (2) Department of Chemical Engineering, Rice University
Prepared out of a wide spectrum of compositions with a high degree of particle size and shape control, nanoparticles (NPs) are an intriguing class of materials because their reduced physical dimensionality leads to the appearance of catalytic, chemical, optoelectronic, and magnetic properties not found in bulk materials. They remain rather difficult to handle for applications, though, due to their colloidal nature and their susceptibility to uncontrolled aggregation. We discovered that, under specific solution conditions, cationic polyelectrolytes can induce negatively-charged SiO2 NPs to form hollow sphere structures rather than the randomly structured precipitate that would ordinarily result from flocculation. The polyelectrolyte (e.g., polyallylamine) forms aggregates under the crosslinking action of a multivalent salt (e.g., EDTA), and these metastable aggregates act as templates around which SiO2 NPs deposit to form a multilayer-thick shell. This form of templated self-assembly is driven by the favorable charge interactions among the polymer, salt, and NPs. The synthesis occurs at room temperature, atmospheric pressure, and in near-neutral pH water, allowing for water-soluble compounds to be encapsulated easily and without damage, for and the microcapsule formation process to be scaled up. In this talk, I will discuss my research group's current efforts in elucidating the NP self-assembly process through zeta potential and hydrodynamic diameter measurements, optical microscopy, and electron microscopy.
COLL 28 Bionanoparticles from vitamin C-based surfactants Pierandrea Lo Nostro, Department of Chemistry and CSGI, University of Florence, via della Lastruccia 3, 50019 Sesto Fiorentino (Firenze), Italy, Fax: +390554573036, pln@csgi.unifi.it, Moira Ambrosi, Dept. Chemistry and CSGI, University of Florence, Barry W. Ninham, Department of Applied Mathematics, Research School of Physical Sciences and Engineering, Institute of Advanced Studies, National Australian University, and Piero Baglioni, Deparment of Chemistry and CSGI, University of Florence
Novel surface-active molecules (esters) have been synthesized from L-ascorbic acid. The final products keep the same antioxidant property and optical activity of the parent molecule. The ester derivatives produce either micellar or viscous lamellar phases in water, that form a semicrystalline hydrate (“coagel”) upon cooling below a transition temperature that depends on the chain's length, surfactant's concentration, and cosolutes. DSC, surface tension, XRD, ESEM, and conductivity measurements have been performed to characterize the different phases.
COLL 29 Carotenoid-based bio-inorganic hybrids Linda de la Garza, Zoran Saponjic, Tijana Rajh, Marion C. Thurnauer, and Nada M. Dimitrijevic, Chemistry Division, Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL 60439, delagarza@anl.gov
There is considerable interest to develop functional nanomaterials that mimic the exquisite control over energy and electron transfer that occurs in natural energy transducing processes such as photosynthesis and vision. Truly functional nanomaterials that operate via a response to photon energy must reproduce the efficiency, versatility, and long term consistency of natural processes. In this regard, nature exploits a class of natural pigments: carotenoids. We have assembled hybrid nanostructures that link the special electronic properties of inorganic nanomaterials with those of carotenoids. Hybrid materials were constructed by chemically linking organic carotenoids to titanium dioxide nanoparticles using dopamine as the linker. By linking the carotenoids to titanium dioxide via a dopamine linker, we expect enhanced electron/energy transfer pathways compared to the direct linkage of carotenoid acid to titanium dioxide. We have characterized these hybrids by absorption spectroscopy, electron paramagnetic resonance spectroscopy, and photoelectrochemistry.
COLL 30 Characterization of magnetic-field-induced assemblies of cobalt nanoparticles Guangjun Cheng, Gerald T. Fraser, and Angela R. Hight Walker, Optical Technology Division, National Institute of Standards and Technology, 100 Bureau Drive, Mail Stop 8443, Gaithersburg, MD 20899, Fax: 301-975-6991, guangjun.cheng@nist.gov
We have shown that under the influence of a small magnetic field, cobalt nanoparticles assemble into centimeter-long rigorous chains along the direction of the applied field in a colloidal solution. Such magnetic-field-induced (MFI) assembly offers a possible alternative for magnetic device fabrication. Optical microscopy and transmission electron microscopy (TEM) have been used to characterize these assemblies. A superconducting quantum interference device (SQUID) provided a measurement of the magnetic properties of MFI assemblies of cobalt nanoparticles, while differential scanning calorimetry (DSC) measurements were performed to study the solvent phase transition of the colloid solution. Neutron scattering experiments are carried out to investigate the effects of temperature and magnetic fields on these MFI assemblies.
COLL 31 Characterization, sorption properties, and reactivity of yttrium oxide nanoparticles Wesley O. Gordon, Brian M. Tissue, and John R. Morris, Department of Chemistry, Virginia Tech, Blacksburg, VA 24061-0212, wegordon@vt.edu
Metal oxide nanoparticles can have enhanced adsorption and reactivity with chemical warfare agent simulants; which can be exploited to develop sensors or destructive sorbants for chemical warfare agents. In this study, Y2O3 nanoparticles, prepared by a laser-heated gas-phase condensation method, were characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy, and reflection adsorption infrared spectroscopy (RAIRS). The particles were then exposed to the simulant dimethyl methyl phosphonate (DMMP). Reactions were followed with in situ RAIRS while gas phase products were tracked with mass spectrometry. Surface-bound products were analyzed by temperature-programmed desorption, and XPS. The physical properties of the nanoparticles were varied by control of the synthetic conditions in order to investigate the effects of structure and particle size on the interactions with DMMP.
COLL 32 Electrochemical and bioelectrochemical reactions gated by hydrophobic magnetic nanoparticles Eugenii Katz, Institute of Chemistry, The Hebrew University of Jerusalem, Givat Ram, Jerusalem 91904, Israel, Fax: 972-2-6527715, ekatz@vms.huji.ac.il
Magnetic nanoparticles consisting of undecanoate-capped magnetite were used to control and switch the hydrophobic or hydrophilic properties of the electrode surface. The magnetic attraction of the functionalized nanoparticles to the electrode surface by means of an external magnet yields a hydrophobic interface that acts as insulating layer prohibiting interfacial electron transfer. The retraction of the magnetic nanoparticles from the electrode to the upper toluene phase by means of the external magnet generates a hydrophilic electrode that reveals effective interfacial electron transfer. This was used to switch reversibly bioelectrocatalytic reactions. The hydrophobic magnetic nanoparticles were also used to control biorecognition and biocatalytic processes on biomaterial-functionalized interfaces, such as DNA hybridization, polymerization and scission.
COLL 33 Understanding conductive polypyrrole deposition via micro- and nano-scale observations Bor Yann Liaw, Vojtech Svoboda, Forest Quinlan, and Michael J Cooney, Hawaii Natural Energy Institute, SOEST, University of Hawaii at Manoa, 1680 East-West Rd., POST 109, Honolulu, HI 96822, Fax: 808-956-2336, bliaw@hawaii.edu
We will discuss a unique approach employing in-situ imaging ellipsometry documentation of polypyrrole film growth to evaluate the effect of various controlling parameters, such as growth rate, monomer concentration, etc., on nano-scale to micro-scale microstructure development on biocatalytic electrode surface. We believe that this observation is critical in defining the proper microstructure for enzyme fuel cell performance and bioelectrocatalysis. The film quality strongly depends on deposition conditions and the monomer concentration, exhibiting in both activation and mass transport regimes. Data from imaging ellipsometry suggest that the growth of polypyrrole films began with a 1-D filament growth. As the density of the filaments increased with film thickness to a threshold, the growth pattern changed from 1-D to 2-D as the film continues to grow. The density, porosity, and microstructure of the film are therefore varied as the film is being developed.
COLL 34 Protein immunosensor using single-wall carbon nanotube forests with electrochemical detection of enzyme labels Xin Yu1, Sang Nyon Kim2, Voymesh Patel3, Silvio Gutkind3, Joseph Gong1, Ashwinkumar Bhirde1, Fotios Papadimitrakopoulos4, and James F. Rusling1. (1) Department of Chemistry, University of Connecticut, U-60, 55 N. Eagleville Rd., Storrs, CT 06269-3060, xin.yu@huskymail.uconn.edu, (2) Nanomaterials Optoelectronics Laboratory, Polymer Program, Institute of Materials Science, University of Connecticut, (3) Oral and Pharyngeal Cancer Branch, National Institute of Dental Research, National Institutes of Health, (4) Nanomaterials Optoelectronics Laboratory, Polymer Program, Institute of Materials Science, Department of Chemistry, University of Connecticut
Vertically aligned arrays of single-wall carbon nanotubes (SWNT forests) on pyrolytic graphite surfaces were developed for amperometric enzyme-linked immunoassays. Enhanced performance with aged nanotubes was monitored using SWNT forests with bound peroxidase enzymes, showing a 3.5-fold-better sensitivity and improved detection limits for H2O2 than fresh nanotubes. Absence of improvements by electron mediation for detection of H2O2 suggested very efficient electron exchange between nanotubes and enzymes attached to their ends. Protein immunosensors were made by attaching antibodies to the carboxylated ends of nanotube forests. Utilizing casein/Tween-20 to minimize non-specific binding, a 75 nM detection limit was achieved for Human Serum Albumin in unmediated sandwich immunosensors using horseradish peroxidase labels. Electron mediation of the immunosensors by water soluble mediator hydroquinone lowered the detection limit to 1 nM, providing significantly better performance than alternative methods. Using similar method, Prostate Specific Antigen, a biomarker for prostate cancer, was detected at 0.1 nM and below.
COLL 35 Preparation of biocatalytic nanofibers with high activity and stability via enzyme aggregate coating on polymer nanofibers Byoung Chan Kim1, Sujith Nair2, Jungbae Kim3, Ja Hun Kwak3, Jay W. Grate4, Seong H. Kim2, and Man Bock Gu1. (1) Department of Environmental Science and Engineering, Advanced Environmental Monitoring Research Center, Gwangju Institute of Science and Technology, 1, Oryoung-Dong, Puk-Gu, Gwangju 500-712, South Korea, Fax: 82-62-970-2434, bckim@gist.ac.kr, (2) Department of Chemical Engineering, Pennsylvania State University, (3) Pacific Northwest National Laboratory, (4) Fundamental Sciences Directorate, Pacific Northwest National Laboratory
We have developed a unique approach for the fabrication of enzyme aggregate coatings on the surfaces of electrospun nanofibers. This approach employs covalent attachment of seed enzymes onto nanofibers consisting of a mixture of polystyrene and poly(styrene-co-maleic anhydride), followed by a glutaraldehyde treatment that crosslinks additional enzyme molecules and aggregates from solution onto the covalently-attached seed enzyme molecules. These crosslinked enzyme aggregates are expected to improve the enzyme activity due to increased enzyme loading, and also the enzyme stability. To demonstrate the principle, we coated α-chymotrypsin (CT). The initial activity of CT-aggregate-coated nanofibers was 9 times higher than nanofibers with just a layer of covalently-attached CT. The enzyme stability of CT-aggregate-coated nanofibers was greatly improved with no loss of activity over a month of observation under rigorous shaking conditions. This approach of enzyme coating on nanofibers creates a useful biocatalytic enzyme system with potential applications in bioconversion, bioremediation, and biosensors.
COLL 36 Self-assembling biologically responsive nanotubes Sang Beom Lee1, Sara Wargo1, and Alan J. Russell2. (1) Department of Bioengineering, University of Pittsburgh, Suite 200, 100 Technology Drive, Pittsburgh, PA 15219, Fax: 412-235-5290, SBL4@pitt.edu, (2) Department of Surgery and McGowan Institute for Regenerative Medicine, University of Pittsburgh
We have shown that a single-chain diacetylene amine HBr salt and the lipids self-assembled into uniform nanotubes in dichloromethane/hexane with high purity. If we were able to stabilize these remarkable nanostructures we would have a fascinating matrix around which to assemble enzyme catalysts. Despite the many published accounts of self-assembled diacetylenic tubular microstructures, there have been no reports on the polymerization or hardening of these structures. In this presentation we report the first such polymerization of a diacetylenic nanotube and we report initial attempts to perform chemistry at the surface of the tube. The reason that no one has succeeded in tube polymerization is that an exact alignment of each diacetylene monomer is essential for the hardening reaction to proceed. We have successfully performed photopolymerization of our tubes in hexane. The polymerized tubes are responsive to their environment and could form the basis for a new class of biosensors.
COLL 37 Immobilized Lipase activity on micron to nanoscale carriers: Influence of particle size, pore diameter and surface chemistry Richard A. Gross1, Bo Chen2, M. Elizabeth Miller3, and James C. Bohling3. (1) Othmer Department of Chemical and Biological Sciences and Engineering, NSF I/UCR Center for Biocatalysis and Bioprocessing of Macromolecules, Polytechnic University, Six Metrotech Center, Brooklyn, NY 11201, rgross@poly.edu, (2) Othmer Department of Chemical and Biological Sciences and Engineering, Polytechnic University, (3) Advanced Biosciences, P.O. Box 904, Rohm and Haas Company
Abstract
Efficiency of immobilized enzymes to perform catalysis can be dramatically improved by tailoring its local environment. By decrease in size of enzyme supports and by minimizing diffusion limitations between substrates and enzymes, large increases in activity were achieved. A series of supports with diameters from about 600 microns to 70 nm were used to immobilize Candida Antartica Lipase B (CAL-B). The importance of various parameters such as pore dimensions, particle diameter, immobilization method and surface chemistry will be discussed. Non-porous nanoparticles with core and shell structures consisting of polystyrene and poly(glycidyl methacrylate), respectively, were prepared and evaluated. In addition, immobilization of a lipase on g-Fe2O3 magnetic nanoparticles to facilitate its recovery will be discussed. A method will also be introduced by which chemical and physical parameters of particle surfaces can be fine-tuned using model spin coated surfaces of copolymers with structures that are systematically varied.
COLL 38 Controlling protein orientation on charged self-assembled monolayers Shaoyi Jiang, Department of Chemical Engineering, University of Washington, Seattle, WA 98195, Fax: 206-685-3451, sjiang@u.washington.edu
Protein orientation on surfaces is critical to biocatalysis (e.g., immobilized enzymes) and biosensors (immobilized antibodies). Due to the charge distribution within a protein molecule, the orientation of adsorbed proteins can be controlled via adjusting microenvironments. The charge-driven protein orientation principle will be demonstrated under a wide range of conditions using two types of monoclonal anti-human chorionic gonadotropin (anti-hCG), i.e., IgG1 and IgG2a as model systems. The orientations of IgG1 and IgG2a on charged self-assembled monolayers (SAMs) are investigated using surface plasmon resonance (SPR) sensor, time-of-flight secondary ion mass spectroscopy (ToF-SIMS) and molecular simulations. Distinct protein orientations are observed on different charged surfaces. Control of protein orientation on charged surfaces will be also demonstrated for several proteins other than antibodies. How protein orientation and conformation affect their biological activities on surfaces will be discussed.
COLL 39 Atomic force microscopy investigations of protein conformation: Influence of nanoscale surface chemistry and structure Cindy L. Berrie1, Jill E. Headrick1, Katherine L. Marchin1, Son B. Phung1, and Nikki Williams2. (1) Department of Chemistry, University of Kansas, 1251 Wescoe Hall Drive Rm 1027, Department of Chemistry, Malott Hall, Lawrence, KS 66045, cberrie@ku.edu, (2) Haskell Indian Nations University
Protein surface interactions are being investigated using atomic force microscopy to probe the orientation and conformation of surface-adsorbed protein molecules. The orientation and conformation of these surface-adsorbed protein molecules is important for the activity of the protein. Well-characterized model substrates including self-assembled monolayer films have been used to investigate the effect of surface structure and chemistry on the adsorption of fibrinogen and other protein systems. Dramatic differences in the average size and shape of fibrinogen molecules adsorbed to hydrophobic and hydrophilic substrates have been observed. These changes can be readily seen in AFM images of individual molecules with sub-molecular resolution. In addition, on graphite substrates clustering of molecules at steps and a clearing of molecules near the step edges has been observed; on a chemically similar self-assembled monolayer surface, the distribution of molecules on the surface appears quite uniform. Preliminary results will also be presented on the kinetics of fibrinogen adsorption to model self-assembled monolayer films. In addition, methods for patterning nanostructured substrates for use in these experiments have been investigated as well as methods for chemically functionalizing AFM probe tips in order to obtain information beyond topography.
COLL 40 Controlling the grafting density of single stranded DNA on gold by adenine nucleotide adsorption Aric M. Opdahl1, Dmitri Y. Petrovykh2, Hiromi Kimura-Suda1, Lloyd J. Whitman3, and Michael J. Tarlov1. (1) National Institute of Standards and Technology, Gaithersburg, MD 20899, (2) University of Maryland & Naval Research Laboratory, (3) Naval Research Laboratory
The grafting density and conformation of surface immobilized ssDNA strongly influences its hybridization properties. We demonstrate that the spacing between DNA strands immobilized on gold can be controlled by making use of a previously observed strong adenine-gold interaction. The adsorption of oligonucleotides, d(Tm-An), with systematically varied thymine (dT) and adenine (dA) nucleotide block lengths, m and n, was characterized by FTIR and XPS. The d(A) blocks preferentially adsorb on the gold and the d(T) blocks extend away from the substrate. The grafting density is largely determined by the length of the d(A) block: oligos with longer d(A) blocks exhibit lower grafting densities. After immobilization, d(T) brush strands in the films display reversible hybridization behavior. Importantly, d(T) strands attached via d(A) blocks maintain “upright” conformations at grafting densities 5 to 10 times lower than films immobilized using standard alkanethiol linkers - a property expected to lead to efficient surface hybridization.
COLL 41 Probing DNA-DNA and DNA-Au interactions by exposure to mercaptohexanol Dmitri Y. Petrovykh1, Aric M. Opdahl2, Hiromi Kimura-Suda2, Michael J. Tarlov2, and Lloyd J. Whitman3. (1) University of Maryland & Naval Research Laboratory, Washington, DC 20375, Fax: 202-767-3321, dmitri.petrovykh@nrl.navy.mil, (2) National Institute of Standards and Technology, (3) Naval Research Laboratory
An understanding of basic interactions within single-stranded DNA (ssDNA) immobilized on surfaces is important for the rational design of ssDNA sequences in bio- and nanotechnology applications. The complexity of practical ssDNA films, however, makes it difficult to study such interactions during immobilization. We have found that the ability of mercaptohexanol (MCH) to displace DNA immobilized on Au can be used to probe DNA-DNA and DNA-Au interactions. We study these interactions using homo-oligonucleotides (dA, dT, and dC) on Au characterized ex-situ by XPS and FTIR. The oligonucleotides (thiol-modified and unmodified) are immobilized on Au, and then exposed to 1 mM aqueous solutions of MCH. The small MCH molecules penetrate through the DNA films and form nearly-complete monolayers on the gold surface. Strong DNA-DNA interactions are required to resist displacement by MCH, presumably because nearest-neighbor interactions effectively provide multiple attachment points for each DNA molecule. A particularly wide range of interactions can be observed with this method in oligo(dC) films.
COLL 42 Controlling macromolecular adsorption by nano-patterned self-assembled monolayers Alain M. Jonas, Gabriel Baralia, Bernard Nysten, and Antoine Pallandre, Polymer Physics and Chemistry, Université catholique de Louvain, Place Croix du Sud, 1, Louvain-la-Neuve B1348, Belgium, Fax: +32-10-451593, alain.jonas@poly.ucl.ac.be
We have combined electron beam nanolithography with silanation of silicon oxide, or thiolisation of gold, to produce chemical nano-patterns with typical feature sizes in the 20-100 nm range. The resulting patterns are compared and their quality discussed with respect to the inherent limitations of silanation and thiolisation. These nano-patterns have been subsequently used to direct the assembly of macromolecules on patches of size close to their characteristic dimensions. Here, we specifically report on the directed adsorption of a globular antigen, and on the repeated surface complexation of polyelectrolytes to build nano-confined polyelectrolyte multilayers. The amount and layer thickness of adsorbed antigen macromolecules are found to decrease with pattern size, due to the easier relaxation of compact globular macromolecules adsorbing on nano-patches. In contrast, a dramatic increase of thickness is observed for polyelectrolyte multilayers grown on nano-patterns, due to conformational perturbations of polyelectrolyte chains when confined to sizes below their extended length.
COLL 43 Ethylene oxide molecules covalently bonded to silicon and resulting protein resistance Christina A. Hacker1, Priscilla Liu2, David J. Vanderah1, Curt A. Richter1, and Lee J. Richter3. (1) Semiconductor Electronics Division, National Institute of Standards and Technology, 100 Bureau Drive, Mail stop 8120, Gaithersburg, MD 20899, Fax: 301-975-8069, christina.hacker@nist.gov, (2) Georgetown University, (3) Surface and Microanalysis Science Division, National Institute of Standards and Technology
Ethylene oxide monolayers have been well studied on surfaces for their ability to resist protein adsorption. Self-assembled monolayers on metals have been shown to differ in molecular conformation and packing density, which ultimately alters the protein resistance properties. Moving from a metal substrate to a semiconductor substrate offers many advantages. While robust protein resistance is necessary for biocompatible applications of silicon such as implants and biosensors, the monolayer conformation remains largely unknown. We examine four custom synthesized ethylene oxide molecules on the silicon surface that differ by the reactive functional group; thiol, alcohol, aldehyde, and alkene. These molecules react with hydrogen-terminated silicon to form covalently bonded monolayers. The differing reactivity of the functional groups leads to differing surface coverage. Thorough characterization of ethylene oxide monolayers on silicon and the resultant protein resistive properties will be presented.
COLL 44 Mixed monolayers of ω-functionalized α-(4-amidinophenoxy)alkanes: Towards reversible SAMs Ravindra R Deshmukh and Börje Sellergren, University of Dortmund Chem. Dept, INFU, Otto-Hahn str.6, Dortmund 44221, Germany, Fax: +49-231-7554084, ravindra@infu.uni-dortmund.de
Selfassembled monolayers (SAMs) of chemisorbed thiols on gold play an important role as platforms for biosensors, for advanced electronic applications or as model systems for the study of protein adsorption, cell adhesion or biomineralization. We recently showed that stable ordered SAMs and multilayers can also be prepared by noncovalent adsorption of amphiphiles.[1-4] The pH controlled amphiphile adsorptiondesorption is rapid allowing repeated assembly-test-disassembly of the layer structure for regeneration of e.g. a sensor interface after use. Thus, α,ω-(4-amidinophenoxy)alkanes form pH-switchable ordered mono-and bilayers on carboxylic acid functionalised thiol SAMs on gold. These multilayers can in turn act as substrates for the selective adsorption of negatively charged biomolecules.[1,2,4,5] In order to extend the repertory of exposed headgroups of the SAMs we have synthesised a series of ω-functionalized α(4-amidinophenoxy)alkanes (see Figure). Evidence for the structure and order of the resulting SAMs came from in situ Ellipsometry, IRAS, wetting studies and AFM. As for the bisbenzamidines these heterofunctional bola amphiphiles all form highly ordered but pH switchable monolayers. Furthermore binary mixtures of the amphiphiles formed monolayers which tended to be randomly mixed such as (1)/(4) (see Figure) or where the amphiphiles tended to selfassociate (e.g. (1)/(2)). By introducing biologically active ligands (e.g. (5)) as one of the head groups in such mixed SAMs we envisage a reversible biosensor platform with multiple tuning opportunities using one single substrate.
(1) F. Auer, et al. Chem. Eur. J. 5 (1999) 1150-1159. (2) B. Sellergren, F. Auer, T. Arnebrant, Chem. Commun. (1999) 2001-2002. (3) F. Auer, G. Nelles, B. Sellergren, Chem. Eur. J. 2004, 10, 3232-3240. (4) B. Sellergren, A. Swietlow, T. Arnebrant, K. Unger, Anal. Chem. 68 (1996) 402-7. (5) F. Auer, M. Scotti, A. Ulman, R. Jordan, B. Sellergren, J. Garno, G.-Y. Liu, Langmuir 16 (2000) 7554-7557.
COLL 45 Self assembly of anionic-cationic surfactant mixtures on alumina: Adsorption capacity and adsolubilization potential David A. Sabatini1, A. Fuangswasdi2, A. Charoensaeng2, John F. Scamehorn3, Edgar J. Acosta4, K. Osathaphan2, and S. Khaodhiar2. (1) Civil and Environmental Engineering and Institute for Applied Surfactant Research, University of Oklahoma, Norman, OK 73069, Fax: 405-325-4271, sabatini@ou.edu, (2) Chulalongkorn University, (3) Institute for Applied Surfactant Research and School of Chemical Engineering and Materials Science, The University of Oklahoma, (4) Department of Chemical Engineering, University of Toronto
This research reports on the self-assembly of surfactant bilayers on solid surfaces using mixtures of anionic and cationic surfactants having single and twin head groups. The surfactant mixtures investigated were: (a) a single-head anionic surfactant, sodium dodecyl sulfate (SDS), in mixture with the twin-head cationic surfactant pentamethyltallow alkyl-1,3-propane diammonium dichloride (PADD) adsorption was studied on negatively-charged silica; and (b) a twin-head anionic surfactant, sodium hexadecyl-diphenyloxide disulfonate (SHDPDS), and the single-head cationic surfactant dodecylpyridinium chloride (DPCl) - adsorption was studied on positively-charged alumina. While the mixed surfactant system of SHDPDS/DPCl showed comparable adsorption on alumina to SHDPDS alone, the mixed surfactant system of SDS/PADD showed increased adsorption on silica as compared to PADD alone. The adsorption of the SDS/PADD mixture increased as the anionic and cationic system approached an equimolar ratio. The adsolubilization potential of the self-assembled bilayers was evaluated using two molecular probes (adsorbates): styrene and ethylcyclohexane. While mixtures of anionic and cationic surfactants had little effect on the adsolubilization of styrene, the adsolubilization of ethylcyclohexane was greater in mixed SHDPDS/DPCl systems than for SHDPDS alone. Thus, the self-assembly of adsorbed anionic-cationic surfactant mixtures can increase the amount of surfactant adsorbed and the adsolubilization (surface accumulation) of solutes that hydrophobically partition into the adsorbed layer.
COLL 46 Some recent advances in DWS based optical microrheology Frank Scheffold1, F. Cardinaux2, and Peter Schurtenberger1. (1) Department of Physics, University of Fribourg, Chemin de Musee 3, CH-1700 Fribourg, Switzerland, frank.scheffold@unifr.ch, (2) Physics Department, University of Fribourg- Perolles
We discuss an application of DWS based optical microrheology [1,2] to a typical Maxwell fluid [3] and compare our results to oscillatory shear experiments both in the low and high frequency regime. Access to long relaxation times is obtained using a new detection scheme for diffusing wave spectroscopy (DWS) based on a two-cell setup. This is achieved by putting a fast rotating diffuser in the optical path between laser and sample. We show that the recorded (multi-speckle) correlation echoes provide an ensemble averaged signal that does not require additional time averaging [4]. We find the performance of our experimental scheme comparable or better to other multi-speckle techniques that rely on direct spatial averaging. Furthermore, combined with traditional two-cell DWS [2], the full intensity autocorrelation function can be measured with a single experimental setup-up covering 10 decades in correlation time or more.
[1] Mason, TG and Weitz DA,Physical Review letters 74, 1250-1253 (1995) [2] F. Scheffold and P. Schurtenberger, Soft Materials 1, 139-165, (2003) [3] P. Fischer and H. Rehage, Langmuir 13, 7012-7020 (1997) [4] Pavel Zakharov, Frédéric Cardinaux, Frank Scheffold, in preparation.
COLL 47 Microrheology in polymer solutions: Depletion and the shell model Alexander Levine, Department of Chemistry and Biochemistry, UCLA, 607 Charles E. Young Drive East, Box 951569, Los Angeles, CA 90095-1569, Fax: +1-310-206-4038
Microrheology is a rapidly developing experimental technique that uses the thermal motion of colloidal tracers embedded in a viscoelastic medium to make rheological measurements. Since this technique uses only the equilibrium thermal motion of the tracers to extract the medium's rheological behavior, it can be employed in extremely fragile materials, including a variety of biomaterials. In such fragile materials, however, the presence of the colloidal particles locally perturbs the medium so that the observed tracer motion depends on both the local and bulk material rheology in a complex way.
In this talk I will review the theory of one- and two-particle microrheology. Using the shell model to combine information regarding the correlated motion of pairs of tracers with single-tracer motion, one can extract the mechanical properties of both the bulk material and the local environment of the tracers. I will discuss the application of this "rheological microscopy" to microrheological studies of semidilute lambda-DNA solutions and show that this combination of one- and two-particle microrheology allows one to examine the local environment of the tracers at length scales down to 100nm.
COLL 48 Probing the nanoscale structure of colloid-semiflexible polymer suspensions Ji Yeon Huh and Eric M. Furst, Department of Chemical Engineering, University of Delaware, Colburn Lab, 150 Academy St., Newark, DE 19716, huh@che.udel.edu
Semiflexible polymers demonstrate distinctive rheological properties due to their large aspect ratio of persistence length to molecular diameter. It is important to understand interactions, structure, and responses to control the colloid-semilfexible polymer suspensions found in nanocomposites, high performance coatings, and the microrheology of biological cell. In this work, we report diffusing wave spectroscopy (DWS) studies of the dynamics of particles suspended in F-actin solutions in time scales 10-6<t<10-2s, and in the concentration of 0.63mg/ml. F-actin is a helical protein filament with an average diameter ~7nm and persistence length ~15mm. Monodisperse polystyrene latex spheres (1.072 and 2.855mm diameter) are coated with bovin serum albumin to reduce the protein adsorption. Actin filaments of different lengths (0.05~10mm) are prepared by polymerizing in the presence of various amounts of actin binding protein gelsolin. As the molar ratio of gelsolin to actin increases, the mobility of particles approaches free diffusion. We show an abrupt transition of the dependence of the diffusion coefficient on the filament length near the semi-dilute overlap concentration. In addition, we investigate the effect of particle concentration on the structure of F-actin solutions. For the ratio of length to particle diameter, L/D~10, the diffusivities decrease as increasing particle volume fraction or increasing actin concentration. These are related to recent theories of polymer-induced local clustering and the interference of depletion layer between particles[1, 2].
[1] Langmuir 18, 7354 (2002) [2] J. Phys. Chem. B 108, 6687 (2004)
COLL 49 Influence of alginate and ionic composition on aggregate structure of hematite colloids Kai Loon Chen1, Steven E. Mylon2, and Menachem Elimelech1. (1) Department of Chemical Engineering, Environmental Engineering Program, Yale University, New Haven, CT 06520, Fax: 203-432-2895, kailoon.chen@yale.edu, (2) Department of Chemistry, Lafayette College
The aggregation kinetics of bare and alginate-coated hematite nanoparticles are measured in the presence of monovalent (sodium chloride) and divalent (calcium chloride) electrolytes by dynamic light scattering. The monodispersed, spherical hematite colloids are synthesized by the forced hydrolysis of ferric chloride, resulting in an average particle diameter of 75 nm. Coated particles are prepared by introducing a sample of the hematite colloids into alginate solution adjusted to pH 5.2 for optimum adsorption to occur. Reaction and diffusion-limited regimes are observed for the bare and alginate-coated hematite colloids in NaCl. As expected, TEM images reveal compact and open aggregate structures at low and high NaCl concentrations, respectively. However, for the alginate-coated hematite particles in calcium chloride, no distinct reaction and diffusion-limited regimes are observed. TEM also shows aggregate structures in calcium chloride much different from what are traditionally observed in the two regimes.
COLL 50 Microviscosity and solvation dynamics in a wide range of molecular weight non-ionic surfactant PEO-PPO-PEO triblock copolymer aggregates Christian D Grant, Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, 610 Taylor Rd, Piscataway, NJ 08854-8087, Fax: 732-445-5312, cdgrant@rci.rutgers.edu, and Edward W. Castner Jr., Department of Chemistry, Rutgers University
The local environments within triblock copolymer aggregates are investigated by fluorescence using solvatochromic coumarin dye-probes. Aqueous poly (ethylene oxide)-poly (propylene oxide)-poly (ethylene oxide) (PEO-PPO-PEO) copolymers form unimer, rod-like and spherical micelles, or hydrogel structures with increasing temperature or concentration. Aggregation (unimers-to-micelles) is driven by variable hydration of the polymer blocks. Our previous studies have shown that we can selectively probe different aggregate regions (interfacial, interior, and exterior) depending on the choice of the appropriate hydrophilic (C343—/Na+), intermediate (C102), or hydrophobic (C153) 7-aminocoumarin solvatochromic fluorescence probe. The fluorescence anisotropy technique provides information on microviscosity while polymer and solvent reorganization (solvation) dynamics are probed by time-resolved emission shifts. The current study focuses on how microviscosity and solvation dynamics are altered in these complex aqueous systems by variation of the molecular weight of the exterior PEO block (2100-11600 g/mol) and the interior PPO block (950-3000 g/mol).
COLL 51 Monitoring the folding behavior of proteins and polymers on chip Paul S. Cremer1, Yanjie Zhang2, Steven M. Furyk1, and David E. Bergbreiter1. (1) Department of Chemistry, Texas A&M University, MS 3255, College Station, TX 77843, Fax: 979-845-7561, cremer@mail.chem.tamu.edu, (2) Chemistry, Texas A&M University
We have designed temperature gradient microfluidic devices that allow high throughput assays to be performed on the lower critical solution temperature (LCST) behavior of thermoresponsive polymers and proteins. These systems are insoluble at high temperatures, but become hydrated and unfold as the temperature is decreased in a process analogous to the cold denaturation of proteins. Our assays enable highly precise measurements to be made on the physical behavior of the polymers with very low sample volumes in a high throughput manner. The device is specifically used to obtain data on poly (N-isopropylacrylamide) and alpha-elastin at multiple concentrations in the presence of a variety of ions. The physical properties of these systems will be discussed.
COLL 52 Monitoring solvent-induced changes in the structure of polymers in solution Raymond S. Tu, Jun Sato, and Victor Breedveld, School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Dr NW, Atlanta, GA 30332-0100, Fax: 404-894-2866, rtu@chbe.gatech.edu, victor.breedveld@chbe.gatech.edu
Particle tracking microrheology capitalizes on the Brownian motion of colloidal particles to probe the mechanical properties of the surrounding medium. The main advantage of the method is that very small samples can be studied (< 1 microliter). We have applied the technique to study the properties of solvent-responsive polymers in solution.
First, we have studied the unfolding of BSA (bovine serum albumin) upon addition of urea as denaturing agent. Although viscosity is listed in textbooks as a suitable technique for studying protein unfolding, few –if any– quantitative rheological studies have been reported, mainly due to technical difficulties. With microrheology, we have been able to quantify the size of folded and unfolded proteins, as well as the Gibbs free energy of unfolding.
Secondly, by integrating microfluidics and microrheology, we have constructed a dialysis cell for microrheology, which provides unique opportunities for studying the dynamics of structural changes induced by solvent composition. We will present data on the viscosity response of polyelectrolyte solutions to changes in ionic strength.
COLL 53 Polymer-controlled nanoparticle size: Kinetic vs. equilibrium mechanism Rina Tannenbaum, School of Materials Science and Engineering, Georgia Institute of Technology, 771 Ferst Drive, Atlanta, GA 30332, Fax: 404-894-9140, rina.tannenbaum@mse.gatech.edu, and Nily Dan, Department of Chemical and Biological Engineering, Drexel University
Studies have shown that inorganic nanoparticles synthesized in a polymeric environment are characterized by a narrow size distribution when compared to synthesis in similar, small molecule solvents. It has been suggested that the polymer chains preferentially adsorb on particles whose diameter is a particular value, thereby 'capping' them and inhibiting further growth, but this mechanism has not been studied to date. In this study we examine the mechanism of nucleation and growth of iron-oxide nanoparticles in different types of bulk polymeric media. We find that the nanoparticle size is not set by an equilibrium process of 'capping' by an adsorbed polymer layer. An alternative hypothesis for the narrow particle size distribution is that the polymer affects the kinetics of nucleation and growth in a manner that favors a particular diameter. Our results show that the polymeric nature of the medium suppresses growth, thereby leading to a uniform size distribution. However, contrary to expectation, it is not the increased viscosity or reduced diffusivity of the metal fragments in the medium that affect the nucleation and growth, but the unique interfacial properties of the polymer layer at the interface.
COLL 54 Shear thickening in polymer stabilized colloidal dispersions Norman J. Wagner1, Lakshmi-narasimhan Krishnamurthy1, and Jan Mewis2. (1) Department of Chemical Engineering, University of Delaware, Center for Molecular and Engineering Thermodynamics, Colburn Laboratory, Newark, DE 19716, Fax: 302-831-1048, wagner@che.udel.edu, (2) Katholieke Universiteit
The shear thickening transition in polymer stabilized colloidal dispersions is analyzed in terms of a micromechanical model that incorporates both the stabilizing forces of the polymer brush and the associated modification of the hydrodynamic interactions due to the brush. Comparison is made to simulations and experiments on model, well characterized dispersions. The model is shown to provide a quantitative prediction for the onset of shear thickening. Comparison with experiment indicates the sensitivity of the shear thickening transition to both the interaction potential arising from the brush as well as the hydrodynamic permeability of the brush.
COLL 55 Polarized X-ray absorption spectroscopy (XAS) of oriented CdSe nanorod assemblies Deborah M. Aruguete1, Matthew A. Marcus2, Liang-shi Li3, A. Williamson4, Sirine C. Fakra2, Giulia Galli4, and A. Paul Alivisatos5. (1) Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720, Fax: 510-642-6911, aruguete@berkeley.edu, (2) Advanced Light Source, Lawrence Berkeley National Laboratory, (3) Department of Chemistry, Northwestern University, (4) Quantum Simulations Group, Lawrence Livermore National Laboratory, (5) University of California, Berkeley, Department of Chemistry; Lawrence Berkeley National Laboratory, Materials Sciences Division
Semiconductor nanocrystals, especially those with anisotropic shapes, display many interesting properties quite distinct from their bulk counterparts. Nanocrystals differ from bulk materials by having a much larger surface-to-volume ratio; hence their surface structure and composition can greatly influence their physical and chemical properties. Surface and internal structure can be further altered in nanocrystals with novel, non-spherical shapes. Until now, a detailed structural analysis of anisotropic nanocrystals has been lacking. Our group has developed a synthesis for monodisperse CdSe nanorods that spontaneously assemble into liquid crystals, providing an ideal system for orientation-specific study. By studying this system with linearly-polarized XAS, we have detected oriented distortions of the atomic structure that arise from the anisotropic shape. We have found an unexpected bond contraction along the long axis of the nanorods, as well as greatly reduced surface atom coordination. These results imply shape-induced deformations which may affect technologically important properties of these materials.
COLL 56 Colloidal metal nanoparticles for biological applications Catherine J. Murphy, Department of Chemistry and Biochemistry, University of South Carolina, 631 Sumter St., Columbia, SC 29208, Fax: 803-777-9521, murphy@mail.chem.sc.edu
Metal nanoparticles with dimensions of 4 nm to 500 nm can be made in various shapes, which in turn implies various visible optical properties. These optical properties are valuable for sensing and imaging applications relevant to the biomedical field. Examples of surface-enhanced Raman spectroscopy, visible color changes as a function of engineered aggregation, and darkfield microscopy imaging using elastic light scattering, will be discussed.
COLL 57 Solvent and core size effects on the electrochemistry of 1-2 nm gold nanopaticles Rui Guo, Balasubramanian Ramjee, and Royce W. Murray, Department of Chemistry, The University of North Carolina at Chapel Hill, Kenan labs C-345, Chapel Hill, NC 27599-3290, Fax: 919-962-2388
Solvent and core size effects on the electrochemistry of Au38(SC2Ph)24 and Au75(SC2Ph)40 are studied. It was found that the redox potentials of 1st and 2nd oxidation peaks of both nanoparticles correlate well with the dielectric constant, donor number of the solvents with exceptions of THF and pyridine; however they correlate poorly with the other solvent parameters such as acceptor number, dipole moment, softness parameter,1/dielectric constant,etc. The most interesting thing is the higher the dielectric constant of the solvent,the higher oxidation potentials the nanoparticles have, which is opposite to common observation---solvents with higher dielectric constant tend to stabilize the cation better(oxidation potentials are lower correspondingly) than lower ones. We attribute this abnormal effect to the interactions between the solvent and the monolayer of the nanoparticles. The redox potentials of two different core size nanoparticles Au38(SC2Ph)24, Au75(SC2Ph)40 in the same CH2Cl2 solvent are also compared.
COLL 58 The role of ligand functionalization in nanoparticle assembly and cross-linking at fluid-fluid interfaces Elizabeth Glogowski1, Ravisubash Tangirala2, Yao Lin2, Habib Skaff2, Anthony Dinsmore3, Thomas P. Russell4, and Todd Emrick2. (1) University of Massachuestts Amherst, Amherst, MA 01003, lizg@mail.pse.umass.edu, (2) Polymer Science and Engineering Department, University of Massachusetts at Amherst, 120 Governors Drive, Amherst, MA 01003, Fax: 413-545-0082, (3) Physics Department, University of Massachusetts at Amherst, (4) Department of Polymer Science and Engineering, University of Massachusetts at Amherst
This presentation will emphasize the role of ligand density and functionality on CdSe, Au, and silsesquioxane nanoparticles as it impacts the stabilization of fluid-fluid interfaces, and the cross-linking of the nanoparticles at those interfaces.
COLL 59 Controlling nanoparticle location in block copolymer domains B. J. Kim1, J. J. Chiu1, Joona Bang2, Craig J. Hawker3, D. J. Pine4, and E. J. Kramer4. (1) Department of Chemical Engineering, UCSB, Santa Barbara, CA 93106, bjmanse2@engineering.ucsb.edu, (2) Materials Research Laboratory, UCSB, (3) Materials Research Laboratory, University of California, (4) Departments of Materials and Chemical Engineering, UCSB, Santa Barbara, CA 93106, edkramer@mrl.ucsb.edu
A simple procedure is described to incorporate 4 nm diameter gold nanoparticles and control their location within symmetric poly(styrene-b-2 vinyl-pyridine) (PS-PVP) diblock copolymers. Gold nanoparticles coated with thiol-terminated PS and/or PVP homopolymer chains (Mn ~ 1,300 and 1,500 g/mol respectively) are incorporated into alternating lamellar layers of PS and PVP (total Mn ~ 196,500 g/mol). The location of the particles is controlled by varying the composition of the homopolymer ligands on the particle surfaces. In particular, gold particles coated with 100% PS or PVP reside near the center of the respective polymer domains while particles coated with a mixture of both homopolymers reside at the interfaces between the two blocks. The range of particle surface composition over which the nanoparticles segregate to the interface is very broad. For example, nanoparticles with a surface coating with only 10% PVP still segregate to the interface. These phenomena raise interesting questions about the surface distribution of PS and PVP on the gold surface, questions that can be explored by comparing the result for Au nanoparticles covered by mixtures of PS and PVP chains with those covered by PS-r-PVP-SH copolymer chains synthesized by controlled radical polymerization.
COLL 60 Bio-programmed assembly of nanostructured materials into functional architectures Chad Mirkin, Chemistry Dept, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208, Fax: 847-467-5123
Nature routinely constructs materials such as biopolymers and microorganisms that exhibit extensive structural diversity and complexity. Here we describe methods that rely on the use of an arsenal of biologically derived molecules and structures to direct the organization and construction of nanostructured materials. Specifically, various microorganisms are used as templates for the assembly of DNA-modified nanostructures into hierarchically ordered micro- and macroscopic materials and for the fabrication of isolable nanostructured metallic microshells. The unique electrical, optical, and spectroscopic enhancement properties of these materials, both polymeric DNA-nanoparticle matrices and metallic microshells, are presented.
COLL 61 Single enzyme nanoparticles: A novel enzyme stabilization method Jay W. Grate and Jungbae Kim, Pacific Northwest National Laboratory, 902 Battelle Blvd., PO Box 999, Mailstop K8-93, Richland, WA 99352, Fax: 509-376-5106, jwgrate@pnl.gov
Nanoparticles and nanoparticle-based materials are attracting great interest for their unique properties and potential for application in diverse areas. We have developed a new nanostructure containing an enzyme within a hybrid organic/inorganic polymer network with sufficient porosity to allow substrates to diffuse to the active site. The synthetic procedure, entailing enzyme modification and two orthogonal polymerization steps, yields nanoparticles containing a single enzyme, which can be observed by transmission electron microscopy. In experiments with chymotrypsin, incorporation into the nanostructure dramatically increased the enzymatic stability. Furthermore, the nanoscale structure around the enzyme is sufficiently thin that it does not impose a significant mass transfer limitation on the substrate. Because these nanoparticles remain soluble or suspended in solutions, they can be processed into a variety of forms. They can be used in solution, cast into thin films, or adsorbed within larger mesoporoous structures. Given enzymatic specificity and the great diversity reactions catalyzed by enzymes, coupled with the flexibility in the use of single enzyme nanoparticles, these new nanostructures are very promising for