[show abstract][hide abstract] ABSTRACT: A new 2D molecular imprinting technique based on nanotemplating and soft-lithography techniques is reported. This technique allows the creation of target-specific synthetic recognition sites on different substrates using a uniquely oriented and immobilized template and the attachment of a molecularly imprinted polymer on a substrate. The molecularly imprinted polymer was characterized by AFM, fluorescence microscopy, and ATR-FTIR. We evaluated the rebinding ability of the sites with theophylline (the target molecule). The selectivity of the molecularly imprinted polymer was determined for the theophylline-caffeine couple. The molecularly imprinted polymer exhibited selectivity for theophylline, as revealed by competitive rebinding experiments. Fluorescence microscopy experiments provided complementary proof of the selectivity of the molecularly imprinted polymer surfaces toward theophylline. These selective molecularly imprinted polymers have the potential for chemical sensor applications. Because of its 2D nature, this novel chemical sensor technology can be integrated with many existing high-sensitivity multichannel detection technologies.
[show abstract][hide abstract] ABSTRACT: Surface-confined telechelic poly(ε-caprolactone) macroligand with two distinct functional groups per polymeric chain has been synthesized and characterized. The molecular microstructure of the macroligand with regard to the properties of the end-capped functionalities and with those on surface substrate has been studied by solution and surface analytical methods (i.e., X-ray photoelectron spectroscopy (XPS), grazing angle reflectance-Fourier transform IR spectroscopy (GA-FTIR), water contact angle measurements, and atomic force microscopy (AFM)) to elucidate the structure and properties of such multifunctional polymer on gold (111) substrate.
[show abstract][hide abstract] ABSTRACT: A novel alkylthioacetyl-capped hydroxyethyl methacrylate monomer and its corresponding homopolymer have been synthesized and characterized. Direct chemisorption of these moieties have been carried out on gold-coated substrate and found to form a strong surface bonding. The surface coverage and the properties of the resultant self-assembled layers have been investigated by multiple surface characterization techniques (i.e. ellipsometry, GA-FTIR, XPS, AFM, and contact angle measurements). These analyses have all confirmed the occurrence of complete chemisorption reactions with typical n-alkanethiol self-assembled characteristics.
[show abstract][hide abstract] ABSTRACT: A preparative route for a nanocrystalline CdSe/polymer nanocomposite that is easily integrated into photovoltaic device fabrication has been developed. Microwave assisted synthesis is used to initiate the reaction of relatively safe, inexpensive and air stable precursors. Particles size may be varied from 20 Å to 60 Å in diameter. The CdSe nanocrystals show near band-edge photoemission, are crystalline and may be incorporated into a poly(9,9-dioctylfluorene-2,7-diyl-alt-9-octylcarbazole-3,6-diyl) copolymer. This polymer/CdSe composite can be directly cast, without complicated work-up, for the preparation of photovoltaic devices.
Journal of Materials Chemistry 10/2005; · 5.97 Impact Factor
[show abstract][hide abstract] ABSTRACT: Platinum-ruthenium nanoparticles stabilized within a conductive polymer matrix are prepared using microwave heating. Polypyrrole di(2-ethylhexyl) sulfosuccinate, or PPyDEHS, has been chosen for its known electrical conductivity, thermal stability, and solubility in polar organic solvents. A scalable and quick two-step process is proposed to fabricate alloyed nanoparticles dispersed in PPyDEHS. First a mixture of PPyDEHS and metallic precursors is heated in a microwave under reflux conditions. Then the nanoparticles are extracted by centrifugation. Physical characterization by TEM shows that crystalline and monodisperse alloyed nanoparticles with an average size of 2.8 nm are obtained. Diffraction data show that crystallite size is around 2.0 nm. Methanol electro-oxidation data allow us to propose these novel materials as potential candidates for direct methanol fuel cells (DMFC) application. The observed decrease in sulfur content in the polymer upon incorporation of PtRu nanoparticles may have adversely affected the measured catalytic activity by decreasing the conductivity of PPyDEHS. Higher concentration of polymer leads to lower catalyst activity. Design and synthesis of novel conductive polymers is needed at this point to enhance the catalytic properties of these hybrid materials.
The Journal of Physical Chemistry B 09/2005; 109(32):15339-44. · 3.61 Impact Factor
[show abstract][hide abstract] ABSTRACT: Stable polymer coated platinum–ruthenium nanoparticles were prepared. The effects of several preparation parameters have been studied in view of optimizing the particles' composition and structure characteristics. Solutions of hexachloroplatinic acid and ruthenium chloride in ethylene glycol were reduced at 173 °C in the presence of poly(N-vinyl-2-pyrrolidone) with rapid refluxing in a commercial microwave system. These nanoparticles form stable colloidal solutions in ethanol for several months without any precipitation. Transmission electron microscopy (TEM) analysis revealed the presence of metallic clusters with a uniform size of about 2–3 nm. Photo-correlation spectroscopy (PCS) measurements revealed an average hydrodynamic particle size of about 10 nm. X-Ray photoelectron spectroscopy (XPS) indicates that most of the Pt and Ru atoms are in reduced metallic state. X-Ray diffraction (XRD) revealed alloyed single-crystal clusters with diameters barely smaller than corresponding TEM measurements. The above TEM, PCS, XPS and XRD observations converge on a simple picture of monodisperse, uniformly alloyed Pt–Ru nanoparticles with uniform diameters in the range of 2–3 nm for the PVP-coated samples. Their compositions are comparable with the metal content of the reactants. The PVP layer is less than 7 nm thick, and probably very porous. In the absence of PVP, agglomerated, larger nanoparticles were obtained with a Pt-rich core and Ru-rich shell.
Journal of Materials Chemistry 01/2004; 14(22). · 5.97 Impact Factor
[show abstract][hide abstract] ABSTRACT: A simple procedure has been described for the fabrication of multi-wall carbon nanotube (CNT) based electrochemical sensors. 3-Aminopropyltriethoxysilane (APTES) induced solubilization of CNTs allowed for the modification of electrode surfaces. With glucose oxidase (GOx), a flavin (FAD) containing enzyme as a model system, APTES was used as a solubilizing agent for CNTs as well as an immobilization matrix for GOx to construct a mediatorless biosensor. Our biosensor was able to efficiently monitor direct electroactivity of GOx at the electrode surface. A well-defined glucose response was observed at -0.45?V (vs. Ag/AgCl) whereas relevant physiological levels (0.1?mM) of three common interfering species, uric acid, ascorbic acid, and acetaminophen, resulted in no response. Although CNTs modified by APTES acted as semiconductors to reduce the exposed sensing surface, we reasoned nanoscale ldquodendritesrdquo of CNTs modified by APTES formed a network and projected outwards from the electrode surface and acted like bundled ultra-microelectrodes that allowed access to the active FAD site and facilitated direct electron transfer to the immobilized enzyme. The glucose biosensor prepared using a carbon fiber (11?mum) exhibited picoamperometric current response within 5?s with detection limits of 5-10?muM.
[show abstract][hide abstract] ABSTRACT: Abstract: This paper describes a new strategy for fabricating continuous gold films based on the self-assembly of the gold colloid monolayer on a poly(diallyldimethylammonium chloride)-modified glass slide, followed by electroless plating. Hydroxylamine-mediated reduction was proven as an excellent route to enlargement of immobilized nanoparticles on polymer-coated glass substrates in comparison to formaldehyde-mediated reduction. Au colloidal surface-catalyzed reduction of Au3+ by hydroxylamine exhibited very fast kinetics as monitored and confirmed by UV-vis spectroscopy in real time. The nanoscale morphology of the gold film was dependent on the initial coverage of gold nanoparticles and thermal annealing. Atomic force micrographs further revealed that enlarged particles were neither spherical nor cyclindrical, but highly complex in shape. The gold film thickness and its corresponding surface roughness could be easily controlled by setting the electroless deposition time. X-ray diffraction certified uniformity of deposits with the Au(111) crystallographic structure as the predominant one. No organic contamination during the course of electroless plating was observed as confirmed by both X-ray photoelectron spectroscopy and contact angle measurements. The stable and continuous gold films were used as electrodes for electrochemical experiments.
[show abstract][hide abstract] ABSTRACT: Chemisorption of peptides and active moieties onto gold and silver coated surfaces is an attractive method for studying the effect of fundamental surface properties on biological interactions. In theory, the monolayers formed have a high density of the active group of interest, and the relatively mild conditions associated with chemisorption should allow biological activity to be maintained. While the conditions for chemisorption are widely reported in the literature, significant differences exist between research groups and the effects of changing these conditions on the resultant surface have not been fully examined. Furthermore, comparisons have not been made between gold and silver as potential substrates in these applications. In the current work, glutathione and cysteine were chemisorbed onto gold- and silver-coated polymers. The effect of varying the chemisorption conditions was evaluated by XPS analysis of the resultant surfaces. Factors identified as having potentially significant effects on chemisorption procedure included chemisorption time, peptide concentration, peptide, pH of the chemisorption solution, mixing and material of the incubation container. Factor significance was evaluated using a two level fractional factorial design of experiments (DOE), with sulfur content determined by XPS used as a measure of chemisorption effectiveness. Significant differences were noted between the silver and gold-coated surfaces, with a higher amount of sulfur and hence, by inference, peptide found in general on silver surfaces reacted under identical conditions. On the gold surfaces, peptide concentration, peptide type, and chemisorption time were found to have a significant effect on the composition of the resulting surface. On the silver surfaces, factor specific differences were not as significant but there were a number of two factor interactions. The results provide further evidence of the differences in interactions with thiol between silver and gold and suggest that changes in the chemisorption conditions can dramatically affect the resultant surface composition.
[show abstract][hide abstract] ABSTRACT: Gold-coated polyurethanes were chemisorbed with three cell-adhesion peptides having an N-terminal cysteine: cys-arg-gly-asp (CRGD), cys-arg-glu-asp-val (CREDV), and the cyclic peptide cys-cys-arg-arg-gly-asp-try-leu-cys (CCRRGDWLC). The peptides were selected based on their presumed preferential interactions with the cell-surface integrins on vascular endothelial cells. The ability of the surfaces to support the preferential adhesion of human vascular endothelial cells was studied by comparing in vitro adhesion results for these cells with those from mouse 3T3 fibroblasts. Surface modification with the peptides was confirmed by water-contact angles and XPS. Surface morphology was determined by AFM and SEM. In vitro cell-culture studies in conjunction with plasma-protein adsorption and immunoblotting were performed on the various modified surfaces. The data suggest that peptide-modified surfaces have significant potential for supporting cell adhesion. Little or no cell adhesion was noted on gold- or cysteine-modified control surfaces. Human vascular endothelial cells showed the greatest adhesion to the CCRRGDWLC-modified surfaces, and the 3T3 fibroblasts adhered best to the CREDV-modified surfaces. Protein adsorption studies suggest that the preferential adsorption of the cell-adhesive proteins fibronectin and vitronectin is not likely mediating the differences noted. It is concluded that the cell-adhesive peptide-modified gold-coated polymers have significant potential for further development both as model substrates for fundamental studies and for use in biomaterials applications.
Journal of Biomedical Materials Research 03/2001; 54(2):272-83.
[show abstract][hide abstract] ABSTRACT: Bitumen, separated from oil sands by the hot water extraction process, contains ultra-fine (< 200 nm), inorganic solids (BS). Surfaces of BS particles are coated with toluene insoluble organic matter (TIOM). This organic material is polar and aromatic with contributions from both humic and asphaltene-like components. Although the surfaces of BS particles are dominated by TIOM, the coverage is patchy rather than continuous. As a result, these solids are capable of stabilizing fine water emulsions in the bitumen phase. The nature of the organic matter on the surfaces of the particles is such that it has a high propensity to form coke. Therefore, these particles can also play a role in fouling on equipment and catalysts.Le bitume séparé des sables pétrolifères par le procédé d'extraction à air chaud, contient des solides inorganiques (BS) ultrafins (<200 mm). Les surfaces des particules BS sont recouvertes de matière organique insoluble au toluène (TIOM). Cette matière organique est polaire et aromatique avec des contributions provenant de composants humiques et proches de l'asphaltène. Bien que les surfaces des particules BS soient dominées par le TIOM, le revêtement est irrégulier plutôt que continu. Par conséquent, ces solides sont capables de stabiliser des émulsions aqueuses fines dans la phase du bitume. La nature de la matière organique sur les surfaces des particules est telle qu'elle a une forte propension à former du coke. Ces particules peuvent donc jouer un rôle dans l'encrassement des équipements et des catalyseurs.
The Canadian Journal of Chemical Engineering 07/2000; 78(4):610 - 616. · 1.00 Impact Factor
[show abstract][hide abstract] ABSTRACT: Raman spectroscopy has been used to characterize neat alkanethiol and various metal-alkanethiolate materials. Neat alkanethiol gives rise to two CS stretching peaks at 662 and 735 cm−1, assigned to gauche and trans rotamers respectively. Only one CS stretching peak positioned at 725 cm−1 was found from CuC12 and AgC12 layered compounds, implying the absence of gauche rotamer near the thiolate group. An all-trans conformation of the chain is inferred from the peak position values of the CC stretching modes of CuC12 and AgC12 layered compounds. Gauche rotamers were observed in silver colloids capped with alkanethiolate.
Spectrochimica Acta Part A-molecular and Biomolecular Spectroscopy - SPECTROCHIM ACTA PT A-MOL BIO. 01/1999; 55(6):1229-1236.
[show abstract][hide abstract] ABSTRACT: In the present work, we have used reflection−absorption infrared spectroscopy (RAIRS) to investigate the temperature behavior of n-alkanethiols adsorbed on gold substrates. A careful examination of the spectra (frequencies, integrated intensities, and line widths) reveals at least two different types of thermally induced disorder as the temperature is increased. These observations are discussed in light of other recent studies using complementary techniques. The overall picture that emerges is that an initial stage is characterized by a gradual untilting of the alkyl chain and the appearance of gauche conformational defects near the surface, and both of these effects are largely reversible. The subsequent nonreversible disordering of the monolayer is characterized by a large number of defects located below the surface. Infrared spectroscopy is particularly well suited for detecting these changes.