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At least 397 records · Page 22Linked to original sources
PubMed2006

Nanostructured biosensors built by layer-by-layer electrostatic assembly of enzyme-coated single-walled carbon nanotubes and redox polymers.

In this study, we describe the construction of glucose biosensors based on an electrostatic layer-by-layer (LBL) technique. Gold electrodes were initially functionalized with negatively charged 11-mercaptoundecanoic acid followed by alternate immersion in solutions of a positively charged redox polymer, poly[(vinylpyridine)Os(bipyridyl)2Cl(2+/3+)], and a negatively charged enzyme, glucose oxidase (GOX), or a GOX solution containing single-walled carbon nanotubes (SWNTs). The LBL assembly of the multilayer films were characterized by UV-vis spectroscopy, ellipsometry, and cyclic voltammetry, while characterization of the single-walled nanotubes was performed with transmission electron microscopy, Raman spectroscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy. When the GOX solution contained single-walled carbon nanotubes (GOX-SWNTs), the oxidation peak currents during cyclic voltammetry increased 1.4-4.0 times, as compared to films without SWNTs. Similarly the glucose electro-oxidation current also increased (6-17 times) when SWNTs were present. By varying the number of multilayers, the sensitivity of the sensors could be controlled.

Aspergillus niger↗
PubMed2006

Layer-by-layer PMIRRAS characterization of DMPC bilayers deposited on a Au111 electrode surface.

A combination of Langmuir-Blodgett and Langmuir-Schaefer techniques was employed to deposit 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) bilayers at a gold electrode surface. One leaflet consisted of hydrogen-substituted acyl chains, and the second leaflet was composed of molecules with deuterium-substituted acyl chains. This architecture allowed for layer-by-layer analysis of the structure of the bilayer. Photon polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) was used to determine the conformation and orientation of the acyl chains of DMPC molecules in the individual leaflets as a function of the potential applied to the gold electrode. The bilayer is adsorbed onto the metal surface when the field applied to the membrane does not exceed approximately 108 V/m. When adsorbed, the bottom leaflet is in contact with a hydrophobic metal surface, and the top leaflet is interacting with the aqueous solution. The asymmetry of the environment has an effect on the orientation of the DMPC molecules in each leaflet. The tilt angle of the acyl chains of the DMPC molecules in the bottom leaflet that is in contact with the gold is approximately 10 degrees smaller than that observed for the top leaflet that is exposed to the solution. These studies provide direct evidence that the structure of a phospholipid bilayer deposited at an electrode surface is affected by interaction with the metal.

Dimyristoylphosphatidylcholine↗
PubMed2007

Layer-by-layer assembly of pH-responsive, compositionally controlled (co)polyelectrolytes synthesized via RAFT.

Homo- and block copolyelectrolytes that have well-defined structures and are responsive to pH were synthesized via reversible addition-fragmentation chain-transfer (RAFT) polymerization and employed to produce layer-by-layer (LBL) films. Acrylamido monomers with carboxylate, sulfonate, and amine functionality were utilized to provide both strong and weak homopolyelectrolytes and mixed strong/weak copolyelectrolyte systems. Multilayer films were prepared under specified conditions of pH and ionic strength and analyzed via atomic force microscopy and ellipsometry to study the effects of changes in the local molecular environment on film morphologies. The pH responsiveness and integrity of the multilayer assemblies were investigated by exposing films to solutions of varying pH in a fluid cell and performing in situ AFM analysis. The multilayer dimensions, morphology, and integrity were found to depend on the molecular architecture of the polyelectrolytes, with changes in segmental type and repeating unit distribution producing dramatic differences in film characteristics. These results suggest the possibility of producing LBL assemblies of precisely controlled dimensions and properties by specifically tailoring copolymer structure. To our knowledge, this is the first report of LBL assembly of RAFT-synthesized homo- and copolyelectrolyte multilayer complexes.

Journal Article↗
PubMed2007

Nanopatterning and fabrication of memory devices from layer-by-layer poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) ultrathin films.

A write-read-erasable memory device was fabricated on layer-by-layer (LbL) ultrathin films prepared from poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT-PSS) and poly(diallyldimethylammonium chloride) (PDDA). By use of current-sensing atomic force microscopy (CS-AFM), nanopatterns were formed by applying a bias voltage between a conductive tip (Pt-coated Si3N4 cantilever) in contact with the polymer film and gold substrate. The dependence of the nanopatterns on film thickness, applied bias, and writing speed was studied. Moreover, the height of the patterns was 3-5 times higher than the original thickness of the films, opening the possibility for three-dimensional nanopatterning. The ability of the patterns to be erased after nanowriting was also investigated. By comparing the I-V characteristics under ambient conditions and under N2 environment, a joule-heating activated, water meniscus-assisted anion doping mechanism for the nanopatterning process was determined. Write-read-erase memory device capability was demonstrated on the nanopatterns.

Journal Article↗
PubMed2006

Catalytic membranes prepared using layer-by-layer adsorption of polyelectrolyte/metal nanoparticle films in porous supports.

Layer-by-layer adsorption of polyelectrolytes and gold nanoparticles within porous supports provides a convenient method for forming catalytic membranes. The polyelectrolyte film effectively immobilizes the gold nanoparticles without inhibiting access to catalytic sites, as shown by the similar rate constants for nanoparticle-catalyzed 4-nitrophenol reduction in solution and in membranes. Modified alumina membranes reduce >99% of 0.4 mM 4-nitrophenol at linear flow rates of 0.98 cm/s, and the modification process is also applicable to track-etched polycarbonate supports.

Adsorption↗
PubMed2005

Cofacial porphyrin multilayers via layer-by-layer assembly.

This paper reports a new layer-by-layer assembly approach to fabricate multilayers of cofacially aligned porphyrins on solid supports by a selective siloxane formation utilizing tetraphenylporphyrinatosilicon(IV) chloride as the building block.

Journal Article↗
PubMed2004

A functional chimaeric S-layer-enhanced green fluorescent protein to follow the uptake of S-layer-coated liposomes into eukaryotic cells.

The chimaeric gene encoding a C-terminally truncated form of the S-layer protein SbpA of Bacillus sphaericus CCM 2177 and the EGFP (enhanced green fluorescent protein) was ligated into plasmid pET28a and cloned and expressed in Escherichia coli. Just 1 h after induction of expression an intense EGFP fluorescence was detected in the cytoplasm of the host cells. Expression at 28 degrees C instead of 37 degrees C resulted in clearly increased fluorescence intensity, indicating that the folding process of the EGFP moiety was temperature sensitive. To maintain the EGFP fluorescence, isolation of the fusion protein from the host cells had to be performed in the presence of reducing agents. SDS/PAGE analysis, immunoblotting and N-terminal sequencing of the isolated and purified fusion protein confirmed the presence of both the S-layer protein and the EGFP moiety. The fusion protein had maintained the ability to self-assemble in suspension and to recrystallize on peptidoglycan-containing sacculi or on positively charged liposomes, as well as to fluoresce. Comparison of fluorescence excitation and emission spectra of recombinant EGFP and rSbpA(31-1068)/EGFP revealed identical maxima at 488 and 507 nm respectively. The uptake of liposomes coated with a fluorescent monomolecular protein lattice of rSbpA(31-1068)/EGFP into HeLa cells was studied by confocal laser-scanning microscopy. The major part of the liposomes was internalized within 2 h of incubation and entered the HeLa cells by endocytosis.

Bacterial Proteins↗
PubMed2003

Cerebellar hypoplasia with heterotopic purkinje cells in the molecular layer and preservation of the granule layers associated with severe encephalopathy. A new entity?

We present the case of an infant girl, born to first cousins, with a clinical phenotype consisting of microcephaly, hypotonia, strabismus and severe psychomotor retardation. Magnetic resonance imaging (MRI) showed global cerebellar atrophy involving the vermis and both hemispheres. The patient's serum transferrin levels were consistently unremarkable. Cerebellar biopsy, performed at 13 months of age, revealed heterotopic Purkinje cells in the molecular layer, but preservation of the external and internal granular layers. To our knowledge, this histological pattern of cerebellar cortical disorganization has not been described previously. The consanguinity of the parents suggests an autosomal recessive inheritance.

Brain Diseases↗
PubMed2006

[Success rates of two-layer, microsurgical vasovasostomy. Results from a patient questionnaire and comparison with one-layer technique].

UNLABELLED: Vasovasostomy is the most commonly performed procedures in the therapy for occlusive azoospermia after vasectomy. In our clinic the two-layer microsurgical technique (DL VVST) is considered to be the gold standard. We have examined the results of DL VVST by means of a questionnaire and compared them with those of the monolayer technique (ML VVST). MATERIALS AND METHOD: In the period from 1996 to 2001, a microsurgical DL VVST with 10 x 0 Prolene sutures under the operation microscope was performed in 141 patient. Aspects of the operation, social aspects and postoperative results (results of spermiogram, birth rates) were assessed by means of a questionnaire. The results were compared with those of a historical patient collective who had undergone a modified monolayer VVST with 7 x 0 Prolene (n = 64). RESULTS: The questionnaire could be sent to 90/141 patients, the response rate was 63/90 (70 %). The time interval between vasectomy and VVST was on average 9.5 years. The patency rate was 86 %, the birth rate 24 %. Severe or moderately sever complications did not occur. In the historical patient collective, the average occlusion interval was 6.9 years. The patency rate in these patients in whom the VVST was performed merely under the loupe and in a monolayer technique was 87 %, the pregnancy rate 48 %. CONCLUSION: The highly positive results of VVST with pregnancy rates > 80 % from earlier publications could not be reproduced. According to our results, the two-layer VVST does not afford better results than the monolayer technique.

Adult↗
PubMed1993

Localization of 3 beta-hydroxysteroid dehydrogenase in the chicken ovarian follicle shifts from the theca layer to granulosa layer with follicular maturation.

3 beta-Hydroxysteroid dehydrogenase (3 beta-HSD) catalyzes the conversion of pregnenolone to progesterone in the delta 4-3-ketosteroid metabolic pathway and dehydroepiandrosterone to androstenedione in the delta 5-3 beta-hydroxysteroid pathway. It has been suggested that small follicles of the chicken ovary that have not entered the follicular hierarchy metabolize steroids via the delta 5-3 beta-hydroxysteroid pathway, whereas preovulatory follicles that have entered the hierarchy metabolize steroids via the delta 4-3-ketosteroid pathway. Our objective was to localize 3 beta-HSD in follicles of the chicken ovary by immunocytochemistry using an anti-human placental 3 beta-HSD polyclonal antiserum to identify steroidogenic cells that convert pregnenolone to progesterone and/or dehydroepiandrosterone to androstenedione. Three groups of follicles of different maturities were examined: small follicles (1-10 mm in diameter and that have not entered the hierarchy), preovulatory follicles (10-35 mm in diameter and that have entered the hierarchy), and the most recent postovulatory follicle. Chicken ovaries were obtained 2 h after oviposition and fixed with Bouin's solution. Tissues were dehydrated with a series of ethanol, embedded in Paraplast (Brunswick Company, St. Louis, MO), and sectioned. Sections (4 microns) were immunostained for 3 beta-HSD with a Rabbit ExtrAvidin Staining Kit (Sigma Chemical Co., St. Louis, MO). 3 beta-HSD was localized in the single theca layer of cortical follicles (approximately 1 mm in diameter), which are still embedded in the stromal tissue, and in the theca interna and externa of other small follicles (< 10 mm in diameter). No immunoreactivity was observed in the granulosa layer of the majority of small follicles.(ABSTRACT TRUNCATED AT 250 WORDS)

3-Hydroxysteroid Dehydrogenases↗