Biomedical subjects

Nicholas L Abbott

Publications and source records attributed to Nicholas L Abbott.

At least 19 recordsLinked to original sources

PubMed2006

Infrared spectroscopy of competitive interactions between liquid crystals, metal salts, and dimethyl methylphosphonate at surfaces.

We report the use of Fourier transform polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS) to characterize the influence of dimethyl methylphosphonate (DMMP) on the molecular interactions occurring within thin films of nitrile-containing liquid crystals supported on surfaces presenting metal perchlorate salts. Infrared spectra obtained using thin films of 4'-octyl-4-biphenylcarbonitrile (8CB) supported on copper(II) perchlorate salts reveal the nitrile groups of 8CB to be coordinated to the copper(II) on these surfaces, and subsequent exposure of the system to DMMP to result in the elimination of these coordinated nitrile groups. Concurrently, evidence of coordination of the phosphoryl group of DMMP with copper(II) is provided by measurement of a shift of the phosphoryl stretch from 1246 to 1198 cm(-1). In contrast, surfaces presenting nickel(II) perchlorate salts only weakly coordinate with DMMP [the phosphoryl peak shifts from 1246 to 1213 cm(-1) in the presence of nickel(II)], and exposure of 8CB to DMMP results in only partial loss of coordination of the nitrile groups of 8CB with nickel(II). These PM-IRRAS measurements and others reported in this article provide insights into the molecular origins of macroscopic ordering transitions that are observed when micrometer-thick films of nitrile-containing liquid crystals supported on copper(II) or nickel(II) perchlorate are exposed to DMMP: Upon exposure to DMMP, nematic phases of 4'-pentyl-4-biphenylcarbonitrile (5CB) supported on copper(II) perchlorate salts undergo ordering transitions, whereas 5CB supported on nickel(II) perchlorate salts do not. Our IR results support the hypothesis that these ordering transitions reflect the relative strengths of coordination interactions occurring between the 5CB, DMMP, and the metal salts at these interfaces.

Journal Article↗

PubMed2006

Influence of 4-cyano-4'-biphenylcarboxylic acid on the orientational ordering of cyanobiphenyl liquid crystals at chemically functionalized surfaces.

We report two methods that involve tailoring of the chemical composition of the nematic liquid crystal 4-cyano-4'-pentylbiphenyl to achieve control over the orientational ordering of the liquid crystal on chemically functionalized surfaces. The first method involves the direct addition of 4-cyano-4'-biphenylcarboxylic acid to 4-cyano-4'-pentylbiphenyl. The second method involves exposure of 4-cyano-4'-pentylbiphenyl to ultraviolet light and photochemical generation of a range of products, including 4-cyano-4'-biphenylcarboxylic acid. The addition of the acid or exposure to ultraviolet light accelerated the rate at which the liquid crystal exhibited an orientational transition from planar to perpendicular (homeotropic) alignment on surfaces presenting ammonium groups. The appearance of the homeotropic orientation of the UV-treated 4-cyano-4'-pentylbiphenyl on ammonium-terminated surfaces was dependent on the thickness of the film of liquid crystal (13-50 mum), consistent with a dipolar coupling between the liquid crystal and the electric field associated with an electrical double layer generated at the ammonium surface. Although the addition of 4-cyano-4'-biphenylcarboxylic acid or UV treatment of the liquid crystal also promoted homeotropic orientations on surfaces presenting hydroxyl groups, the orientations of the UV-treated liquid crystal on the hydroxyl-terminated surface did not change with thickness of the film of liquid crystal in the manner observed on the ammonium-terminated surfaces. The latter result indicates that the mechanism leading to homeotropic anchoring on hydroxyl-terminated surfaces is distinct from that on ammonium-terminated surfaces. Measurements performed using polarization modulation infrared reflection-absorption spectroscopy suggest that hydrogen bonding between the 4-cyano-4'-biphenylcarboxylic acid and the hydroxyl-terminated surface is responsible for the homeotropic anchoring on the surface. Finally, the orientation of the liquid crystal on methyl-terminated surfaces was not influenced by the addition of 4-cyano-4'-biphenylcarboxylic acid nor UV treatment. These results illustrate how the chemical composition of liquid crystals can be manipulated to achieve control over their ordering on surfaces that possess chemical functionality relevant to the development of liquid crystal-based sensors and diagnostic tools. We illustrate the utility of this approach by using the tailored liquid crystal to amplify and optically transduce the presence of proteins arrayed on ammonium-terminated surfaces.

Biphenyl Compounds↗

PubMed2006

Anchoring energies of liquid crystals measured on surfaces presenting oligopeptides.

We report a methodology that permits quantitation of the azimuthal anchoring energy of the nematic liquid crystal 4-cyano-4'-pentyl-biphenyl on surfaces patterned with oligopeptides. The oligopeptide (IYGEFKKKC), an optimized substrate for the Src protein kinase, was covalently immobilized via the terminal cysteine to monolayers of amine-terminated tetra(ethylene glycol) formed on gold films. The measurements of anchoring energies, which were based on a torque-balance method, revealed a systematic decrease in anchoring energy from 3.7 +/- 0.6 microJ/m2 with increasing surface density of oligopeptide. We calculate that a mass density of oligopeptide of less than 1 ng/cm2 can lead to a measurable change in the anchoring energy of the nematic liquid crystal. These results suggest that measurements of anchoring energies of liquid crystals on surfaces may offer the basis of quantitative and label-free methods for detecting biomolecules on surfaces.

Liquid Crystals↗

PubMed2006

Characterization of protein immobilization at silver surfaces by near edge X-ray absorption fine structure spectroscopy.

Ribonuclease A (RNase A) is immobilized on silver surfaces in oriented and random form via self-assembled monolayers (SAMs) of alkanethiols. The immobilization process is characterized step-by-step using chemically selective near-edge X-ray absorption fine structure spectroscopy (NEXAFS) at the C, N, and S K-edges. Causes of imperfect immobilization are pinpointed, such as oxidation and partial desorption of the alkanethiol SAMs and incomplete coverage. The orientation of the protein layer manifests itself in an 18% polarization dependence of the NEXAFS signal from the N 1s to pi* transition of the peptide bond, which is not seen for a random orientation. The S 1s to C-S sigma* transition exhibits an even larger polarization dependence of 41%, which is reduced to 5% for a random orientation. A quantitative model is developed that explains the sign and magnitude of the polarization dependence at both edges. The results demonstrate that NEXAFS is able to characterize surface reactions during the immobilization of proteins and to provide insight into their orientations on surfaces.

Absorption↗

PubMed2006

Anisotropic nanoparticles immersed in a nematic liquid crystal: defect structures and potentials of mean force.

We report results for the potential of mean force (PMF) and the defect structures that arise when spherocylindrical nanoparticles are immersed in a nematic liquid crystal. Using a dynamic field theory for the tensor order parameter Q of the liquid crystal, we analyzed configurations, including one, two, and three elongated particles, with strong homeotropic anchoring at their surfaces. For systems with one nanoparticle, the most stable configuration is achieved when the spherocylinder is placed with its long axis perpendicular to the far-field director, for which the defect structure consists of an elongated Saturn ring. For systems with two or three nanoparticles with their long axes placed perpendicular to the far-field director, at small separations the defect structures consist of incomplete Saturn rings fused with new disclination rings orthogonal to the original ones, in analogy to results previously observed for spherical nanoparticles. The shape of these orthogonal rings depends on the nanoparticles' configuration, i.e., triangular, linear, or parallel with respect to their long axis. A comparison of the PMFs indicates that the latter configuration is the most stable. The stability of the different arrays depends on whether orthogonal disclination rings form or not, their size, and the curvature effects in the interparticle regions. Our results suggest that the one-elastic-constant approximation is valid for the considered systems; similar results were obtained when a three-constant expression is used to represent the elastic free energy. The attractive interactions between the elongated particles were compared to those observed for spheres of similar diameters. Similar interparticle energies were observed for linear arrays; in contrast, parallel and triangular arrays of spherocylinders yielded interactions that were up to 3.4 times stronger than those observed for spherical particles.

Journal Article↗

PubMed2006

Lyotropic liquid crystals from designed helical beta-peptides.

We demonstrate that 14-helical beta-peptides can self-assemble to form lyotropic liquid crystalline (LC) phases in water. beta-Peptides 1-4 were designed to form globally amphiphilic 14-helices of increasing length. Optical microscopy showed that several of these beta-peptides formed LC phases in aqueous solutions at concentrations as low as 2.5 wt % (15 mM). Liquid crystallinity appears to require the adoption of a globally amphiphilic conformation because a scrambled sequence, 5, does not display LC behavior. Thermal stability and reversibility of LC phase formation were assessed by variable temperature 2H NMR spectroscopy and optical microscopy. The LC phase formed by beta-peptide 3 at 10 wt % is disrupted above 40 degrees C in D2O and re-forms within minutes upon cooling. LC phase behavior for solutions of 3 is influenced by concentration and net charge. These studies demonstrate that highly folded 14-helical beta-peptides can produce LC phases at shorter lengths than do alpha-helical alpha-peptide mesogens and can provide a basis for tailoring properties of LC phases for future applications.

Hydrogen Bonding↗

PubMed2006

Measurement of the azimuthal anchoring energy of liquid crystals in contact with oligo(ethylene glycol)-terminated self-assembled monolayers supported on obliquely deposited gold films.

We report measurements of the orientations and azimuthal anchoring energies of the nematic liquid crystal 4-cyano-4'-pentylbiphenyl (5CB) on polycrystalline gold films that are deposited from a vapor at an oblique angle of incidence and subsequently decorated with organized monolayers of oligomers of ethylene glycol. Whereas the gold films covered with monolayers presenting tetra(ethylene glycol) (EG4) lead to orientations of 5CB that are perpendicular to the plane of incidence of the gold, monolayers presenting tri(ethylene glycol) (EG3) direct 5CB to orient parallel to the plane of incidence of the gold during deposition of the gold film. We also measure the azimuthal anchoring energy of the 5CB to be smaller on the surfaces presenting EG3 (3.2 +/- 0.8 microJ/m2) as compared to EG4 (5.5 +/- 0.9 microJ/m2). These measurements, when combined with other results presented in this paper, are consistent with a physical model in which the orientation and anchoring energies of LCs on these surfaces are influenced by both (i) short-range interactions of 5CB with organized oligomers of ethylene glycol at these surfaces and (ii) long-range interactions of 5CB with the nanometer-scale topography of the obliquely deposited films. For surfaces presenting EG3, these short- and long-range interactions oppose each other, leading to small net values of anchoring energies that we predict are dependent on the level of order in the EG3 SAM. These measurements provide insights into the balance of interactions that control the orientational response of LCs to biological species (proteins, viruses, cells) on these surfaces.

Biphenyl Compounds↗

PubMed2006

Ferrocene-containing cationic lipids for the delivery of DNA: oxidation state determines transfection activity.

The ability of two redox-active, ferrocene-containing cationic lipids [11-(ferrocenylundecyl)trimethylammonium bromide (FTMA) and bis(11-ferrocenylundecyl)dimethylammonium bromide (BFDMA)] to transfect mammalian cells was investigated. This study sought to determine the range of conditions over which these lipids were capable of transfecting cells and whether the oxidation state of the ferrocenyl groups in these materials could be used to influence the extent of transfection. Experiments conducted in the COS-7 cell line demonstrated that reduced and oxidized FTMA were substantially cytotoxic and did not transfect cells. Subsequent experiments conducted using BFDMA and reporter plasmids encoding enhanced green fluorescent protein (EGFP) and firefly luciferase demonstrated that BFDMA was able to transfect cells. However, the extent of transfection depended significantly upon both the concentration of BFDMA and the oxidation state of the lipid. Quantitative characterization of cytotoxicity and gene expression demonstrated that a window of concentration existed over which reduced BFDMA was non-cytotoxic and yielded high levels of transfection, but over which electrochemically oxidized BFDMA yielded very low (background) levels of transfection. Characterization of lipoplexes using dynamic light scattering demonstrated that reduced and oxidized BFDMA formed small aggregates (ca. 90 to 250nm) at concentrations of lipid ranging from 2 to 10 microM. Taken together, these results demonstrate that the oxidation state of BFDMA, which can be controlled electrochemically, can be used to control the extent of cell transfection. These results could form the basis of transfection procedures that exploit the redox behavior of ferrocene-containing lipids to achieve active spatial and temporal control over transfection using electrochemical methods.

Animals↗

PubMed2006

Anchoring of nematic liquid crystals on viruses with different envelope structures.

The ordering of synthetic liquid crystals near surfaces is known to be dependent on the nanoscopic structure and chemical functionality of surfaces. In this letter, we report that the orientational ordering of synthetic liquid crystals on surfaces decorated with viruses is also dependent on the structures of the viruses. Each of the four virions investigated had diameters of approximately 100 nm, but three of the viruses (influenza virus, La Crosse virus, and vesicular stomatitis virus) were enveloped in a lipid bilayer, whereas one virus (adenovirus) was not. We observed that lipid bilayer-enveloped viruses induce homeotropic (perpendicular) ordering of a nematic liquid crystal upon contact with the liquid crystal. In contrast, nonenveloped virus (adenovirus)-treated surfaces caused a near-planar orientation of the liquid crystal. We conclude that the homeotropic ordering of liquid crystals is a signature of the presence of enveloped viruses present on surfaces. These results suggest new approaches to the design of nanostructured materials that incorporate viruses as well as suggest methods that can be used to amplify the presence of nanoscopic virions into micrometer-sized domains of liquid crystal that can be optically probed.

Adenoviridae↗

PubMed2006

Tailoring the interfaces between nematic liquid crystal emulsions and aqueous phases via layer-by-layer assembly.

We report the assembly of polyelectrolyte multilayer (PEM) films at the interfaces of thermotropic liquid crystal (LC) droplets dispersed in an aqueous phase. Exposure of PEM-coated droplets to surfactant slowed the bipolar-to-radial ordering transition of the LCs by 2 orders of magnitude relative to naked droplets. This shows that PEMs can be used to influence the interactions of analytes with the LC cores of the droplets, allowing tuning of the LC emulsion sensing properties.

Crystallization↗

PubMed2005

Electrochemical control of the interactions of polymers and redox-active surfactants.

We report the characterization of aqueous solutions (0.1 M Li(2)SO(4)) of dilute ethyl(hydroxyethyl) cellulose (EHEC) mixed with the redox-active surfactant (11-ferrocenylundecyl)trimethylammonium bromide (FTMA) by measurements of clouding temperatures and dynamic light scattering. The investigation sought to test the hypothesis that FTMA, which forms micelles in aqueous solution in its reduced state but not in its oxidized state, would permit reversible control over the formation of polymer-surfactant complexes in solution. Our measurements revealed that low concentrations of reduced FTMA enhance aggregation, whereas high concentrations of reduced FTMA disperse polymer-surfactant aggregates. This behavior is qualitatively similar to both dodecyltrimethylammonium bromide and sodium dodecyl sulfate and reflects cooperative interactions between FTMA and EHEC. In contrast, oxidized FTMA was found not to promote EHEC aggregation at low concentrations of oxidized FTMA nor disperse EHEC aggregates at high concentrations. Measurements of dynamic light scattering revealed that the reduction of oxidized FTMA in solutions of EHEC containing 0.1-0.3 mmolal FTMA causes an increase in the sizes of polymer-surfactant aggregates of more than 1 order of magnitude. Our cloud point measurements also revealed that clouding can be induced isothermally via the electrochemical reduction of oxidized FTMA at room temperature at FTMA concentrations between 0.4 and 10 mmolal. In contrast, at concentrations of FTMA greater than 15 mmolal, the reduction of oxidized FTMA induces the clearing of EHEC solutions. We conclude that aggregation of EHEC in dilute solutions can be controlled by the manipulation of the oxidation state of FTMA.

Micelles↗

PubMed2005

Ferrocene-containing cationic lipids: influence of redox state on cell transfection.

A ferrocene-containing, redox-active cationic lipid that can be transformed using electrochemical methods yields large differences in cell transfection depending on the oxidation state of the lipid. Expression of enhanced green fluorescent protein and firefly luciferase occurs at very high levels when DNA lipoplexes are formulated using the lipid in the reduced state. In contrast, transfection is negligible when oxidized lipid is used. These observations suggest the basis of a general method that could be used to transform inactive lipoplex formulations to an active form through the application of externally applied electrical potentials. The ability to activate lipoplexes toward transfection electrochemically and "on demand" could create new opportunities to deliver DNA in vitro and in vivo with both spatial and temporal control.

Animals↗

PubMed2005

Interactions of liquid crystal-forming molecules with phospholipid bilayers studied by molecular dynamics simulations.

Recent experiments have shown that liquid crystals can be used to image mammalian cell membranes and to amplify structural reorganization in phospholipid-laden liquid crystal-aqueous interfaces. In this work, molecular dynamics simulations were employed to explore the interactions between commonly used liquid crystal-forming molecules and phospholipid bilayers. In particular, umbrella sampling was used to obtain the potential of mean force of 4-cyano-4'-pentylbiphenyl (5CB) and 4'-(3,4-difluor-phenyl)-4-pentyl-bicylohexyl (5CF) molecules partitioning into a dipalmitoylphosphatidylcholine bilayer. In addition, results of simulations are presented for systems consisting of a fully hydrated bilayer with 5CB or 5CF molecules at the lowest (4.5 mol %) and highest (20 mol %) concentrations used in recent laboratory experiments. It is found that mesogens preferentially partition from the aqueous phase into the membrane; the potential of mean force exhibits highly favorable free energy differences for partitioning (-18 k(B)T for 5CB and -26 k(B)T for 5CF). The location and orientation of mesogens associated with the most stable free energies in umbrella sampling simulations of dilute systems were found to be consistent with those observed in liquid-crystal-rich bilayers. It is found that the presence of mesogens in the bilayer enhances the order of lipid acyl tails, and changes the spatial and orientational arrangement of lipid headgroup atoms. These effects are more pronounced at higher liquid-crystal concentrations. In comparing the behavior of 5CB and 5CF, a stronger spatial correlation (i.e., possibly leading to aggregation) is observed between 5CB molecules within a bilayer than between 5CF molecules. Also, the range of molecular orientations and positions along the bilayer normal is larger for 5CB molecules. At the same time, 5CF molecules were found to bind more strongly to lipid headgroups, thereby slowing the lateral motion of lipid molecules.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed2005

Influence of surfactant tail branching and organization on the orientation of liquid crystals at aqueous-liquid crystal interfaces.

We have examined the influence of two aspects of surfactant structure--tail branching and tail organization--on the orientational ordering (so-called anchoring) of water-immiscible, thermotropic liquid crystals in contact with aqueous surfactant solutions. First, we evaluated the influence of branches in surfactant tails on the anchoring of nematic liquid crystals at water-liquid crystal interfaces. We compared interfaces that were laden with one of three linear surfactants (sodium dodecyl sulfate, sodium dodecanesulfonate, and isomerically pure linear sodium dodecylbenzenesulfonate) to interfaces laden with branched sodium dodecylbenzenesulfonate. We carried out these experiments at 60 degrees C, above the Krafft temperatures of all the surfactants studied, and used the liquid crystal TL205 (a mixture of cyclohexane-fluorinated biphenyls and fluorinated terphenyls), which forms a nematic phase at 60 degrees C. Linear surfactants caused TL205 to assume a perpendicular orientation (homeotropic anchoring) above a threshold concentration of surfactant and parallel orientation (planar anchoring) at lower concentrations. In contrast, branched sodium dodecylbenzenesulfonate caused planar anchoring of TL205 at all concentrations up to the critical micelle concentration of the surfactant. Second, we used sodium dodecanesulfonate and a commercial linear sodium dodecylbenzenesulfonate to probe the influence of surfactant tail organization on the orientations of liquid crystals at water-liquid crystal interfaces. Commercial linear sodium dodecylbenzenesulfonate, which comprises a mixture of ortho and para isomers, has been previously characterized to form less ordered monolayers than sodium dodecanesulfonate at oil-water interfaces at room temperature. We found sodium dodecanesulfonate to cause homeotropic anchoring of both TL205 and 4'-pentyl-4-cyanobiphenyl (5CB, nematic at room temperature), whereas commercial linear sodium dodecylbenzenesulfonate caused predominantly planar and tilted orientations of both TL205 and 5CB. These results, when combined, lead us to conclude that (1) interactions between the aliphatic tails of surfactants and liquid crystals largely dictate the orientations of liquid crystals at aqueous-liquid crystal interfaces, (2) the interactions that orient the liquid crystals at these interfaces are sensitive to the branching and degree of disorder in the surfactant tails, and (3) differences in the chemical composition of TL205 and 5CB, most notably fluorination of TL205, lead to subtle differences in the orientations of these two nematic liquid crystals.

Crystallization↗

PubMed2005

Small-angle neutron scattering from mixtures of sodium dodecyl sulfate and a cationic, bolaform surfactant containing azobenzene.

This paper reports on the microstructures formed in aqueous solutions containing mixtures of sodium dodecyl sulfate (SDS) and a photosensitive, bolaform surfactant, bis(trimethylammoniumhexyloxy)azobenzene dibromide (BTHA). By using quasi-elastic light scattering and small-angle neutron scattering, we determined that aqueous solutions containing SDS and the trans isomer of BTHA (0.1 wt % total surfactant, 15 mol % BTHA, 85 mol % SDS) form vesicles with average hydrodynamic diameters of 1350 +/- 50 angstroms and bilayer thicknesses of 35 +/- 2 angstroms. The measured bilayer thickness is consistent with a model of the vesicle bilayer in which the trans isomer of BTHA spans the bilayer. Upon illumination with UV light, the BTHA underwent photoisomerization to produce a cis-rich photostationary state (80% cis isomer). We measured this photoisomerization to drive the reorganization of vesicles into cylindrical aggregates with cross-sectional radii of 19 +/- 3 angstroms and average hydrodynamic diameters of 240 +/- 50 angstroms. Equilibration of the cis-rich solution in the dark at 25 degrees C for 12 h or illumination of the solution with visible light leads to the recovery of the trans-rich photostationary state of the solution and the reformation of vesicles, thus demonstrating the potential utility of this system as the basis of a tunable fluid.

Azo Compounds↗

PubMed2005

Orientations of nematic liquid crystals on surfaces presenting controlled densities of peptides: amplification of protein-peptide binding events.

We report a study of the orientations of nematic liquid crystals (LCs) in contact with peptide-modified, oligoethylene glycol-containing, self-assembled monolayers (SAMs). The SAMs were formed on gold films that were prepared by physical vapor deposition at an oblique angle of incidence. Two peptides were investigated: the optimized substrate for the Src protein kinase (IYGEFKKKC) and the synthetic equivalent of that peptide after kinase modification (IpYGEFKKKC). Polarization modulation-infrared reflectance absorbance spectroscopy (PM-IRRAS) was used to characterize the relative areal densities and orientations of these peptides at the interface. We conclude that the presence/absence of a phosphate group can influence the maximum packing density of immobilized peptide. We evaluated the orientations of the nematic liquid crystal 5CB in contact with these peptide-modified surfaces by using polarized microscopy. The time required for the nematic phase of 5CB to exhibit long-range orientational ordering (uniform alignment) was found to increase with increasing areal densities of immobilized peptide. We also found that the specific binding event between anti-phosphotyrosine IgG and the surface-immobilized phosphopeptide leads to an increase in the time required for the liquid crystal to achieve uniform anchoring (exceeding the experimentally accessible time scales). These results, when combined, suggest that the areal density and size of biomolecules at an interface can influence the time required for liquid crystals in contact with nanostructured surfaces to exhibit long-range orientational order. Finally, we illustrate the potential utility of this system by demonstrating that liquid crystals can be used to amplify and report protein binding events occurring on a spatially resolved peptide array.

Amino Acid Sequence↗

PubMed2005

Functional monolayers for improved resistance to protein adsorption: oligo(ethylene glycol)-modified silicon and diamond surfaces.

The interaction of proteins with semiconductors such as silicon and diamond is of great interest for applications such as electronic biosensing. We have investigated the use of covalently bound oligo(ethylene glycol), EG, monolayers on diamond and silicon to minimize nonspecific protein adsorption. Protein adsorption was monitored by fluorescence scanning as a function of the length of the ethylene glycol chain (EG3 through EG6) and the terminal functional group (methyl- versus hydroxyl-terminated EG3 monolayer). More quantitative measurements were made by eluting adsorbed avidin from the surface and measuring the intensity of fluorescence in the solution. The attachment chemistry of the tri(ethylene glycol) molecules and monolayer orientation was studied by X-ray photoelectron spectroscopy. Improvement in the selectivity of surfaces modified with EG functionality was demonstrated in two model biosensing assays. We find that high-quality EG monolayers are formed on silicon and diamond and that these EG3 monolayers are as effective as EG3 self-assembled monolayers on gold at resisting nonspecific avidin adsorption. These results show promise for use of silicon and diamond materials in many potential applications such as biosensing and medical implants.

Adsorption↗

PubMed2005

Using liquid crystals to report membrane proteins captured by affinity microcontact printing from cell lysates and membrane extracts.

The chemical heterogeneity of proteins makes development of general and facile surface-based methods for protein analysis a substantial challenge, particularly when analyzing transmembrane proteins. Here, we report a simple surface-based procedure that permits detection of transmembrane proteins from crude cell lysates and cell membrane extracts. The method relies on the use of thermotropic liquid crystals to amplify and report the presence of the transmembrane proteins captured by an affinity ligand on the surface of an elastomeric stamp. A merit of this approach is that the proteins can be imaged on surfaces without requiring the use of matched pairs of antibodies, labels, or complex instrumentation. Detection of epidermal growth factor receptor, a transmembrane glycoprotein, is demonstrated.

Affinity Labels↗