-
[show abstract]
[hide abstract]
ABSTRACT: Abstract The respiratory system is one of the portals of entry into the body, and hence inhalation of engineered nanomaterials is an important route of exposure. The broad range of physicochemical properties that influence biological responses necessitate the systematic study to contribute to understanding occupational exposure. Here, we report on the influence of nanoparticle charge and dose on human airway epithelial cells, and show that this platform can be used to evaluate consequences of exposure to engineered nanomaterials.
Nanotoxicology 07/2012; · 5.76 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Membrane active peptides exert their biological effects by interacting directly with a cell's lipid bilayer membrane. These therapeutically promising peptides have demonstrated a variety of activities including antimicrobial, cytolytic, membrane translocating, and cell penetrating activities. Here, we use electrochemical impedance spectroscopy (EIS) on polymer-cushioned supported lipid bilayers constructed on single crystal silicon to study two pairs of closely related membrane active peptides selected from rationally designed, combinatorial libraries to have different activities in lipid bilayers: translocation, permeabilization, or no activity. Using EIS, we observed that binding of a membrane translocating peptide to the lipid bilayer resulted in a small decrease in membrane resistance followed by a recovery back to the original value. The recovery may be directly attributable to peptide translocation. A nontranslocating peptide did not decrease the resistance. The other pair, two membrane permeabilizing peptides, caused an exponential decrease of membrane resistance in a concentration-dependent manner. This permeabilization of the supported bilayer occurs at peptide to lipid ratios as much as 1000-fold lower than that needed to observe effects in vesicle leakage assays and gives new insights into the fundamental peptide-bilayer interactions involved in membrane permeabilization.
Langmuir 03/2012; 28(14):6088-96. · 4.19 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Applications in nanomedicine, such as diagnostics and targeted therapeutics, rely on the detection and targeting of membrane biomarkers. In this article we demonstrate absolute quantitative profiling, spatial mapping, and multiplexing of cancer biomarkers using functionalized quantum dots (QDs). We demonstrate highly selective targeting molecular markers for pancreatic cancer with extremely low levels of nonspecific binding. We confirm that we have saturated all biomarkers on the cell surface, and, in conjunction with control experiments, extract absolute quantitative values for the biomarker density in terms of the number of molecules per square micron on the cell surface. We show that we can obtain quantitative spatial information of biomarker distribution on a single cell, important because tumors' cell populations are inherently heterogeneous. We validate our quantitative measurements (number of molecules per square micron) using flow cytometry and demonstrate multiplexed quantitative profiling using color-coded QDs. FROM THE CLINICAL EDITOR: This paper demonstrates a nice example for quantum dot-based molecular targeting of pancreatic cancer cells for advanced high sensitivity diagnostics and potential future selective therapeutic purposes.
Nanomedicine: nanotechnology, biology, and medicine 02/2012; 8(7):1043-51. · 5.44 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The water solubilization of nanoparticles is key for many applications in biomedicine. Despite the importance of surface functionalization, progress has been largely empirical and very few systematic studies have been performed. Here we report on the water solubilization of quantum dots using lipid encapsulation. We systematically evaluate the monodispersity, zeta potential, stability, and quantum yield for quantum dots encapsulated with single and double acyl-chain lipids, pegylated double acyl-chain lipids, and single alkyl-chain surfactant molecules with charged head groups. We show that charged surfactants and pegylated lipids are important to obtain monodisperse suspensions with high yield and excellent long-term stability. FROM THE CLINICAL EDITOR: This study reports on solubilization of nanoparticles in water, a key, but often neglected aspect for biomedical applications. The authors demonstrate that charged surfactants and PEGylated lipids are important to obtain monodisperse suspensions with high yield and long-term stability.
Nanomedicine: nanotechnology, biology, and medicine 12/2011; 8(7):1190-9. · 5.44 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Electrochemical deposition of metals onto foreign substrates usually occurs through Volmer–Weber island growth. The mechanism of island nucleation and growth dictates the shape, orientation and number density of islands, and ultimately, the structure and properties of thin films. With increasing emphasis on deposition of ultrathin films and nanostructures, it is critically important to understand the kinetics of nucleation and growth. Here we provide a comprehensive review of island growth in electrodeposition and summarize methods for mechanistic analysis in both the kinetic and diffusion limited regimes.
Journal of Physics D Applied Physics 10/2011; 44(44):443001. · 2.54 Impact Factor
-
Small 09/2011; 7(22):3148-52. · 8.35 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Protein imprinting in hydrogels is one approach for developing artificial receptors capable of specific recognition and binding of a target molecule. Through selection of monomers with side groups that can interact with the target protein and control over the degree of cross-linking, the architecture and spatial distribution of interaction points can be optimized for a target protein. Here we report on the imprinting of polyacrylamide-based hydrogels with maltose binding protein (MBP). To design the optimum architecture, we analyze the distribution of surface amino acid residues on the protein surface. We show that the selectivity of MBP recognition is increased by incorporating monomers that can introduce sites for hydrogen bonding, hydrophilic interactions, and electrostatic interactions. MBP-imprinted films showed high specificity and could discriminate between reference proteins with similar molecular weight, dimensions, and isoelectric point.
04/2011;
-
[show abstract]
[hide abstract]
ABSTRACT: Protein switches are engineered fusion proteins with an input domain that recognizes and responds to an input signal and an output domain whose function is regulated by the state of the input domain. Here we demonstrate a fully functional surface tethered protein switch that offers a potential route to a universal biosensing platform.
Chemical Communications 02/2011; 47(12):3398-400. · 6.17 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Metastasis is a complex, multistep process responsible for >90% of cancer-related deaths. In addition to genetic and external environmental factors, the physical interactions of cancer cells with their microenvironment, as well as their modulation by mechanical forces, are key determinants of the metastatic process. We reconstruct the metastatic process and describe the importance of key physical and mechanical processes at each step of the cascade. The emerging insight into these physical interactions may help to solve some long-standing questions in disease progression and may lead to new approaches to developing cancer diagnostics and therapies.
Nature Reviews Cancer 01/2011; 11(7):512-22. · 29.54 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Upon cortical retraction in mitosis, mammalian cells have a dramatically decreased physical association with their environment. Hence, mechanisms that prevent mitotic detachment and ensure appropriate positioning of the resulting daughter cells are critical for effective tissue morphogenesis and repair, and are the subject of this study. We find that, unlike low-motility cells, highly motile cells spread isotropically upon division and do not typically reoccupy their mother-cell footprint, and often even disseminate their mitotic cells. To elucidate these different motility-based phenotypes, we investigated their partial recapitulation and rescue using defined molecular perturbations. We show that activated RhoA is localized at the mitotic cell cortex, and Rho-associated kinase inhibition increases the degree of reoccupation of the mother-cell outline in highly motile cells. Conversely, we show that induction of motility in low-motility cells by RasV12 overexpression results in increased isotropic daughter-cell spreading. We thus propose that a balance between cortical retraction forces, which depend in part on RhoA activation, and substrate adhesion forces, which diminish with increasing motility rates, governs the integrity of mitotic actin retraction fibers and influences subsequent daughter-cell spreading. This balance of forces during mitosis has implications for cancer metastasis.
Biophysical Journal 12/2010; 99(11):3526-34. · 3.65 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We compare the kinetics of copper island growth in the kinetic regime in the presence and absence of anion adsorption and show that the growth exponents are inconsistent with a direct attachment model. In sulfate solution, anion adsorption leads to instantaneous nucleation, equal lateral and vertical growth exponents, and suppressed vertical growth. In perchlorate solution, island growth is characterized by progressive nucleation, enhanced vertical growth, and different lateral and vertical growth exponents. Avrami analysis and analysis of the surface power spectra suggest that island growth is controlled by surface diffusion to the island perimeter.
Nanoscale 11/2010; 2(11):2431-5. · 5.91 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The impedance of alkanethiol self-assembled monolayers at the solid/liquid interface exhibits unusual behavior. The capacitance Cm is independent of applied potential, however, the resistance Rm decreases exponentially at potentials negative to the potential of zero charge (PZC). At potentials positive to the PZC, the monolayer resistance is very large and independent of temperature, whereas at potentials negative to the PZC, the monolayer resistance shows Arrhenius behavior with an activation energy of 0.20 eV. We provide evidence that this effect is related to field-induced torque on the alkanethiol molecules that leads to increasing ion penetration into the monolayer.
Applied Physics Letters 07/2010; 97(4):043110-043110-3. · 3.84 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Programmed subcellular release is an in vitro technique for the quantitative study of cell detachment. The dynamics of cell contraction are measured by releasing cells from surfaces to which they are attached with spatial and temporal control. Release of subcellular regions of cells is achieved by plating cells on an electrode array created by standard microfabrication methods. The electrodes are then biochemically functionalized with an arginine-glycine-aspartic acid (RGD)-terminated thiol. Application of a voltage pulse results in electrochemical desorption of the RGD-terminated thiols, triggering cell detachment. This method allows for the study of the full cascade of events from detachment to subsequent subcellular reorganization. Fabrication of the electrode arrays may take 1-2 d. Preparation for experiments, including surface functionalization and cell plating, can be completed in 10 h. A series of cell release experiments on one device may last several hours.
Nature Protocol 07/2010; 5(7):1273-80. · 8.36 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The assembly of electrically addressable, planar supported bilayers composed of biologically relevant lipids, such as those used in vesicular systems, will greatly enhance the experimental capabilities in membrane and membrane protein research. Here we assess the electrical properties of bilayers composed of a wide range of physiologically relevant lipids and lipid combinations. We demonstrate that robust, biologically relevant, planar supported bilayers with high resistance composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 25 mol % cholesterol can be constructed with high reproducibility. Furthermore, to enable studies of pore-forming peptides, which are commonly cationic, we demonstrate the construction of bilayers with biologically relevant outer leaflets incorporating up to 10 mol % negatively charged lipids. Unique features of the platform are that (1) the substrate is commercially available, atomically smooth, single-crystal silicon, (2) the polymer cushion allows for the natural incorporation of membrane proteins, and (3) the platform is highly reproducible.
Langmuir 05/2010; 26(14):12054-9. · 4.19 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A robust biomimetic cell membrane platform is critical for mechanistic studies of membrane protein channels. While polymer cushions are believed to facilitate the incorporation of membrane proteins in such a platform, a systematic characterization and optimization of such cushions is rarely performed. Here, we examine the influence of a polymer cushion on the electrical properties of supported 1,2-diphytanoyl-sn-glycero-3-phosphocholine (DPhPC) bilayers produced via a Langmuir-Blodgett deposition/vesicle fusion assembly process on single-crystal silicon. We show that the resistance of DPhPC bilayers is maximized at the calculated crossover concentration of the polymer (5.9 mol % PEG-lipids). Additionally, these bilayers are sufficiently stable to allow impedance analyses to be performed for nearly 3 weeks. These studies reveal the optimal PEG concentration that yields electrically robust bilayers and demonstrate the utility of the platform for future studies of membrane protein channels and membrane active peptides.
Langmuir 03/2010; 26(5):3544-8. · 4.19 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Reductive desorption of alkanethiols is a tool for spatially and temporally controlled release of small molecules or particles from individually addressable gold electrodes. Here we report on the dynamics of release using fluorophore-terminated C6 or C11 thiols. We show that the release kinetics for C6 thiols are determined solely by diffusive transport, whereas for C11 thiols the release kinetics are attenuated by the low solubility that limits the rate at which the desorbed thiols can diffuse away from the surface. The release of multiple different molecules from the same electrode is demonstrated using red- and green-emitting fluorophores. The fraction of the monolayer released is dependent on the electrode potential.
Langmuir 11/2009; 26(3):1420-3. · 4.19 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Defects in nuclear morphology often correlate with the onset of disease, including cancer, progeria, cardiomyopathy, and muscular dystrophy. However, the mechanism by which a cell controls its nuclear shape is unknown. Here, we use adhesive micropatterned surfaces to control the overall shape of fibroblasts and find that the shape of the nucleus is tightly regulated by the underlying cell adhesion geometry. We found that this regulation occurs through a dome-like actin cap that covers the top of the nucleus. This cap is composed of contractile actin filament bundles containing phosphorylated myosin, which form a highly organized, dynamic, and oriented structure in a wide variety of cells. The perinuclear actin cap is specifically disorganized or eliminated by inhibition of actomyosin contractility and rupture of the LINC complexes, which connect the nucleus to the actin cap. The organization of this actin cap and its nuclear shape-determining function are disrupted in cells from mouse models of accelerated aging (progeria) and muscular dystrophy with distorted nuclei caused by alterations of A-type lamins. These results highlight the interplay between cell shape, nuclear shape, and cell adhesion mediated by the perinuclear actin cap.
Proceedings of the National Academy of Sciences 11/2009; 106(45):19017-22. · 9.68 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Cell detachment is central to a broad range of physiopathological changes, but there are no quantitative methods to study this process. Here we report programmed subcellular release, a method for spatially and temporally controlled cellular detachment, and present quantitative results of the detachment dynamics of 3T3 fibroblasts at the subcellular level.
Nature Methods 03/2009; 6(3):211-3. · 19.28 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Here we report on the synthesis of CdSe quantum dots from a noncoordinating solvent. We show that nucleation and growth is very fast and is completed within 100 s. The subsequent increase in average particle size is due to diffusion limited coarsening. Growth and coarsening can be quenched by injection of dodecanethiol. Finally, we compare the size distribution obtained from analysis of the absorption edge with the size distribution obtained from analysis of transmission electron microscope images.
10/2008;
-
[show abstract]
[hide abstract]
ABSTRACT: Electrochemical impedance spectroscopy performed on surface-supported bilayer membranes allows for the monitoring of changes in membrane properties, such as thickness, ion permeability, and homogeneity, after exposure to antimicrobial peptides (AMPs). We show that two model cationic peptides, very similar in sequence but different in activity, induce dramatically different changes in membrane properties as probed by impedance spectroscopy. Moreover, the impedance results excluded the "barrel-stave" and the "toroidal pore" models of AMP mode of action, and are more consistent with the "carpet" and the "detergent" models. The impedance data provide important new insights about the kinetics and the scale of the peptide action which currently are not addressed by the "carpet" and the "detergent" models. The method presented not only provides additional information about the mode of action of a particular AMP, but offers a means of characterizing AMP activity in reproducible, well-defined quantitative terms.
Biochimica et Biophysica Acta 10/2008; 1778(10):2430-6. · 4.66 Impact Factor
