Now showing 1 - 10 of 18
  • Publication
    Affinity Separation: M13 Bacteriophage-Activated Superparamagnetic Beads for Affinity Separation
    The growth of the biopharmaceutical industry has created a demand for new technologies for the purification of genetically engineered proteins.The efficiency of large-scale, high-gradient magnetic fishing could be improved if magnetic particles offering higher binding capacity and magnetization were available. This article describes several strategies for synthesizing microbeads that are composed of a M13 bacteriophage layer assembled on a superparamagnetic core. Chemically cross-linking the pVIII proteins to a carboxyl functionalized bead produced highly responsive superparamagnetic particles (SPM) with a side-on oriented, adherent virus monolayer. Also, the genetic manipulation of the pIII proteins with a His6 peptide sequence allowed reversible assembly of the bacteriophage on a nitrilotriacetic acid functionalized core in an end-on configuration. These phage-magnetic particles were successfully used to separate antibodies from high-protein concentration solutions in a single step with a > 90 % purity. The dense magnetic core of these particles makes themfive times more responsive to magnetic fields than commercial materialscomposed of polymer-iron oxide compositesand a monolayer of phage could produced a 1000 fold higher antibody binding capacity. These new bionanomaterials appear to be well-suited to large-scale high-gradient magnetic fishing separation and promise to be cost effective as a result of the self-assembling and self-replicating properties of genetically engineered M13 bacteriophage
  • Publication
    Neuron Sub-Populations with Different Elongation Rates and DCC Dynamics Exhibit Distinct Responses to Isolated Netrin-1 Treatment
    (American Chemical Society, 2015) ; ;
    Correct wiring of the nervous system requires guidance cues, diffusible or substrate-bound proteins that steer elongating axons to their target tissues. Netrin-1, the best characterized member of the Netrins family of guidance molecules, is known to induce axon turning and modulate axon elongation rate; however, the factors regulating the axonal response to Netrin-1 are not fully understood. Using microfluidics, we treated fluidically isolated axons of mouse primary cortical neurons with Netrin-1 and characterized axon elongation rates, as well as the membrane localization of deleted in colorectal cancer (DCC), a well-established receptor of Netrin-1. The capacity to stimulate and observe a large number of individual axons allowed us to conduct distribution analyses, through which we identified two distinct neuron subpopulations based on different elongation behavior and different DCC membrane dynamics. Netrin-1 reduced the elongation rates in both subpopulations, where the effect was more pronounced in the slow growing subpopulation. Both the source of Ca2+ influx and the basal cytosolic Ca2+ levels regulated the effect of Netrin-1, for example, Ca2+ efflux from the endoplasmic reticulum due to the activation of Ryanodine channels blocked Netrin-1-induced axon slowdown. Netrin-1 treatment resulted in a rapid membrane insertion of DCC, followed by a gradual internalization. DCC membrane dynamics were different in the central regions of the growth cones compared to filopodia and axon shafts, highlighting the temporal and spatial heterogeneity in the signaling events downstream of Netrin-1. Cumulatively, these results demonstrate the power of microfluidic compartmentalization and distribution analysis in describing the complex axonal Netrin-1 response.
    Scopus© Citations 12  677
  • Publication
    Neuronal Cell Bodies Remotely Regulate Axonal Growth Response to Localized Netrin-1 Treatment via Second Messenger and DCC Dynamics
    Netrin-1 modulates axonal growth direction and speed. Its best characterized receptor, Deleted in Colorectal Cancer (DCC), is localized to growth cones, but also observed in the cell bodies. We hypothesized that cell bodies sense Netrin-1 and contribute to axon growth rate modulation, mediated by the second messenger system. We cultured mouse cortical neurons in microfluidic devices to isolate distal axon and cell body microenvironments. Compared to isolated axonal treatment, global Netrin-1 treatment decreased the axon elongation rate and affected the dynamics of total and membranous DCC, calcium, and cyclic nucleotides. Signals induced by locally applied Netrin-1 propagated in both anterograde and retrograde directions, demonstrated by the long-range increase in DCC and by the increased frequency of calcium transients in cell bodies, evoked by axonal Netrin-1. Blocking the calcium efflux from endoplasmic reticulum suppressed the membranous DCC response. Our findings support the notion that neurons sense Netrin-1 along their entire lengths in making axonal growth decisions.
      320Scopus© Citations 12
  • Publication
    In vitro study of the interaction of heregulin-functionalized magnetic-optical nanorods with MCF7 and MDA-MB- 231 cells
    Multifunctional nanoparticles that actively target specific cells are promising tools for cancer diagnosis and therapy. In this article we review the synthesis and surface chemistry of Fe–Au nanorods and their characterization using microscopy. The diameter of the rods used in this study was selected to be 150–200 nm so that they did not enter the cells. The 80 nm-long Au tips of the nanorods were functionalized with heregulin (HRG), and the micron-long Fe portion was coated with a poly(ethylene glycol) monolayer to minimize non-specific interactions. Nanorods functionalized with HRG were found to preferentially bind to MCF7 cells that express high levels of the receptor tyrosine-protein kinase ErbB2/3. Magnetic tweezers measurements were used to characterize the kinetic properties of the bond between the HRG on the rods and ErbB2/3 on the surface of the cells. The strong magnetization of Fe–Au nanorods makes them excellent candidates for in-vitro and in-vivo imaging, and magnetic therapeutic applications targeting cancer cells in circulation.
    Scopus© Citations 2  642
  • Publication
    Mechanochemical Stimulation of MCF7 Cells with Rod-Shaped Fe-Au Janus Particles Induces Cell Death through Paradoxical Hyperactivation of ERK
    Multifunctional nanoparticles that actively target-specific tissues are studied for cancer diagnosis and treatment. Magnetically and optically active particles are of particular interest because they enable multiple imaging modalities and physically modulated therapies, such as magnetic hyperthermia. Fe–Au nanorods are synthesized that have a long iron segment, coated with polyethylene glycol, and a short gold tip functionalized with heregulin (HRG), a known ligand of ErbB family of receptors. HRG–nanorods preferentially target MCF7 cells relative to MDA-MB-231 cells, as demonstrated in a novel microfluidics device. Targeting rates of these classical breast cancer cells correlate with their differential expression of ErbB2/3 receptors. HRG–nanorod binding stimulates the extracellular signal-regulated kinase 1/2 (ERK) phosphorylation in MCF7 cells. The increase in ERK phosphorylation is linked to 'active zones,' dynamic regions in the cell periphery, which exhibit higher rates of particle binding than the rest of the cell. Periodically stretching cells using magnetic tweezers further activates ERK, which leads to cell death in cells co-treated with B-Raf inhibitors, through ERK hyperactivation. Although to a lesser extent, cell death is also achieved through magnetic hyperthermia. These results demonstrate nanoscale targeting and localized mechanochemical treatment of specific cancer cell lines based on their receptor expression using multifunctional nanoparticles.
    Scopus© Citations 28  778
  • Publication
    Characterization of carboxylate nanoparticle adhesion with the fungal pathogen Candida albicans
    Candida albicans is the lead fungal pathogen of nosocomial bloodstream infections worldwide and has mortality rates of 43%. Nanoparticles have been identified as a means to improve medical outcomes for Candida infections, enabling sample concentration, serving as contrast agents for in vivo imaging, and delivering therapeutics. However, little is known about how nanoparticles interact with the fungal cell wall. In this report we used laser scanning confocal microscopy to examine the interaction of fluorescent polystyrene nanoparticles of specific surface chemistry and diameter with C. albicans and mutant strains deficient in various C. albicans surface proteins. Carboxylate-functionalized nanoparticles adsorbed mainly to the hyphae of wild-type C. albicans. The dissociative binding constant of the nanoparticles was ∼150, ∼30 and ∼2.5 pM for 40, 100 nm and 200 nm diameter particles, respectively. A significant reduction in particle binding was observed with a Δals3 strain compared to wild-type strains, identifying the Als3 adhesin as the main mediator of this nanoparticle adhesion. In the absence of Als3, nanoparticles bound to germ tubes and yeast cells in a pattern resembling the localization of Als1, indicating Als1 also plays a role. Nanoparticle surface charge was shown to influence binding – positively charged amine-functionalized nanoparticles failed to bind to the hyphal cell wall. Binding of carboxylate-functionalized nanoparticles was observed in the presence of serum, though interactions were reduced. These observations show that Als3 and Als1 are important targets for nanoparticle-mediated diagnostics and therapeutics, and provide direction for optimal diameter and surface characteristics of nanoparticles that bind to the fungal cell wall.
      474Scopus© Citations 15
  • Publication
    Flow enhanced non-linear magnetophoretic separation of beads based on magnetic susceptibility
    (Royal Society of Chemistry, 2013-08-20) ; ; ;
    Magnetic separation provides a rapid and efficient means of isolating biomaterials from complex mixtures based on their adsorption on superparamagnetic (SPM) beads. Flow enhanced non-linear magnetophoresis (FNLM) is a high-resolution mode of separation in which hydrodynamic and magnetic fields are controlled with micron resolution to isolate SPM beads with specific physical properties. In this article we demonstrate that a change in the critical frequency of FNLM can be used to identify beads with magnetic susceptibilities between 0.01 and 1.0 with a sensitivity of 0.01 Hz(-1). We derived an analytical expression for the critical frequency that explicitly incorporates the magnetic and non-magnetic composition of a complex to be separated. This expression was then applied to two cases involving the detection and separation of biological targets. This study defines the operating principles of FNLM and highlights the potential for using this technique for multiplexing diagnostic assays and isolating rare cell types.
    Scopus© Citations 22  436
  • Publication
    Isolation of Bowman-Birk-Inhibitor from soybean extracts using novel peptide probes and high gradient magnetic separation
    (Elsevier, 2012-10-15) ; ;
    Soybean proteins offer exceptional promise in the area of cancer prevention and treatment. Specifically, Bowman-Birk Inhibitor (BBI) has the ability to suppress carcinogenesis in vivo, which has been attributed to BBI’s inhibition of serine protease (trypsin and chymotrypsin) activity. The lack of molecular probes for the isolation of this protein has made it difficult to work with, limiting its progress as a significant candidate in the treatment of cancer. This study has successfully identified a set of novel synthetic peptides targeting the BBI, and has demonstrated the ability to bind BBI in vitro. One of those probes has been covalently immobilised on superparamagnetic microbeads to allow the isolation of BBI from soy whey mixtures in a single step. Our ultimate goal is the use of the described synthetic probe to facilitate the isolation of this potentially therapeutic protein for low cost, scalable analysis and production of BBI.
    Scopus© Citations 23  605
  • Publication
    A microfluidic dual gradient generator for conducting cell-based drug combination assays
    We present a microfluidic chip that generates linear concentration gradients of multiple solutes that are orthogonally-aligned to each other. The kinetics of gradient formation was characterized using a fluorescent tracer matching the molecular weight of small inhibitory drugs. Live-cell signalling and motility experiments were conducted to demonstrate the potential uses and advantages of the device. A431 epidermoid carcinoma cells, where EGF induces apoptosis in a concentration-dependent manner, were simultaneously exposed to gradients of MEK inhibitor and EGF receptor (EGFR) inhibitor. By monitoring live caspase activation in the entire chip, we were able to quickly assess the combinatorial interaction between MEK and EGFR pathways, which otherwise would require costly and time consuming titration experiments. We also characterized the motility and morphology of MDA-MB-231 breast cancer cells exposed to orthogonal gradients of EGF and EGFR inhibitor. The microfluidic chip not only permitted the quantitative analysis of a population of cells exposed to drug combinations, but also enabled the morphological characterization of individual cells. In summary, our microfluidic device, capable of establishing concentration gradients of multiple compounds over a group of cells, facilitates and accelerates in vitro cell biology experiments, such as those required for cell-based drug combination assays.
    Scopus© Citations 21  549
  • Publication
    Micromagnet arrays for on-chip focusing, switching, and separation of superparamagnetic beads and single cells
    Nonlinear magnetophoresis (NLM) is a powerful approach for on-chip transport and separation of superparamagnetic (SPM) beads, based on a travelling magnetic field wave generated by the combination of a micromagnet array (MMA) and an applied rotating magnetic field. Here, we present two novel MMA designs that allow SPM beads to be focused, sorted, and separated on-chip. Converging MMAs were used to rapidly collect the SPM beads from a large region of the chip and focus them into synchronized lines. We characterise the collection efficiency of the devices and demonstrate that they can facilitate on-chip analysis of populations of SPM beads using a single-point optical detector. The diverging MMAs were used to control the transport of the beads and to separate them based on their size. The separation efficiency of these devices was determined by the orientation of the magnetisation of the micromagnets relative to the external magnetic field and the size of the beads relative to that of micromagnets. By controlling these parameters and the rotation of the external magnetic field we demonstrated the controlled transport of SPM bead-labelled single MDA-MB-231 cells. The use of these novel MMAs promises to allow magnetically-labelled cells to be efficiently isolated and then manipulated on-chip for analysis with high-resolution chemical and physical techniques.
    Scopus© Citations 10  440