Poul Martin Bendix

IT University of Copenhagen, København, Capital Region, Denmark

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Publications (25)155.94 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: We reveal that the gel to fluid phase transition causes spherical membrane vesicles to release a finite number of molecules in several consecutive and localized events. By locally melting Giant Unilamellar lipid Vesicles (GUVs), using an optically trapped gold nanoparticle (AuNP) as a local heat source, we establish a local phase transition on the spherical GUV membrane clearly visualized using a phase sensitive fluorescent marker. We measure transient permeation events through this transition zone visualized as de-quenching of calcein as it escapes the interior of the GUV. Since biological membranes share several features with melting membranes, like nanoscale domain formation and critical density fluctuations, similar passive membrane transport could potentially be abundant in living cells.
    Soft Matter 04/2014; · 3.91 Impact Factor
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    ABSTRACT: Heating of irradiated metallic e-beam generated nano-structures was quantified through direct measurements paralleled by novel model based numerical calculations. By comparing discs, triangles and stars we showed how particle shape and composition determines the heating. Importantly, our results revealed that substantial heat is generated in the titanium adhesive layer between gold and glass. Even when the Ti layer is as thin as 2 nm it absorbs as much as a 30 nm Au layer and hence should not be ignored.
    Nano Letters 01/2014; · 13.03 Impact Factor
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    ABSTRACT: Optical manipulation of nanostructures offers new exciting possibilities for building new nano-architectures and for exploring the fundamental interactions between light andnanopar- ticles. The optical properties of nanostructures differ substantially from those of similar bulk material and exhibit an exquisite sen- sitivity on nanoparticle shape and composition. The plethora of particles available today expands the possibilities of optical ma- nipulation to include control over particle temperature, lumines- cence, orientation, and even over the rotational optical momen- tum transferred to the nanoparticle. Here, we summarize recent experimental advances within optical manipulation of individual nanoparticles and quantum dots with a focus on resonant versus non-resonant trapping, optically induced heating, spherical aber- ration, and orientation control.Also, we present novel quantitative data on the photonic interaction between gold nanoshells and a fo- cused laser beam. Lastly, promising applications of the biophoton- ical properties of nanoparticles within nanoscience and biophysics are pointed out.
    IEEE Journal of Selected Topics in Quantum Electronics 01/2014; 20(3):4800112. · 4.08 Impact Factor
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    Dino Ott, Poul M Bendix, Lene B Oddershede
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    ABSTRACT: In the study of living soft matter, we often seek to understand the mechanisms underlying the motion of a single molecule, an organelle, or some other tracer. The experimentally observed signature of the tracer is masked by its thermal fluctuations, inherent drift of the system, and instrument noise. In addition, the timing or length scales of the events of interest are often unknown. In the current issue of ACS Nano, Chen et al. present a general method for extracting the underlying dynamics from time series. Here, we provide an easily accessible introduction to the method, put it into perspective with the field, and exemplify how it can be used to answer important out-standing questions within soft matter and living systems.
    ACS Nano 10/2013; · 12.06 Impact Factor
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    ABSTRACT: Membrane fusion consists of a complex rearrangement of lipids and proteins that results in the merger of two lipid bilayers. We have developed a model system that employs synthetic DNA-lipid conjugates as a surrogate for the membrane proteins involved in the biological fusion reaction. We previously showed that complementary DNA-lipids, inserted into small unilamellar vesicles, can mediate membrane fusion in bulk. Here, we use a model membrane architecture developed in our lab to directly observe single-vesicle fusion events using fluorescence microscopy. In this system, a planar tethered membrane patch serves as the target membrane for incoming vesicles. This allows us to quantify the kinetics and characteristics of individual fusion events from the perspective of the lipids or the DNA-lipids involved in the process. We find that the fusion pathways are heterogeneous, with an arrested hemi-fusion state predominating, and we quantitate the outcome and rate of fusion events to construct a mechanistic model of DNA-mediated vesicle fusion. The waiting times between docking and fusion are distributed exponentially, suggesting that fusion occurs in a single step. Our analysis indicates that when two lipid bilayers are brought into close proximity, fusion occurs spontaneously, with little or no dependence on the number of DNA hybrids formed.
    Biophysical Journal 07/2013; 105(2):409-19. · 3.67 Impact Factor
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    ABSTRACT: We study uptake of gold nanoparticles by cancer cells. By laser-induced heating we control escape of the gold nanoparticles from the endosomes into the cytoplasm and liberate miRNA coating the gold nanoparticles targeting gene silencing.
    Bio-Optics: Design and Application; 04/2013
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    ABSTRACT: Syndapin 1 FBAR, a member of the Bin-amphiphysin-Rvs (BAR) domain protein family, is known to induce membrane curvature and is an essential component in biological processes like endocytosis and formation and growth of neurites. We quantify the curvature sensing of FBAR on reconstituted porcine brain lipid vesicles and show that it senses membrane curvature at low density whereas it induces and reinforces tube stiffness at higher density. FBAR strongly up-concentrates on the high curvature tubes pulled out of Giant Unilamellar lipid Vesicles (GUVs), this sorting behavior is strongly amplified at low protein densities. Interestingly, FBAR from syndapin 1 has a large affinity for tubular membranes with curvatures larger than its own intrinsic concave curvature. Finally, we studied the effect of FBAR on membrane relaxation kinetics with high temporal resolution and found that the protein increases relaxation time of the tube holding force in a density-dependent fashion.
    Scientific Reports 03/2013; 3:1565. · 2.93 Impact Factor
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    Anders Kyrsting, Poul Martin Bendix, Lene B Oddershede
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    ABSTRACT: The photonic interactions between a focused Gaussian laser beam and a nanoscopic particle are highly dependent on exact particle location and focal intensity distribution. So far, the 3D focal intensity distribution and the preferred position of a nanoparticle confined within the focal region were only theoretically predicted. Here, we directly map the three dimensional focal intensity distribution, quantify stable trapping positions, and prove that certain sizes of nanoparticles stably trap in front of the focus.
    Nano Letters 12/2012; · 13.03 Impact Factor
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    ABSTRACT: Optically trapped metallic nanoparticles hold great promise as heat transducers in photothermal applications such as drug delivery assays or photothermal therapy. We use the heat dissipated from an optically trapped gold nanosphere to perform a controlled release of a fluorescently labeled vesicle lumen. In the assay, the ambient temperature is kept below the phase transition temperature of the vesicle. When the temperature reaches the phase transition temperature of the lipid, the vesicle becomes leaky and the fluorescently marked lumen diffuses out. We used gel phase vesicles as sensors to quantify the temperature profile around a nanoparticle optically trapped in three dimensions in a similar way as presented in Ref.1 Trapping of 200 nm gold particles resulted in lower than expected heating, which may be accredited to the displacement of the particle from the optical focus due to high scattering forces experienced by the particle.
    Proc SPIE 10/2012;
  • Haiyan Ma, Poul Martin Bendix, Lene B. Oddershede
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    ABSTRACT: When irradiated at its resonance frequency, a metallic nanoparticle efficiently converts the absorbed energy into heat which is locally dissipated. This effect can be used in photothermal treatments, e.g., of cancer cells. However, to fully exploit the functionality of metallic nanoparticles as nanoscopic heat transducers, it is essential to know how the photothermal efficiency depends on parameters like size and shape. Here we present the measurements of the temperature profile around single irradiated gold nanorods and nanospheres placed on a biologically relevant matrix, a lipid bilayer. [1] We developed a novel assay based on molecular partitioning between two coexisting phases, the gel and fluid phase, within the bilayer. [2, 3] This assay allows for a direct measurement of local temperature gradients, an assay which does not necessitate any pre-assumptions about this system and is generally applicable to any irradiated nanoparticle system. The nanorods are irradiated with a tightly focused laser beam at a wavelength of 1064 nm where biological matter exhibits a minimum in absorption. By controlling the polarization of the laser light we show that the absorption of light by the nanorod and the corresponding dissipated heat strongly depends on the orientation of the nanorod with respect to the polarization. Finally, by comparing to spherical gold nanoparticles, we demonstrate how a change in shape, from spherical to rod like, leads to a dramatic enhancement of heating when using near infrared light.
    Proc SPIE 10/2012;
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    Haiyan Ma, Poul M Bendix, Lene B Oddershede
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    ABSTRACT: We quantify the extreme heating associated with resonant irradiation of individual gold nanorods by using a novel assay based on partitioning of lipophilic dyes between membrane phases. The temperature increase is sensitively dependent on the angle between the laser polarization and the orientation of the nanorod. A dramatic and irreversible decrease in the heating of a nanorod occurs at high-illumination intensities; this effect is attributed to surface melting of the nanorod causing it to restructure into a more spherical shape and lose its extreme photothermal properties.
    Nano Letters 06/2012; 12(8):3954-60. · 13.03 Impact Factor
  • Biophysical Journal 01/2012; 102(3):605-. · 3.67 Impact Factor
  • Poul M. Bendix, Lene Oddershede
    Biophysical Journal 01/2012; 102(3):87-. · 3.67 Impact Factor
  • Poul M Bendix, Lene B Oddershede
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    ABSTRACT: Small unilamellar lipid vesicles with diameters down to 50 nm enclosing high refractive index sucrose cores can be optically trapped individually in three dimensions using a focused laser beam. Combined optical trapping and confocal microscopy allows for simultaneous quantitative measurements of the forces exerted on individual vesicles and of their size and shape. The position of individual vesicles in three dimensions is measured with nanometer spatial and ∼10 μs temporal resolution.
    Nano Letters 11/2011; 11(12):5431-7. · 13.03 Impact Factor
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    ABSTRACT: Synaptic transmission is achieved by exocytosis of small, synaptic vesicles containing neurotransmitters across the plasma membrane. Here, we use a DNA-tethered freestanding bilayer as a target architecture that allows observation of content transfer of individual vesicles across the tethered planar bilayer. Tethering and fusion are mediated by hybridization of complementary DNA-lipid conjugates inserted into the two membranes, and content transfer is monitored by the dequenching of an aqueous content dye. By analyzing the diffusion profile of the aqueous dye after vesicle fusion, we are able to distinguish content transfer across the tethered bilayer patch from vesicle leakage above the patch.
    Biophysical Journal 10/2011; 101(8):L37-9. · 3.67 Impact Factor
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    ABSTRACT: We have developed lipid based assays which can measure the temperature of any nanoscale irradiated object. As a demonstration we apply this to gold nanoparticles irradiated by focused near infrared laser light
    Optical Trapping Applications; 04/2011
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    ABSTRACT: Irradiated metallic nanoparticles hold great promise as heat transducers in photothermal applications such as drug delivery assays or photothermal therapy. We quantify the temperature increase of individual gold nanoparticles trapped in three dimensions near lipid vesicles exhibiting temperature sensitive permeability. The surface temperature can increase by hundreds of degrees Celsius even at moderate laser powers. Also, there are significant differences of the heat profiles in two-dimensional and three-dimensional trapping assays.
    Nano Letters 02/2011; 11(2):888-92. · 13.03 Impact Factor
  • Biophysical Journal 01/2011; 100(3). · 3.67 Impact Factor
  • Minsub Chung, Poul Martin Bendix, Namdoo Kim, Steven G. Boxer
    Biophysical Journal 01/2011; 100(3). · 3.67 Impact Factor
  • Biophysical Journal 01/2011; 100. · 3.67 Impact Factor

Publication Stats

125 Citations
155.94 Total Impact Points

Institutions

  • 2014
    • IT University of Copenhagen
      København, Capital Region, Denmark
  • 2011–2013
    • Stanford University
      • Department of Chemistry
      Palo Alto, CA, United States
  • 2008–2013
    • University of Copenhagen
      • • Niels Bohr Institute
      • • Department of Neuroscience and Pharmacology
      Copenhagen, Capital Region, Denmark