Zhihong Zhang, Vishal I. Kottadiel, Reza Vafabakhsh, Li Dai, Yann R. Chemla, Taekjip Ha, Venigalla B. Rao
Complex viruses are assembled from simple protein subunits by sequential and irreversible assembly. During genome packaging in bacteriophages, a powerful molecular motor assembles at the special portal vertex of an empty prohead to initiate packaging. The capsid expands after about 10%–25% of the genome is packaged. When the head is full, the motor cuts the concatemeric DNA and dissociates from the head. Conformational changes, particularly in the portal, are thought to drive these sequential transitions. We found that the phage T4 packaging machine is highly promiscuous, translocating DNA into finished phage heads as well as into proheads. Optical tweezers experiments show that single motors can force exogenous DNA into phage heads at the same rate as into proheads. Single molecule fluorescence measurements demonstrate that phage heads undergo repeated initiations, packaging multiple DNA molecules into the same head. These results suggest that the phage DNA packaging machine has unusual conformational plasticity, powering DNA into an apparently passive capsid receptacle, including the highly stable virus shell, until it is full. These features probably led to the evolution of viral genomes that fit capsid volume, a strikingly common phenomenon in double-stranded DNA viruses, and will potentially allow design of a novel class of nanocapsid delivery vehicles.
DOI
Monday, March 7, 2011
Selective optical trapping based on strong plasmonic coupling between gold nanorods and slab
Y. J. Zheng, H. Liu, S. M. Wang, T. Li, J. X. Cao, L. Li, C. Zhu, Y. Wang, S. N. Zhu, and X. Zhang
A resonance plasmon mode is formed between a gold nanorod and an infinite slab in infrared range, with local electric field enhancement factor over 40. A strong optical attractive force is exerted on the rod by the slab at resonance frequency. Based on Maxwell stress tensor method and numerical simulations, the optical force was calculated to be over 2.0 nN/(mW/μm2). For a fixed incident wavelength, the enhanced optical force is obtained only for the rods with particular length when the diameter is fixed. This strong optical force could be used as a possible selective optical trapping technique in the future.
DOI
A resonance plasmon mode is formed between a gold nanorod and an infinite slab in infrared range, with local electric field enhancement factor over 40. A strong optical attractive force is exerted on the rod by the slab at resonance frequency. Based on Maxwell stress tensor method and numerical simulations, the optical force was calculated to be over 2.0 nN/(mW/μm2). For a fixed incident wavelength, the enhanced optical force is obtained only for the rods with particular length when the diameter is fixed. This strong optical force could be used as a possible selective optical trapping technique in the future.
DOI
Optical tweezers for studying taxis in parasites
A A de Thomaz, A Fontes, C V Stahl, L Y Pozzo, D C Ayres, D B Almeida, P M A Farias, B S Santos, J Santos-Mallet, S A O Gomes, S Giorgio, D Feder and C L Cesar
In this work we present a methodology to measure force strengths and directions of living parasites with an optical tweezers setup. These measurements were used to study the parasites chemotaxis in real time. We observed behavior and measured the force of: (i) Leishmania amazonensis in the presence of two glucose gradients; (ii) Trypanosoma cruzi in the vicinity of the digestive system walls, and (iii) Trypanosoma rangeli in the vicinity of salivary glands as a function of distance. Our results clearly show a chemotactic behavior in every case. This methodology can be used to study any type of taxis, such as chemotaxis, osmotaxis, thermotaxis, phototaxis, of any kind of living microorganisms. These studies can help us to understand the microorganism sensory systems and their response function to these gradients.
DOI
In this work we present a methodology to measure force strengths and directions of living parasites with an optical tweezers setup. These measurements were used to study the parasites chemotaxis in real time. We observed behavior and measured the force of: (i) Leishmania amazonensis in the presence of two glucose gradients; (ii) Trypanosoma cruzi in the vicinity of the digestive system walls, and (iii) Trypanosoma rangeli in the vicinity of salivary glands as a function of distance. Our results clearly show a chemotactic behavior in every case. This methodology can be used to study any type of taxis, such as chemotaxis, osmotaxis, thermotaxis, phototaxis, of any kind of living microorganisms. These studies can help us to understand the microorganism sensory systems and their response function to these gradients.
DOI
Microparticle movements in optical funnels and pods
José A. Rodrigo, Antonio M. Caravaca-Aguirre, Tatiana Alieva, Gabriel Cristóbal, and María L. Calvo
Three-dimensional microparticle movements induced by laser beams with a funnel- and tubular pod-like structure, in the neighbourhood of the focal plane of an optical trapping setup, are experimentally studied. The funnel and pod beams constructed as coherent superpositions of helical Laguerre-Gaussian modes are synthesized by a computer generated hologram using a phase-only spatial light modulator. Particle tracking is achieved by in-line holography method which allows an accurate position measurement. It is experimentally demonstrated that the trapped particle follows different trajectories depending on the orbital angular momentum density of the beam. In particular applying the proposed pod beam the particle rotates in opposite directions during its movement in the optical trap. Possible applications of these single-beam traps for volumetric optical particle manipulation are discussed.
DOI
Three-dimensional microparticle movements induced by laser beams with a funnel- and tubular pod-like structure, in the neighbourhood of the focal plane of an optical trapping setup, are experimentally studied. The funnel and pod beams constructed as coherent superpositions of helical Laguerre-Gaussian modes are synthesized by a computer generated hologram using a phase-only spatial light modulator. Particle tracking is achieved by in-line holography method which allows an accurate position measurement. It is experimentally demonstrated that the trapped particle follows different trajectories depending on the orbital angular momentum density of the beam. In particular applying the proposed pod beam the particle rotates in opposite directions during its movement in the optical trap. Possible applications of these single-beam traps for volumetric optical particle manipulation are discussed.
DOI
Friday, March 4, 2011
Laser tweezers Raman spectrum of normal breast cell line and carcinoma breast cell line
Xie, Y.-A., Leng, Z.-H., Meng, L.-J. , Luo, X.-L. , Zhang, W.-M. , Kuang, Z.-P.
OBJECTIVE: To detect the interaction between Raman spectrum of normal breast cell line (HBL-100) and carcinoma breast cell line (MCF-7), as well as the change of biological tissue composition from normal cell to carcinogenesis. In the end, Characteristic Raman spectra of cancer cells were presented. METHODS: Raman spectrum of normal breast cell line and carcinoma breast cell line were recorded, The result of which was performed by principal component analysis(PCA). RESULTS: Significant differences of average Raman spectrums were founded between the normal cell and the carcinoma one; The spectra line of carcinoma cell became strong at the whole; The strength of 936, 1002, 1298 and 1445 cm-1 increased; the peak of 1102 cm-1 shifted to 1094 cm-1; the peak of 484 cm-1 disappeared; Additionally, the structure and the amount of protein, nucleic acid, lipids and other such molecules had also changed. Average Raman spectrum of monocell was analyzed with the principal component of PCA, the result of which suggested normal cell and carcinoma cell could be differentiated with PCA, The discrimination rate was 87% (13/15). CONCLUSIONS: Judging normal breast cell and carcinoma cell with laser tweezers Raman spectrums is an efficient method. Single cells laser tweezers raman spectra technique can become a new way to diagnose cancer, which has very wide prospect.
DOI
OBJECTIVE: To detect the interaction between Raman spectrum of normal breast cell line (HBL-100) and carcinoma breast cell line (MCF-7), as well as the change of biological tissue composition from normal cell to carcinogenesis. In the end, Characteristic Raman spectra of cancer cells were presented. METHODS: Raman spectrum of normal breast cell line and carcinoma breast cell line were recorded, The result of which was performed by principal component analysis(PCA). RESULTS: Significant differences of average Raman spectrums were founded between the normal cell and the carcinoma one; The spectra line of carcinoma cell became strong at the whole; The strength of 936, 1002, 1298 and 1445 cm-1 increased; the peak of 1102 cm-1 shifted to 1094 cm-1; the peak of 484 cm-1 disappeared; Additionally, the structure and the amount of protein, nucleic acid, lipids and other such molecules had also changed. Average Raman spectrum of monocell was analyzed with the principal component of PCA, the result of which suggested normal cell and carcinoma cell could be differentiated with PCA, The discrimination rate was 87% (13/15). CONCLUSIONS: Judging normal breast cell and carcinoma cell with laser tweezers Raman spectrums is an efficient method. Single cells laser tweezers raman spectra technique can become a new way to diagnose cancer, which has very wide prospect.
DOI
Optical Forces in Hybrid Plasmonic Waveguides
Xiaodong Yang, Yongmin Liu, Rupert F. Oulton, Xiaobo Yin, and Xiang Zhang
We demonstrate that in a hybrid plasmonic system the optical force exerted on a dielectric waveguide by a metallic substrate is enhanced by more than 1 order of magnitude compared to the force between a photonic waveguide and a dielectric substrate. A nanoscale gap between the dielectric waveguide and the metallic substrate leads to deep subwavelength optical energy confinement with ultralow mode propagation loss and hence results in the enhanced optical forces at low input optical power, as numerically demonstrated by both Maxwell’s stress tensor formalism and the coupled mode theory analysis. Moreover, the hybridization between the surface plasmon modes and waveguide modes allows efficient optical trapping of single dielectric nanoparticle with size of only several nanometers in the gap region, manifesting various optomechanical applications such as nanoscale optical tweezers.
DOI
We demonstrate that in a hybrid plasmonic system the optical force exerted on a dielectric waveguide by a metallic substrate is enhanced by more than 1 order of magnitude compared to the force between a photonic waveguide and a dielectric substrate. A nanoscale gap between the dielectric waveguide and the metallic substrate leads to deep subwavelength optical energy confinement with ultralow mode propagation loss and hence results in the enhanced optical forces at low input optical power, as numerically demonstrated by both Maxwell’s stress tensor formalism and the coupled mode theory analysis. Moreover, the hybridization between the surface plasmon modes and waveguide modes allows efficient optical trapping of single dielectric nanoparticle with size of only several nanometers in the gap region, manifesting various optomechanical applications such as nanoscale optical tweezers.
DOI
Heat profiling of three-dimensionally optically trapped gold nanoparticles using vesicle cargo release
Anders Kyrsting, Poul M. Bendix, Dimitrios G. Stamou, and Lene B. Oddershede
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.
DOI
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.
DOI
Mechanistic Basis of Otolith Formation during Teleost Inner Ear Development
David Wu, Jonathan B. Freund, Scott E. Fraser and Julien Vermot
Otoliths, which are connected to stereociliary bundles in the inner ear, serve as inertial sensors for balance. In teleostei, otolith development is critically dependent on flow forces generated by beating cilia; however, the mechanism by which flow controls otolith formation remains unclear. Here, we have developed a noninvasive flow probe using optical tweezers and a viscous flow model in order to demonstrate how the observed hydrodynamics influence otolith assembly. We show that rotational flow stirs and suppresses precursor agglomeration in the core of the cilia-driven vortex. The velocity field correlates with the shape of the otolith and we provide evidence that hydrodynamics is actively involved in controlling otolith morphogenesis. An implication of this hydrodynamic effect is that otolith self-assembly is mediated by the balance between Brownian motion and cilia-driven flow. More generally, this flow feature highlights an alternative biological strategy for controlling particle localization in solution.
DOI
Otoliths, which are connected to stereociliary bundles in the inner ear, serve as inertial sensors for balance. In teleostei, otolith development is critically dependent on flow forces generated by beating cilia; however, the mechanism by which flow controls otolith formation remains unclear. Here, we have developed a noninvasive flow probe using optical tweezers and a viscous flow model in order to demonstrate how the observed hydrodynamics influence otolith assembly. We show that rotational flow stirs and suppresses precursor agglomeration in the core of the cilia-driven vortex. The velocity field correlates with the shape of the otolith and we provide evidence that hydrodynamics is actively involved in controlling otolith morphogenesis. An implication of this hydrodynamic effect is that otolith self-assembly is mediated by the balance between Brownian motion and cilia-driven flow. More generally, this flow feature highlights an alternative biological strategy for controlling particle localization in solution.
DOI
Photothermal trapping of dielectric particles by optical fiber-ring
Hongbao Xin, Hongxiang Lei, Yao Zhang, Xingmin Li, and Baojun Li
The removal of dielectric particles and bacteria from water is an extremely important global issue, particularly, for drinking and sanitation. This work provides a demonstration of optical purification of water using an optical fiber-ring. The size of particles suspended in water for trapping is 2.08 μm in diameter and the wavelength of light used for inducing photothermal effect is 1.55 μm with a power of 97 mW. The fiber, 6 μm in diameter, was formed to a racket-shaped ring with a minimum diameter of 167 μm and a maximum one of 350 μm. Experiment indicates that the particles moved toward the ring with the highest velocity of 4.2 μm/s and are trapped/assembled in the center of the ring once the laser beam of 1.55-μm wavelength was launched into the fiber. With a moving of the fiber-ring, the trapped/assembled particles were moved and the water can be purified by removal of the particles.
DOI
The removal of dielectric particles and bacteria from water is an extremely important global issue, particularly, for drinking and sanitation. This work provides a demonstration of optical purification of water using an optical fiber-ring. The size of particles suspended in water for trapping is 2.08 μm in diameter and the wavelength of light used for inducing photothermal effect is 1.55 μm with a power of 97 mW. The fiber, 6 μm in diameter, was formed to a racket-shaped ring with a minimum diameter of 167 μm and a maximum one of 350 μm. Experiment indicates that the particles moved toward the ring with the highest velocity of 4.2 μm/s and are trapped/assembled in the center of the ring once the laser beam of 1.55-μm wavelength was launched into the fiber. With a moving of the fiber-ring, the trapped/assembled particles were moved and the water can be purified by removal of the particles.
DOI
Behavior of colloidal particles at a nematic liquid crystal interface
Mohamed Amine Gharbi, Maurizio Nobili, Martin In, Guillaume Prévot, Paolo Galatola, Jean-Baptiste Fournier and Christophe Blanc
We examine the behavior of spherical silica particles trapped at an air–nematic liquid crystal interface. When a strong normal anchoring is imposed, the beads spontaneously form various structures depending on their area density and the nematic thickness. Using optical tweezers, we determine the pair potential and explain the formation of these patterns. The energy profile is discussed in terms of capillary and elastic interactions. Finally, we detail the mechanisms that control the formation of a hexagonal lattice and analyze the role of gravity for curved interfaces.
DOI
We examine the behavior of spherical silica particles trapped at an air–nematic liquid crystal interface. When a strong normal anchoring is imposed, the beads spontaneously form various structures depending on their area density and the nematic thickness. Using optical tweezers, we determine the pair potential and explain the formation of these patterns. The energy profile is discussed in terms of capillary and elastic interactions. Finally, we detail the mechanisms that control the formation of a hexagonal lattice and analyze the role of gravity for curved interfaces.
DOI
Subscribe to:
Posts (Atom)