Michael Geiselmann, Renaud Marty, Jan Renger, F. Javier García de Abajo and Romain Quidant
Nanopositioning of single quantum emitters to control their coupling to integrated photonic structures is a crucial step in the fabrication of solid-state quantum optics devices. We use the optical near-field enhancement produced by nanofabricated gold antennas subject to near-infrared illumination to deterministically trap and position single nanodiamonds (NDs) hosting nitrogen-vacancy (NV) centers. The positioning of the NDs at the antenna regions of maximum field intensity is first characterized using both fluorescence and electron microscopy imaging. We further study the interaction between the nanoantenna and the delivered NV center by analyzing its change in fluorescence lifetime, which is driven by the increase in the local density of optical states at the trapping positions. Additionally, the plasmonic enhancement of the near-field intensity allows us to optically control the NV excited lifetime using relatively low NIR illumination intensities, some 20 times lower than in the absence of the antennas.
DOI
Sunday, June 29, 2014
Spectral analysis by a video camera in a holographic optical tweezers setup
SŁAWOMIR DROBCZYŃSKI, KAMILA DUŚ-SZACHNIEWICZ, KRZYSZTOF SYMONOWICZ, DARIA GŁOGOCKA
We discuss the basic parameters of the holographic tweezers equipped with a diode laser and cheap video camera. We compare these parameters with the system using a fast camera and high power Nd:YAG laser. The measured parameters are: the power spectra density calculated from tracing the position of the micron polystyrene beads and the trap stiffness. We show that this cheap optical tweezers system is sufficient for experiments in microbiology.
DOI
We discuss the basic parameters of the holographic tweezers equipped with a diode laser and cheap video camera. We compare these parameters with the system using a fast camera and high power Nd:YAG laser. The measured parameters are: the power spectra density calculated from tracing the position of the micron polystyrene beads and the trap stiffness. We show that this cheap optical tweezers system is sufficient for experiments in microbiology.
DOI
Optical gradient force of cosh-Gaussian with sine-azimuthal and half-space phase modulation
RUI FU, XIUMIN GAO, HAIBIN SHEN, QING XIN, XINMIAO LU, LINGWEI GUO
The optical gradient force distributions in focal plane of cosh-Gaussian beams with sine-azimuthal variation wavefront and half space phase modulation were investigated. Results show that optical gradient force distributions can be affected considerably by the phase retardation of half-space phase modulation, of a phase parameter that indicates the phase change frequency on an increasing azimuthal angle, and beam parameters in cosh terms of the incident beams. Many gradient force patterns occur, including cross-shape, multiple optical trap arrays, multiple-trap wheel, and many kinds of gradient force lines and curves. Symmetry of the whole gradient force pattern can also be altered remarkably. Above results may find wide applications in optical trapping systems.
DOI
The optical gradient force distributions in focal plane of cosh-Gaussian beams with sine-azimuthal variation wavefront and half space phase modulation were investigated. Results show that optical gradient force distributions can be affected considerably by the phase retardation of half-space phase modulation, of a phase parameter that indicates the phase change frequency on an increasing azimuthal angle, and beam parameters in cosh terms of the incident beams. Many gradient force patterns occur, including cross-shape, multiple optical trap arrays, multiple-trap wheel, and many kinds of gradient force lines and curves. Symmetry of the whole gradient force pattern can also be altered remarkably. Above results may find wide applications in optical trapping systems.
DOI
Single-molecule manipulation and detection platform for studying cancer cell chemotaxis
May-Show Chen, Pei-Wen Peng, Bing-Chun Liou, Hsiao-Chen Kuo, Keng-Liang Ou, Tzu-Sen Yang
Chemotaxis of cancer cells is an essential component of tumor dissemination. The chemotactic response is comprised of three separate steps, including chemosensing, polarization and locomotion. We present an innovative approach on chemotaxis assay to address cancer cell chemotaxis. We applied a high-resolution optical tweezers system to manipulate epidermal growth factor (EGF)-coated beads positioned close to the filopodia, to locally stimulate HT29 cells expressing the EGF receptor (EGFR). We demonstrated that membrane protrusion at the leading edge induced by an EGF chemotaxis occurred at about 30∼40 s. In addition, the present observation revealed that the locomotion of HT29 cell depended on whether the HT29 cell sensed the presence of the chemoattractant EGF. We anticipate the proposed approach based on optical tweezers, together with the platform at single-cell level, could be applied to build a quick screening method for detection and treatment evaluation of many types of cancer during chemotaxis.
DOI
Chemotaxis of cancer cells is an essential component of tumor dissemination. The chemotactic response is comprised of three separate steps, including chemosensing, polarization and locomotion. We present an innovative approach on chemotaxis assay to address cancer cell chemotaxis. We applied a high-resolution optical tweezers system to manipulate epidermal growth factor (EGF)-coated beads positioned close to the filopodia, to locally stimulate HT29 cells expressing the EGF receptor (EGFR). We demonstrated that membrane protrusion at the leading edge induced by an EGF chemotaxis occurred at about 30∼40 s. In addition, the present observation revealed that the locomotion of HT29 cell depended on whether the HT29 cell sensed the presence of the chemoattractant EGF. We anticipate the proposed approach based on optical tweezers, together with the platform at single-cell level, could be applied to build a quick screening method for detection and treatment evaluation of many types of cancer during chemotaxis.
DOI
Efficient Optical Trapping of CdTe Quantum Dots by Femtosecond Laser Pulses
Wei-Yi Chiang, Tomoki Okuhata, Anwar Usman, Naoto Tamai, and Hiroshi Masuhara
The development in optical trapping and manipulation has been showing rapid progress, most of it is in the small particle sizes in nanometer scales, substituting the conventional continuous-wave lasers with high-repetition-rate ultrashort laser pulse train and nonlinear optical effects. Here, we evaluate two-photon absorption in optical trapping of 2.7 nm-sized CdTe quantum dots (QDs) with high-repetition-rate femtosecond pulse train by probing laser intensity dependence of both Rayleigh scattering image and the two-photon-induced luminescence spectrum of the optically trapped QDs. The Rayleigh scattering imaging indicates that the two-photon absorption (TPA) process enhances trapping ability of the QDs. Similarly, a nonlinear increase of the two-photon-induced luminescence with the incident laser intensity fairly indicates the existence of the TPA process.
DOI
The development in optical trapping and manipulation has been showing rapid progress, most of it is in the small particle sizes in nanometer scales, substituting the conventional continuous-wave lasers with high-repetition-rate ultrashort laser pulse train and nonlinear optical effects. Here, we evaluate two-photon absorption in optical trapping of 2.7 nm-sized CdTe quantum dots (QDs) with high-repetition-rate femtosecond pulse train by probing laser intensity dependence of both Rayleigh scattering image and the two-photon-induced luminescence spectrum of the optically trapped QDs. The Rayleigh scattering imaging indicates that the two-photon absorption (TPA) process enhances trapping ability of the QDs. Similarly, a nonlinear increase of the two-photon-induced luminescence with the incident laser intensity fairly indicates the existence of the TPA process.
DOI
Rotation, oscillation and hydrodynamic synchronization of optically trapped oblate spheroidal microparticles
Alejandro V. Arzola, Petr Jákl, Lukáš Chvátal, and Pavel Zemánek
While the behavior of optically trapped dielectric spherical particles has been extensively studied, the behavior of non-spherical particles remains mainly unexplored. In this work we focus on the dynamics of oblate spheroidal particles trapped in a tightly focused elliptically-polarized vortex beam. In our experiments we used polystyrene spheroids of aspect ratio of major to minor axes equal to 2.55 and of a volume equal to a sphere of diameter 1.7μm. We demonstrate that such particles can be trapped in three dimensions, with the minor axis oriented perpendicular to both the beam polarization (linear) and the beam propagation, can spin in a circularly polarized beam and an optical vortex beam around the axis parallel with the beam propagation. We also observed that these particles can exhibit a periodic motion in the plane transversal to the beam propagation. We measured that the transfer of the orbital angular momentum from the vortex beam to the spheroid gives rise to torques one order of magnitude stronger comparing to the circularly polarized Gaussian beam. We employed a phase-only spatial light modulator to generate several vortex beam traps with one spheroid in each of them. Due to independent setting of beams parameters we controlled spheroids frequency and sense of rotation and observed hydrodynamic phase and frequency locking of rotating spheroids. These optically driven spheroids offer a simple alternative approach to the former techniques based on birefringent, absorbing or chiral microrotors.
DOI
While the behavior of optically trapped dielectric spherical particles has been extensively studied, the behavior of non-spherical particles remains mainly unexplored. In this work we focus on the dynamics of oblate spheroidal particles trapped in a tightly focused elliptically-polarized vortex beam. In our experiments we used polystyrene spheroids of aspect ratio of major to minor axes equal to 2.55 and of a volume equal to a sphere of diameter 1.7μm. We demonstrate that such particles can be trapped in three dimensions, with the minor axis oriented perpendicular to both the beam polarization (linear) and the beam propagation, can spin in a circularly polarized beam and an optical vortex beam around the axis parallel with the beam propagation. We also observed that these particles can exhibit a periodic motion in the plane transversal to the beam propagation. We measured that the transfer of the orbital angular momentum from the vortex beam to the spheroid gives rise to torques one order of magnitude stronger comparing to the circularly polarized Gaussian beam. We employed a phase-only spatial light modulator to generate several vortex beam traps with one spheroid in each of them. Due to independent setting of beams parameters we controlled spheroids frequency and sense of rotation and observed hydrodynamic phase and frequency locking of rotating spheroids. These optically driven spheroids offer a simple alternative approach to the former techniques based on birefringent, absorbing or chiral microrotors.
DOI
Raman spectroscopy provides a rapid, non-invasive method for quantitation of starch in live, unicellular microalgae
Yuetong Ji, Yuehui He, Yanbin Cui, Tingting Wang, Yun Wang, Yuanguang Li, Wei E. Huang and Jian Xu
Conventional methods for quantitation of starch content in cells generally involve starch extraction steps and are usually labor intensive, thus a rapid and noninvasive method will be valuable. Using the starch-producing unicellular microalga Chlamydomonas reinhardtii as a model, we employed a customized Raman Spectrometer to capture the Raman spectra of individual single-cells under distinct culture conditions and along various growth stages. The results revealed a nearly linear correlation (R2=0.9893) between the signal intensity at 478 cm-1 and the starch content of the cells. We validated the specific correlation by showing that the starch-associated Raman peaks were eliminated in a mutant strain where the AGPase gene was disrupted and consequentially the biosynthesis of starch blocked. Furthermore, the method was validated in an industrial algal strain of Chlorella pyrenoidosa. This is the first demonstration of starch quantitation at individual live cells. Compared to existing cellular-starch quantitation methods, this single-cell Raman spectra based approach is rapid, label-free, noninvasive, culture-independent, low-cost and potentially able to simultaneously track multiple metabolites in individual live cells, therefore should enable many new applications.
DOI
Conventional methods for quantitation of starch content in cells generally involve starch extraction steps and are usually labor intensive, thus a rapid and noninvasive method will be valuable. Using the starch-producing unicellular microalga Chlamydomonas reinhardtii as a model, we employed a customized Raman Spectrometer to capture the Raman spectra of individual single-cells under distinct culture conditions and along various growth stages. The results revealed a nearly linear correlation (R2=0.9893) between the signal intensity at 478 cm-1 and the starch content of the cells. We validated the specific correlation by showing that the starch-associated Raman peaks were eliminated in a mutant strain where the AGPase gene was disrupted and consequentially the biosynthesis of starch blocked. Furthermore, the method was validated in an industrial algal strain of Chlorella pyrenoidosa. This is the first demonstration of starch quantitation at individual live cells. Compared to existing cellular-starch quantitation methods, this single-cell Raman spectra based approach is rapid, label-free, noninvasive, culture-independent, low-cost and potentially able to simultaneously track multiple metabolites in individual live cells, therefore should enable many new applications.
DOI
Mechanisms of Cellular Proteostasis: Insights from Single-Molecule Approaches
Carlos J. Bustamante, Christian M. Kaiser, Rodrigo A. Maillard, Daniel H. Goldman, and Christian A.M. Wilson
Cells employ a variety of strategies to maintain proteome homeostasis. Beginning during protein biogenesis, the translation machinery and a number of molecular chaperones promote correct de novo folding of nascent proteins even before synthesis is complete. Another set of molecular chaperones helps to maintain proteins in their functional, native state. Polypeptides that are no longer needed or pose a threat to the cell, such as misfolded proteins and aggregates, are removed in an efficient and timely fashion by ATP-dependent proteases. In this review, we describe how applications of single-molecule manipulation methods, in particular optical tweezers, are shedding new light on the molecular mechanisms of quality control during the life cycles of proteins.
DOI
Cells employ a variety of strategies to maintain proteome homeostasis. Beginning during protein biogenesis, the translation machinery and a number of molecular chaperones promote correct de novo folding of nascent proteins even before synthesis is complete. Another set of molecular chaperones helps to maintain proteins in their functional, native state. Polypeptides that are no longer needed or pose a threat to the cell, such as misfolded proteins and aggregates, are removed in an efficient and timely fashion by ATP-dependent proteases. In this review, we describe how applications of single-molecule manipulation methods, in particular optical tweezers, are shedding new light on the molecular mechanisms of quality control during the life cycles of proteins.
DOI
Friday, June 27, 2014
Modification of the surface plasmon enhanced optical forces on metal nanorod pairs by axial rotation and by dielectric intralayer
Aybike Ural Yalçın, Özgür E. Müstecaplıoğlu, Kaan Güven
We investigate numerically the effect of axial rotation and the presence of a dielectric intralayer on the spectral behavior of the optical force on a gold nanorod pair. The frequency spectrum of the optical force is obtained through the Maxwell stress tensor formulation and the full vectorial solution of electromagnetic waves. The common and the relative forces, which are defined through the optical force acting on each nanorod, are computed for different axial rotations and for different permittivity and thickness of the dielectric intralayer. We found that both the misalignment and the dielectric intralayer can be utilized to tailor the magnitude and direction of the relative optical force, providing a tunable attractive or repulsive response between the nanorods.
DOI
We investigate numerically the effect of axial rotation and the presence of a dielectric intralayer on the spectral behavior of the optical force on a gold nanorod pair. The frequency spectrum of the optical force is obtained through the Maxwell stress tensor formulation and the full vectorial solution of electromagnetic waves. The common and the relative forces, which are defined through the optical force acting on each nanorod, are computed for different axial rotations and for different permittivity and thickness of the dielectric intralayer. We found that both the misalignment and the dielectric intralayer can be utilized to tailor the magnitude and direction of the relative optical force, providing a tunable attractive or repulsive response between the nanorods.
DOI
Optical Trapping Effect and Its Calibration Method in Resonance Light Scattering Correlation Spectroscopy of Gold Nanoparticles in Solution
Bocheng Zhang, Tao Lan, Xiangyi Huang, Chaoqing Dong, and Jicun Ren
In this work, we reported an efficient method for eliminating the optical trapping effect on characterization of nanoparticle diffusion parameters by resonance light scattering correlation spectroscopy (RLSCS). The RLSCS represents a new single nanoparticle method and its principle was based on measuring the resonance light scattering fluctuations in a highly focused laser beam due to the Brownian motion of single nanoparticles such as gold nanoparticles (GNPs), which resembled fluorescence correlation spectroscopy (FCS). In RLSCS analysis, the polarizability of nanoparticles are much higher than fluorescent molecules in FCS, and the sizes of them are larger, therefore, the optical trapping force significantly affects the diffusion behaviors of nanoparticles under a highly focused laser beam. In this study, we used the 632.8 nm He—Ne laser as the light source, which was close to the resonance scattering band of GNPs, and chose GNPs (from 20 to 100 nm) as model samples. We theoretically and experimentally investigated the optical trapping effect of GNPs in RLSCS, and observed a good linear relation between the characteristic diffusion times of GNPs and laser intensity in the certain condition (below 100 μW). This result was in line with the theoretical deduction. By the extrapolation strategy, we effectively eliminated the optical trapping effect and accurately obtained the diameter of GNPs, which was in good agreement with that obtained by transmission electron microscopy. The method described here can extend to FCS analysis of fluorescent nanoparticles as well.
DOI
In this work, we reported an efficient method for eliminating the optical trapping effect on characterization of nanoparticle diffusion parameters by resonance light scattering correlation spectroscopy (RLSCS). The RLSCS represents a new single nanoparticle method and its principle was based on measuring the resonance light scattering fluctuations in a highly focused laser beam due to the Brownian motion of single nanoparticles such as gold nanoparticles (GNPs), which resembled fluorescence correlation spectroscopy (FCS). In RLSCS analysis, the polarizability of nanoparticles are much higher than fluorescent molecules in FCS, and the sizes of them are larger, therefore, the optical trapping force significantly affects the diffusion behaviors of nanoparticles under a highly focused laser beam. In this study, we used the 632.8 nm He—Ne laser as the light source, which was close to the resonance scattering band of GNPs, and chose GNPs (from 20 to 100 nm) as model samples. We theoretically and experimentally investigated the optical trapping effect of GNPs in RLSCS, and observed a good linear relation between the characteristic diffusion times of GNPs and laser intensity in the certain condition (below 100 μW). This result was in line with the theoretical deduction. By the extrapolation strategy, we effectively eliminated the optical trapping effect and accurately obtained the diameter of GNPs, which was in good agreement with that obtained by transmission electron microscopy. The method described here can extend to FCS analysis of fluorescent nanoparticles as well.
DOI
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