Thursday, July 19, 2018

Enhance of optical trapping efficiency by nonlinear optical tweezers

Ho Quang, Quy, Doan Quoc Tuan, Thai Doan Thanh, Nguyen Manh Thang

In this article, enhance of optical trapping efficiency by the nonlinear optical tweezers is investigated. The expressions described the longitudinal and transverse optical trapping efficiencies are theoretically derived. The influence of average laser power on the optical trapping efficiency is observed and discussed in comparison with that of linear optical tweezers. Remarkably, the optical trapping efficiency of nonlinear optical tweezers can be enhanced by using average laser power, and get several times higher than that of the linear optical ones having the same configuration.


A Molecular Grammar Governing the Driving Forces for Phase Separation of Prion-like RNA Binding Proteins

Jie Wang, Jeong-Mo Choi, Alex S. Holehouse, Hyun O. Lee, Xiaojie Zhang, Marcus Jahnel, Shovamayee Maharana, Régis Lemaitre, Andrei Pozniakovsky, David Drechsel, Ina Poser, Rohit V. Pappu, Simon Alberti, Anthony A. Hyman

Proteins such as FUS phase separate to form liquid-like condensates that can harden into less dynamic structures. However, how these properties emerge from the collective interactions of many amino acids remains largely unknown. Here, we use extensive mutagenesis to identify a sequence-encoded molecular grammar underlying the driving forces of phase separation of proteins in the FUS family and test aspects of this grammar in cells. Phase separation is primarily governed by multivalent interactions among tyrosine residues from prion-like domains and arginine residues from RNA-binding domains, which are modulated by negatively charged residues. Glycine residues enhance the fluidity, whereas glutamine and serine residues promote hardening. We develop a model to show that the measured saturation concentrations of phase separation are inversely proportional to the product of the numbers of arginine and tyrosine residues. These results suggest it is possible to predict phase-separation properties based on amino acid sequences.


1064 nm Dispersive Raman Microspectroscopy and Optical Trapping of Pharmaceutical Aerosols

Peter J. Gallimore, Nick M. Davidson, Markus Kalberer, Francis D. Pope, and Andrew D. Ward

Raman spectroscopy is a powerful tool for investigating chemical composition. Coupling Raman spectroscopy with optical microscopy (Raman microspectroscopy) and optical trapping (Raman tweezers) allows microscopic length scales and, hence, femtolitre volumes to be probed. Raman microspectroscopy typically uses UV/visible excitation lasers, but many samples, including organic molecules and complex tissue samples, fluoresce strongly at these wavelengths. Here we report the development and application of dispersive Raman microspectroscopy designed around a near-infrared continuous wave 1064 nm excitation light source. We analyze microparticles (1–5 μm diameter) composed of polystyrene latex and from three real-world pressurized metered dose inhalers (pMDIs) used in the treatment of asthma: salmeterol xinafoate (Serevent), salbutamol sulfate (Salamol), and ciclesonide (Alvesco). For the first time, single particles are captured, optically levitated, and analyzed using the same 1064 nm laser, which permits a convenient nondestructive chemical analysis of the true aerosol phase. We show that particles exhibiting overwhelming fluorescence using a visible laser (514.5 nm) can be successfully analyzed with 1064 nm excitation, irrespective of sample composition and irradiation time. Spectra are acquired rapidly (1–5 min) with a wavelength resolution of 2 nm over a wide wavenumber range (500–3100 cm–1). This is despite the microscopic sample size and low Raman scattering efficiency at 1064 nm. Spectra of individual pMDI particles compare well to bulk samples, and the Serevent pMDI delivers the thermodynamically preferred crystal form of salmeterol xinafoate. 1064 nm dispersive Raman microspectroscopy is a promising technique that could see diverse applications for samples where fluorescence-free characterization is required with high spatial resolution.

Physiological Hypoxia (Physioxia) Impairs the Early Adhesion of Single Lymphoma Cell to Marrow Stromal Cell and Extracellular Matrix. Optical Tweezers Study

Kamila Duś-Szachniewicz, Sławomir Drobczyński, Piotr Ziółkowski, Paweł Kołodziej, Kinga M. Walaszek, Aleksandra K. Korzeniewska, Anil Agrawal, Piotr Kupczyk and Marta Woźniak

Adhesion is critical for the maintenance of cellular structures as well as intercellular communication, and its dysfunction occurs prevalently during cancer progression. Recently, a growing number of studies indicated the ability of oxygen to regulate adhesion molecules expression, however, the influence of physiological hypoxia (physioxia) on cell adhesion remains elusive. Thus, here we aimed: (i) to develop an optical tweezers based assay to precisely evaluate single diffuse large B-cell lymphoma (DLBCL) cell adhesion to neighbor cells (mesenchymal stromal cells) and extracellular matrix (Matrigel) under normoxia and physioxia; and, (ii) to explore the role of integrins in adhesion of single lymphoma cell. We identified the pronouncedly reduced adhesive properties of lymphoma cell lines and primary lymphocytes B under physioxia to both stromal cells and Matrigel. Corresponding effects were shown in bulk adhesion assays. Then we emphasized that impaired β1, β2 integrins, and cadherin-2 expression, studied by confocal microscopy, account for reduction in lymphocyte adhesion in physioxia. Additionally, the blockade studies conducted with anti-integrin antibodies have revealed the critical role of integrins in lymphoma adhesion. To summarize, the presented approach allows for precise confirmation of the changes in single cell adhesion properties provoked by physiological hypoxia. Thus, our findings reveal an unprecedented role of using physiologically relevant oxygen conditioning and single cell adhesion approaches when investigating tumor adhesion in vitro.


Sub-10  nm particle trapping enabled by a plasmonic dark mode

Fajun Xiao, Yuxuan Ren, Wuyun Shang, Weiren Zhu, Lei Han, Hua Lu, Ting Mei, Malin Premaratne, and Jianlin Zhao

We demonstrate that a highly localized plasmonic dark mode with radial symmetry, termed quadrupole-bonded radial breathing mode, can be used for optically trapping the dielectric nanoparticles. In particular, the annular potential well produced by this dark mode shows a sufficiently large depth to stably trap the 5 nm particles under a relatively low optical power. Our results address the quest for precisely trapping sub-10 nm particles with high yield and pave the way for placing sub-10 nm particles conforming to a specific geometric pattern.


Controlled spin of a nonbirefringent droplet trapped in an optical vortex beam

Maksym Ivanov, Dag Hanstorp

The spin part of the angular momentum of light can cause a birefringent particle to spin around its axis, while having no effect on a nonbirefringent particle. The orbital part of light’s angular momentum, on the other hand, can cause both birefringent and nonbirefringent particles to orbit around the axis of a light beam. In this paper, we demonstrate that nonbirefringent particles can also be made to spin around their axis when trapped in an optical vortex beam. The rotation of the particle depends on the ratio of the size of the particle and the diameter of the laser beam in which the particle is trapped. It can therefore be controlled by varying the position of the particle with respect to the focal point of the laser beam. The rotational frequency can also be controlled by changing the polarization state of the beam, since spin–orbit coupling affects the total angular momentum experienced by the trapped particle. The motion of the trapped particle is detected by a photodiode and a high-speed camera. Most microparticles found in nature are nonbirefringent, and the method presented in this paper will therefore open up new applications for optically induced rotations.


Monday, July 16, 2018

Low-frequency Noise Reduction in Dual-Fiber Optical Trap using Normalized Differential Signal of Transmission Lights

Tengfang Kuang; Guangzong Xiao; Wei Xiong; Xiang Han; Xinlin Chen; Jie Yuan

The accuracy of long-term position detection in dual-fiber optical trap is limited by low-frequency noise. We propose a technique that can reduce such noise. A position detection system for dual-fiber optical trap using a quadrant photodiode is built. The transmission light from the trapped particle is detected by two photodiodes. The normalized differential signal of transmission lights is demonstrated to carry the noise caused by asymmetric laser power fluctuation irradiating the microsphere, which is proved to dominate low-frequency noise. By subtracting this normalized difference from the position signal, the noise-reduction capability of this technique is remarkably 67% depending on detection bandwidth. It is expected to be applied to integrated and microfluidic fiber-optic trap system.


Optical levitation measurement on hygroscopic behaviour and SVOC vapour pressure of single organic/inorganic aqueous aerosol

Chen Cai,Chunsheng Zhao

Quantifying the gas/particle partitioning of organic compounds is of great significance to the understanding of atmospheric aerosol indirect effect. Accurate determination of the hygroscopicities and vapour pressures of semi-volatile organic compounds (SVOC) is of crucial importance in studying their partitioning behaviour into atmospheric aerosol, as the influences on SVOCs evaporation from participation of inorganic species remains unclear. In this study we first present thermodynamic quantitative simulation and tweezed single particle measurement of hygroscopicity and volatility of single aerosol droplets. With thermodynamics simulation of the hygroscopicity, SVOC time dependent evaporation and potential chloride depletion reaction in a single trapped droplet, we illustrate influences from different process towards the trapped droplet. In optical tweezers measurement, the trapped droplet in the aerosol optical tweezers acts as a microcavity, which stimulates the cavity enhanced Raman spectroscopy (CERS) signal. Size and composition of the particle are calculated from Mie fit to the positions of the "whispering gallery modes" in the CERS fingerprint. Hygroscopic behaviours and SVOC saturated vapour pressure can then be extracted from the correlation between the changing droplet radius and solute concentration (derived from experimentally determined real part of refractive index (RI)) with good accuracy and reliability.


Optomechanical Cavities for All-Optical Photothermal Sensing

Marcel W. Pruessner, Doewon Park, Todd H. Stievater, Dmitry A. Kozak, and William S. Rabinovich

Cavity optomechanics enables strong coupling of optics and mechanics. Although remarkable progress has been made, practical applications of cavity optomechanics are only recently being realized. In this work we propose an all-optical sensing technique enabling the measurement of photothermally induced strains with ultrahigh-resolution. We demonstrate an optomechanical sensor consisting of a silicon nitride (Si3N4) microring cavity that is evanescently coupled to a suspended SiNx micromechanical (MEMS) oscillator. Experiments show that MEMS resonances are excited purely via cavity-enhanced gradient optical forces. However, small levels of absorption in the oscillator result in photothermally induced strains that shift the mechanical resonance frequencies. By measuring absorption-induced frequency shifts our technique enables high-resolution with nanostrain sensitivity corresponding to fJ-levels of absorption. As a demonstration, we perform absorption spectroscopy on the MEMS device and measure the known Si–H absorption feature of deposited silicon nitride. The unprecedented sensitivity enabled by absorption-induced frequency shifts enables entirely new sensors in fields ranging from materials and chemical sensing to bolometers and imaging arrays.


Sorting Metal Nanoparticles with Dynamic and Tunable Optical Driven Forces

Fan Nan and Zijie Yan

Precise sorting of colloidal nanoparticles is a challenging yet necessary task for size-specific applications of nanoparticles in nanophotonics and biochemistry. Here we present a new strategy for all-optical sorting of metal nanoparticles with dynamic and tunable optical driven forces generated by phase gradients of light. Size-dependent optical forces arising from the phase gradients of optical line traps can drive nanoparticles of different sizes with different velocities in solution, leading to their separation along the line traps. By using a sequential combination of optical lines to create differential trapping potentials, we realize precise sorting of silver and gold nanoparticles in the diameter range of 70–150 nm with a resolution down to 10 nm. Separation of the nanoparticles agrees with the analysis of optical forces acting on them and with simulations of their kinetic motions. The results provide new insights into all-optical nanoparticle manipulation and separation and reveal that there is still room to sort smaller nanoparticle with nanometer precision using dynamic phase-gradient forces.