Hollow-core photonic crystal fiber based multifunctional optical system for trapping, position sensing, and detection of fluorescent particles

V. K. Shinoj and V. M. Murukeshan

We demonstrate a novel multifunctional optical system that is capable of trapping, imaging, position sensing, and fluorescence detection of micrometer-sized fluorescent test particles using hollow-core photonic crystal fiber (HC-PCF). This multifunctional optical system for trapping, position sensing, and fluorescent detection is designed such that a near-IR laser light is used to create an optical trap across a liquid-filled HC-PCF, and a 473 nm laser is employed as a source for fluorescence excitation. This proposed system and the obtained results are expected to significantly enable an efficient integrated trapping platform employing HC-PCF for diagnostic biomedical applications.

DOI

Optical Tweezers with Assistance of Sub-Microsecond-Duration Pulse Laser Beam

Saki Maeda, Tadao Sugiura, and Kotaro Minato

We report optical tweezers with the assistance of a strong instantaneous force generated by a focused pulse laser beam of sub-microsecond duration. A strong instantaneous force is required in biological applications. A suitable pulse duration for pulse assistance in water is derived on the order of 100 to 1000 ns from motion analysis of a micrometer-sized particle. We performed optical tweezers experiments with a focused pulse beam of 160 ns duration coaxially incident with a CW laser beam. From the experiments on particle extraction from a glass surface, the required energy for extraction is smaller than the case of 150 µs duration by a factor of 60.

DOI

Two examples of using physical mechanics approach to evaluate colloidal stability

ZhiWei Sun and ShengHua Xu

Since Mr. Tsien brought up his idea of physical mechanics, as a new field in engineering science, to public attention in the early 50’s of the 20th century, innumerable application examples of physical mechanics approach in diverse fields have manifested its strong vitality increasingly. One of important aspects in applications of physical mechanics is to appropriately choose the microscopic quantity for the system in consideration and build a bridge to connect its relevant microscopic information to its desired macroscopic properties. We present two unique cases of using the physical mechanics approach to study colloidal stability. In the first case we measured the outcomes from artificially induced collisions at individual particle levels, by means of directly observing artificially induced collisions with the aid of optical tweezers. In the second case, by using T-matrix method, the microscopic quantity extinction cross section of the doublet can be accurately evaluated and therefore the measurement range and accuracy of the turbidity methodology for determining the CRC are greatly improved.

DOI

Torque Generation of Kinesin Motors Is Governed by the Stability of the Neck Domain

Melanie Brunnbauer, Renate Dombi, Thi-Hieu Ho, Manfred Schliwa, Matthias Rief, Zeynep Ökten

In long-range transport of cargo, prototypical kinesin-1 steps along a single protofilament on the microtubule, an astonishing behavior given the number of theoretically available binding sites on adjacent protofilaments. Using a laser trap assay, we analyzed the trajectories of several representatives from the kinesin-2 class on freely suspended microtubules. In stark contrast to kinesin-1, these motors display a wide range of left-handed spiraling around microtubules and thus generate torque during cargo transport. We provide direct evidence that kinesin's neck region determines the torque-generating properties. A model system based on kinesin-1 corroborates this result: disrupting the stability of the neck by inserting flexible peptide stretches resulted in pronounced left-handed spiraling. Mimicking neck stability by crosslinking significantly reduced the spiraling of the motor up to the point of protofilament tracking. Finally, we present a model that explains the physical basis of kinesin's spiraling around the microtubule. 

DOI

Circular motion of particles suspended in a Gaussian beam with circular polarization validates the spin part of the internal energy flow

O. V. Angelsky, A. Ya. Bekshaev, P. P. Maksimyak, A. P. Maksimyak, I. I. Mokhun, S. G. Hanson, C. Yu. Zenkova, and A. V. Tyurin

Non-spherical dielectric microparticles were suspended in a water-filled cell and exposed to a coherent Gaussian light beam with controlled state of polarization. When the beam polarization is linear, the particles were trapped at certain off-axial position within the beam cross section. After switching to the right (left) circular polarization, the particles performed spinning motion in agreement with the angular momentum imparted by the field, but they were involved in an orbital rotation around the beam axis as well, which in previous works [Y. Zhao et al, Phys. Rev. Lett. 99, 073901 (2007)] was treated as evidence for the spin-to orbital angular momentum conversion. Since in our realization the moderate focusing of the beam excluded the possibility for such a conversion, we consider the observed particle behavior as a demonstration of the macroscopic “spin energy flow” predicted by the theory of inhomogeneously polarized paraxial beams [A. Bekshaev et al, J. Opt. 13, 053001 (2011)].

DOI

Looking through the mirror: Optical microcavity-mirror image photonic interaction

Lei Shi, E. Xifré-Pérez, F. J. García de Abajo, and F. Meseguer

Although science fiction literature and art portray extraordinary stories of people interacting with their images behind a mirror, we know that they are not real and belong to the realm of fantasy. However, it is well known that charges or magnets near a good electrical conductor experience real attractive or repulsive forces, respectively, originating in the interaction with their images. Here, we show strong interaction between an optical microcavity and its image under external illumination. Specifically, we use silicon nanospheres whose high refractive index makes well-defined optical resonances feasible. The strong interaction produces attractive and repulsive forces depending on incident wavelength, cavity-metal separation and resonance mode symmetry. These intense repulsive photonic forces warrant a new kind of optical levitation that allows us to accurately manipulate small particles, with important consequences for microscopy, optical sensing and control of light by light at the nanoscale.

DOI

Spectroscopy of 3D-trapped particles inside a hollow-core microstructured optical fiber

Charithra Rajapakse, Fan Wang, Tiffany C. Y. Tang, Peter J. Reece, Sergio G. Leon-Saval, and Alexander Argyros

We report on the demonstration of three-dimensional optical trapping inside the core of a hollow-core microstructured optical fiber specifically designed and fabricated for this purpose. Optical trapping was achieved by means of an external tweezers beam incident transversely on the fiber and focused through the fiber cladding. Trapping was achieved for a range of particle sizes from 1 to 5 µm, and manipulation of the particles in three-dimensions through the entire cross-section of the fiber core was demonstrated. Spectroscopy was also performed on single fluorescent particles, with the fluorescence captured and guided in the fiber core. Video tracking methods allowed the optical traps to be characterized and photobleaching of single particles was also observed and characterized.

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Fluctuations, linear response and heat flux of an aging system

J. R. Gomez-Solano, A. Petrosyan and S. Ciliberto

We measure the fluctuations of the position of a Brownian particle confined by an optical trap in an aging gelatin droplet after a fast quench. Its linear response to an external perturbation is also measured. We compute the spontaneous heat flux from the particle to the bath due to the non-equilibrium formation of the gel. We show that the mean heat flux is quantitatively related to the violation of the equilibrium fluctuation-dissipation theorem as a measure of the broken detailed balance during the aging process.

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Effect of polarization on transport of particles in air by optical vortex beam

N O Eckerskorn, N Zeng, V G Shvedov, W Krolikowski and A V Rode

Experiments on transport of spherical particles in air by optical vortex beam show that the speed of transport depends drastically on light polarization. There is a clear correlation between the speed of particle transport in a pipeline formed by cross-polarized vortices: a horizontally polarized beam moves particles faster than a vertically polarized one. To elucidate this effect we demonstrate, both in theory and experiments, that a radial shift of particles away from the vortex axis due to gravity results in polarization dependence of the laser intensity absorbed by the particle and thus determines the speed of transport. The results demonstrate an additional degree of freedom to control particle transport by varying the polarization of the driving vortex beams.

DOI

Erythrocyte deformation in high-throughput optical stretchers

Ihab Sraj, Alex C. Szatmary, Sanjay A. Desai, David W. M. Marr, and Charles D. Eggleton
Optical stretchers can be used to quantify elastic and homeostatic properties of cells. Because they can apply forces to cells without requiring direct contact, they may noninvasively measure mechanical properties related to cell and membrane health. Present-day optical stretchers are, however, limited to measurements on individual stationary cells, limiting throughput. To overcome this limitation and allow study of variations in cell populations, we recently developed and tested a microfluidic chamber that measures optical stretching parameters for erythrocytes under dynamic flowing conditions. The method uses a single linear diode laser bar and permitted measurements at low flow rates and higher throughput. Here, we numerically investigate the feasibility of further increasing the measurement rates of the optical stretcher in parameter domains where hydrodynamic and optical forces are of comparable magnitude. To do this we couple a recently implemented dynamic optical ray-tracing technique with a fluid-structure interaction solver to simulate the deformation of osmotically swollen erythrocytes in fluid flow of variable rate. Our results demonstrate that a detectable steady-state stretch is induced at nominal optical powers and flow rates. In addition, we find that flow rates can be increased significantly with no major effect on net cell stretch showing the feasibility of application of this technique at greatly increased throughputs.

DOI