Resolving Stable Axial Trapping Points of Nanowires in an Optical Tweezers Using Photoluminescence Mapping

Wang, Fan; Toe, Wen Jun; Lee, Woei Ming; McGloin, David; Gao, Qiang; Tan, Hark Hoe; Jagadish, Chennupati; Reece, Peter J.

doi:10.1021/nl304607v

Cited by 36 publications

(24 citation statements)

References 31 publications

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“…Two techniques were used to measure the forcedisplacement characteristics of the optically trapped particles: Stokes drag [20] and trap stepping [25]. The Stokes drag measurements were performed by dragging the particle through the medium in a direction parallel to its long axis at a constant velocity, and measuring its displacement relative to its equilibrium position.…”

Section: Methodsmentioning

confidence: 99%

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Shape-induced force fields in optical trapping

et al. 2014

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Advances in optical tweezers, coupled with the proliferation of 2-photon polymerisation systems, mean that it is now becoming routine to fabricate and trap non-spherical particles. The shaping of both light beams and particles allows fine control over the flow of momentum from the optical to mechanical regimes. However, understanding and predicting the behaviour of such systems is highly complex in comparison with the traditional optically trapped microsphere. In this paper we present a conceptually new and simple approach, based on the nature of the optical force density. We illustrate the method through the design and fabrication of a shaped particle capable of acting as a passive force clamp; we demonstrate its use as an optically trapped probe for imaging surface topography. Further applications of the design rules highlighted here may lead to new sensors for probing bio-molecule mechanics, as well as to the development of optically actuated micro-machines.It is well known that the high intensity gradients generated in a tightly focused laser beam can be used to trap and manipulate micron-sized particles [1]. An optically trapped sphere is an elegant example of a microscopic harmonic oscillator, capable of measuring fN-scale forces, which has proved invaluable for the study of molecular motors and single biopolymer mechanics [2]. However, there are other desirable features of a force field that can only be introduced by modifying the particle shape or dielectric structure beyond that of a simple homogeneous sphere [3,4]. For example, optical torques can be applied to a particle whose symmetry has been lowered either by shape modification With increasing complexity of shape, the problem of predicting, and optimising, the 2 force profile of the trapped particle becomes ever more challenging. Although specialised software packages are available to compute the optical forces [13], their use is not routine.In this paper, therefore, we address this problem and describe a straightforward method for predicting the optical forces acting on extended dielectric particles of general shape. We support the description with rigorous 3-dimensional T-matrix calculations. To illustrate the approach, we describe the design and fabrication of a passive force clamp based on a tapered cylinder and capable of applying a constant force over displacements of several microns. We demonstrate its use in an optically-controlled scanning probe microscope for ultra-low force imaging. Potential future applications of this device may include the imaging of sensitive biological membranes. Results Background theory

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Section: Methodsmentioning

confidence: 99%

“…This technique cannot capture local minima in the force-displacement profiles, as the particle would simply jump past them. To circumvent this, the force characteristics were also measured by stepping the trap position and observing the velocity with which the particle returned to equilibrium [25].…”

Section: Experimental Verificationmentioning

confidence: 99%

Shape-induced force fields in optical trapping

et al. 2014

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“…Photoluminescence spectroscopy is routinely integrated with OTs as it is a relatively simple optical method to measure fluorescence, electronic and structural properties of the trapped objects. Microphotoluminescence has, for instance, been used to identify different crystal phases in the trapped object or map structural inhomogeneities along its entire span for selection before assembly into a device . The optical response including strong nonlinearities and even the chirality of certain nanomaterials can be readily investigated.…”

Section: Analytical Techniquesmentioning

confidence: 99%

Nanoscale Optical Trapping: A Review

Bradac

2018

Advanced Optical Materials

118

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The First TrapIn 1969, a "back-of-the-envelope" calculation inspired Ashkin to conduct a simple experiment and determine whether it was feasible to use light radiation pressure to accelerate objects to practical speeds. Photons carry momentum hν/c (with h, ν and c being the Planck's constant, the frequency of the photon and the speed of light, respectively). If light from a source with power P shines on a mirror, P/hν photons hit the surface every second and transfer a total momentum of (2P/hν)(hν/c) = 2P/c onto it. A perfectly reflecting mirror should therefore-due to conservation-acquire an equal momentum in the same direction light propagates.Based on this crude calculation, Ashkin predicted that a light source of power P = 1 W, would produce a force (on an ideally reflecting mirror) of ≈10 nN-indeed small in absolute terms. [3] Nevertheless, if a laser beam is used as the light source and is focused on a spot of ≈1 µm 2 to hit a particle ≈1 µm in diame ter, the resulting force does become relevant. Assuming the particle is perfectly reflective and has a density of 1 g cm −3 , the calculated acceleration is ≈10 9 cm s −2 , i.e., roughly 10 6 times the acceleration of gravity. In the experiment, Ashkin conducted to test his hypotheses, [2] a cw argon laser (wavelength λ = 514.5 nm, waist radius w 0 = 6.2 µm at the focal point) was employed to accelerate latex spheres (diameter 0.59, 1.31, and 2.68 µm), which were freely suspended in water, in a glass chamber. With just milliwatts of laser power, Ashkin observed that the particles were pushed in the direction of the mildly focused Gaussian laser beam, with values for the acceleration consistent with his rough predictions. Interestingly, he also observed an unanticipated phenomenon. Particles located in the fringes of the beam were drawn toward the beam axiswhere the light intensity is the highest-before being accelerated and pushed with ≈µm s −1 speeds toward the back of the chamber. They would disperse by Brownian motion away from the beam axis once the laser was switched off, yet they would be drawn again toward the center of the beam upon turning the laser back on-as the radiation pressure had a transverse component to the force, as well as the predicted longitudinal one.The origin of both the transversal and longitudinal force is usually understood by considering two distinct regimes, depending on the relative size of the particles to the wavelength of the laser beam: the geometrical (ray optics) regime and the Rayleigh (dipole approximation) regime.Optical trapping is the craft of manipulating objects with light. Decades after its first inception in 1970, the technique has become a powerful tool for ultracold-atom physics and manipulation of micron-sized particles. Yet, optical trapping of objects at the intermediate-nanoscale-range is still beyond full grasp. This matters because the nanometric realm is where several promising advances, from mastering single-molecule experiments in biology, to fabricating hybrid devices for nanoelectronics and photonics, a...

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“…11 While optical tweezers has been widely applied to the task of nanoparticle manipulation, [12][13][14][15][16][17] there is increasing interest in techniques for promoting self-organisation. 18,19 Optical binding offers one such possibility.…”

Section: Introductionmentioning

confidence: 99%

Optical binding between knotted and chiral nanoparticles

Simpson

Hanna

2016

SPIE Proceedings

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General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. ABSTRACTOptical binding occurs when systems of both dielectric particles are illuminated by intense light fields, and results in the formation of clusters and coupled dynamical behaviour. Optical binding between spheres has been studied extensively, but little has appeared in the literature describing binding in lower symmetry systems. Here we discuss computer simulations of optical binding between hypothetical knotted nanowires. The knots chosen are drawn from the class of knots known as torus knots which may be represented with n-fold chiral rotational symmetry. We examine the binding properties of the knots in circularly polarised counter propagating beams.

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Resolving Stable Axial Trapping Points of Nanowires in an Optical Tweezers Using Photoluminescence Mapping

Cited by 36 publications

References 31 publications

Shape-induced force fields in optical trapping

Shape-induced force fields in optical trapping

Nanoscale Optical Trapping: A Review

Optical binding between knotted and chiral nanoparticles

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