Determination of rotation in the pitch degree of freedom for a spherical birefringent particle
04 May 2018-Vol. 10672, pp 33-37
TL;DR: In this paper, the 2-fold asymmetry in the scattered signal was measured using video microscopy for a microsphere attached with a kinesin molecule while moving along a microtubule.
Abstract: A three dimensional rigid spherical microscopic object can rotate in either the pitch, yaw or roll fashion. Among these, yaw motion has been conventionally studied using the intensity of the scattered light from birefringent microspheres through crossed polarizers. So far, however, there is no way to study the pitch rotational motion in spherical microspheres. Here we suggest a new method towards the study of such pitch motion in birefringent microspheres under crossed polarizers by measuring the 2-fold asymmetry in the scattered signal using video microscopy. We show a simple example of pitch rotation determination using video microscopy for a microsphere attached with a kinesin molecule while moving along a microtubule. It can also be extended to optical tweezers.
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Journal Article•
TL;DR: The Brownian motion of isolated ellipsoidal particles in water confined to two dimensions is studied and the effects of coupling between rotational and translational motion are elucidated by using digital video microscopy and Langevin theory and numerical simulations.
Abstract: We studied the Brownian motion of isolated ellipsoidal particles in water confined to two dimensions and elucidated the effects of coupling between rotational and translational motion. By using digital video microscopy, we quantified the crossover from short-time anisotropic to long-time isotropic diffusion and directly measured probability distributions functions for displacements. We confirmed and interpreted our measurements by using Langevin theory and numerical simulations. Our theory and observations provide insights into fundamental diffusive processes, which are potentially useful for understanding transport in membranes and for understanding the motions of anisotropic macromolecules.
336 citations
TL;DR: In this article, an optical torque can be induced on microscopic birefringent particles of calcite held by optical tweezers, which can either become aligned with the plane of polarization or spin with constant rotation frequency.
Abstract: Light-induced rotation of absorbing microscopic particles by transfer of angular momentum from light to the material raises the possibility of optically driven micromachines. The phenomenon has been observed using elliptically polarized laser beams or beams with helical phase structure. But it is difficult to develop high power in such experiments because of overheating and unwanted axial forces, limiting the achievable rotation rates to a few hertz. This problem can in principle be overcome by using transparent particles, transferring angular momentum by a mechanism first observed by Beth in 1936, when he reported a tiny torque developed in a quartz waveplate due to the change in polarization of transmitted light. Here we show that an optical torque can be induced on microscopic birefringent particles of calcite held by optical tweezers. Depending on the polarization of the incident beam, the particles either become aligned with the plane of polarization (and thus can be rotated through specified angles) or spin with constant rotation frequency. Because these microscopic particles are transparent, they can be held in three-dimensional optical traps at very high power without heating. We have observed rotation rates in excess of 350 Hz.
129 citations
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TL;DR: In this article, an optical torque can be induced on microscopic birefringent particles of calcite held by optical tweezers, which can be held in three-dimensional optical traps at very high power without heating.
Abstract: Light-induced rotation of absorbing microscopic particles by transfer of angular momentum from light to the material raises the possibility of optically driven micromachines. The phenomenon has been observed using elliptically polarized laser beams1 or beams with helical phase structure2,3. But it is difficult to develop high power in such experiments because of overheating and unwanted axial forces, limiting the achievable rotation rates to a few hertz. This problem can in principle be overcome by using transparent particles, transferring angular momentum by a mechanism first observed by Beth in 19364, when he reported a tiny torque developed in a quartz ‘wave-plate’ owing to the change in polarization of transmitted light. Here we show that an optical torque can be induced on microscopic birefringent particles of calcite held by optical tweezers5. Depending on the polarization of the incident beam, the particles either become aligned with the plane of polarization (and thus can be rotated through specified angles) or spin with constant rotation frequency. Because these microscopic particles are transparent, they can be held in three-dimensional optical traps at very high power without heating, leading to rotation rates of over 350 Hz.
913 citations
TL;DR: It is shown that for small distortions, contrary to intuition, DNA overwinds under tension, reaching a maximum twist at a tension of ∼30 pN, and the observed twist–stretch coupling predicts that DNA should also lengthen when overwound under constant tension, an effect that is quantitatively confirmed.
Abstract: Physical intuition predicts that DNA should unwind under tension as it is pulled towards a denatured structure, but this is not the case. Pulling of a single DNA molecule first leads to overwinding, which causes it to lengthen, not shorten. These results can be explained by a coupling between stretch and twist, such that the DNA inner radius changes under tension. DNA is often modelled as an isotropic rod1,2,3,4, but its chiral structure suggests the possible importance of anisotropic mechanical properties, including coupling between twisting and stretching degrees of freedom. Simple physical intuition predicts that DNA should unwind under tension, as it is pulled towards a denatured structure4,5,6,7,8. We used rotor bead tracking to directly measure twist–stretch coupling in single DNA molecules. Here we show that for small distortions, contrary to intuition, DNA overwinds under tension, reaching a maximum twist at a tension of ∼30 pN. As tension is increased above this critical value, the DNA begins to unwind. The observed twist–stretch coupling predicts that DNA should also lengthen when overwound under constant tension, an effect that we quantitatively confirm. We present a simple model that explains these unusual mechanical properties, and also suggests a possible origin for the anomalously large torsional rigidity of DNA. Our results have implications for the action of DNA-binding proteins that must stretch and twist DNA to compensate for variability in the lengths of their binding sites9,10,11. The requisite coupled DNA distortions are favoured by the intrinsic mechanical properties of the double helix reported here.
375 citations
TL;DR: An apparatus that can measure the instantaneous angular displacement and torque applied to a quartz particle which is angularly trapped and is ideal for the study of known biological molecular motors is described.
Abstract: We describe an apparatus that can measure the instantaneous angular displacement and torque applied to a quartz particle which is angularly trapped. Torque is measured by detecting the change in angular momentum of the transmitted trap beam. The rotational Brownian motion of the trapped particle and its power spectral density are used to determine the angular trap stiffness. The apparatus features a feedback control that clamps torque or other rotational quantities. The torque sensitivity demonstrated is ideal for the study of known biological molecular motors.
360 citations
Journal Article•
TL;DR: The Brownian motion of isolated ellipsoidal particles in water confined to two dimensions is studied and the effects of coupling between rotational and translational motion are elucidated by using digital video microscopy and Langevin theory and numerical simulations.
Abstract: We studied the Brownian motion of isolated ellipsoidal particles in water confined to two dimensions and elucidated the effects of coupling between rotational and translational motion. By using digital video microscopy, we quantified the crossover from short-time anisotropic to long-time isotropic diffusion and directly measured probability distributions functions for displacements. We confirmed and interpreted our measurements by using Langevin theory and numerical simulations. Our theory and observations provide insights into fundamental diffusive processes, which are potentially useful for understanding transport in membranes and for understanding the motions of anisotropic macromolecules.
336 citations
"Determination of rotation in the pi..." refers methods in this paper
...For an elongated particle, the yaw, which is the rotation about the direction of propagation of the incident light in an optical microscope, and the pitch, which is the rotation about one of the axes orthogonal to propagation direction, can be both measured relying upon the projection on the image plane.(1) However, for a spherical microparticle, only the yaw degree of freedom has been measured by making the particle birefringent and utilizing the total intensity of light scattered under crossed polarizers....
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TL;DR: It is shown that the displacement sensitivity of the tweezers is modulated by a standing light wave between the microsphere and the surface, and the data suggest that microspheres can experience attractive and/or repulsive forces close to surfaces.
Abstract: Optical tweezers are widely used to measure molecular forces in biology. Such measurements are often influenced by a nearby surface that can perturb both the calibration of the tweezers as well as ...
238 citations
"Determination of rotation in the pi..." refers methods in this paper
...The equipartition theorem should also hold in this sense too which can be used to calibrate the pitch signal in the usual fashion.(17) We show an example of determination of the pitch angle for a birefringent microsphere being pulled along by a kinesin molecule on some microtubule in Fig....
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