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Methods Protoc. 2018, 1(4), 44; https://doi.org/10.3390/mps1040044

Optical Trapping and Manipulation of Superparamagnetic Beads Using Annular-Shaped Beams

Laboratório de Física Biológica, Departamento de Física, Universidade Federal de Viçosa, Viçosa 36570-900, Brazil
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Received: 9 October 2018 / Revised: 12 November 2018 / Accepted: 14 November 2018 / Published: 20 November 2018
(This article belongs to the Special Issue Single-Molecule Techniques)
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Abstract

We propose an optical tweezers setup based on an annular-shaped laser beam that is efficient to trap 2.8 μ m-diameter superparamagnetic particles. The optical trapping of such particles was fully characterized, and a direct absolute comparison with a geometrical optics model was performed. With this comparison, we were able to show that light absorption by the superparamagnetic particles is negligible for our annular beam tweezers, differing from the case of conventional Gaussian beam tweezers, in which laser absorption by the beads makes stable trapping difficult. In addition, the trap stiffness of the annular beam tweezers increases with the laser power and with the bead distance from the coverslip surface. While this first result is expected and similar to that achieved for conventional Gaussian tweezers, which use ordinary dielectric beads, the second result is quite surprising and different from the ordinary case, suggesting that spherical aberration is much less important in our annular beam geometry. The results obtained here provide new insights into the development of hybrid optomagnetic tweezers, which can apply simultaneously optical and magnetic forces on the same particles. View Full-Text
Keywords: optical tweezers; optical trapping; superparamagnetic particles; trap stiffness; annular beam optical tweezers; optical trapping; superparamagnetic particles; trap stiffness; annular beam
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Oliveira, L.; Campos, W.H.; Rocha, M.S. Optical Trapping and Manipulation of Superparamagnetic Beads Using Annular-Shaped Beams. Methods Protoc. 2018, 1, 44.

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