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Title

Optical deflection and sorting of microparticles in a near-field optical geometry

Author(s)

Marchington, Robert F.;  Mazilu, Michael;  Kuriakose, Smitha;  Garcés-Chávez, V.;  Reece, Peter J.;  Krauss, Thomas F.;  Gu, Min;  Dholakia, Kishan

Abstract

Near-field optical micromanipulation permits new possibilities for controlled motion of trapped objects. In this work, we report an original geometry for optically deflecting and sorting micro-objects employing a total internal reflection microscope system. A small beam of laser light is delivered off-axis through a total internal reflection objective which creates an elongated evanescent illumination of light at a glass/water interface. Asymmetrical gradient and scattering forces from this light field are seen to deflect and sort polystyrene microparticles within a fluid flow. The speed of the deflected objects is dependent upon their intrinsic properties. We present a finite element method to calculate the optical forces for the evanescent waves. The numerical simulations are in good qualitative agreement with the experimental observations and elucidate features of the particle trajectory. In the size range of 1 μm to 5 μm in diameter, polystyrene spheres were found to be guided on average 2.9 ± 0.7 faster than silica spheres. The velocity increased by 3.0 ± 0.5 μms-1 per μm increase in diameter for polystyrene spheres and 0.7 ± 0.2 μms-1 per μm for silica. We employ this size dependence for performing passive optical sorting within a microfluidic chip and is demonstrated in the accompanying video.

Publication type

Journal article

Research centre

Swinburne University of Technology. Faculty of Engineering and Industrial Sciences. Centre for Micro-Photonics

Source

Optics Express, Vol. 16, no. 6 (2008), p. 3712-3726

Publication year

2008

Keyword(s)

Near-field microscopy;  Optical manipulation;  Optical tweezers;  Optics at surfaces;  Physical optics;  Surface waves;  Total internal reflection

Publisher

Optical Society of America

ISSN

1094-4087

Publisher URL

http://dx.doi.org/10.1364/OE.16.003712

Copyright

Copyright © 2008 Optical Society of America. Published version of the paper reproduced here in accordance with the copyright policy of the publisher. This paper was published in Optics Express and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://dx.doi.org/10.1364/OE.16.003712. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.

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