Abstract
In this work we demonstrate an integrated microfluidic/photonic architecture for performing dynamic optofluidic trapping and transport of particles in the evanescent field of solid core waveguides. Our architecture consists of SU-8 polymer waveguides combined with soft lithography defined poly(dimethylsiloxane) (PDMS) microfluidic channels. The forces exerted by the evanescent field result in both the attraction of particles to the waveguide surface and propulsion in the direction of optical propagation both perpendicular and opposite to the direction of pressure-driven flow. Velocities as high as 28 mum/s were achieved for 3 mum diameter polystyrene spheres with an estimated 53.5 mW of guided optical power at the trapping location. The particle-size dependence of the optical forces in such devices is also characterized.
Highlights
Within microfluidic systems, optical forces represent an additional form of particle transport that complements traditional manipulation techniques such as pressure driven flow and electro-kinetics [1]
Examples of such works include the sorting of particles using various 3-D optical lattices [6], laser diode bars [7], micro-mirrors [8], and single beam free space trapping [9,10,11,12,13], all involving the combination of microfluidics and optical trapping, but without the additional advantages provided by the use of waveguiding structures
Analogous to the advantages seen for telecom and datacom applications, the use of planar photonic structures in microfluidic devices removes the need for table-top free-space optics, potentially reducing costs and
Summary
Optical forces represent an additional form of particle transport that complements traditional manipulation techniques such as pressure driven flow and electro-kinetics [1]. The most well exploited use of optical forces [2,3,4,5] in such microfluidic devices has been the ability to sort microscale objects based on properties such as size, refractive index, absorption, and dispersion Examples of such works include the sorting of particles using various 3-D optical lattices [6], laser diode bars [7], micro-mirrors [8], and single beam free space trapping [9,10,11,12,13], all involving the combination of microfluidics and optical trapping, but without the additional advantages provided by the use of waveguiding structures. The nature of lithographic methods used to produce planar photonic devices allows for the creation of thousands of parallel systems on the same substrate so that many trapping processes can be performed simultaneously over a large area Another advantage of using high refractive–index-contrast materials is that they allow for controlled distribution of the optical energy over dimensions much smaller than the free-space wavelength of light. This combination allows for the creation of a simple yet functional optical manipulation system for lab-on-chip applications
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