Abstract
We propose a novel design of the dual-waveguide trap for trapping and Raman identification of microscopic particles and biological objects in a fluid. The device is based on two embedded Si3N4waveguides launching counterpropagating beams into the fluidic channel of a lab-on-a-chip. For waveguides with a square cross-section of 1 µm2, a 5 µm gap in between and for a 785 nm operation wavelength, we perform finite-difference time-domain simulations of the beam profiles and the trapping forces acting on polystyrene beads (diameter 0.2-1.4 µm). The forces reach values up to 16 pN/W for a bead diameter of 1.4 µm, indicating that the trap is very suitable to trap particles in a fluid. This is confirmed by the trapping potentials deduced from the force curves. The design of waveguides and chip is completely compatible with glass-based microfluidic technology, thus enabling mass production and widespead application, contrary to previous approaches.
Highlights
The combination of photonics with a lab-on-a-chip attracts strong attention in view of its applicability in bio-sensing [1]
In dual-beam traps the scattering force acts in the axial direction of the beams and the gradient force in the transverse direction [3]
Various dual-waveguide traps have been integrated in a fluidic chip, either using fibers [4]–[6] or liquid core waveguides [7]
Summary
The combination of photonics with a lab-on-a-chip attracts strong attention in view of its applicability in bio-sensing [1]. Combining laser tweezing and Raman spectroscopy [2], enabling both trapping and identification of single cells in a fluid, is an important development. New in this is miniaturization of the tweezers and their integration in the fluidic chip using optical waveguides. This leads to an integrated photonics version of Ashkin’s dual-beam trap [3] which avoids cumbersome free-space laser beams and lenses.
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