Abstract
Near field generated by plasmonic structures has recently been proposed to trap small objects. We report the first integration of plasmonic trapping with microfluidics for lab-on-a-chip applications. A three-layer plasmo-microfluidic chip is used to demonstrate the trapping of polystyrene spheres and yeast cells. This technique enables cell immobilization without the complex optics required for conventional optical tweezers. The benefits of such devices are optical simplicity, low power consumption and compactness; they have great potential for implementing novel functionalities for advanced manipulations and analytics in lab-on-a-chip applications.
Highlights
Optical tweezers were first proposed by Ashkin and his collaborators in 1970 [1]
While conventional tweezers rely on far field interactions, a new class of trapping experiments based on the near field has emerged over the last few years
The paper is organized in the following manner: in Sec. 2 we investigate numerically how a gold nanostructure can create a stable trap for a dielectric sphere; Sec. 3 describes the integration of this plasmonic structure into microfluidics; Sec. 4 demonstrates experimentally the trapping of dielectric spheres and yeast cells flowing into the microfluidic channel
Summary
Optical tweezers were first proposed by Ashkin and his collaborators in 1970 [1]. Small objects are trapped in the middle of a tightly focused laser beam by the optical field gradient. Plasmon resonances represent resonant excitation of the free electrons in a metal and manifest either as localized modes in particles or delocalized modes in thin films [14]; they can occur in the visible or near–infrared spectrum range in metals such as gold, silver, copper and aluminum Since these modes produce very strong and localized electromagnetic fields, they have the potential of creating even stronger trapping potentials than a tightly focused laser beam. Compared to a conventional optical tweezer, trapping based on plasmonic nanostructures provides a significant improvement in that it does not require complicated optics to create the trap, which instead is generated by the near field of the plasmonic nanostructure For this reason, plasmonic trapping can be integrated with microfluidics for lab–on–a–chip applications in order to produce novel chips with increased functionalities.
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