UWEE Tech Report Series

Opto-plasmonic tweezers for manipulation and rotation of micro/nano objects


UWEETR-2006-0009

Author(s):
Xiaoyu Miao and Lih Y. Lin

Keywords:
optical tweezers, optical manipulation, optical rotation, bio-photonics, dielectrophoresis, plasmonics.

Abstract

Non-invasive manipulation of single micro- and nano-sized particles is an important tool for basic biological research. It allows cells, cellular components, and synthetic particles treated with biochemical tags to be collected, concentrated, and transported without damage to the objects themselves. Among various non-invasive manipulation mechanisms, a particularly desired one is the ability to control the orientation of the biological cells, in addition to trapping and moving them. In the past, electro-rotation by dielectrophoresis (DEP) has been the most widely employed method for such purpose. Such approach often requires micro-fabrication for the fixed electrodes, the manipulation area is constrained, and the resolution of rotation is limited. We propose a new approach called Opto-Plasmonic Tweezers for manipulation and rotation of micro- and nano-biological particles that utilizes polarization of light and localized surface plasmon resonance excitation from Au nanostructures. The resonant scattering field from the Au nanostructures is analyzed to determine the induced dielectrophoresis force exerted on a micro-sphere. The modeling results suggest that the Opto-Plasmonic Tweezers is able to generate the same trapping force with much lower optical-intensity requirement than conventional optical tweezers. This provides the flexible ability to manipulate the single biological cell by scanning the light beam and avoid the photodamage to the cell. Subsequently, the theoretical model is expanded to non-spherical objects to calculate the light-induced dielectrophoresis force and torque. Throughout the discussion, L. monocytogenes is used as an example biological cell to simulate the trapping behavior and the orientation control ability through tuning the polarization state of the incident light. Correspondingly, a progression of self-assembly steps to form an Au nanostructure array with large density is confirmed. Ultimately, the research will potentially lead to an instrument to perform the single cell manipulation with high resolution in orientation control and low optical intensity requirement. Such capability will be essential to biological researchers in probing various force mechanism of molecular motors, building structured biomaterials, as well as potential applications in constructing biofilms and human tissue engineering.

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