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Title: Integration of optical tweezers in a digital microfluidic platform for magnetic particle manipulation in a microwell array
Authors: Decrop, Deborah
Brans, Toon
Beunis, Filip
Lammertyn, Jeroen
Issue Date: 6-Oct-2014
Conference: Novel Technologies for In Vitro Diagnostics (DIATECH2014) edition:1 location:Leuven date:6-8 october 2014
Article number: 39
Abstract: Recently, optical tweezers have been used for isolating and manipulating single cells in PDMS microwell arrays showing great potential for cell fusion, fertilization, and cell migration [1, 2]. However, a similar tool has not been developed for single magnetic particles seeded in a Teflon microwell array. The combination of magnetic particles and microwells allows the implementation of digital bioassays for detecting single protein or DNA molecules. This work describes the integration of optical tweezers (Fig. 1A) with a digital microfluidic (DMF) chip bearing a Teflon microwell array (Fig. 1B), to develop a platform for the manipulation of single magnetic particles, functionalized with biomolecules.
To obtain this, a double-plated DMF device was used. The DMF top-plate was coated with a thick Teflon layer in which a microwell array was fabricated using a dry lift-off technique [3]. The fabrication process results in a hexagonal array of femtoliter-sized microwells. The microwells are 4.5 μm in diameter and can accommodate only one magnetic particle (Fig. 1B). Figure 1A illustrates the optical tweezer setup used for manipulating single magnetic particles. The infrared laser was focused into an inverted microscope using a beam expansion telescope, beam steering lenses and a high numerical aperture objective. To achieve stable particle trapping, the light intensity gradient force must exceed the light scattering force. Once the focused laser beam was aimed on a particle in a microwell, the particle got attracted to the point of highest light intensity, which is right above the microwell plane. By changing the focus, the magnetic particle could be released in the above droplet (Fig. 2). Using electrowetting-on-dielectric method, the droplet was dragged off the array collecting released particles. It was demonstrated that particles could be retrieved from the microwells only in the presence of certain non-ionic surfactants, which prevent particles from adhering to both Teflon and glass. In order to find a relationship between bead surface properties and retrieval performance differently functionalized particles were tested. Beside the particle retrieval, also the transportation and positioning in other microwells were demonstrated. The following link gives access to a movie illustrating the mechanism of particle retrieval: (https://www.dropbox.com/s/8r3ct2fppc3rkq3/P68_05001.avi).
We have combined a microwell array on a DMF chip and optical tweezers technology to obtain a single magnetic particle manipulation tool. This tool shows great potential for bio-receptor screening, digital assays and aptamer selection. The technique also offers the possibility to combine single molecule detection with other on-chip methods (like sequencing), without removing the particles from the chip.
[1] X. Wang, X. Gou, S. Chen, X. Yan, and D. Sun, J. Micromechanics Microengineering, vol. 23, no. 7, p. 075006, Jul. 2013.
[2] X. Wang, S. Chen, Y. T. Chow, C. Kong, R. a. Li, and D. Sun, RSC Adv., vol. 3, no. 45, p. 23589-23595, 2013.
[3] D. Witters, K. Knez, F. Ceyssens, R. Puers, and J. Lammertyn, “Lab Chip, no. 207890, p. 2047-2054, 2013.
Publication status: published
KU Leuven publication type: IMa
Appears in Collections:Division of Mechatronics, Biostatistics and Sensors (MeBioS)

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