Optical Manipulation of Objects in Microfluidic Devices
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OPTICAL MANIPULATION OF OBJECTS IN MICROFLUIDIC DEVICES ERHAN ATA, AARON L. BIRKBECK, MIHRIMAH OZKAN*, CENGIZ S. OZKAN**, RICHARD FLYNN, MARK WANG AND SADIK ESENER Electrical Engineering Department, University of California, San Diego * Electrical Engineering Department, University of California, Riverside ** Mechanical Engineering Department, University of California, Riverside ABSTRACT In this paper, we present object manipulation methodologies in microfluidic devices based on object-photon interactions. Devices were fabricated by polydimethylsiloxane (PDMS) elastomer molding of channel structures over photolithographically defined patterns using a thick negative photoresist. Inorganic objects including polystyrene spheres and organic objects including live cells were transferred into fluidic channels using a syringe pump. The objects were trapped and manipulated within the fluidic channels using optical tweezers formed by VCSEL arrays, with only a few mW of optical power. We have also shown that it is possible to manipulate multiple objects as a whole assemble by using an optically-trapped particle as a handle, or an “optical handle”. Optical manipulation will have applications in biomedical devices for drug discovery, cytometry and cell biology research. INTRODUCTION In recent years, efforts have been focused on miniaturization of systems for biological and chemical analysis which resulted in a number of lab-on-a-chip technologies useful for applications in combinatorial chemistry [1,2], immunoassay analysis [3], PCR amplification [4] , DNA analysis [5], implantable drug systems, etc. Such devices, which generally utilize electrostatic, magnetic, and micro-mechanical forces, can significantly enhance the speed of analysis while utilizing ultra small sample and reagent volumes of biological samples, on the order of a few nanoliters. In the last decade, well practiced silicon microfabrication techniques have been the primary means of device fabrication. More recently, less expensive plastic micro-replication techniques, glass micromachining and PDMS (polydimethylsiloxane) molding techniques are being used [6]. Microfluidic devices utilize electrostatic, magnetic and micro-mechanical forces for inducing the flow of fluids and biological media into the channels. New device technologies are being explored for the controlled manipulation of biological cells for applications in forming cellular arrays for biological research, cancer cell cytometry and drug discovery studies [7]. Cell membranes are highly deformable and excessive shear stresses induced during fluid flow can cause rupture of the membrane or destruction of the cell. Depending on the specific application, high throughput cell handling might be required (such as in cell cytometry) which may require parallel manipulation of cells. In this paper, we present two methodologies for handling objects in microfluidic devices, based on optical gradient and optical scattering forces. We will demonstrate the concepts via experiments conducted using polystyrene microsp
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