Figure 1. Air-liquid Cavity Acoustic Transducers (ALCATs). The air is trapped within side channels. The interface between the air and liquid will vibrate when ultrasound is applied causing streaming patterns indicated by the arrows. The net flow of liquid is in the direction of the black arrows. The swirling red arrows represent eddies where erythrocytes are predominantly trapped. RAPID BLOOD PLASMA SEPARATION WITH AIR-LIQUID CAVITY ACOUSTIC TRANSDUCERS Arlene Doria* 1 , Maulik Patel 1 , and Abraham P. Lee 1 1 Department of Biomedical Engineering, University of California - Irvine, USA biomint.eng.uci.edu ABSTRACT Herein we present a fast and low cost separation strategy that utilizes air-liquid cavity acoustic transducers (ALCATs) to extract plasma from human whole blood. ALCATs are oscillating air-liquid interfaces that are acoustically driven and produce microstreaming within liquids in microfluidic channels. With whole blood, the streaming patterns induced by ALCATs include swirling eddies where erythrocytes become aggregated. The device is designed to have a dense array of ALCATs that simultaneously serve to pump fluid forward and to trap red blood cells. Due to the trapping effect, red blood cells have a longer path to be propelled downstream while plasma continues flowing forward resulting in a rapid extraction of plasma. With microsample volumes in one device, 40% of plasma was yielded from a 16 μL sample of EDTA spiked whole blood within minutes of activating the acoustic source. The plasma volumes and plasma extraction rates can be of practical use in many point-of-care applications. KEYWORDS: point of care, blood plasma separation, sample preparation, air-liquid cavity acoustic transducers, whole blood, red blood cells, erythrocytes, point of care diagnostics INTRODUCTION A fast and low cost on-chip sample preparation method is a critical component for effective point-of-care (POC) diagnostics [1]. The rapid extraction of plasma from whole blood is an important sample prep method to prevent blood components from interfering with assay analyses downstream. Specifically, aggregation of erythrocytes in a chip’s optical detection zone can precipitously degrade signal quality. In the absence of a blood-plasma separation method, extra wash steps are required, thus, increasing sample-to-answer times. A lot of effort has been devoted to the separation of components from blood in various microfluidic systems. Separation strategies include the use of mechanical forces (e.g. centrifugation, filtration, sedimentation, and the Zweifach–Fung effect), magnetic interactions, optical interactions, and dielectrophoresis [2] [3]. However, many of these strategies have practical limitations in cost, time, and scale up. For example, centrifugation and sedimentation methods can be time-consuming. Many commercial filtration methods in POC utilize glass fiber or membrane filters that require complex and costly processing of filters with multiple reagents in order to reduce non-specific binding of the analyte of interest or to reduce hemolysis effects. Furthermore, most methods have limited control of the quantity of plasma that can be extracted. Many microfluidic separation methods also require diluted blood samples. Hence, there is increasing demand for better plasma separation strategies from whole blood. THEORY When liquid fills the main microchannels of hydrophobic devices, pockets of air are trapped within dead-end side channels. Applying an acoustic source will cause the interfaces between air and liquid to oscillate, thereby, creating microstreaming patterns within a localized region of the surrounding liquid (Figure 1). These air liquid cavity acoustic transducers (ALCATs) have been shown to be useful for pumping, mixing, and bead trapping [4]. When whole blood is pumped through an array of activated ALCATs, the red blood cells will agglomerate within streaming eddies. These eddies 978-0-9798064-4-5/μTAS 2011/$20©11CBMS-0001 1882 15th International Conference on Miniaturized Systems for Chemistry and Life Sciences October 2-6, 2011, Seattle, Washington, USA