Specific binding and magnetic concentration of CD8+ T-lymphocytes on electrowetting-on-dielectric platform

Abstract

In the quest to create a low-power portable lab-on-a-chip system, we demonstrate the specific binding and concentration of human CD8+ T-lymphocytes on an electrowetting-on-dielectric ͑EWOD͒-based digital microfluidic platform using antibody-conjugated magnetic beads ͑MB-Abs͒. By using a small quantity of nonionic surfactant, we enable the human cell-based assays with selective magnetic binding on the EWOD device in an air environment. High binding efficiency ͑ϳ92%͒ of specific cells on MB-Abs is achieved due to the intimate contact between the cells and the magnetic beads ͑MBs͒ produced by the circulating flow within the small droplet. MBs have been used and cells manipulated in the droplets actuated by EWOD before; reported here is a cell assay of a clinical protocol on the EWOD device in air environment. The present technique can be further extended to capture other types of cells by suitable surface modification on the MBs. © 2010 American Institute of Physics. ͓doi:10.1063/1.3509457͔ I. BACKGROUND AND MOTIVATION A. EWOD as a lab-on-a-chip platformDue to its simple design, low-power consumption, and reprogrammable fluid paths, dropletbased or digital microfluidics driven by electrowetting-on-dielectric ͑EWOD͒ 1-5 is an attractive platform to develop microfluidic devices and systems for portable or point-of-care "lab-on-a-chip" applications.6 Unlike continuous flow through channels, fluids are handled in the form of individual droplets by the locally applied electric potentials. Power consumption in EWOD ͑well below 1 mW͒ is much smaller than typical continuous microfluidic systems.7 Moreover, droplet movement is directly controlled by electrical signals, and no other inputs such as thermal, pneumatic, optical, etc., are required. These features make EWOD uniquely suited for battery operation, thus addressing a critical requirement of a portable system. Moving parts such as pumps and valves, which could be failure-prone, are not required for EWOD, enhancing its simplicity and reliability. Unlike "hardwired" channels, the fluid ͑droplet͒ path in EWOD is reconfigurable purely through software, allowing the choice between multiple testing operations on the same device using the same system. Economical mass fabrication of EWOD test chips is possible, for example, using Printed Circuit Board ͑PCB͒ fabrication 8 or rapid prototyping. 9Despite the various advantages over channel-based continuous microfluidics for a lab-on-achip platform, cell-based assays on an EWOD platform have been difficult due to "biofouling" ͑biomolecular adsorption of cells and proteins͒ on the hydrophobic EWOD surface. The ability to actuate cell samples on EWOD in an air environment has been demonstrated only recently, 10 opening up the possibility of cell separation assays on EWOD, such as the one reported here.

A fluorogenic heterogeneous immunoassay for cardiac muscle troponin cTnI on a digital microfluidic device

“…The first modern EWOD device was shown in 2000 [10], to change the focal length of a drop of water in oil for an optical lens. EWOD has been used in many different of ways, for example, detection of trinitrotoluene [11], PCR [12], cell separation [13] and, most recently, for reagent dispensing [14,15]. Programmable arrays of up to 4,096 independently addressable electrodes have also been demonstrated [16].…”

Theory, fabrication and applications of microfluidic and nanofluidic biosensors

“…In addition, detection methods could also rely on mechanical changes induced owing to adsorption of target molecules or analytes to cantilevers [35][36][37] or nanowires [33], changes to inherent biomolecular charge in the case of field-effect transistors, sometimes also classified as microarray-type biosensors [38][39][40][41][42][43], or electrochemical changes such as those arising from redox reactions inducing variations in current flow [44,45]. Therefore, biosensors form a complex area of research given the diversity of target molecules, need for low false positives and variety of detection platforms available [46][47][48][49][50] with a brief summary presented in table 1a.…”

Building bio-assays with magnetic particles on a digital microfluidic platform

“…Later, research focused on concentration and isolation of cells on chip [64,65] and in this context magnetic particles appeared as a powerful tool to efficiently capture, isolate and concentrate the cells. Shah et al [66], integrated for the first time magnetic particles on a DMF chip for cell-based applications. By merging and mixing two droplets containing, respectively, beads functionalized with specific antibodies and cell samples, they successfully isolated CD8+ lymphocytes from other peripheral blood components.…”