Direct-Referencing Two-Dimensional-Array Digital Microfluidics Using Multilayer Printed Circuit Board

Abstract

Digital (i.e. droplet-based) microfluidics, by the electrowetting-on-dielectric (EWOD) mechanism, has shown great potential for a wide range of applications, such as lab-on-a-chip. While most reported EWOD chips use a series of electrode pads essentially in one-dimensional line pattern designed for specific tasks, the desired universal chips allowing user-reconfigurable paths would require the electrode pads in two-dimensional pattern. However, to electrically access the electrode pads independently, conductive lines need to be fabricated underneath the pads in multiple layers, raising a cost issue especially for disposable chip applications. In this article, we report the building of digital microfluidic plates based on a printed-circuit-board (PCB), in which multilayer electrical access lines were created inexpensively using mature PCB technology. However, due to its surface topography and roughness and resulting high resistance against droplet movement, as-fabricated PCB surfaces require unacceptably high (~500 V) voltages unless coated with or immersed in oil. Our goal is EWOD operations of aqueous droplets not only on oil-covered but also on dry surfaces. To meet varying levels of performances, three types of gradually complex post-PCB microfabrication processes are developed and evaluated. By introducing land-grid-array (LGA) sockets in the packaging, a scalable digital microfluidics system with reconfigurable and low-cost chip is also demonstrated. Index TermsElectrowetting; electrowetting on dielectric (EWOD); lab-on-a-chip; microfluidics; micro total analysis system (μ TAS); surface tension I. BACKGROUND A. Digital Microfluidics DIGITAL (i.e. droplet-based) microfluidics use discrete fluid packets as carriers to achieve various fluidic functions, bio-chemical reactions, and detections in the microscale. Although droplet manipulations can also be performed inside microchannels [1], [2], non-channel configurations allow for much simpler systems and do not require external pressure sources (i.e. eliminating the need for pumps and valves). Also, electrically-driven channel-free devices are flexible for operators, allowing electronically reconfigurable two-dimensional movement on surfaces. Manipulation of droplets or bubbles has been achieved with various driving mechanisms such as electrostatic [3], dielectrophoretic (DEP) [4], continuous electrowetting (CEW) [5], electrowetting [6], electrowetting-on-dielectric (EWOD) [7], temperature gradient NIH Public Access B. Two-dimensional digital microfluidics platesThe advantages of digital microfluidics lie mostly in its simplicity and reconfigurability for parallel liquid operation in large scale, which requires two-dimensional addressable control sites for droplet manipulation [7], [10]. For an electrical control method such as EWOD, this means a two-dimensional plate with the ability to electrically access (i.e. reference) each point independently in the MxN grid. While simple fabrication of EWOD chips with a single layer of conduction lines can produ...

Droplet Microfluidics for Chip-Based Diagnostics

“…A majority of DMF devices are fabricated on silicon or glass substrates, as most fabrication facilities are well accustomed to handling such substrates. More recently, the use of polymers and other disposable substrates has been investigated for reducing the projected device cost in bio-diagnostic applications [ 34 , 36 ]. The use of a printed circuit board (PCB) as substrates is also becoming popular; especially for DMF devices dealing with microliter or larger droplet aliquots.…”

“…The use of a printed circuit board (PCB) as substrates is also becoming popular; especially for DMF devices dealing with microliter or larger droplet aliquots. The PCB substrates are advantageous because of their low cost printing and the possibility of integrating the wiring patterns and droplet actuation electrodes on a single substrate, through the use of the multilayer format of PCB substrates [ 36 ]. In more recent investigations regarding disposable DMF micro-chips, paper-based substrates have been micro-patterned using ink-jet printing techniques to print silver electrodes on custom paper-based substrates to form the bottom surface of the two-surface DMF micro-chip [ 37 , 38 ].…”

Simulation of feedback-driven PCR assays on a 2D electrowetting array using a domain-specific high-level biological programming language

“…Electrowetting-on-Dielectric (EWoD) has enabled the creation of software-programmable digital microfluidic platforms, which can perform a wide variety of biochemical applications [6,10,20,21,24] (Fig. 1).…”

A Universal Electrode Approach for Automated Electrochemical Molecular Analyses

“…Several system integration approaches, such as digital, multiphase, magnetic, optofluidic, centrifugal, and electrokinetic techniques, have been developed for performing sample preparation procedures in microfluidic systems [6-9]. For point-of-care diagnostics, electrokinetics is one of the most promising platforms due to the cost-effectiveness, simplicity in microelectrode fabrication, and advancement in portable electronic interface [10, 11].…”