Macquarie University ResearchOnline This is the published version of: Christian Leiterer; Matthias Urban; Wolfgang Fritzsche; Ewa Goldys; David Inglis; “Printed circuit boards as platform for disposable lab-on-a-chip applications”. Proc. SPIE 9668, Micro+Nano Materials, Devices, and Systems, 96680X (December 22, 2015) Access to the published version: http://dx.doi.org/10.1117/12.2202413 Copyright: Copyright 2015 Society of Photo-Optical Instrumentation Engineers (SPIE). One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited. Printed circuit boards as platform for disposable Lab-on-a-Chip applications Christian Leiterer,a,b Matthias Urban,b Wolfgang Fritzsche,b Ewa Goldys a and David Inglisa* aMacquarie University, Department of Physics and Engineering, 2109 Sydney, Australia bUniversity Jena / Leibniz-Institute of Photonic Technology, Albert-Einstein-Strasse 9, Jena, Germany Abstract. An increasing demand in performance from electronic devices has resulted in continuous shrinking of electronic components. This shrinkage has demanded that the primary integration platform, the printed circuit board (PCB), follow this same trend. Today, PCB companies offer ~100 micron sized features (depth and width) which mean they are becoming suitable as physical platforms for Lab-on-a-Chip (LOC) and microfluidic applications. Compared to current lithographic based fluidic approaches; PCB technology offers several advantages that are useful for this technology. These include: Being easily designed and changed using free software, robust structures that can often be reused, chip layouts that can be ordered from commercial PCB suppliers at very low cost (1 AUD each in this work), and integration of electrodes at no additional cost. Here we present the application of PCB technology in connection with microfluidics for several biomedical applications. In case of commercialization the costs for each device can be even further decreased to approximately one tenth of its current cost. Keywords: PCB, microfluidics, dielectrophoresis. *Christian Leiterer, E-mail: [email protected] 1 Introduction Due to the ongoing miniaturization of microelectronics, PCB fabrication has seen parallel reductions in size and increases in precision. To reach higher and higher circuit densities, multilayer technology and vias in the PCB area have become standard and present opportunities for electronic LOC devices to easily integrate sensors, actuators and light sources (e.g. LEDs) directly. Furthermore, PCBs themselves can be stacked on top of each other. Therefore PCBs have become excititng components for use in on-chip fluidic applications. This lego brick like assembly and exchange of components makes this platform a versatile technology for prototyping LOC solutions without the use of conventional lithographic steps. Lately ideas have been published which propose, not only integrating electrodes and microfluidics into a PCB-LOC device, but also driving forces to realize the transportation of the liquid on the device. One widespread PCB-based LOC application is electro-wetting, which allows the directed manipulation of single droplets using pads on a PCB1,2. The intent here is to create a fully integrated system in one chip which can be operated autonomously. The most promising approaches are using surface-acoustic waves3–5, electromagnetic valves6 or electrolysis7,8. Usually the microfluidic channels for LOC devices are fabricated by silicon or glass etching or soft lithographic methods like PDMS stamping9,10. These microfluidic systems are then often SPIE Micro+Nano Materials, Devices, and Systems, edited by Benjamin J. Eggleton, Stefano Palomba Proc. of SPIE Vol. 9668, 96680X · © 2015 SPIE · CCC code: 0277-786X/15/$18 · doi: 10.1117/12.2202413 Proc. of SPIE Vol. 9668 96680X-1 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 04/10/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx mounted on top of the printed circuit board, requiring further processing step to realize the alignment of the layers and integration of electrical components and sensors. In some cases this is acceptable, and we show one such example; however, an easy way to avoid this additional integration step is to use the PCB tracks and pads to realize microfluidic channels directly on the PCB. This is possible because the tracks and pads typically protrude from the surface about 100 microns, thereby setting the channel depth. In this proceeding we present two LOC devices, which are realized using PCBs to show the feasibility of this approach. The first device demonstrates the separation of two different kind of polystyrene beads (charged and non-charged) by dielectrophoresis. The second device demonstrates mixing of two dyes in a microfluidic channel formed by metal tracks on the PCB. These metal tracks which form the side walls of the channel are also used as electrodes to affect yeast cells with dielectrophoresis. 2 Experimental 2.1 Dielectrophoresis using PCB-Chips A checkerboard like arrangement of electrodes was designed with PCB CAD design software (freeware examples: Eagle: CadSoft Computer, Pleiskirchen) to realize a cell separation device using dielectrophoresis as the driving force. Electrodes are protrude 0.1 mm above the surface and are 0.6 mm x 0.6 mm with gaps of 0.2 mm. Square-shaped as well as circular-shaped electrodes are shown to apply sufficient force to either pull cells or similar sized florescent polystyrene beads to high-field-gradient regions (positive dielectrophoresis) or low-field-gradient regions (negative dielectrophoresis)11. To comfortably inject a cell suspension onto the chip, a small home-build chamber was made (shown in the bottom left of figure 1). The chamber consists of an aluminum framework (10 mm x 20 mm x 40mm) where the tube connectors are fixated, this framework holds also an inner smaller PDMS chamber (1.3 mm x 12.8 mm x 17.1 mm) which constraints the liquid sample and therefore defines the volume of the liquid sample on the chip. The tube connectors are connected to the chip via drill holes (0.8 mm) in the PCB sealed with small PDMS plugs. The PCB-Chip itself can be mounted into the chamber for the experiment. If the chip becomes damaged or worn out due to electrolysis, mechanical forces or contamination, it can be easily replaced while the chamber itself is reusable. For the experiment the sample was applied to the chamber using a standard syringe. To minimize electrolysis based damage to the printed circuit boards which would typically occur using electrodes made from copper, the PCBs were ordered with an ENIG (Electroless Nickel Immersion Gold) finish. This consists of gold plating with an underlying nickel layer to prevent oxidation. The following figure (Figure 1) shows the PCB-Chips, mounting chamber and the electrode polarity for the experiment (alternating current, ac). Proc. of SPIE Vol. 9668 96680X-2 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 04/10/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx ,!0 5mm ' Figure 1. PCB-Chips for dielectrophoresis. Circular and square shaped copper electrodes plated with nickel and gold to minimize electrochemical oxidation on the electrodes (top). Disposable chip mounted in the fluidic chamber, the schematic shows the checker board like arrangement of the electrode polarity (bottom). As a simple alternative to biological samples (e.g. cells, DNA), different fluorescent polystyrene beads were injected on the chip. Within a few seconds the beads are observed to cluster on the chip within high-field-gradient or low-field-gradient regions depending on the type of beads. In general the collection in the low-field-gradient regions was easier for this experiment, which is probably due to the significant electro-osmotic flow and heat based convection (applied voltages of 10 - 20V). 10-µm sized fluorescent polystyrene beads (green) can be collected in the low- field-gradient region (electrode gap and on top of the electrodes) of the PCB-Chip device (Figure 2, green beads). Carboxylated (negatively charged) 1-µm sized red fluorescent polystyrene beads on the other hand side can be collected in the high-field-gradient regions (electrode edges). These results are consistent with the findings of previous publications that used photolithographicly fabricated silicon chip technology12,13. 1. I 4' . Figure 2. Dielectrophoresis based collection of fluorescent beads on the PCB chip device. At frequencies from 10- 1000 kHz the 10-µm, non-charged, green fluorescent beads can be collected in the low-field-gradient regions on the PCB-chip (gap), while the 1-µm, negatively charged, carboxylated red fluorescent beads are collected at the high- field-gradient regions on the chip (edges). Proc. of SPIE Vol. 9668 96680X-3 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 04/10/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx 2.2 Simple microfluidics using a PCB A very simple way to build a microfluidic chip is using a PCB CAD-Software (e.g. Eagle) to create a channel design, hereby the tracks and pads (metal parts) will act as channel walls while the non-conductive substrate will form the base of the channel. This arrangement forms a square shaped channel cross section(100 µm wide and 100 µm deep). The top of the chip can be sealed using an olefin-sheet and pressure sensitive adhesive which is commonly used to seal 96-well plates (T9571, Sigma-Aldrich). This way of sealing the microfluidic chip ensures withstanding moderate pressure and does not require any alignment. Pre-drilled holes from PCB manufactures can be used as connectors to apply external tubing using common syringe tubing connectors. Typically a hole/connector size of 1.7 mm was used and a barbed fitting inserted. However, in principle any hole/connector size can be fabricated und applied through the drill service provided by the PCB supplier.