Realization of a flow injection analysis in PCB technology

Sensors and Actuators A 133 (2007) 231–235

Realization of a flow injection analysis in PCB technology Stefan Gaßmann ∗ , Ingo Ibendorf, Lienhard Pagel University of Rostock, Faculty of Computer Science and Electrical Engineering, Institute of Electronic Appliances and Circuits, A.-Einstein-Str. 2, 18059 Rostock, Germany Received 15 August 2005; received in revised form 3 March 2006; accepted 6 April 2006 Available online 30 May 2006

Abstract In this paper a microflow injection analysis (FIA) is presented, which was developed completely in printed circuit board (PCB) technology. The multilayer printed circuit board, which was made as stack of four individual printed circuit boards, contains both the passive and active fluid elements, and necessary electronics for the control and evaluation. For a reference reaction the FIA detects Fe3+ . A calibration curve was recorded and a reproducibility measurement was carried out. An accuracy of 10% was reached. Data acquisition and control was made with the help of a PC and a Labview-program. © 2006 Elsevier B.V. All rights reserved. Keywords: Flow injection analysis (FIA); Lab-on-board; PCB; Fluidics; PCBMEMS

1. Introduction The flow injection analysis (FIA) is a very versatile method of quantitative measurements in analytical chemistry. Because of its high sample throughput and the automated function it is often used in quality control of chemical processes but also in monitoring of environmental parameters. For these measurements a portable micro-FIA that consumes less energy and reagents is a great tool not only for chemists but also for ecologists. The combination of several FIAs for the most important substances that contains all needed reagents and all electronics for a simple and quick evaluation of the results, a so called total analysis system, is a really needed device. The presented work shows a possibility to build such a system in a cheap and easy way. In the following two sections the technology and the application are shortly depicted. 1.1. The printed circuit board (PCB) technology for microfluidics The miniaturization is also in chemical processes a new trend with many advantages like less usage of resources, better control of process parameters and portability. The need for ∗

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0924-4247/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.sna.2006.04.009

fluidic microsystems leads to a development of technologies for microfluidics. Besides the well known technologies like micromachining, silicon technologies and LIGA is still a need for a low cost technology for small volumes and special applications. At the University of Rostock we developed such a technology. This technology is based on PCB technology and allows hybrid integration of both electronic and fluidic components at low cost. This technology uses printed circuit boards consisting of epoxy laminate (FR4) with copper coating on both sides. These boards are structured by drilling and milling (for the whole board) and by etching for the copper plating. These boards and the treatment are standard in the electronic industry and are very cheap. The basic element in the fluidic is a channel, which is created from copper lines as borders. By stacking two PCBs with the same layout (one on the bottom and other on the top side) cavities exist that lets space for the fluid. These cavities are our channels or reservoirs. The PCB stack is fixed by gluing. By adding a movable element in the stack, in our case an 8 ␮m Kapton foil, active fluid elements are feasible, like pumps, valves and sensors [1–4]. The main advantages of this technology are: cheap materials; cheap, well established and highly available technologies; compatibility between electronics and fluidics. This technology is unique as other researchers who use the PCBs as basic material for the fluidics do not integrate active components in the stack of PCBs [5–8]. These researchers use

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other technologies for stacking the PCBs like the solder-ring technology [7] or for creating the channels like the mask less technology [8].

is made optically by the measurement of the absorption at a wavelength of 480 nm. 1.3. Motivation

1.2. The flow injection analysis The FIA is an automated procedure of analytical chemistry for the quantitative measurement of components (ions, atoms and molecules) in solutions and was developed by Ruzicka and Hansen in the year 1975 (see [9]). The goal of a FIA is the automated quantitative measurement of components in solutions. The basic principle of a FIA is mixing a substance with a solution that contains the detectable component. The added substance (reagent) reacts with the component and forms a detectable reaction product which can be measured in the detector. The automation of this principle is done in the following way: a fluid flows continuously trough the FIA system (carrier). In a simple realization this can be the reagent. Into this flow a precisely dosed amount of the solution that contains the detectable component (sample) is injected by a valve, therefore the term “flow injection”. Now the sample and the reagent should be mixed. This is done in the reaction coil by diffusion. That is the reason why the reaction coil needs to be adapted for the detection. The reaction coil is a further significant element in a FIA system and, if desired, apart from the mixture of both fluids other processes such as enrichment, dilution, chemical reactions, medium exchange, etc. can take place. After the reaction coil detection takes place. The reaction product passes the detector and forms a transient peak. The height and area of the peak are proportional to the concentration of the compound. By comparison to samples of known concentration (calibration curve), the concentration of the compound is determined. The detection can be done photometrically (UV–vis/IR) or electrochemically (see [10]). A simple FIA manifold is shown in Fig. 1. FIA systems are characterized by very short response times. A high sample throughput is reached. Therefore, FIA is applied in quality control of technical processes (see [11]). For our experiment the detection of Iron(III)-ions was selected. Thiocyanate (SCN− ), also called Rhodanide, is used as reagent. The reaction of Iron(III)-ions with the Thiocyanate produces the red coloured Ironthiocyanate Fe (SCN)3 . If Thiocyanate in the surplus is used, the following simplified chemical reaction applies. Fe3+ + 3SCN−  Fe(SCN)3

The FIA is chosen for the demonstration of the capabilities of our technology. It is the first complete system created in our fluidic PCB technology. The FIA is a good system to show the advantages: - Miniaturization of the system: In a miniaturized system the amount of reagents used are much smaller, because of the shorter paths for the fluids the response time is much shorter. - Portable device: The FIA can be used in the field. A transportation of the samples to the laboratory is not needed. When a total analysis system is build by combining several FIAs this would be a great tool for ecologists. - Integration of electronics and fluidics: A complete system combining electronics and fluidics is possible in our technology. This reduces size and costs for interconnection. - Cheap technology: A FIA system must often be optimized for the specific detection. The length and the width of the reaction coil must be adapted. This can be done cheap and fast with our technology in comparison with other microtechnologies. In this technology for every detection one optimized system is possible because of the low costs for a system. In the following design, the realization and the evaluation of the achieved results are depicted. 2. Design of a new micro-FIA in PCB technology The system fulfils all requirements of a FIA system. The reagent and the sample are connected via small tubes in the system. The first pump of the FIA press the carrier (in our case the reagent Thiocyanate) through the system. A second pump delivers a defined volume of sample. After the reaction coil, detection takes place. The detection is done photometrically. The absorption is measured at a wavelength of 480 nm. For this purpose a LED and a photodiode are used. Fig. 2 shows the conceptual layout of the micro-FIA. It consists of a fluid part, the electronic part and the user interface. The fluidic and the electronic part are realized on the PCB. The evaluation of the data and the control take place with the help of a Labview-program on a PC.

(1)

The reaction proceeds within milliseconds. Additional catalysts or energy are not necessary. The detection of the Ironthiocyanate

Fig. 1. Principle of a simple FIA.

Fig. 2. Conceptual scheme of the PCB–FIA.

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The fluid part consists of two independently controlled pumps, one for the carrier current (Sodiumthiocyanate) and one pump for the sample (Fe3+ in solution), an injection point, a reaction coil and the detector. The structure is nearly the same like a normal FIA. The main difference is that the system works without an injection valve. The injection of a defined quantity of sample is realized by one pump. The electronic part consists of an optical detector (photodiode and light emitting diode), the necessary control circuit for the detector, the control circuit for the pumps, a microcontroller and a USB interface. The microcontroller realizes the temperature compensation of the detector, the power control for the LED, the power control for the pumps and controls the workflow of the elements. 3. Realization of the micro-FIA in PCB technology The technology uses printed normal PCBs as basic elements for the structure of a 3D-stack. The basic element forms a channel, which contains copper lines as borders. This technology is described in [1]. Using this technology pumps (see [2,3]), valves (see [4]) and further elements have already been manufactured. The FIA system is realized as a stack of four structured PCBs. PCB pumps with thermopneumatic actuator are used. These pumps are described in detail in [2,3]. For the realization of these pumps four layers of structured printed circuit boards of 0.46 mm thick base material (FR4) and 105 ␮m copper coating are necessary. The pump requires a moving element as border of the actuator chamber and for the diaphragms of the passive valves. For this purpose a layer of Kapton foil of 8 ␮m thickness is introduced. These pumps achieve a maximum flow of 500 ␮l/min and a maximum backpressure of 150 mbar. As size for the FIA system we chose 50 mm × 50 mm due to the available alignment tool for stacking. The FIA system needs less space and could be made smaller. In Fig. 3, a 3D model of the FIA is presented. The left pump in Fig. 3 represents the pump for the sample; the right pump is responsible for the delivery of the reagent (carrier). The output valve of the sample pump is at the same time the injection valve. If in the pump a positive pressure is produced, the output valve opens and injects a certain amount of sample into the carrier

Fig. 3. 3D model of the FIA system.

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current. As a reaction coil a snake like shaped structure of 87 mm length is used, provided with eighteen 180◦ -curves. The crosssection is about 1.2 mm × 0.8 mm. Investigations resulted in that the relatively short mixing channel was sufficient. Longer channels result in longer peaks. This means that the mixing and reaction is very efficient. This was not expected. When mixing is only done by diffusion as normal in microfluidics because of the laminar flow the channel should be much longer. The reason for this is the pulsating flow of the pumps. The mixing is most efficient when the pumps were switched acyclic with a phase shift of a 1/4 period. In this case we achieve a radial flow pattern, which is responsible for the good mixing. The pumps are operated with a supply voltage of 5 V and a frequency of 1 Hz with a duty cycle of 0.1. They achieved a middle volume of 3.3 ␮l per pumping stroke, which corresponds to a flow of approx. 180 ␮l/min. Fig. 3 shows the assembled stack of PCBs. The top left inlet is for the sample, the top right inlet for the reagent. In the PCBs under the inlets the pumps are realized. The reaction coil in the middle of the PCB is milled through the first whole PCB. To make the mixing (reaction) process visible it is provided with a transparent cover. In Fig. 4 the exploded view of the PCB stack is depicted. The four PCBs that are needed for the creation of the pumps are clearly visible. The Kapton foil is in the middle of the stack and forms the border between the actuator chamber (two big holes in the second PCB) and the pump chamber (cavities in the third PCB). The detector consists of LED with a specific wavelength of 480 nm (type E1S03-AB1A7, MARL). The photodiode is of the type BPW-34-B from Siemens. It is located at the end of the reaction coil in the left bottom part of the PCBs (see Fig. 3, photodiode). The optical path goes through the whole printed circuit board stack thus guaranteeing an optimal sensitivity also in case of small concentrations. Fig. 5 shows a realized prototype of the PCB–FIA. On the lefthand picture the fluidic site is shown. In the left part of the picture both inlets are shown (the upper for the reagent and lower for the sample). The inlets are shortcircuit by a small

Fig. 4. Exploded view of the PCB stack for the FIA system.

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Fig. 5. Photos of a prototype of the PCB–FIA (left: fluidic site; right: electronic part and size comparison with a coin of D 1).

tube during storage and transport to avoid contaminations. The mixing channel is seen in the middle of the picture. Besides the mixing channel are the photodiode and the outlet. On the righthand picture the electronic part is seen. On the top left in the picture is a USB-connector. The coin of D 1 is there for size comparison. 4. Evaluation of the results With the developed prototypes test measurements have been performed. The test procedure is always the same. The pump for the reagent works continuously. The pump for the sample pumps three strokes of 3.3 ␮l with a phase shift of 1/4 period to the reagent pump. In the reagent coil the reagent and the sample are mixed and build the detectable red coloured Fe(SCN)3 . In the detector the absorption is measured. The transient peak is recorded. For evaluation the peak height and the peak area are calculated.

Fig. 6. Signals of the reproducibility measurement.

For the examination of the reproducibility a set of measurements with the same concentration was carried out. Concentrations of 30 mM NaSCN as reagent and 4 mM Iron(III)-sulfate as sample were applied. Ten microliters sample was injected by the micropump by means of three pumping strokes. Fig. 6 shows the results. The peak width was approx. 25 s in a usual range for normal FIAs. The peak form is evaluated positively. A very good mixing of the sample was achieved and the dilution was not too strong. Fig. 6 shows the data of the reproducibility measurements. The voltage at the photo detector is shown and is a measurement for the absorption. The peak heights (V) and the peak areas (V s) are written in the diagram. The reproducibility of the peak heights is about 10%, those of the peak areas about 15%. The reason for this span was investigated. The amount of the injected sample in this structure is only determined by the pumping strokes. In our pumps several parameters like backpressure and temperature have an influence on the pumped volume

Fig. 7. Peaks of the calibration measurement.

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tion of many components simply by choosing other reagents and reaction parameters. The advantage of the presented solution is that an optimized system for the selected detection can be built easily. With the combination of several micro-FIAs in PCB technology for different detections a portable easy to use total analysis system will be available. References

Fig. 8. Calibration curve.

in one stroke. A measurement of the volume of the single pumping strokes resulted that the strokes differ about 12% in volume. This correlates with the reproducibility. Furthermore a calibration curve was recorded. A reagent NaSCN with a concentration of 30 mM was used. A calibration solution Iron(III)-sulfate was used in the following concentrations: 20 mM, 10 mM, 4 mM, 2 mM, 0.8 mM, 0.16 mM and 32 ␮M. Each concentration was measured three times. Absorption could be registered starting from 0.16 mM. The 20 mM lay far outside of the linear range, therefore we achieved a meaningful measuring range between 0.16 mM and 10 mM. Fig. 7 shows the peaks of the calibration measurements. The calibration curve is represented in Fig. 8. Measurements with accuracy of 10% are possible with the available FIA using this calibration. Further research on the improvement of the accuracy is currently carried out. 5. Conclusion The realization of the flow injection analysis is the first complete system that is built in our fluidic PCB technology. A FIA system for the detection of Fe3+ -ions in a range from 0.16 mM to 10 mM with an accuracy of 10% is realized. The electronics direct on the system and the USB interface made this system really easy to use. In further optimisations the accuracy must be improved. Next steps are the integration of filters and a reservoir, so that the sample preparation and the reagent find space in the system. The first results are very optimistic so that a precise measurement will be possible with this system. The FIA described here is tested for the detection of Fe3+ -ions but the FIA is a method that is very versatile and can be applied for the detec-

[1] T. Merkel, M. Gr¨aber, L. Pagel, A new technology for fluidic microsystems based on PCB technology, Sens. Actuators A77 (1999) 98–105. [2] A. Wego, Entwicklung einer thermopneumatischen Mikromembranpumpe auf Basis der Leiterplattentechnologie, Dissertation, Universit¨at Rostock, 2001. [3] A. Wego, L. Pagel, A self-filling micropump based on PCB technology, Sens. Actuators A88 (3) (2001) 220–226. [4] M. Weicker, L. Pagel, M. H¨ammerle, Thermomechanisches Mikroventil mit Zustandsr¨uckmeldung, German Patent DE10250758A1, 2004. [5] H. Ilgen, Printed circuit board with feedback controlled internal watercooling, in: IECON ’98. Proceedings of the 24th Annual Conference of the IEEE, vol. 4, Aachen, 1998, pp. 2348–2349. [6] M. Sch¨unemann, K. Amiri Jam, V. Grosser, R. Leutenbauer, G. Bauer, W. Sch¨afer, H. Reichl, MEMS modular packaging and interfaces IEEE, in: 50th IEEE Electronic Components and Technology Conference, Las Vegas, NV, USA, May 21–24, 2000. [7] F. Schindler-Saefkow, K. Amiri Jam, V. Großer, H. Reichl, A 3D-package technology for fluidic applications based on MATC-X, ACTUATOR, in: 9th International Conference on New Actuators, Bremen, Germany, 14–16 June, 2004, pp. 208–211. [8] D. Fries, G. Steimle, S. Natarajan, S. Ivanov, H. Broadbent, T. Weller, Maskless lithographic PCB/laminate MEMS for a salinity sensing system, in: IMAPS 35th Annual Symposium on Microelectronics, Denver, CO, September 2002. [9] B. Karlberg, G.E. Pacey, Flow Injection Analysis, A Practical Guide, ELSEVIER, Sollentuna (Schweden) and Oxford, 1989. [10] www.globalfia.com, February 2006. [11] K. Cammann, Instrumentelle Analytische Chemie, Akademischer Verlag Spektrum, M¨unster, 2001.

Biographies Stefan Gaßmann was born in 1970 in Greifswald, Germany. From 1991 to 1997 he studied electrical engineering at the University of Rostock and at IRESTE, Nantes, France. After graduation he worked as a development engineer for medical devices. In 2003 he joined the “Institute of Electronic Appliances and Circuits” at University of Rostock. His main interests are development of fluidic systems. Ingo Ibendorf was born in 1979 in Greifswald, Germany. From 1999 to 2004 he studied electrical engineering at the University of Rostock. After graduation he joined the “Institute of Drive Engineering and Mechatronics” at University of Rostock. His main interests are development, controlling and timing of a test facility for gearboxes. Lienhard Pagel has been professor in microsystems and Director of the “Institute of Electronic Appliances and Circuits” at the University of Rostock since 1994. Prior to this he worked in research and development in the semiconductor industry for 10 years. Since 1994 his main topic has been the realization of microfluidics systems in PCB technology.