Fabrication of gold-plated electrodes on a printed circuit board (PCB) for electrical impedance tomography (EIT) measurement in fluid environment Nadira Jamil1, Yunjie Yang2, Jiabin Jia2, Alan Murray1 and Stewart Smith1 (
[email protected]) 1Scottish Microelectronics Centre, Institute for Bioengineering, The University of Edinburgh (UK) 2Institute for Digital Communications, The University of Edinburgh (UK)
Introduction
Proposed design
Electrical impedance tomography (EIT) is a technique that has the ability to produce images by identifying the electrical conductivity distribution of the test sample. High temporal resolution images in 2D or 3D can be produced by EIT technique. This paper introduces various shapes of electrode tips on the printed circuit board (PCB) and how these shapes are affecting the efficacy of EIT measurement using the low cost FabLab+ rapid prototyping facility for the PCB fabrication. 16 electrodes in each EIT device The full PCB has four sets of sensors with different designs for the tip geometry
Electrical impedance tomography measurement The impedance measurement was performed on an EIT system, designed in-house. A 3 mA peak-to-peak current was applied [2] on the first electrode-pair, E1-E2, of the first ring and voltage measurement was acquired on the neighbouring electrode-pair, E3-E4, over a fixed frequency of 100 kHz using time difference imaging method. The step was replicated for subsequent electrode-pairs in all four rings.
Advantage The design is capable in analysing four samples simultaneously
The fabricated PCB has fluid reservoirs attached to place fluids under investigation
Figure 3: EIT measurement
Methodology
Results
Nickel and gold electroplating The electrodes were fabricated using copper (Cu) traces hence a thin nickel (Ni) and gold (Au) layers were electrochemically coated on the Cu electrode tips. Au-plated electrode tips (biocompatible)
Cu electrode tips Ni barrier layer [1] Ni thickness: 0.2 ยตm Counter electrode: Pt-coated metal mesh Reference electrode: Ag/AgCl
Figure 4: The in-house designed EIT system
Au thickness: 0.5 ยตm Counter electrode: Pt-coated metal mesh Reference electrode: Ag/AgCl
The sensor was tested with two different types of wire: โข Conductive metal wire โข Non-conductive plastic wire The intensity changes were found to be dependent on the conductivity of the material. EIT sensor
Figure 1: Nickel (Ni) and gold (Au) electroplating process
The time required for each electroplating process is defined in the equation: ๐๐๐๐ญ๐จ ๐ป๐๐๐ = ๐๐ด๐ where: t = Ni or Au thickness to be electroplated ๐ = metal density of Ni or Au n = number of electrons to be transferred (from Ni2+ to Ni and from Au+ to Au) F = Faraday constant of Ni or Au A = total area of the Ni or Au electroplating to occur i = 20 mA Mw = molecular weight of Ni or Au
Non-conductive plastic wire
Conductive metal wire
Two wires (nonconductive and conductive)
Figure 5: Observation from the EIT system
2D EIT images were reconstructed from the EIT system where the resistivity colour scale denotes the difference between non-conductive and conductive wires.
High resistivity (non-conductive)
Low resistivity (conductive) Figure 6: The resistivity colour scale
Conclusion 4 different shapes of electrode tips
Figure 2: Fabricated EIT PCB with different electrode morphologies after gold electroplating process
โข This work has indicated that EIT is a viable technique for analysing the characteristics of biological materials through electrical conductivity distribution โข Future work: To scale down the present EIT device to microelectrodes for porous 3D scaffolds imaging [1] Kohl, P. A. (2010) Electrodeposition of Gold. Modern Electroplating, Fifth Edition. [2] Sun, T. et al. (2010) On-chip electrical impedance tomography for imaging biological cells. Biosens. Bioelectron
