Published at : 30 Dec 2022
Volume : IJtech
Vol 13, No 8 (2022)
DOI : https://doi.org/10.14716/ijtech.v13i8.6124
Habib Alfarobi | Department of Electrical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, West Java 16424 Indonesia |
Elly Septia Yulianti | Department of Electrical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, West Java 16424 Indonesia |
Nurul Intan | Research Center for Biomedical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, West Java 16424 Indonesia |
Yudan Whulanza | 1. Department of Mechanical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, West Java 16424 Indonesia, 2. Research Center for Biomedical Engineering, Faculty of Engineerin |
Don-Hee Park | 1. Interdisciplinary Program of Bioenergy and Biomaterial Engineering, Chonnam National University, Gwangju 500-757, Republic of Korea, 2. Department of Biotechnology and Bioengineering, Chonnam Natio |
Siti Fauziyah Rahman | 1. Department of Electrical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, West Java 16424 Indonesia, 2. Research Center for Biomedical Engineering, Faculty of Engineerin |
A biosensor is an analytical device that combines certain biological and
physical elements. Several types of transducers are used for physical elements,
such as optical, electrochemical, thermic, or gravimetric. Nowadays,
electrochemical transducers have become widely used for the application of
biomedical sensors. Electrochemical measurement devices called screen-printed
electrodes (SPEs) are created by printing several types of ink on a ceramic or
plastic substrate. SPEs enable speedy in-situ examination with high
repeatability, sensitivity, and accuracy. In this study, SPEs were fabricated
using a personalized CNC machine with carbon conductive ink as the electrode and
polyethylene terephthalate (PET) as the substrate. The mask, stencil, and
screen-printing dimensions were measured using a DinoLite microscope. SPEs
characterization was performed using Scanning Electron Microscopy (SEM) to observe the surface
morphology. This simple approach method shows a promising result that SPEs can be produced up to 5 screen printing layers with the ability to flow the electrical current under a resistance of
350.4 K.
Biosensor; Electrochemical; PET; Screen-printed electrode
The screen-printed
electrode is an electrode arrangement commonly used in biomedical sensor applications,
consisting of a working electrode, reference electrode, and counter electrode.
The screen-printing technique uses a mesh to support the stencil and an
emulsion to hold the ink. During the screen-printing process, the squeegee will
move across the screen stencil to press a printed material (i.e., ink)
through the mesh. In printing multiple layers of ink, it is necessary to ensure
that the previously printed ink is first thermally compacted. Finally, it is
possible to apply protective ink to isolate the conductive path between the
electrodes (Li et al., 2012).
A procedure to improve the electrode layer is pretreatment on a
polyethylene terephthalate (PET) substrate. The main objective of the treatment
is to remove the insulating polymer on the polyethylene (Haque et al.,
2017), and
increase the surface roughness. In addition, this treatment ensures the
precision and quality of screen-printing results, where ink adhesion can be
greatly affected by the hydrophilicity or hydrophobicity of the substrate. In
addition, the hydrophilicity of the suitable substrate is favorable for the
adhesion of carbon inks and adds to the excellent electrochemical performance (Du et al., 2016).
SPEs for biosensor applications have been developed with various
materials and modifications to detect specific analytes. Table 1 describes in
detail various studies related to SPE, which are explicitly used as electrodes
for dopamine biosensors, and includes some characteristics of each
modification.
Table 1 Recent studies of SPCE in dopamine biosensor applications.
Some of the summaries
above show how powerful SPCE performance is when applied to the dopamine
biosensor. In addition, research conducted by Charmet et al. also shows that
the homemade method of fabrication with a simple approach can also produce
sensors with competitive performance (Charmet et al.,
2020). In the formation of SPCE, research
conducted by Randviir et
al. used a screen-printing method with silver/silver chloride as a reference
electrode (Randviir et al.,
2014). The next layer is
carbon ink printed on a counter layer and working electrode, as well as a
liaison between the three electrodes printed on a flexible polyester (PE)
substrate. Subsequently, the dielectric paste will be printed on the substrate
and dried at 60? for 30 minutes before the SPCE is ready for use. This study aimed to
fabricate screen printing electrodes using a personalized CNC machine for
screen printing purposes using conductive carbon as electrode ink and
polyethylene terephthalate (PET) as substrate.
Conductive carbon ink was purchased from
mjstation (Tangerang). Polyethylene terephthalate (PET) was purchased from the
Emake store (China). Screen emulsion liquid (photoxol 188), screen printing
sensitizer, superxol m-3 diluent, superxol 3 stencil remover, T180 mesh screen,
and screen-printing squeegee were purchased from Provenio Indonesia. The
voltammetric characterization used EmStat4s LR with the PSTrace 5.9 interface
(PalmSens, Netherlands). A personalized CNC 3018 Pro tabletop machine for
screen printing and an HP LaserJet Pro MFP M117fw printer for making masks were
obtained from the Manufacturing Research Center (MRC FTUI).
2.1. Electrochemical Cell
Design
Figure 1 is an electrochemical
cell design using the Inventor 3D design application. The electrochemical
cell's geometry follows a typical electrochemical cell geometry (de Araujo &
Paixão, 2014), with modifications to the electrode legs
to match the PalmSens SPE adapter.
Figure 1 Electrochemical
cell geometry design
2.2. Screen-Printing Mask
Fabrication
The
electrochemical cell design will be printed on Yashica transparent paper. The
process uses an HP LaserJet Pro MFP M117fw printer. The result of the electrochemical
cell design on Yashica transparent paper is called a mask. The mask is then
used to make stencils for screen printing using photolithography.
2.3. Screen-Printing Stencil
Fabrication
Screen
printing is coated with screen emulsion liquid (Superxol 188) mixed with a
sensitizer in a successive ratio of 5:1, then mixed and poured over the screen
evenly. Furthermore, it will be dried at low light intensity at room
temperature for 25 minutes, followed by the transfer of the design from the
mask to the screen printing by a photolithography method using a 40-watt lamp
for 14 minutes. In the following process, the development process will be
carried out by flushing the formed SPE with pressurized water to identify the screen's resistance.
2.4. Screen-Printing Process
Figure 2
shows a screen-printing scheme with carbon as the ink paste for the process.
The substrate used is polyethylene terephthalate (PET). The printing process
takes place using a personalized CNC 3018 Pro machine. It occurs when the
squeegee presses the screen to initiate contact between the screen and the
substrate, and the ink will be pushed down into the opening, a permeable area
that forms the desired image.
Parameters in the screen-printing process are the mesh screen size, the snap off-distance, and the number of layers of screen printing. The mesh screen size used is T180, where the code T (tick) is a term commonly used in Asia to denote the number of threads sewn every 1 cm. The higher T value results in tighter stitches and more precise screen printing. Snap-off distance is the distance between the substrate and the screen printing; while the snap-off distance applied in this study is 2.5mm, and the screen-printing process layer consists of 5 layers. Each layer of the ink screen printing process is dried for 15 minutes at room temperature, followed by 30 minutes of drying at a temperature of 70? C after the desired number of layers has been achieved. The overall process of fabricating the screen printing electrode is shown in Figure 2.
Figure 2 Fabrication of screen printing electrode
3.1. Screen-printing Stencil
The irradiation time was varied in the stencil fabrication process on the T180 screen.
There is a difference in the results of the stencil formation at each time variation. The irradiation time that formed the best stencil was 14 minutes. Within 8 to 12 minutes, the emulsion on the screen was damaged and did not form the desired SPE stencil when the development process was applied with pressurized water. Meanwhile, at 16 to 18 minutes, the emulsion on the screen is challenging to develop due to prolonged irradiation time. The optimum duration for irradiation is 14 minutes. Figure 3 shows the photolithographic process using a 40-watt light source. The light source consists of five T5 LED lamps arranged in parallel. Lighting level affects irradiation time to get appropriate stencil. The higher lighting level requires less irradiation time. However, if the irradiation time is too long, the development process cannot occur.
Figure 3 Photolithography process
3.2. Microscope
The mask observation for screen-printing was measured using a DinoLite microscope. It is done on the straight-line section of the SPE. Figure 4 shows the results of mask measurements for screen printing.
Figure 4 Screen printing mask dimension
The print quality using the HP LaserJet Pro MFP M117fw printer is relatively acceptable. The mask works well since it can withstand the light from the photolithography process to produce a stencil on the screen.
Figure 5 Dimensional comparison graph of the initial design and the printed mask.
In this process, there are dimensional differences between the initial design and the printed mask. Figure 5 shows the print capability of the HP LaserJet Pro MFP M117fw printer on YASHICA paper. The most significant deviation between the design and print dimensions is 0.485 mm, and the slightest deviation is 0.469 mm. So, it can be concluded that the HP LaserJet Pro MFP M11fw printer machine can print an average dimension of approximately 0.977±0.008 mm (977 µm).
The screen printing stencils used in fabricating 5-layer SPE required a set with a mesh size of T180 and a snap-off distance of 2.5 mm. The following stencil results from photolithography using a mask, as described previously. Figure 6 shows changes in the dimensions of the stencil when it is used for the screen-printing process ten times.
Figure 6 Dimensional comparison of (a) the initial stencil and (b) the stencil after ten times use
It is seen that the initial stencil dimensions are similar to the mask size. The change in dimension is because the stencil edges are not perfectly exposed to the light source due to the diffused light source during the photolithography process. It causes the particular area to not be scattered apart during the development process. Figure 6b shows that the Dimensional changes after the screen printing process that can be caused by multiple cleaning of the screen from ink. In the screen printing process, the screen needs to be cleaned with superxol M-3 liquid each time. When used repeatedly, the liquid possibly removes or damages the hardened emulsion liquid on the screen. When the layers increase, the dimensions tend to be larger than the previous layer.
Figure 7 depicts the difference between the initial stencil's average width and the stencil's width after ten times use.
Figure 7 Dimension comparison graph of initial and ten times use a stencil
The average dimensions of the initial stencil T180 are approximately 0.742±0.031 mm (742 µm), and the dimensions of the stencil after ten uses are approximately 1.084±0.127 mm. The dimensional deviation between the mask and the initial stencil was 13.64%, while the stencil after ten uses was 18.69%.
The screen-printing process involves polyethylene terephthalate (PET) substrates with different coating levels.