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Highly Sensitive Multi-Channel IDC Sensor Array for Low Concentration Taste Detection.

Khan MR, Kang SW - Sensors (Basel) (2015)

Bottom Line: The proposed IDC taste sensor array was compared with the potentiometric taste sensor with respect to sensitivity, dynamic range width, linearity and response time.We found that the proposed IDC sensor array has better performance.Finally, principal component analysis (PCA) was applied to discriminate different types of taste of the mixed taste substances.

View Article: PubMed Central - PubMed

Affiliation: School of Electronics Engineering, Kyungpook National University, 1370 Sankyuk-Dong, Bukgu, Daegu 702-701, Korea. rajibur@ee.knu.ac.kr.

ABSTRACT
In this study, we designed and developed an interdigitated capacitor (IDC)-based taste sensor array to detect different taste substances. The designed taste sensing array has four IDC sensing elements. The four IDC taste sensing elements of the array are fabricated by incorporating four different types of lipids into the polymer, dioctyl phenylphosphonate (DOPP) and tetrahydrofuran (THF) to make the respective dielectric materials that are individually placed onto an interdigitated electrode (IDE) via spin coating. When the dielectric material of an IDC sensing element comes into contact with a taste substance, its dielectric properties change with the capacitance of the IDC sensing element; this, in turn, changes the voltage across the IDC, as well as the output voltage of each channel of the system. In order to assess the effectiveness of the sensing system, four taste substances, namely sourness (HCl), saltiness (NaCl), sweetness (glucose) and bitterness (quinine-HCl), were tested. The IDC taste sensor array had rapid response and recovery times of about 12.9 s and 13.39 s, respectively, with highly stable response properties. The response property of the proposed IDC taste sensor array was linear, and its correlation coefficient R2 was about 0.9958 over the dynamic range of the taste sensor array as the taste substance concentration was varied from 1 μM to 1 M. The proposed IDC taste sensor array has several other advantages, such as real-time monitoring capabilities, high sensitivity 45.78 mV/decade, good reproducibility with a standard deviation of about 0.029 and compactness, and the circuitry is based on readily available and inexpensive electronic components. The proposed IDC taste sensor array was compared with the potentiometric taste sensor with respect to sensitivity, dynamic range width, linearity and response time. We found that the proposed IDC sensor array has better performance. Finally, principal component analysis (PCA) was applied to discriminate different types of taste of the mixed taste substances.

No MeSH data available.


Step-by-step fabrication process of the interdigitated electrode: (a) polyimide substrate; (b) Cr layer on the polyimide substrate; (c) Cu layer; (d) photoresist layer; (e) placing the mask pattern on the photoresist layer; (f) transferring the mask pattern onto the photoresist layer; (g) depositing Cu via electroplating; (h) removing the photoresist; (i) removing the Cr layer; (j) depositing the Sn layer onto the Cu layer via electroplating; and (k) cutting the residual polyimide substrate.
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sensors-15-13201-f003: Step-by-step fabrication process of the interdigitated electrode: (a) polyimide substrate; (b) Cr layer on the polyimide substrate; (c) Cu layer; (d) photoresist layer; (e) placing the mask pattern on the photoresist layer; (f) transferring the mask pattern onto the photoresist layer; (g) depositing Cu via electroplating; (h) removing the photoresist; (i) removing the Cr layer; (j) depositing the Sn layer onto the Cu layer via electroplating; and (k) cutting the residual polyimide substrate.

Mentions: We fabricated the interdigitated electrode (IDE) used in our experiment on a polyimide (PI) substrate. Polyimide, e.g., Kapton®, is a high-performance polymer that has a number of desirable properties, including a high degree of thermal stability, chemical stability, low dissipation factor and good dielectric properties; as a result, polyimide can be used as substrate material for flexible printed boards, multilayer PCBs and ribbon cables. In our experiment, we used the Kapton® HN-type polyimide substrate with a thickness of 5 mil, because it exhibits an excellent balance of physical, chemical and electrical properties over a wide temperature range. The fabrication process of the IDE on a PI substrate is described step-by-step below and represented schematically in Figure 3. The PI substrate was first cleaned with ethanol, methanol and deionized (DI) water. Then, a thin (15 nm) layer of chromium (Cr) was grown on the PI substrate via a vacuum evaporation process (the advantage of using Cr is that it provides superior adhesion performance). Next, we deposited an approximately 100 nm-thick copper layer onto the Cr layer; in turn, the Cu-layer was covered with photoresist SU-8 25 or AZ-4620 using a spin coater, with the choice of photoresist based on which was suitable for molding a relatively high aspect ratio electrode structure. Then, a Karl Suss MJB3 UV300 mask aligner was used to transfer a mask pattern onto the Cu-layer via UV exposure. Using a copper electroplating solution at an applied current density of 45 mA/cm2, a copper (Cu) layer was electroplated onto the Cu layer, after which the photoresist mold, unnecessary Cu layer and the bottom layer of Cr were removed using solvent suitable for avoiding short-circuiting. Finally, the Cu-interdigitated electrode was overlapped by a very thin layer of electroplated tin using an electroplating solution. In our experiment to deposit the Cu layer properly on the Cr layer, firstly, we deposited a very thin of the Cu layer on Cr layer, then we electroplated a thick layer of Cu of approximately 50 µm on the thin Cu layer. This step also reduces the fabrication cost and time. Tin is a useful metal that has non-toxic, ductile and corrosion resistance properties. Tin also has the ability to protect the Cu from oxidation. Thus, in our experiment, we deposit a thin layer of tin of approximately 30 nm on Cu IDE. Since the capacitance of a capacitor depends on the gap between the two plates, in our experiment, firstly, we selected/fixed the width W of the fingers to be about 80 µm. Then, we changed the space S between the electrodes with different values, such as S = W = 80 µm, S = 0.5 W, S = 1.5 W and S = 2 W, to observe the performance of the IDC and found that when S = 1.5 W = 120 µm, then the IDC offers better performance. That is why, in our study, we selected the gap between the fingers to be about 120 µm. The thickness of the fabricated IDE was approximately 50 μm, with gaps between fingers of about 120 μm and a width per finger of approximately 80 μm, as measured by a scanning electron microscope (S-4800, Hitachi, Ibaraki, Japan). SEM images of the top view and cross-sectional view of the fabricated IDE is shown in Figure 4a,b, respectively.


Highly Sensitive Multi-Channel IDC Sensor Array for Low Concentration Taste Detection.

Khan MR, Kang SW - Sensors (Basel) (2015)

Step-by-step fabrication process of the interdigitated electrode: (a) polyimide substrate; (b) Cr layer on the polyimide substrate; (c) Cu layer; (d) photoresist layer; (e) placing the mask pattern on the photoresist layer; (f) transferring the mask pattern onto the photoresist layer; (g) depositing Cu via electroplating; (h) removing the photoresist; (i) removing the Cr layer; (j) depositing the Sn layer onto the Cu layer via electroplating; and (k) cutting the residual polyimide substrate.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4507581&req=5

sensors-15-13201-f003: Step-by-step fabrication process of the interdigitated electrode: (a) polyimide substrate; (b) Cr layer on the polyimide substrate; (c) Cu layer; (d) photoresist layer; (e) placing the mask pattern on the photoresist layer; (f) transferring the mask pattern onto the photoresist layer; (g) depositing Cu via electroplating; (h) removing the photoresist; (i) removing the Cr layer; (j) depositing the Sn layer onto the Cu layer via electroplating; and (k) cutting the residual polyimide substrate.
Mentions: We fabricated the interdigitated electrode (IDE) used in our experiment on a polyimide (PI) substrate. Polyimide, e.g., Kapton®, is a high-performance polymer that has a number of desirable properties, including a high degree of thermal stability, chemical stability, low dissipation factor and good dielectric properties; as a result, polyimide can be used as substrate material for flexible printed boards, multilayer PCBs and ribbon cables. In our experiment, we used the Kapton® HN-type polyimide substrate with a thickness of 5 mil, because it exhibits an excellent balance of physical, chemical and electrical properties over a wide temperature range. The fabrication process of the IDE on a PI substrate is described step-by-step below and represented schematically in Figure 3. The PI substrate was first cleaned with ethanol, methanol and deionized (DI) water. Then, a thin (15 nm) layer of chromium (Cr) was grown on the PI substrate via a vacuum evaporation process (the advantage of using Cr is that it provides superior adhesion performance). Next, we deposited an approximately 100 nm-thick copper layer onto the Cr layer; in turn, the Cu-layer was covered with photoresist SU-8 25 or AZ-4620 using a spin coater, with the choice of photoresist based on which was suitable for molding a relatively high aspect ratio electrode structure. Then, a Karl Suss MJB3 UV300 mask aligner was used to transfer a mask pattern onto the Cu-layer via UV exposure. Using a copper electroplating solution at an applied current density of 45 mA/cm2, a copper (Cu) layer was electroplated onto the Cu layer, after which the photoresist mold, unnecessary Cu layer and the bottom layer of Cr were removed using solvent suitable for avoiding short-circuiting. Finally, the Cu-interdigitated electrode was overlapped by a very thin layer of electroplated tin using an electroplating solution. In our experiment to deposit the Cu layer properly on the Cr layer, firstly, we deposited a very thin of the Cu layer on Cr layer, then we electroplated a thick layer of Cu of approximately 50 µm on the thin Cu layer. This step also reduces the fabrication cost and time. Tin is a useful metal that has non-toxic, ductile and corrosion resistance properties. Tin also has the ability to protect the Cu from oxidation. Thus, in our experiment, we deposit a thin layer of tin of approximately 30 nm on Cu IDE. Since the capacitance of a capacitor depends on the gap between the two plates, in our experiment, firstly, we selected/fixed the width W of the fingers to be about 80 µm. Then, we changed the space S between the electrodes with different values, such as S = W = 80 µm, S = 0.5 W, S = 1.5 W and S = 2 W, to observe the performance of the IDC and found that when S = 1.5 W = 120 µm, then the IDC offers better performance. That is why, in our study, we selected the gap between the fingers to be about 120 µm. The thickness of the fabricated IDE was approximately 50 μm, with gaps between fingers of about 120 μm and a width per finger of approximately 80 μm, as measured by a scanning electron microscope (S-4800, Hitachi, Ibaraki, Japan). SEM images of the top view and cross-sectional view of the fabricated IDE is shown in Figure 4a,b, respectively.

Bottom Line: The proposed IDC taste sensor array was compared with the potentiometric taste sensor with respect to sensitivity, dynamic range width, linearity and response time.We found that the proposed IDC sensor array has better performance.Finally, principal component analysis (PCA) was applied to discriminate different types of taste of the mixed taste substances.

View Article: PubMed Central - PubMed

Affiliation: School of Electronics Engineering, Kyungpook National University, 1370 Sankyuk-Dong, Bukgu, Daegu 702-701, Korea. rajibur@ee.knu.ac.kr.

ABSTRACT
In this study, we designed and developed an interdigitated capacitor (IDC)-based taste sensor array to detect different taste substances. The designed taste sensing array has four IDC sensing elements. The four IDC taste sensing elements of the array are fabricated by incorporating four different types of lipids into the polymer, dioctyl phenylphosphonate (DOPP) and tetrahydrofuran (THF) to make the respective dielectric materials that are individually placed onto an interdigitated electrode (IDE) via spin coating. When the dielectric material of an IDC sensing element comes into contact with a taste substance, its dielectric properties change with the capacitance of the IDC sensing element; this, in turn, changes the voltage across the IDC, as well as the output voltage of each channel of the system. In order to assess the effectiveness of the sensing system, four taste substances, namely sourness (HCl), saltiness (NaCl), sweetness (glucose) and bitterness (quinine-HCl), were tested. The IDC taste sensor array had rapid response and recovery times of about 12.9 s and 13.39 s, respectively, with highly stable response properties. The response property of the proposed IDC taste sensor array was linear, and its correlation coefficient R2 was about 0.9958 over the dynamic range of the taste sensor array as the taste substance concentration was varied from 1 μM to 1 M. The proposed IDC taste sensor array has several other advantages, such as real-time monitoring capabilities, high sensitivity 45.78 mV/decade, good reproducibility with a standard deviation of about 0.029 and compactness, and the circuitry is based on readily available and inexpensive electronic components. The proposed IDC taste sensor array was compared with the potentiometric taste sensor with respect to sensitivity, dynamic range width, linearity and response time. We found that the proposed IDC sensor array has better performance. Finally, principal component analysis (PCA) was applied to discriminate different types of taste of the mixed taste substances.

No MeSH data available.