TECHNICAL FIELD

Engmeering and fields of science related to the fabrication of an interdigitated array of electrodes for electrochemical sensors and electronic applications.

BACKGROUND

This invention is related to the process of production of interdigitated arrays of electrodes (IDAE). In general, IDAE are a pair of arrays of band electrodes. Common examples of materials used for the fabrication of IDAE are gold, platinum or other metals. According to some implementations of the current disclosure, IDAE may be arranged on a substrate (1) as shown in Fig. 1, where each electrode array comprises a series of micrometer- sized bands (4) and a connection pad (5) at one end of the bands (4). Each band electrode of the first electrode array (2) is placed between bands of the other electrode array (3), such that two consecutive bands are separated by distances in the micrometer range and are meant not to have electrical contact with each other. Connection pads (5) are used as an interface with an external electrical signal supply, and in certain situations the connection pads (5) may have an insulating layer (6) which covers them partially.

Existing fabrication methods of IDAE were adopted from microfabrication and are mainly based on photolithographic techniques, for example: etching and lift-off shown in Figures 2a and 2b. In the etching process shown in Fig. 2a, a substrate (9) is coated with at least one thin metallic film (10, 11), followed by coating a photosensitive chemical (12), also called photoresist, on top of the metallic film. In the case shown, the first layer of metallic film (10) acts as an adhesion layer rather than the metallic film of interest. In other cases, there may be multiple layers of thin metallic film of interest. Later this photoresist layer is selectively exposed to UV light (14) by using a photomask (13) and selectively removed in a series of chemical steps, so that the metallic film is covered by photoresist in the desired regions only. Finally, the etching process consists of chemically removing all metal that is not protected by the photoresist. Figure 2b shows another technique for metal patterning which is called lift-off, and consists of selectively coating one or more metallic film layers (e.g. 10 and 11 in Figure 2b) on regions of the substrate (9) that were not previously protected with photoresist (12). The etching process shown in Figure 2a includes a single metallic layer (11) of interest on top of a metal adhesion layer (10). Nevertheless, in the case of microfabrication of IDAE, more than one metallic layers of interest may be required. Therefore, the processes mentioned previously may be repeated in order to process all the metallic layers of interest that constitute the IDAE. Normally the fabrication of IDAE requires an adhesion layer of chromium or titanium (10) coated directly on the substrate (9), followed by coating the metallic film of interest (11), commonly gold, platinum or other metals.

Photolithographic techniques allow the production of high resolution patterns at the cost of multiple complex steps that require expensive production equipment and the use of several chemicals at each step of the production. Because of these problems, a different method for the fabrication of IDAE is disclosed, which uses of screen printing and printing technologies for hydrophobic material.

Screen printing technology is a technique for patterning diverse substrates, for example shirts, various utensils, and scientific equipment such as electrochemical electrodes patterned on plastic. This technology consists of printing ink on a substrate by pressing it through a stencil mesh made of textile or stainless steel threads. Screen printing allows printers to directly shape a single film of ink in a desired pattern. Therefore, the number of steps in the patterning process of a single layer can be substantially reduced when compared with photolithographic techniques. Therefore, a process for patterning IDAE by using screen and printing techniques for wax is presented. The process is described using the example of production of IDAE-based electrochemical cells, but it is envisioned that the proposed process can also be used in different electronic applications. For example the IDAE production process disclosed herein may be used in the production of interdigitated antennas, interdigitated capacitors and devices where interdigitated electrodes are an important component, such as capacitively-loaded antennas, microbatteries and micro-supercapacitors.

SUMMARY OF THE INVENTION

Disclosed is an improved process of production of IDAE using screen printing techniques which is simpler than photolithographic IDAE production. The advantage of this improvement is that the process can be used with flexible and inexpensive substrates, such as diverse kinds of paper, plastics, textiles and membranes. These substrates are appropriate for applications involving elastic surfaces, such as skin, or other curved surfaces. An example of the fabrication process of an IDAE with an embedded electrochemical cell is shown. This device, which can be applied to electrochemical sensors, is fabricated by screen printing the electrodes on chromatography paper (flow rates between approximately 115 mm / 30 min and approximately 130 mm / 30 min) or materials with similar membrane characteristics, such as cellulose membrane, cellulose acetate membrane, nitrocellulose membrane and nylon membrane or other porous substrates which allow the flow of liquid.

In some implementations, before screen printing the IDAE, an electrochemical chamber (15) is fabricated in the chromatography paper by printing hydrophobic material. A barrier (17) is used around the electrochemical cell region, as shown in Fig. 3 a. Subsequently, the desired inks are screen printed on both sides of the chromatography paper (16), which is used as supporting material or substrate. The carbon IDAE is screen printed on the front side of the electrochemical cell, as shown in Fig. 3c. The material of IDAE can be substituted with other materials which can be chosen from among Au ink, Bi ink and Pt ink. The reference electrode (22) is screen printed at the back side of the chromatography paper (16), extending across and perpendicular to the bands of the IDAE as shown in Fig. 3b. The reference electrode is made from silver-chloride (AgCl) inks or any other materials which can be chosen from carbon, Au and Pt inks. The electrochemical chamber (15) is located in between the IDAE and the reference electrode (22), as shown in Fig. 3d.

One advantage of the process disclosed herein, is that the IDAE produced in this way includes an embedded chamber with a three-electrode system, so it is ready to be used in electrochemical measurement. Also, a very small separation between the IDAE and the reference electrode is achieved. The separation corresponds to the thickness of the porous membrane used as substrate. Consequently, the internal ohmic drop in the electrochemical cell is much lower than the case where all electrodes are placed at the same side of the substrate. Moreover, the disclosed IDAE does not need complicated fabrication steps and doesn't require high-end equipment. The use of paper as substrate also introduces an additional advantage in terms of waste handling, especially when the IDAE is used in a device for diagnosis of infectious diseases, since the used devices can be directly incinerated.

The disclosed process of fabrication of IDAE can be also applied to the fabrication of other electronic devices such as interdigitated antenna, interdigitated capacitor, capacitively- loaded antenna with IDAE, micro batteries, micro-supercapacitor and/or other devices which incorporate IDAE. BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows examples of an IDAE printed on a non-porous substrate according to some implementations.

a) Configuration of the IDAE

b) Configuration of the IDAE with an embedded reference electrode

Fig. 2 shows the prior art fabrication steps of an IDAE by photolithography techniques. a) IDAE patterning by etching technique

b) IDAE patterning by lift-off technique

Fig. 3 shows components of an IDAE-based electrochemical cell printed on paper according to some implementations.

a) An electrochemical chamber formed by printing hydrophobic material (before printing the electrodes)

b) A reference electrode on the electrochemical cell (back side of the paper) c) An IDAE on the electrochemical cell (front side of the paper)

d) All components of the IDAE electrochemical cell (paper is shown as a transparent outline)

Fig. 4 shows an electrochemical chamber design used for actual production and fabricated by printing hydrophobic material according to some implementations.

Fig. 5 shows IDAE design used for actual production and fabricated by screen printing technique according to some implementations.

Fig. 6 shows reference electrode design used for actual production and fabricated by screen printing technique according to some implementations.

Fig. 7 shows a setup for electrochemical measurement using an IDAE electrochemical cell according to some implementations.

Fig. 8 shows current response of 1 mM ferrocyanide + 1 mM ferricyanide in 0.1 M PBS pH 7.0. The measurements were performed 5, 10, 15 and 20 minutes after dropping the chemical sample in the IDAE electrochemical cell according to some implementations. The cell comprises a carbon IDAE with an embedded Ag/AgCl reference electrode. Fig. 9 is a steady state voltammogram of 1 mM ferrocyanide + 1 mM ferricyanide in 0.1 M PBS pH 7.0. The measurements were performed using an electrochemical cell comprising a carbon IDAE with an embedded Ag/AgCl reference electrode according to some implementations. DISCLOSURE OF THE INVENTION

The process of producing interdigitated array of electrodes disclosed herein includes two main processes:

1. Fabrication of IDAE on a substrate by screen printing technique; and

2. Insulating layer fabrication on the substrate by screening printing or printing hydrophobic material.

The details of the production process follow.

1. The process of production of IDAE by screen printing technique includes

1.1 Pattern design

First, the electrodes are designed. In some implementations, the design is done by using vector-graphics software. The area of the design should fit the size of the substrate, as well as the screen block. Markers are added on the design area to produce good alignment between the substrate, the screen, and the design.

1.2 The selection of stencil mesh resolution

The width of the electrode bands depends on the mesh size of the stencil (number of threads per inch). The higher the mesh size number, the higher the resolution of the printed pattern, consequently resulting in a smaller IDAE for the same design.

IDAEs with an electrode band width of 200, 300 and 400 μπι were fabricated using stencil mesh sizes of 120 and 200 threads per inch. The results show that, for a mesh size of 120 threads per inch, the standard deviation of the electrode band width was not higher than 38%. When using a mesh size 200 threads per inch, a smaller standard deviation not surpassing 4% was obtained.

1.3 Printing alignment

In order to position the design precisely for printing, markers are added on the design frame. The screen block and the substrate are aligned with the design before printing. 1.4 Printing process

1.4.1 General description of the process

Two different processes may be used depending on the size of the pattern to be screen printed. For pattern sizes over 400 μπι, the screen block and the substrate can be placed in direct contact with each other and a first pass of ink can be used.

For pattern sizes less than 400 μηι, a gap in the range of approximately 2-3 mm is set between the screen block and the substrate by placing acrylic spacers or coins at each corner of the substrate layer. In this alternate printing process, the first pass of ink is discarded and the second pass of ink is the one used to produce the pattern. After the selected pattern (either a pattern less than 400 μπι or a larger pattern) is ready, the screen block is cleaned using solvent.

The ink for screen printing may be carbon ink or another material chosen from among bismuth (Bi) ink, gold (Au) ink, and platinum (Pt) ink. The screen printing technique conducted here can be used in either batch to batch printing or continuous roll to roll printing.

1.4.2 Notes on screen printing small patterns

In case of pattern features smaller than 400 μιη, the acrylic spacers or coins are placed at each corner of substrate layer in order to decrease the direct pressure exerted on the substrate during the screen printing process. This technique is used to avoid short circuits between electrode bands when spreading the ink.

Also, it was found that the second pass of ink produces higher quality prints than the first pass of ink. A possible reason for this is that, during the first pass, the ink flows through unoccupied holes, passing through completely in some parts of the stencil, whereas in other parts, the ink may not be able to cross (due to non-uniform pressure), leading to inconsistencies and nonuniformity in the printed geometry of the desired pattern. Unlike the first pass of ink, the second one has higher print quality because the ink has already crossed the holes of the stencil during the first pass, therefore, the ink is delivered to the substrate more consistently and uniformly compared to the first pass of ink.

The screen block needs to be cleaned after the second pass of ink. This is because the solvent in the ink composition evaporates during the screen printing process, consequently drying the ink and getting stuck in the holes of stencil, making it difficult to control the quality of printing. Therefore, a third pass of ink is not recommended for printing, especially when a high resolution stencil is used. 2. Process of fabrication of insulating layer either by screen printing and/or printing techniques for wax

The process of fabricating the insulating layer may be combined with any of the screen printing techniques described herein for printing the IDAE.

2.1 Insulating layer on non-porous substrate via screen printing

2.1.1 Pattern design

The insulating layer pattern may be designed by using vector graphics software. The design of the insulating layer is done by taking into account the same frame size and position markers used for patterning the electrode layer.

2.1.2 Selection of the stencil mesh resolution

The criteria for selection of the stencil mesh size is based on the pattern size. If the pattern size is below 400 μιη, the stencil mesh size should be at least 200 threads/inch for optimal results. The stencil may be a textile stencil or other type of stencil as desired.

2.1.3 Printing alignment

For precise positioning during printing, markers are added on the design frame. The screen block and the substrate are aligned to the desired position before printing.

2.1.4 Printing process

The printing of process of the insulating layer follows the same rules as the printing process of the IDAE. For a pattern size over 400 μιη, the screen block and the substrate can be placed in direct contact and the first pass of ink can be used.

If the pattern size is less than 400 μιη, a gap between the screen block and the substrate is set (in the range of approximately 2-3 mm) by placing acrylic spacers or coins at each corner of the substrate layer. In the printing process, the first pass of ink is discarded while the second pass of ink is the one used to produce the screen pattern. After the second pass of ink is screened, the screen block is cleaned by using solvent.

The material used for screen printing can be any generally insulating ink. The screen printing technique conducted here can be used in either batch to batch printing or continuous roll to roll printing.

2.2 Insulating layer on porous substrate via printing wax

2.2.1 Pattern design

The insulating layer pattern is designed by using vector graphics software and takes into account the same frame size and position markers used for patterning the electrode layer. 2.2.2 Wax printing

Printing of wax ink or other hydrophobic materials forms the pattern on the substrate. Printing may be done using a wax printer.

2.2.3 Wax melting for producing insulating hydrophobic barriers

The wax pattern printed on the substrate is baked in an oven at 150=1=5 C for approximately 5-9 minutes to melt the wax, allowing it to penetrate into the pores of the substrate.

The methods disclosed herein may also be used to produce a device for electrochemical analysis comprising an IDAE with an embedded electrochemical chamber. The IDAE is screen printed onto chromatography paper with a flow rate for aqueous solution between 115 mm/ 30 min and 130 mm/ 30 min. Besides chromatography paper, other materials can be used as substrates, including cellulose membrane, cellulose acetate membrane, nitrocellulose membrane, nylon or any other porous materials that can absorb and deliver solution to the electrodes.

The methods and systems disclosed herein may also be used to produce an IDAE electrochemical cell comprising an IDAE and a reference electrode, each fabricated on opposite faces of a substrate (16), and barriers (17) which define the border of the IDAE electrochemical cell chamber (15). The IDAE includes two electrode arrays (18, 19) each having alternating bands (21) fabricated without electrical contact therebetween. Each electrode array of bands (21) is in electrical connection to one of a pair of connector pads (20) which provide an electrical interface between each array of bands (21) and an external signal generator, power supply, measurement device, or combination thereof. The IDAE bands (21) lie on top of the electrochemical cell chamber (15), while the connector pads (20) are placed outside of the electrochemical cell chamber (15) near the barrier (17). The reference electrode (22) is fabricated on the opposite side of the substrate, lying beneath and on the bottom face of the electrochemical cell chamber (15) opposite the IDAE. The reference electrode (22) is attached to a reference connector pad (23) at one end.

In some implementations, the IDAE electrochemical cell is fabricated on chromatography paper having a flow rate between approximately 115 mm per 30 minutes and approximately 130 mm per 30 minutes. In some implementations, the substrate is selected from among chromatography paper, porous substrates that can flow liquids, and substrates with membrane characteristics. In some implementations, substrates with membrane characteristics are selected from among cellulose membranes, cellulose acetate membranes, nitrocellulose membranes, and nylon membranes. In some implementations, the IDAE and connector pads are fabricated with carbon ink or other conductive ink. In some implementations, the barriers (17) are made of wax or any other hydrophobic material. In some implementations, the reference connector pad (23) and the reference electrode (22) are fabricated from silver-chloride inks, carbon inks, bismuth inks, gold inks, or platinum inks. In some implementations, the resistance between the two electrode arrays is not lower than one ΜΩ. In some implementations, the resistance between the reference electrode (22) and each of the electrode arrays is not lower than one ΜΩ.

The configuration and components of the IDAE electrochemical cell on chromatography paper, one implementation of a substrate (16), are shown in Fig. 3. They consist of an electrochemical chamber (15), an IDAE and a reference electrode. The electrochemical chamber (15) is defined by a barrier (17) printed with wax or another hydrophobic material at the border of the electrochemical cell, which is used to confine the electrochemical solution. The IDAE consists of two arrays of electrodes (18) and (19). Each electrode array is composed of a series of electrode bands (21) which are connected at one side of a connector pad (20). The electrode bands of the left array (18) are connected to the right side of the left connector pad. The electrode bands of the right array (19) are connected to the left side of the right connector pad. All bands (21) of both array electrodes (18, 19) are placed on the electrochemical chamber (15), such that each band of one array is located between two consecutive bands of the other array, without having electrical contact between them. Between any two consecutive bands there is a small gap in the micron range. The connector pads (20) are placed outside the electrochemical chamber (15) and can touch the hydrophobic barrier (17). The material used for fabricating the electrode bands (21) and connector pads (20) can be carbon ink or any other conductive ink, preferably chosen from among bismuth (Bi) ink, gold (Au) ink, and platinum (Pt) ink. In some cases, the material may be a commercially available ink, such as nickel (Ni) ink, aluminum (Al) ink, silver (Ag) ink, copper (Cu) ink, or silicon (Si) ink, comprising a composite paste rather than pure material. The reference electrode (22) is placed on the electrochemical chamber (15), opposite the IDAE, on the back side of the chromatography paper substrate. The reference electrode is connected to a connector pad (23), see Fig. 3(b), which is fabricated with the same material as the reference electrode (22). The material used to fabricate the reference electrode (22) and its connector pad (23). can be silver-chloride inks and or any other conductive inks preferably chosen among carbon ink, gold (Au) ink, and platinum (Pt) ink.

According to this design, the gap between the IDAE and the reference electrode is determined by the thickness of the substrate (16), therefore it can go down to micron range or less. This reduces the ohmic-drop in the electrochemical cell, which is a specific advantage of this design since low ohmic-drop is in general desired for electrochemistry applications. If the layers of the IDAE and the reference electrode (7) and reference connector pad (8) are printed at the same side of a substrate, as shown in Fig. lb for a non-porous substrate according to some implementations, the gap between the IDAE and the reference electrode may present two issues. First, the gap between both electrodes would depend on the alignment and resolution of the screen printer which could make it difficult to achieve a gap in the micron range. Since the reference electrode is usually a different material than the IDAE, it is printed with a different pass, introducing additional margins of error in the second alignment process. Second, the gap between all bands of the IDAE and the reference electrode would not be uniform. In particular, the gap between the reference electrode (7) and the first band of the IDAE would be smaller than the gap between the reference electrode (7) and the last band of the IDAE, as illustrated in the configuration shown in Figure 1. Both of these issues are critical for the gap between the IDAE and the reference electrode, therefore placing limitations on the internal ohmic drop of the electrochemical cell.

There are other advantages in the disclosed production process. For example, the steps of production are simple, since there is no need to use expensive machines and other specialized techniques like photolithography or etching techniques. In addition, the disclosed process can be used to fabricate devices on both flexible non-porous substrates such as plastic or porous substrates like paper. The electrode dimensions can reach the micron range, provided the mesh size of the screen block (threads/inch) is high resolution. A mesh size of 200 threads/inch can be used to make electrodes with an electrode band width as small as 200 μπι using the disclosed production process. In terms of waste handling, paper substrate can be easily incinerated which is appropriate for diagnostic applications of an electrochemical cell.

The process of production of an IDAE with embedded electrochemical cell, like the one shown in Fig. 3d, is divided into four steps, explained below, and can use the designs of the different layers shown in Figs. 4-6.

1. The pattern design

The pattern is designed by using vector graphics software and consists of three main layers. The pattern design step takes into account the desired shape and dimensions of the resulting IDAE electrochemical cell. The first layer, shown in Fig. 4, corresponds to the electrochemical chamber (15). In one implementation, it has inner dimensions of a length AA' of 18.5 mm and a width BB' of 5.5 mm. The border line width is 500 μπι. The second layer, shown in Fig. 5, corresponds to the IDAE which is composed of electrode bands (21). In one example, the electrode bands (21) are printed with approximately 200 μηι width and 7 mm length. The electrode bands (21) of one electrode array are put into electrical contact through a connector pad (20). In one example, the connector pad (20) is 5 mm x 25 mm, however the connector pad (20) may be any other suitable size, according to the requirements of the end use. The third layer, shown in Fig. 6, corresponds to the reference electrode (22). In one example, the reference electrode (22) is 1 mm x 2 cm and is attached to a reference connector pad (23) of 5 mm x 5 mm size. In other implementations, the dimensions of the electrochemical chamber, the array electrodes and the connector pad mentioned above can be changed to fit the desired application or experiment.

In the example discussed herein, multiple IDAE electrochemical cells are placed on a frame of size 148 mm x 210 mm and are arranged on the frame in an array-like fashion. The design includes adding alignment marks (24) to be placed in all the frames corresponding to the different layers of the IDAE, in order to coordinate positioning between layers during the printing process. However, the number of IDAE electrochemical cells on a frame as well as the size of the frame can be modified to fit the desired application or experiment.

The design also includes adding three bars (25) for measuring the sheet resistance of the printed film and determining its uniformity. An estimation of the uniformity of the printing process, as well as the sheet resistance of the printed ink, can be obtained by measuring the resistance of the set of three carbon bars (25) located at the top and bottom of the frame in Figure 5. The design also includes a resolution pattern (26). The frame thus includes a resolution pattern (26) with lines of various sizes, to aid in the determination of the resolution of the screen printing process.

2. Fabrication of the electrochemical chamber by printing wax

The barrier (17) is printed by printing wax or another hydrophobic material on the substrate (16) to define the interior of the electrochemical cell chamber (15). After the wax is printed, it requires baking.

The barrier (17) of the electrochemical chamber (15), shown in Fig. 4, can be patterned by printing wax. In the example discussed in this disclosure, chromatography paper is used as substrate, but other substitute materials can be selected. After the wax is printed, it requires baking. In the example discussed in this disclosure, baking at 150±5 °C for approximately 5-9 min, allowed the wax penetrate the pores of the substrate, creating a hydrophobic barrier. The baking temperature and time were optimized to produce an electrochemical chamber of approximately 4 mm ^χ 17 mm after 9±1 min. This resulting electrochemical chamber area is smaller than the pattern originally printed, due to expansion of the hydrophobic material during the baking step.

3. Fabrication of IDAE by screen printing

In this step, the IDAEs are printed with carbon ink and a screen block with 200 threads/inch resolution. The chromatography paper with the patterned electrochemical chambers (15) is used as the substrate. In the screen printing process, the first pass of ink is discarded and the second pass of ink is used in order to keep the size of the printed pattern as close as possible to the original design. The alignment marks are placed on the screen block and printed on the substrate, in order to align subsequent layers of the IDAE in an appropriate position. During screen printing alignment marks on the stencil or screen block are aligned with the alignment marks printed on the substrate. Preferably, the barriers (17) of the electrochemical cell chamber, together with alignment marks, have already been printed on the substrate. The IDAEs are printed on the front side of the substrate, such that only electrochemical bands (21) are inside the electrochemical chamber (15), whereas the connector pads (20) are located only outside the electrochemical chamber and on the hydrophobic barrier (17). The screen printed substrate is baked at approximately 50 - 60 °C for about 10 -12 hours, in order to evaporate the solvents of the ink. A popular choice of ink is carbon ink, but substitute materials can be used as well, which can be chosen from among bismuth (Bi) ink, gold (Au) ink, and platinum (Pt) ink.

The quality of the printed product is assessed by measuring the resistance between both array electrodes of the same IDAE (18, 19) at its the connector pads (20). The acceptance criteria is that the electrical resistance between these two array electrodes is equal to or more than 1 ΜΩ. With such resistance the IDAE is not considered to be short-circuited.

4. Fabrication of the reference electrodes by screen printing

In this step, the reference electrode (22) is printed with silver-chloride (AgCl) ink on the opposite side of the substrate from the IDAE using a stencil or screen block. The gap between the IDAE and the reference electrode is equal to the thickness of the substrate.

In the example shown, the reference electrodes (22) are printed with silver-chloride (AgCl) ink and a screen block with 200 threads/inch resolution. The chromatography paper with pre-patterned electrochemical chambers (15) and IDAEs may be used as a substrate. The reference electrodes (22) are printed on the back side of the substrate, inside the electrochemical chamber (15). A connector pad (23) for the reference electrodes (22) is printed outside the electrochemical chamber. For each electrochemical cell, the reference electrode at the back of the substrate is placed along the IDAE at the front of substrate. Thus the gap between the IDAE and the reference electrode corresponds to the thickness of the substrate. The thickness of the chromatography paper substrate is around 180 - 200 μιη. The printed substrate is baked at about 50 - 60 °C for about 10 -12 h, in order to evaporate the solvents of the ink. The printing for both the IDAE and the reference electrode may be conducted by batch to batch printing or roll to roll printing.

The quality control of the print is conducted by checking the electrical resistance between each electrode array (18,19) and the reference electrode (22), through their connector pads (20, 23). A criteria of acceptance is that the electrical resistance should be equal or more than 1 ΜΩ. This value shows that the electrodes are not short circuited.

The production process disclosed herein uses wax or another hydrophobic material as a hydrophobic barrier (17) to bound the electrochemical chamber (15) region. The ink used for electrode fabrication may be silver-chloride (AgCl) inks or any other substitute material which can be chosen from among bismuth (Bi) inks, gold (Au) inks, and platinum (Pt) inks.

Actual measurement and experimental setup

In order to avoid evaporation of the sample during measurement, an environment with high humidity may be used, which can be produced by using a humidity box as shown in Fig. 7. Here the IDAE electrochemical cell (27) is put inside humidity box (28) which is connected to a potentiostat. The humidity box (28) is a simple box made functional by putting a water absorbing material inside it, which can be chosen from tissue paper, sponge or textile (29). The IDAE electrochemical cell (27) is placed inside this box (28) with a removable lid (30), in order to help avoid evaporation during measurement. The IDAE electrochemical cell (27) is connected to an external signal generator (31) or potentiostat via three connections: working electrode connection (34), counter electrode connection (35) and reference electrode connection (36).

To perform the measurement, an analyte solution (32) is dropped onto the back side of the IDAE electrochemical cell, or in the reference electrode region. The measurement is started once the solution spreads through all of the area of the electrochemical chamber. Fig. 7 illustrates controlling and monitoring the measurement via computer (37).

As an example, results of measurement of a solution containing 1 mM ferrocyanide and 1 mM ferricyanide in a phosphate buffer having pH 7.0 are shown in Fig. 8 and Fig. 9. Fig. 8 shows a highly stable chronoamperometry response, even when using various waiting times after dropping the solution. Fig. 9 shows a steady state voltammogram found using the IDAE.

The IDAE electrochemical cell disclosed herein has several advantages. First, all important electrochemical components are embedded in a single device, therefore it is ready for use in electrochemical measurement. Second, the IDAE decreases the time required to reach steady state compared with conventional electrodes. Third, the electrode arrangement of the IDAE-based electrochemical cell is novel, in the sense that the reference electrode is placed in parallel and along the whole body of the IDAE, and separated from the IDAE by a small gap in the micron range by the thickness of the substrate. This configuration helps to decrease the ohmic drop in the electrochemical cell. Moreover, when paper is used as substrate, it can act as support for the electrodes and as electrochemical chamber at the same time, making the device more convenient for real application use.

The disclosed production process shows the capability for multilayer printing, which can be applied to the fabrication of other related devices such as interdigitated antennas A. Dreyhaupt, S. Winnerl, T. Dekorsy, and M. Helm. "High-intensity terahertz radiation from a microstructured large-area photoconductor". eng. In: Applied Physics Letter 86(2005), pp. 121114; Toshi aki HATTORI , Kazuhiro Egawa, Shin-ichi Ookuma and Taro Itatani. "Intense Terahertz Pulses from Large-Aperture Antenna with Interdigitated Electrodes". Eng. In: Japanese Journal of Applied Physics. 45(2006), pp. L422-L424. DOI: 10.1143/JJAP.45.L422;, interdigitated capacitors Aycan Erentok and Richard W. Ziolkowski, Fellow. "Metamaterial- Inspired Efficient Electrically Small Antennas". Eng. In: IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION. 56. (MARCH 2008), pp. 691-706., capacitively-loaded antennas with embedded IDAE US 9093752 B2; US 2014/0253392, microbatteries and micro- supercapacitors.

INDUSTRIAL APPLICABILITY

IDAE printed by the screen printing techniques disclosed herein can be used in devices, including electrochemical and electronic devices in the industrial and other sectors.