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Article Cite This: ACS Omega 2018, 3, 16866−16873
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Programmable Contact Printing Using Ballpoint Pens with a Digital Plotter for Patterning Electrodes on Paper Veasna Soum,† Haena Cheong,† Kihoon Kim,† Yunpyo Kim,† Mary Chuong,† Soo Ryeon Ryu,† Po Ki Yuen,‡ Oh-Sun Kwon,† and Kwanwoo Shin*,† †
Department of Chemistry and Institute of Biological Interfaces, Sogang University, Seoul 04107, Republic of Korea Science & Technology, Corning Incorporated, Corning, New York 14831, United States
‡
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S Supporting Information *
ABSTRACT: A simple programmable contact printing method using ballpoint pens with silver nanoparticle (AgNP) and carbon nanotube (CNT) ink and a digital plotter were developed for quick patterning of electrodes on paper. This printing method enables sequential and programmable printing with two different inks and with ink consisting of high viscosity materials and is amenable to reproducibility of printed electrodes and customized designs. With this printing method, AgNP and CNT patterns with low electrical resistance and high density of the material can be printed. Using these AgNP and CNT inks, we fabricated disposable electrochemical sensors (ECSs) on paper. The ECSs were successfully used to detect glucose at various concentrations from 0 to 15 mM. The characteristics of the printed AgNP and CNT patterns, such as the printing resolution, surface morphology, and electrical properties, were also studied. The proposed contact printing method opens an avenue for printing paper-based electronics and devices.
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INTRODUCTION The fabrication of paper-based devices through printing methods is rapidly developing because it is simple, quick, inexpensive, and flexible. It allows paper-based devices to be fabricated for both personal and commercial purposes.1−3 Printing with inks made of different materials has been used to fabricate numerous paper-based devices, such as transistors,4 solar cells,5 supercapacitors,6,7 semiconductor,8 displays,9,10 microfluidic chips,11−14 and sensors.13−16 The challenge in fabricating printing-based devices is how to pattern electrodes precisely, easily, and cost-effectively. The printing of electrodes relies on a printing tool and a method to deal with the properties of the materials in the ink. Types of printing techniques, such as flexographic, offset, gravure, screen, inkjet, and ballpoint-pen printing, have been used for depositing inks made of materials such as carbon, polymeric, and metallic nanoparticles.17−21 The ballpoint-pen printing method provides important advantages compared to other printing methods. First, because the ballpoint continuously rolls to deposit the ink, the ballpoint pen can fabricate connected patterns in a single printing while the inkjet method requires repetitive printings.22,23 Second, a customized pattern is more easily obtained with ballpoint-pen printing than with screen printing because screen printing requires a prerequisite process, the fabrication of a silkscreen, to make the pattern.14,22 Third, in addition to portability and low cost, ballpoint-pen printing can be done by laymen; a professional is not needed. Nevertheless, ballpoint pen printing © 2018 American Chemical Society
has some limitations such as the need for manual control, its suitability for mass production, and its reproducibility. For the fabrication of a sensor, materials with various characteristics that depend on the operation principle of the targeted sensor must be printed simultaneously or sequentially. For instance, an electrochemical sensor (ECS), often used with the three-electrode setup for a potentiostat, was fabricated using carbon-based and Ag/AgCl electrodes,12,14 and electrochemical gas sensors were made of carbon nanotube (CNT)based and gold or AgNP electrodes.24 Although the printing of multiple functional materials is a challenging process, it can be done by printing a second material after finishing the first printing. In this research, we developed a straightforward contact printing technique for depositing inks consisting of different materials sequentially on paper within a printing time. We used ballpoint pens and a digital plotter as printing tools. Two ballpoint pens, one with AgNP ink and the other with CNT ink, were developed specifically for this programmable contact printing. By printing with AgNP and CNT inks sequentially, we fabricated a disposable paper-based ECS. In the fabrication of the ECS, AgNP ink was used for printing the quasi-reference electrodes (Ag QREs).20,25,26 The CNT ink was used for printing counter electrodes (CEs) and working electrodes Received: September 29, 2018 Accepted: November 9, 2018 Published: December 7, 2018 16866
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Figure 1. (A) Schematics for the structures of the ballpoint pen, two ballpoint-pen cartridges: one with CNT ink and the other with AgNP ink, and photograph of the ballpoint pen. (B) Photograph of the two ballpoint pens for sequential printing placed into the pen holders by using clamp A and clamp B (in orange color) of the digital plotter. Photographs of (C) printed AgNP patterns on paper and (D) paper-based ECSs printed using the two ballpoint pens with the digital plotter.
Figure 2. (A) AgNP patterns with a variety of widths were printed in straight lines using ballpoint diameters of 0.5, 0.7, and 1.0 mm, and (inset) a curved line was printed using a ballpoint diameter of 0.5 mm. (B) Surface profile of the AgNP patterns printed on the paper. (C) CNT patterns printed using a ballpoint diameter of 1.0 mm and inks containing a variety of CNT concentrations: (1) 0.7, (2) 1.4, and (3) 4.1 wt %. (D) Relations between CNT concentration, ink viscosity, and width of the CNT printed pattern. (E) Design (top) for creating a pattern with a larger surface area and the printed AgNP pattern (bottom). (F) Design (top) for sequential printing of AgNP and CNT patterns and the patterns after printed (bottom).
(WEs)27,28 because it had high electrical conductivity, high surface area originating from the nanocylindrical structure of the CNTs, and high chemical stability.29,30 After the fabrication of the ECS, its characteristics, such as its detection performance, sensitivity, and optimum potential for detection of a substance, were examined, after which it was tested quantitatively to determine its sensitivity for detecting glucose.
deposition gap (Figure S3). The opening of the deposition gap and the rotation of the ballpoint allow the ink to be deposited. Contact Printing Using Ballpoint Pens with a Digital Plotter. A customized ballpoint pen was used for ink storage and as a deposition tool. Ballpoint pens with various ballpoint diameters, such as 0.5, 0.7, and 1.0 mm, could be used to vary the printed pattern’s characteristics: thickness, resolution, and electrical conductivity of the printed patterns. Furthermore, a ballpoint-pen ink cartridge can be refilled with various inks, for example, PEDOT:PSS, carbon powders, copper nanowires, AgNPs, CNTs, and so forth, allowing a variety of electric devices to be fabricated on paper. However, the ink properties must meet certain conditions, mainly viscosity (up to 10 × 103 cP),19 solvent (water-base or ethylene glycol), and dispersed material size (up to 5 μm). To print inks made of different materials sequentially in a programmable way, we placed two ballpoint pens, one with CNT ink and the other with AgNP ink, into clamps A and B of the digital plotter, respectively (Figures 1B−D, S2). The pattern design was prepared using computer software and then printed using the contact printing process through a USB port communication system between the computer and the digital plotter. With the plotter we used in this research, the contact printing could be done on large surfaces of up to 30.5 cm × 30.5 cm. The printing speed was 4.6 cm/s for a horizontal or a vertical line and 5.9 cm/s for a 45°-tilted line.
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RESULTS AND DISCUSSION Ballpoint Pens for Contact Printing. Conventional ballpoint pens have two springs: one, inner spring to maintain the pressure of the rotating ball on the tip, and the other for a retraction of the ballpoint pen tube to a casing. In order to maintain an optimum contact pressure during the automatic writing (contact printing), we customized the ballpoint pen used in our setup by adding an external spring (as shown Figure 1A) to apply a constant pressure during the printing process. The customized ballpoint pen consists of three parts: a metal spring, a barrel, and an ink cartridge with a metal ballpoint. Installation of the spring in the ballpoint pen was one of the key setups to produce homogeneous and reliable contact printing on any rough surface. Moreover, the printing quality and the ballpoint’s lifetime were increased because the printing pressure could be optimized by using the installed spring (Figure S1B). For the deposition of an ink with a specific material, the ballpoint needs contact pressure to widen its 16867
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Figure 3. (A) SEM images of the widths of AgNP patterns printed by using ballpoint diameters of 0.5, 0.7, and 1.0 mm (top to bottom). (B) SEM image of AgNP aggregate on the surface of the paper substrate. (C,D) Cross-sectional SEM and EDS views, respectively, of the AgNP pattern printed by using a 1 mm-diameter ballpoint. (E) SEM images of the widths of CNT patterns printed by using ballpoint diameters of 0.5, 0.7, and 1.0 mm (top to bottom). (F) SEM image of CNT aggregate on the surface of the paper substrate. (G,H) Cross-sectional SEM and EDS views, respectively, of the CNT pattern printed by using a 1 mm-diameter ballpoint.
Figure 4. Electrical properties of AgNP- and CNT-printed patterns. (A) Relationship between surface line resistance and the annealing time for the AgNP pattern. (B) Surface resistance versus the length of the AgNP pattern printed with a 1.0 mm-diameter ballpoint and annealed at 180 °C for 30 min. (C) Surface line resistance of the AgNP pattern vs the number of printings. (D) Surface line resistance vs annealing temperature for the CNT pattern printed with a 1.0 mm-diameter ballpoint and annealed for 30 min. (E) Surface resistance vs length for the CNT pattern printed with a 1.0 mm-diameter ballpoint and annealed at 180 °C for 30 min. (F) Surface line resistance for the CNT pattern versus the CNT concentration in ink; the pattern was annealed for 30 min at 180 °C. All the line resistance values were measured from the printed patterns with a length of 5 cm (n = 5).
Characteristics of the Printed Patterns. Figure 2A and its inset show, respectively, a straight and a curved AgNP pattern printed using various diameters of the ballpoint. Both pattern types have clean edges with homogenous ink deposition. The pattern has a V-shaped surface profile which is about 0.4 μm deep (Figure 2B). This surface geometry was generated by the pressure of the ballpoint tip on the surface of the substrate. The thickness, width, and gap of the printed pattern are approximately 0.3, 200, and 140 μm, respectively (Figure 2B). For the printing of the CNT patterns, CNT ink was prepared with various concentrations of CNTs from 0.7 to 4.1 wt %. The prepared CNT inks were printed on paper by using a ballpoint pen with a 1.0 mm ballpoint diameter (Figure 2C). Figure 2D shows the relationship between the viscosity of the printing ink, the width of the printed pattern, and the concentration of the printing ink. The viscosity of the ink was found to be proportional to the concentration of the CNTs.
Increasing the concentration of the CNTs increases the amount of dispersed solid materials, which contributes to an increase in the fluid flow resistance such that the ink becomes more viscous. Also, the CNT patterns were found to have widths that decreased proportionally with the concentration of CNTs. The decrease in the width was due to the effect of viscosity on the flow of ink during the printing. If a large pattern is to be generated, the printing pattern has to be designed as a group of lines with a maximum center-tocenter distance between adjacent lines of up to approximately 435 μm for the case of printing with a 1 mm-diameter ballpoint. Within this distance, printed patterns can connect to their neighboring patterns. The overlapping area between the patterns is inversely proportional to the center-to-center distance. Figure 2E shows an example of a design (top) for printing a pattern with a 5 mm height. The center-to-center distance between two adjacent lines was roughly 416 μm. The design was printed to generate a pattern height (∼5.5 mm), 16868
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Figure 5. (A) Design and structure of the printed paper-based ECS. (B) Paper-based ECSs for which their CE and WE were printed with a variety of CNT concentrations. (C−E) SEM images of the surfaces of WEs (1), (2), and (3) taken from (B), respectively. (F) CV diagrams for the printed ECSs and a commercial standard ECS.
during the annealing process (Figure S6). Figure 4B shows that the electrical resistance of the printed AgNP pattern increased linearly with increasing pattern length. The linearity increment showed the homogeneity of the printed pattern. When the number of printed layers (n = 1, 2, and 3) and the ballpoint diameter (ϕ = 0.5, 0.7, and 1.0 mm) were increased, the thickness and the width of the pattern, respectively, increased (Figure 4C), providing lower electrical resistance. Annealing a CNT pattern can also improve its electrical performance slightly (Figure 4D). Even without annealing, however, the CNT pattern reached almost minimum electrical resistance. This characteristic could be explained by the length of the CNTs (∼2 μm) being long enough to connect CNTs to CNTs after the water-based solvent had been absorbed into the paper substrate or had evaporated at room temperature. Figure 4E shows a uniform CNT pattern for which the electrical resistance increased linearly with increasing pattern length. The relation between the electrical resistance and the CNT concentration is shown in Figure 4F. Printing with an ink with a higher concentration of CNTs allowed a pattern with a lower electrical resistance to be printed. The maximum printable viscosity for the CNT ink by using ballpoint pen was 41.5 cP. Using this highly viscous ink, we were able to print a CNT pattern with a very low value of electrical resistance (34.31 kΩ/cm) in a single printing with a 1.0 mmdiameter ballpoint. Preparation of Printed Paper-Based ECSs. Because our contact printing allows sequential printing with two different inks, it is advantageous for the fabrication of numerous types of sensors, such as biosensors, capacitive sensors, piezoresistive sensors, temperature sensors, and gas sensors. As a biosensor, we fabricated paper-based ECSs, wherein the CE and the WE were printed using CNT ink while the Ag QRE and the connection pads were printed using AgNP ink (Figure 5A, Video S2). The digital plotter provided another benefit of quick cutting of soft materials when using its cutting feature with a cutting blade (Video S3).31,32 Figure 5A shows a fluidic barrier made of transparent adhesive plastic-based film, whose center was cut out by using the digital plotter blade. The fluidic barrier was attached onto the paper-based ECS to provide a sample-loading window. The fabricated paper-based ECS costed about 0.014 USD in total (Table S1).
which was approximately 0.5 mm larger than the height in the actual design [Figure 2E (bottom)]. The increased area was contributed by half the height of the top pattern and half the height of the bottom pattern. Depending on the design and the setting, one can print CNT and AgNP patterns sequentially (Figure 2F, Video S1). The ballpoint diameters provided the printed patterns with various characteristics. AgNP patterns with widths of approximately 225, 365, and 455 μm were printed using ballpoint diameters of 0.5, 0.7, and 1.0 mm, respectively (Figure 3A). The pattern width was smaller than the printing ballpoint’s diameter because during the printing, only a minor segment of the ballpoint is in direct contact with the substrate. The width of the AgNP pattern increased proportionally with the ballpoint’s diameter. A high-resolution scanning electron microscopy (SEM) image of the AgNP pattern shows the presence of AgNPs (∼50 nm) on the surface of the paper (Figure 3B). An AgNP pattern with a thickness of approximately 421 nm was generated from a single print using a ballpoint diameter of 1.0 mm (Figure 3C). With the energy dispersive spectroscopy (EDS) composition analysis, we could identify the distribution of the printed AgNPs (yellow) at a cross-sectional view (Figure 3D). The elemental labeling for the AgNP pattern and the substrate is shown in Supporting Information (Figure S4). In another printed pattern type, the CNT patterns printed with ballpoint diameters of 0.5, 0.7, and 1.0 mm had widths of approximately 300, 420, and 520 μm, respectively (Figure 3E). Figure 3F shows the presence of CNTs (∼2 μm) on the paper. The thickness of the CNT pattern printed using a ballpoint diameter of 1.0 mm was approximately 205 nm (Figure 3G). Figure 3H shows the distribution of the printed CNTs (blue) at cross-sectional view. The elemental labeling for the CNT pattern and the substrate compositions is shown in Supporting Information (Figure S5). To reduce the electrical resistance of the printed AgNP patterns, we annealed them at 180 °C. When the annealing time was increased, the line resistance decreased exponentially. After the annealing process, the line resistance reached an asymptotic limit of 28 Ω/cm (Figure 4A). The increase in the electrical performance was due to some components of the ink, such as the solvent and the surfactant, having been removed 16869
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Figure 6. (A) Schematic of the fabricated ECS for the detection of glucose. (B) CV diagrams for the printed sensors for six different scan rates (a− f: 20, 40, 60, 80, 100, and 120 mV/s, respectively) in 1 mM [Fe(CN)6]3−/4−. The inset shows the relationship between the anode and the cathode currents and the square root of the scan rate. (C) CV diagrams for the printed ECS in the absence and presence of H2O2. (D) Detection of glucose using the printed ECSs and chronoamperograms for various glucose concentrations of 0, 1, 3, 5, 8, 12, and 15 mM (a−g, respectively) in aqueous solutions. The anode currents at 60 s were selected and plotted as a calibration curve, which is shown in the inset, n = 3.
shows that the redox reaction rate of the electroactive species [Fe(CN)6]3/4− was limited by a diffusion-controlled process on the surface of the electrode.33 This behavior is very similar to the redox reaction happening in most traditional electrochemical cells.34,35 Because the detection of glucose is based on the detection of hydrogen peroxide (H2O2),14 an important step is to confirm that the fabricated sensors can detect H2O2. For this purpose, a 1 mM H2O2 (signal) in phosphate buffered saline (PBS) and only PBS (background) were analyzed using the CV technique at a 100 mV/s scan rate. Figure 6C shows the characteristics of the electrode in the presence and absence of H2O2. The cathode peak of the sample containing 1 mM H2O2 was relatively more significant than the background cathode peak of the sample containing only PBS. This result showed that the fabricated sensors had good sensitivity for detecting the analyte. If H2O2 is to be detected using chronoamperometry, an optimal detection potential is required. Chronoamperometry was used instead of CV because the former is well known to have a higher sensitivity and long-term applicability. To optimize the detection potential, we performed hydrodynamic voltammetry to detect H2O2 (1 mM) at various applied potentials from 0.0 to −0.4 V. The detection potential was determined by using chronoamperometry. The selected currents were plotted against the applied potential (Figure S8A). Each selected current signal for H2O2 (S) was divided by each background signal (B), and the resulting S/B ratio at each potential is shown in Figure S8B. The S/B ratio reached a maximum at an applied potential of −0.2 V. As a result, the optimal detection potential of −0.2 V was applied for the detection. The results of the characterizations showed that the properties of the fabricated sensors were sufficient for them to be used for the detection of glucose. Chronoamperograms for various concentrations of the glucose solution ranging from 0 to 15 mM were measured. The anodic current was recorded
For printing the CE and the WE, we used CNT ink with various concentrations, (1) 0.7, (2) 1.4, and (3) 4.1 wt %, to compare the detection sensitivities (Figure 5B). The CNT electrode (1) was found to have a lower density of CNTs covering the paper substrate (Figure 5C), whereas the CNT electrodes (2) and (3) contained a higher density of CNTs (Figure 5D,E). Figure 5F shows the sensitivities of the ECSs printed with a variety of CNT inks and a commercial standard ECS (screen-printed ceramic gold electrode, BE2050824D1/ 024, Gwent Group), which were obtained through detection of the standard redox couple [Fe(CN)6]3/4− (1 mM). The cyclic voltammetry (CV) measurements showed that the peak oxidation current of the ECS (3) was higher than the commercial standard ECS, the ECS (2), and the ECS (1). The peak oxidation current of the ECS was more significant when an ink with a higher concentration of CNTs was used. This higher sensitivity was due to both the higher surface sensing area and the higher electrical conductivity of the electrodes.30 The higher surface sensing area of the electrodes, generating from highly density of CNTs, enhanced the transfer of anodic oxidized cations and cathode anions. The WE and the CE were, therefore, printed using the CNT ink with a concentration of 4.1 wt % so as to obtain highly sensitive ECSs. Electrochemical Sensing Performance of the PaperBased ECSs. Before the paper-based ECSs were used for electrochemical detection, their electrochemical performances were characterized. As described in eqs 1 and 2, glucose is oxidized by enzyme glucose oxidase (GOx) to produce H2O2. With applying an optimum potential through a RE, the H2O2 is reduced; and then, the electrons are transferred from the analytes to the surfaces of a WE (Figure 6A). Figure 6B shows representative CV curves for the sensors in a 1 mM solution of the redox couple [Fe(CN)6]3/4− at different scan rates of (a) 20, (b) 40, (c) 60, (d) 80, (e) 100, and (f) 120 mV/s. The inset shows that the anode and the cathode peak currents are linearly proportional to the square root of the scan rate (V1/2). This result agrees with the Randles−Sevcik equations and 16870
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sensing performance, we compared the results obtained when using three different concentrations of the CNTs in those inks. After the printing, the ECSs were annealed at 180 °C for 30 min to improve their electrical performance. The surface profile of the printed patterns was measured by using a contact profiler (Dektak-XT, Bruker, USA). The surface morphologies and compositions of the printed electrodes were characterized by using a field emission SEM combined with EDS (JSM7100F, JEOL, USA). The CE, WE, and RE were first designed using computeraided design software (Adobe Illustrator CC 2015) and then exported to an AutoCAD Interchange file (*.DXF). Next, the files were uploaded to an online design space (Cricut Design Space) of the digital plotter for printing. In the printing setup, the patterns to be printed by using the CNT and the AgNP inks were set as the writing function (Clamp A) and the cutting function (Clamp B), respectively. Electrochemical Measurements. Electrochemical measurements, such as CV and chronoamperometry, were performed using a SP-200 modular potentiostat/galvanostat (EC-Lab, Biologic, France). An electrochemical measurement setup, the connection between the ECS and the electrochemical interface, is shown in Figure S7. CV was performed in an aqueous solution of 1 mM [Fe(CN)6]3−/4− (30 μL) at various scan rates, 30, 40, 50, 70, 80, 100, and 120 mV/s, against the REs (Ag QREs). GOx solution (500 U/mL, 10 μL) was mixed with each standard glucose solution (20 μL) and incubated for 15 s before loading into the sample-loading zone for detection. Chronoamperometry was conducted by applying an optimal potential of −0.2 V within a 65 s incubation time. The electrical current obtained from the chronoamperograms during the detection of glucose was selected at 60 s. The electrochemical detection of glucose is based on twostep enzymatic reactions. An oxidative enzyme (GOx) catalyzes the oxidation of glucose to produce hydrogen peroxide (H2O2) (eq 1)
at 60 s, which was the apparent steady-state current (Figure 6D). The selected anode currents were plotted for a calibration curve, and that curve was found to be linear (R2 = 0.98993).
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CONCLUSIONS In summary, we have developed a simple, low-cost, programmable, contact printing method using ballpoint pens and a digital plotter. The ballpoint pens were modified by adding a metal spring to offer an optimum and uniform pressing force to achieve high-quality printing. We sequentially printed AgNP and CNT electrodes in a programmable manner to fabricate disposable paper-based ECSs, and we studied the characteristics of those ECSs for electrochemical detection. We found that the fabricated ECSs were sensitive enough to detect glucose at various concentrations from 0 to 15 mM. Although the proposed contact printing method provides notable features for the printing of ECSs, it has a limitation in which an annealing process is required. However, this annealing process is an after-printing treatment similar to those that are commonly required for most printed electrodes. On the basis of the results achieved in this research, we believe that this contact printing method using ballpoint pens and the digital plotter will become a promising tool for quick printing of paper-based analytical sensing devices, especially for on-site fabrication in a low-resource or do-it-yourself setting.
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EXPERIMENTAL SECTION Chemicals and Materials. CNT ink was prepared as reported in our previous work.36 AgNP ink (Silver jet ink, DGP 40LT-15C) was purchased from Advance Nano Products. Conventional ballpoint pens (diameters of 0.5, 0.7, and 1.0 mm), permanent markers, and polypropylene adhesive film were commercially available. Photopaper was purchased from Epson (S042187). A digital plotter (Cricut Explore Air) was obtained from Provo Craft & Novelty, Inc., USA (Figure S1A). Ferri/ferrocyanide ([Fe(CN)6]3−/4−), PBS (pH 7.4), GOx, and β-D-glucose were obtained from Sigma-Aldrich. Preparation of Ballpoint Pens for the Contact Printing. A customized ballpoint pen was first prepared by assembling different parts taken from a permanent marker and a conventional ballpoint pen (Figure 1A). A metal spring was inserted into the 1.5 cm gap between the end of the ink cartridge and the top cap. Various ballpoint diameters could be used by simply replacing one pen with another one with the desired diameter. After the ink cartridge had been cleaned with distilled water and ethanol and then dried overnight at room temperature, it was refilled with AgNP or CNT ink by using an adjustable pipette. For the printing, we used the AgNP ink with viscosity of 14.20 cP and the CNT ink with various viscosities. In this research, cartridges with ballpoint diameters of 0.5, 0.7, and 1.0 mm were used. Contact Printing for Fabricating Paper-Based ECSs. Disposable ECSs were fabricated on the surface of photo paper by using contact printing with two ballpoint pens, one with CNT ink and the other with AgNP ink. The silica-coated paper (Epson S042187) used as a substrate remains thermally stable up to 200 °C. For lateral movement of the ballpoint pens during printing, a digital plotter was used. CNT inks containing 0.7, 1.4, and 4.1 wt % of CNTs were used to print the WEs and the CEs while AgNP ink was used to print the REs (Ag QREs) and connection pads. To observe if the concentration of CNTs had any significant impact on the
GOx
β‐D‐glucose + O2 ⎯⎯⎯→ gluconic acid + H 2O2
(1)
In the second step, H2O2 is reduced when an optimized potential is applied so that electrons are transferred to the working electrode (eq 2)12,14 H 2O2 → O2 + 2H+ + 2e−
(2)
The transfer of electrons to the surface of the working electrode generates an electric current that is proportional to the concentration of glucose in a sample solution.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsomega.8b02592. Image of the contact printing system and its preparation; schematics and SEM images for the ballpoint tip without contact pressure and with mimic contact pressure; SEM data for the ballpoint pens, SEM and EDS data for AgNP and CNT patterns; Fourier transform infrared spectrum of the AgNP pattern before and after the annealing process; electrochemical measurement setup; electrochemical characterization of the fabricated ECSs; and fabrication cost of the ECS (PDF) 16871
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Ballpoint pens printing for depositing of AgNP and CNT patterns sequentially (AVI) Programmable printing of the paper-based ECS using ballpoint pens and a digital plotter (AVI) Cutting the fabricated paper-based ECS and fluidic barriers with a cutting blade (AVI)
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Veasna Soum: 0000-0003-4164-2379 Kwanwoo Shin: 0000-0002-7563-8581 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The authors gratefully acknowledge financial support from the Basic Science Research Program (2017R1D1A1B03032095 and 2018R1A6A1A03024940) through the National Research Foundation of Korea funded by the Ministry of Science and ICT, Korea and from the Grant Program (20174010201150) funded by the Ministry of Trade, Industry and Energy, Korea.
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DOI: 10.1021/acsomega.8b02592 ACS Omega 2018, 3, 16866−16873
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DOI: 10.1021/acsomega.8b02592 ACS Omega 2018, 3, 16866−16873
