AgCl

Technical Note pubs.acs.org/ac

Simple On-Plastic/Paper Inkjet-Printed Solid-State Ag/AgCl Pseudoreference Electrode Everson Thiago Santos Gerôncio da Silva,†,§ Sandrine Miserere,† Lauro Tatsuo Kubota,§ and Arben Merkoçi*,†,‡ †

Nanobioelectronics & Biosensors Group, Catalan Institute of Nanoscience and Nanotechnology, 08193, Bellaterra, Barcelona, Spain Catalan Institution for Research and Advanced Studies (ICREA), 08010, Barcelona Spain § Department of Analytical Chemistry, Institute of Chemistry−UNICAMP, P.O. Box 6154, 13084-974, Campinas, São Paulo, Brazil ‡

S Supporting Information *

ABSTRACT: A miniaturized, disposable, and low cost Ag/AgCl pseudoreference electrode based on inkjet printing has been developed. Silver ink was printed and chlorinated with bleach solution. The reference electrodes obtained in this work showed good reproducibility and stability during at least 30 min continuous measurement and even after 30 days storage without special care. Moreover, the strategy used in this work can be useful for large scale production of a solid-state Ag/ AgCl pseudoreference electrode with different designs and sizes, facilitating the coupling with different electrical/electrochemical microsensors and biosensors.

O

rapidity of manufacturing and good performance during their intended lifetime. However, this fabrication process is almost incompatible with large-scale production due to the need of electrochemical formation of AgCl layer in each electrode. Herein, we describe a low cost method for the construction of solid-state Ag/AgCl pseudoreference electrode that allows the easy large-scale production and the use of different substrates and designs.

ne of the most important components of electrochemical sensors is the reference electrode (RE). In the past few years, a lot of effort has been made to miniaturize the RE and facilitate its coupling with microsensors and lab-on-a-chip devices for point-of-care diagnostics.1−3 Among the reference electrodes studied, the Ag/AgCl is so far the most common type of RE used for miniaturization, mainly due to the simplicity of construction, safety, and great stability. In this context, some studies have been dedicated to obtain a microfabricated Ag/AgCl RE with filling solution1,4,5 or all solid-state reference electrodes (SSREs) that have a gel or solid junction.6−8 Among these works, screen printed Ag/AgCl reference electrode, generally printed on paper substrates or polyethylene terephthalate (PET) is the most common SSRE used for miniaturized electrochemical devices and sensors.9−11 However, screen printing technique have some drawbacks such as large amount of wastage material, difficulty to change the design, low resolution and it is suitable only for nonfragile substrates due to its contact mode of printing.12 In this regard, the inkjet printing technique can be considered as a great alternative for Ag/AgCl reference electrodes fabrication due to its low cost, simplicity, reduced material wastage, noncontact technique, maskless approach, rapid prototyping, applicability to various substrates, and the use of inks with low viscosity.12−14 Recently, a new class of SSREs without solid junction has been fabricated by inkjet printing of silver ink followed by electrochemical formation of the AgCl layer.15,16 This type of RE, also called pseudoreference electrode (p-RE), is very attractive due to the simplicity and © XXXX American Chemical Society

■

EXPERIMENTAL SECTION In this work both PET and Whatman (no. 1) chromatographic papers were used as substrates to demonstrate the viability of the proposed method for construction of Ag/AgCl p-RE using platforms with different structures and composition. First, a silver nanoparticle ink (20 wt % in ethylene glycol from SigmaAldrich) was inkjet-printed onto each substrate by using a piezoelectric Dimatix Materials Printer (DMP-2800, Fujifilm Dimatix, Inc., Santa Clara, CA) in ambient conditions (Figure 1a) and cured at 120 °C for 20 min (see more details about the inkjet parameters and experimental procedure in the Supporting Information).

■

RESULTS AND DISCUSSION For the formation of the AgCl layer, a simple immersion under commercial bleach solution without dilution (NaClO, 40 mg Received: August 14, 2014 Accepted: October 6, 2014

A

dx.doi.org/10.1021/ac503029q | Anal. Chem. XXXX, XXX, XXX−XXX

Analytical Chemistry

Technical Note

particles of approximately 50 nm (SEM images of paper substrate shown in the Supporting Information). After the chemical reaction in bleach solution, the part of the electrode in contact with the solution became dark purple (Figure 2c) and the nanoparticles became bigger (more than 200 nm), probably due to the formation of silver chloride particles (Figure 2b). The same results were observed when the electrochemical treatment was performed (see the Supporting Information), highlighting the similarity of the results obtained by both methods. Similar results were presented in the literature showing the increase of particle size as an indication of the AgCl layer formation.18 The formation of AgCl layer was confirmed by energydispersive X-ray spectroscopy (EDX), as it can be seen in Figure 2d. As it can be observed, for the silver electrode (black line) only signals relative to Ag particles were observed. However, for Ag/AgCl electrodes (red line), an additional peak can be seen which is related to the presence of chlorides on the surface. Similar results were observed when paper was used as a substrate (see Figure S6 in the Supporting Information). These results showed that the AgCl layer was successfully obtained by simple chemical chlorination in bleach solution. The performance of the p-REs inkjet printed on PET and paper substrates was evaluated by chronopotentiometry in KCl 3.0 mol L−1 versus a commercial Ag/AgCl reference electrode with liquid junction (acquired from CH Instruments). A screen printed reference electrode (SPRE, Acheson Electrodag 6037SS silver/silver chlorade ink) was used as a standard to compare the results obtained with the p-REs proposed. Figure 3 shows the potential stability against a commercial Ag/AgCl∥KCl 3.0 mol L−1, in triplicate, of inkjet printed Ag/

Figure 1. (a) Inkjet printing machine and the printing process of Ag ink with the piezoelectric nozzle. (b) Chlorination steps in bleach solution to form the Ag/AgCl electrode.

mL−1) for a short time (up to 5 min) was performed (Figure 1b). In both substrates, it was possible to observe the change of color from silver to dark purple, indicating the formation of the AgCl layer (Figures 1b and 2c) as already reported in the

Figure 2. SEM images obtained from the (a) silver electrode surface printed on the PET substrate and (b) after AgCl layer formation by immersing in bleach solution for 1 min. (c) Photo of the electrode and (d) the EDX analysis, before and after the chemical chlorination.

Figure 3. Chronopotentiometric analysis of the p-RE inkjet printed on PET and on paper followed by chlorination with bleach solution (SPRE used to compare) against the commercial Ag/AgCl∥KCl 3.0 mol L−1.

literature.16,17 It indicates that the proposed method can produce an AgCl layer without the need of sophisticated equipment, besides it can be performed in various electrodes and/or devices at the same time. After immersing the electrodes in bleach for a short period of time (between 30 and 300 s), they were washed with deionized water and dried by nitrogen stream. Images obtained from scanning electron microscopy (SEM) before and after chlorination of electrodes are presented in Figure 2, where it is possible to observe the modification of the electrode surface after the chemical treatment. For the inkjetprinted silver electrode presented in Figure 2a it is possible to observe a very homogeneous film formed by silver nano-

AgCl p-electrodes on PET and paper, and of SPRE used as standard. As it can be observed, there is no significant difference between electrodes produced by inkjet printing and by screen printing, which highlights the reliability of the proposed p-RE. All the open circuit potential (OCP) values measured were less than 3 mV off the ideal value of zero, and this small error may be attributed to slight differences in the chloride activity in the test solution and the commercial reference filling solution, or to an uncertain junction potential. B



Technical Note

and to highlight the fact that this technique may be used for substrates of different types and porosities. The results obtained have shown that the proposed p-RE can be used during at least 30 min of measurement (see the Supporting Information) that is more than the necessary for the most of electrochemical analysis, and its operation is relatively stable even after 30 days stored in dark environments. The use of bleach solution for the chemical formation of AgCl layer allows the easy development of a solid-state p-RE with possibility of large-scale production, which is very important to turn this product commercial as well as to facilitate the fabrication process.

Storage stability of the p-RE proposed in this work was also evaluated by chronopotentiometry against a commercial Ag/ AgCl∥KCl 3.0 mol L−1 and the results are presented in Figure 4. For this experiment, a p-RE with an AgCl layer obtained

■

ASSOCIATED CONTENT

S Supporting Information *

Experimental procedures, inkjet parameters, characterization of the p-RE inkjet printed on paper, and characterization of the pRE prepared electrochemically. This material is available free of charge via the Internet at http://pubs.acs.org.

■

Figure 4. Storage stability of the p-RE inkjet printed on PET followed by chlorination in bleach solution for 60 s by chronopotentiometry against a commercial Ag/AgCl∥KCl 3.0 mol L−1. An electrochemically produced p-RE was used for the sake of comparison.

AUTHOR INFORMATION

Corresponding Author

*Phone: +34 937 37 4604. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

■

electrochemically (details in the Supporting Information) was used as a standard to compare and prove the viability of using bleach solution to produce Ag/AgCl p-RE. Figure 4 shows the stability of the p-REs printed on PET during 30 days of storage in dark conditions and without other special care. In the graphic presented it is possible to observe that the p-REs produced in this work were very stable even after 15 days of storage, with ΔE < 0.003 V against commercial Ag/AgCl. A small change was observed after 30 days, where the potential against commercial Ag/AgCl increased to approximately 0.005 V for the p-RE produced with bleach solution (also observed for p-RE produced electrochemically). However, in some cases as when, for example, overpotential is applied, this slight increase of ΔE did not affect the final results, and the p-RE can be used without problems even after storing during 30 days. As it was expected, no significant difference was observed for the electrodes produced by the different techniques (chemical with bleach and electrochemical), which indicates that the proposed method of chlorination may simulate very well the most common method reported in the literature (electrochemical method) with the advantage of lower cost and possibility of large scale production. In addition, different materials can be printed with the inkjet printing technology, including metal nanoparticles,12 conductive polymers,19 and graphene,20 which can act as a WE, and other,21 as long as the particle size is below 200 nm, and the solution viscosity range from 10 to 12 cPs. Therefore, a complete electrochemical point-of-care device can be constructed in different substrates using this technique, including a reliable Ag/AgCl p-RE.

ACKNOWLEDGMENTS This work was supported by EU through FP7 “SMS” project (contract number 613844) and the National Council for Scientific and Technological Development, CNPq−Brazil.

■

REFERENCES

(1) Mroz, A.; Borchardt, M.; Diekmann, C.; Cammann, K.; Knoll, M.; Dumschat, C. Analyst 1998, 123, 1373−1376. (2) Wongkaew, N.; Kirschbaum, S. E. K.; Surareungchai, W.; Durst, R. A.; Baeumner, A. J. Electroanalysis 2012, 24 (10), 1903−1908. (3) Zhou, J.; Ren, K.; Zheng, Y.; Su, J.; Zhao, Y.; Ryan, D.; Wu, H. Electrophoresis 2010, 31, 3083−3089. (4) Kakiuchi, T.; Yoshimatsu, T.; Nishi, N. Anal. Chem. 2007, 79, 7187−7191. (5) Noh, J.; Park, S.; Boo, H.; Kim, H. C.; Chung, T. D. Lab Chip 2011, 11, 664−671. (6) Vonau, W.; Oelßner, W.; Guth, U.; Henze, J. Sens. Actuators, B 2010, 144, 368−373. (7) Thomas, H.; Heide, R.; Terfort, A. Sens. Actuators, B 2012, 171− 172, 155−164. (8) Mousavi, Z.; Granholm, K.; Sokalski, T.; Lewenstam, A. Analyst 2013, 138, 5216−5220. (9) Lan, W.-J.; Maxwell, E. J.; Parolo, C.; Bwambok, D. K.; Subramaniam, A. B.; Whitesides, G. M. Lab Chip 2013, 13, 4103− 4108. (10) Rattanarat, P.; Dungchai, W.; Cate, D.; Volckens, J.; Chailapakul, O.; Henry, C. S. Anal. Chem. 2014, 86, 3555−3562. (11) Rivas, L.; Escosura-Muñiz, A.; Pons, J.; Merkoçi, A. Electroanalysis 2014, 26, 1287−1294. (12) Kamyshny, A.; Steinke, J.; Magdassi, S. Open Appl. Phys. J. 2011, 4, 19−36. (13) Kralovaa, M.; Dzika, P.; Veselya, M.; Cihlar, J. Catal. Today 2014, 230, 188−196. (14) Tang, W.; Feng, L.; Zhao, J.; Cui, Q.; Chen, S.; Guo, X. J. Mater. Chem. C 2014, 2, 1995−2000. (15) Jin, X.; Lu, J.; Liu, P.; Tong, H. J. Electroanal. Chem. 2003, 542, 85−96. (16) Maattanen, A.; Vanamo, U.; Ihalainen, P.; Pulkkinen, P.; Tenhu, H.; Bobacka, J.; Peltonen, J. Sens. Actuators, B 2013, 177, 153−162.

■

CONCLUSION In conclusion, we demonstrated in this work the construction of a simple, low cost, and disposable Ag/AgCl pseudoreference electrode by using an inkjet printing machine. PET and chromatographic paper (Whatman no. 1) were used as substrates because these materials have been widely used in recent years for the construction of point-of-care testing devices C



Technical Note

(17) Dickinson, J. W.; Bromley, M.; Andrieux, F. P. L.; Boxall, C. Sensors 2013, 13, 3635−3651. (18) Ha, H.; Payer, J. Electrochim. Acta 2011, 56, 2781−2791. (19) Kim, Y. H.; Sachse, C.; Machala, M. L.; May, C.; MullerMeskamp, L.; Leo, K. Adv. Funct. Mater. 2011, 21, 1076−1081. (20) Li, J. T.; Ye, F.; Vaziri, S.; Muhammed, M.; Lemme, M. C.; Ostling, M. Adv. Mater. 2013, 25, 3985−3992. (21) Sánchez, M. M.; Domingo, C. M.; Ramon, E.; Merkoçi, A. Adv. Funct. Mater. 2014, DOI: 10.1002/adfm.201401180.

D


AgCl

Recommend Documents