Article pubs.acs.org/ac
Inkjet Printing of Nanoporous Gold Electrode Arrays on Cellulose Membranes for High-Sensitive Paper-Like Electrochemical Oxygen Sensors Using Ionic Liquid Electrolytes Chengguo Hu,*,†,‡ Xiaoyun Bai,† Yingkai Wang,† Wei Jin,† Xuan Zhang,† and Shengshui Hu*,†,‡ †
Key Laboratory of Analytical Chemistry for Biology and Medicine (Ministry of Education), College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072, PR China ‡ State Key Laboratory of Transducer Technology, Chinese Academy of Sciences, Beijing 100080, PR China S Supporting Information *
ABSTRACT: A simple approach to the mass production of nanoporous gold electrode arrays on cellulose membranes for electrochemical sensing of oxygen using ionic liquid (IL) electrolytes was established. The approach, combining the inkjet printing of gold nanoparticle (GNP) patterns with the self-catalytic growth of these patterns into conducting layers, can fabricate hundreds of self-designed gold arrays on cellulose membranes within several hours using an inexpensive inkjet printer. The resulting paper-based gold electrode arrays (PGEAs) had several unique properties as thin-film sensor platforms, including good conductivity, excellent flexibility, high integration, and low cost. The porous nature of PGEAs also allowed the addition of electrolytes from the back cellulose membrane side and controllably produced large three-phase electrolyte/electrode/gas interfaces at the front electrode side. A novel paper-based solid-state electrochemical oxygen (O2) sensor was therefore developed using an IL electrolyte, 1-butyl-3methylimidazolium hexafluorophosphate (BMIMPF6). The sensor looked like a piece of paper but possessed high sensitivity for O2 in a linear range from 0.054 to 0.177 v/v %, along with a low detection limit of 0.0075% and a short response time of less than 10 s, foreseeing its promising applications in developing cost-effective and environment-friendly paper-based electrochemical gas sensors.
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restricted by several factors, e.g., the relative low reproducibility due to small volume and high viscosity of added ILs5a,8 and the instability of IL layers due to the uptake of atmospheric moisture altering the IL surface tension.5a Therefore, the development of suitable sensor platforms has become a great challenge for IL-based electrochemical gas sensors. Since the creation of large three-phase electrolyte/electrode/ gas interfaces is essential to the high sensitivity and rapid response of electrochemical gas sensors,10 an “ideal” gas sensor design generally has a porous and uncovered working electrode integrated with porous supports.11 This special structure allows the addition of electrolytes from the back of the working electrode to form as thin as possible electrolyte layers for creating large three-phase interfaces. Nevertheless, though a variety of porous working electrodes5b have been employed for constructing aqueous solution11 or IL-based5b gas sensors that possessed excellent long-term stability, the working electrodes are often physically separated from the counter/reference electrodes, leading to the necessity of specially designed cell
onic liquids (ILs) are of great interest in the field of electrochemical gas sensors because of their unique chemical/physical properties, e.g., wide potential windows, inherent conductivity, chemical robustness, large liquidus range, and low volatility.1 Employment of ILs as solvents can effectively overcome some limitations of aqueous or solid polymer electrolyte-based gas sensors like evaporative loss and drying out of aqueous electrolytes,2 and make possible the fabrication of membrane-free sensors.3 To date, IL-based gas sensors have been successfully applied to the electrochemical detection of various gases, including SO2,4 O2,3b,5 NO2,6 NH3,7 ethylene,8 etc. Unfortunately, the relatively low conductivity manifested by the inherently high viscosity of ILs and the much small diffusion coefficients of gas molecules in ILs usually lead to slow responses and small limiting currents.9 To overcome this deficiency, great attempts are made to facilitate the diffusion of gas analytes in IL electrolytes. The most efficient strategy involves the formation of thin IL layers on a variety of planar sensor arrays, including microfabricated electrode arrays3b,8 and conventional screen-printed carbon electrodes (SPCE).5a This strategy can produce IL layers with thicknesses up to several micrometers at the sensing interfaces and therefore effectively improve the performance of the IL-based sensors. However, the formation of ultrathin IL layers is often © 2012 American Chemical Society
Received: February 2, 2012 Accepted: March 16, 2012 Published: March 16, 2012 3745
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mL/min and 0.06−0.6 m3/h, were utilized to control the flow rate of 5.0% O2 (the O2 source) and pure N2 (the carrier gas) for preparing O2 with desired concentrations, respectively. Typically, the flow rate of the carrier gas was controlled at 0.1 m3/h except for preparing the 0.075% O2 gas at a flow rate of 0.24 m3/h. Inkjet Printing of Gold Electrode Arrays on Cellulose Membranes. An Epson R230 inkjet printer and its continuous ink supply system were employed for printing GNP patterns on cellulose membranes. The procedures for producing the inkjetprinted gold electrode arrays on cellulose membranes and for fabricating the oxygen sensor were illustrated in Scheme 1. A
houses for holding the electrolyte solutions and therefore increasing complexity of the sensors. Recently, paper-based electrochemical devices (PEDs) have attracted considerable attention in developing inexpensive and easy-use techniques for the rapid analysis of multiple-target or complex-matrix samples.12 PEDs are typically comprised of a planar three-electrode array covering on paper-based hydrophilic channels,13 which possess structures similar to a solidstate amperometric O2 sensor consisting of a three-electrode system covered by a supported IL membrane.14 Therefore, PEDs represent a very promising platform for inexpensive solid-state electrochemical gas sensors using IL electrolytes. Currently, the electrode arrays of PEDs are integrated with the paper channels either by screen printing techniques12,13c or by physical attachment.13a,b Both approaches, however, are not suitable for constructing IL-based PEDs of gas sensing. For instance, the polymeric/organic additives in the conducting inks for screen printing may dissolve in ILs while the contact between the detection arrays and the paper channels for physical attachment is hard to control. Therefore, it should be highly attractive to rapidly print highly integrated self-designed electrode arrays on flexible and porous substrates like paper for electrochemical gas sensing. In this work, a simple approach to the mass production of nanoporous gold electrode arrays on cellulose membranes by inkjet printing was established. The produced gold-paper electrode arrays are flexible, conductive, nanoporous, and highly integrated, creating an “ideal” porous thin-film sensor platform for achieving large three-phase interfaces.10,11,15 A novel paper-based solid-state electrochemical oxygen sensor was then constructed using BMIMPF6 electrolyte. The sensor looked like a piece of paper, free of housing and solution, but exhibited performance apparently better than previous IL-based oxygen sensors (Table S-1 in the Supporting Information). The present work thus demonstrated the promising applications of paper-based porous electrode arrays for developing inexpensive and simple-structured electrochemical gas sensors.
Scheme 1. Procedures of Inkjet Printing Gold Electrode Arrays on MCE Membranes for Fabricating Paper-Based Solid-State Electrochemical Oxygen Sensorsa
a
(1) Inkjet printing of GNP patterns, (2) growth of GNP patterns into gold electrode arrays, (3) cutting a PGEA from its ensembles, (4) electric connection and size control of a PGEA, and (5) addition of BMIMPF6 from the back MCE side of a PGEA to fabricate the oxygen sensor.
piece of mixed cellulose ester (MCE) membrane (diameter 100 mm, pore size 0.22 μm, Shanghai Xinya Purifier Devices Factory, China) was firmly fixed on the CD tray of the printer with adhesive tapes. Inkjet printing of the GNP patterns was then performed by EPSONCD for certain cycles (typically seven cycles), and the GNP-MCE composite was dried at 60 °C under vacuum for 1 h (step 1). A piece of 2.5 cm ×6.5 cm strip containing 45 copies of the GNP patterns was cut from the above GNP-MCE composite and placed in a 50 mL plastic vial containing the plating solution (i.e., a freshly prepared aqueous solution containing 200 μL of 0.2 M NH2OH, 400 μL of 1% HAuCl4, and 35 mL of water) for seeded growth (step 2). During each growth cycle, the GNP-MCE composites were placed in the plating solution for 15 min with gentle shaking and then thoroughly rinsed with water. The growth procedure was repeated for certain cycles (typically eight cycles) until well-defined gold patterns with good conductivity were obtained, which were dried at 60 °C under vacuum for half an hour. For a typical three-electrode gold array, the diameter of the working electrode was 2.0 mm and the width of the counter and reference electrodes was 0.5 mm. More details involving the design and the printing of the GNP patterns can be found in the Supporting Information (Figure S-1). Fabrication of Paper-Based Solid-State Electrochemical Oxygen Sensor. A single gold electrode array was cut from the above gold electrode arrays (step 3), and three thin copper wires were attached to the conducting areas of the
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EXPERIMENTAL SECTION Chemicals. Chloroauric acid (HAuCl4·4H2O), hydroxylammonium chloride (NH2OH·HCl), trisodium citrate dehydrate (cit), potassium ferricyanide (K3Fe(CN)6), and sodium dodecyl sulfate (SDS) were purchased from Sinopharm Chemical Reagent Co. Ltd., China. Ferrocene (Fc) was obtained from Fluka. BMIMPF6 was the product of Hangzhou Chemer Chemical Co. Ltd., China. Nitrogen (N2, purity >99.9%) and oxygen (5.0% O2 in high-purity N2) were purchased from WISCO Oxygen, Wuhan, China. The GNP ink used for the inkjet printing of the GNP patterns was prepared according to Li et al.16 with slight modifications (see the Supporting Information). All the chemicals were of analytical grade and used as received without further purification. The water used was doubly distilled. Instrumentation. All electrochemical measurements were performed on a CHI 660B analyzer (CH Instruments, Shanghai, China). UV spectra were obtained on a Tu-1901 spectrometer (Purkinje, Beijing, China). SEM images were obtained on a Sirion 200 microscope (FEI, Holland). XRD measurements were carried out on XRD-2000X (Shimadzu, Japan). The conductivity was measured by a two-electrode method17 using a DT-830 multimeter (UniVolt, Japan). Two rotor flowmeters (LZB, Tianjin Liuliang Instrument and Meters Factory, China), with flow rates varying in the range of 6.0−60 3746
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Figure 1. Photos of an Epson R230 printer (A), the original GNP solution (B), the condensed GNP solution (C), the gold-MCE composite of a Chinese dragon pattern (H), and the conducting test of the gold-MCE composite (I). Parts D and E show the TEM images of the synthesized and the condensed GNPs, respectively. Part F represents the UV absorptions of the synthesized (curve a) and the condensed GNP solutions (curve b). Part G shows the Chinese dragon pattern designed by Photoshop 7.0 in magenta color. The GNP solutions for UV measurements were diluted 10fold with 1.0 mM SDS before use.
Figure 2. SEM images of MCE (A), the GNP-MCE composite (B), the GNP-MCE composites with 1, 2, 3, 5, and 8 cycles of growth (C−G), and the cross-section view of a GNP-MCE composite with 8 cycles of growth (H). The inset shows the amplified SEM image of each sample. The GNP seeds on MCE appearing as tiny white particles are indicated by an arrow in part B.
printed devices.18 A similar printer has been utilized by Yu et al. for constructing gold arrays on gold coated glass sides or compact discs via a wet etching method.19 For the synthesis of the GNP inks, a two-step method reported by Li et al. was selected.16 This method is able to greatly enhance the concentration of GNPs synthesized by the typical citrate reduction method20 (Figure 1B,C) but hardly influence their diameter (about 13 nm) and monodisperison (Figure 1D,E). UV spectra revealed that the GNP solution was condensed for about 17 times as compared with the original solution (Figure 1F). As a proof-of-concept application of this inkjet printing technique, a Chinese gold dragon was fabricated on a MCE membrane (Figure 1G−I). The produced gold-MCE hybrid film exhibits several unique properties for practical applications, e.g., excellent flexibility (Figure 1H), good conductivity (Figure 1I), and low cost. This technique is also applicable to other planar substrates like plastics or glass except that the adhesion of the gold patterns on these substrates is much weaker and can
electrode arrays with silver paste for electric connection (step 4). Considering the porous nature of both the gold electrode array and the supporting MCE membrane, the size of the goldMCE composite was precisely controlled to 4.5 mm × 6.0 mm with epoxy glue. Then, a drop of BMIMPF6 was placed on the back MCE side with a microsyringe and was allowed to reach equilibrium at room temperature for 1 h, producing a housing/ solution-free and paper-like solid-state electrochemical oxygen sensor (step 5).
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RESULTS AND DISCUSSION Inkjet Printing of Gold Conducting Patterns on MCE Membranes. An Epson R230 inkjet printer was selected for inkjet printing because of its Print-CD function (Figure 1A). This function allows the repeated printing of self-designed patterns on its CD support with high speed and excellent reproducibility and thus effectively overcomes the dilemma between printing resolution and surface loading for inkjet3747
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be easily erased (Figure S-2 in the Supporting Information). In contrast, the gold patterns strongly adhered to the MCE film and could be hardly scratched away. Therefore, the advantages of the paper-based gold arrays, together with the merits of inkjet printing (e.g., user-designable patterns, fast and easy fabrication, being contactless and template-free, etc.), provide a simple but efficient approach to the mass production of inexpensive and robust thin-film electronics. Characterization of Inkjet-Printed Gold Layers on MCE Membranes. The growth mechanism of the gold conducting layers on MCE was monitored by SEM images (Figure 2). It is clear that no apparent structural difference exists between the naked (A) and the GNP-coated MCE (B) except for the presence of some tiny particles of about 13 nm on the surface of the GNP-MCE composite, well consistent with the GNP size observed in the TEM images. These GNP seeds are rapidly enlarged but their quantity hardly changes by growing in the plating solution, demonstrating the self-catalytic reduction mechanism of GNP growth (C−E). Moreover, obvious interconnections between adjacent GNPs occur after five cycles of growth (F), and a continuous GNP conducting layer is completely formed after eight cycles of growth (G). Figure 2H shows the cross-section image of the gold-MCE composite. Surprisingly, the GNPs go as deep as about 6 μm into the MCE network, a distance much larger than the actual conducting thickness of the GNP layer (about 0.5 μm), suggesting the possible diffusion movement of the GNPs in the MCE network during printing. The formation of ultrathin gold layers on MCE, together with the material-saving inkjet printing techniques, greatly reduces the cost of the paperbased gold arrays. The XRD pattern of the gold layers on MCE exhibited three peaks at 38.0°, 44.3° and 64.5° (Figure S-3 in the Supporting Information), which can be assigned to the (111), (200), and (220) diffraction peaks of fcc gold metal.21 Moreover, the intensity ratio between the (200) and the (111) diffractions is about 0.30, a value apparently smaller than the bulk value (≈0.53) but very close to that of icosahedron-shaped GNPs (i.e., 0.31).22 Therefore, the combination of inkjet printing with the seeded growth of GNPs can exceptionally fabricate naked and nanoporous gold conducting layers on porous substrates like cellulose membranes. Both printing and growth cycles were proved to apparently lower resolution and improve conductivity of the resulting paper-based electrode arrays (Figure S-4 in the Supporting Information). Specifically, the average electrical resistivity (ρ) of six gold strips (0.5 mm ×17.5 mm) with seven printing cycles and eight growth cycles was 2.37 × 10−7 Ω m, about 1/ 10th of the resistivity of bulk gold (i.e., 2.40 × 10−8 Ω m). In addition, this technique is able to fabricate conducting lines as thin as 0.3 mm with intervals of about 0.25 mm (Figure S-5 in the Supporting Information). It should be pointed out that though some other inkjet printing techniques have been developed for constructing metal23 or carbon-based electronics,18b the produced conducting layers are usually solid or partially covered by insulated protection reagents, which are not suitable for creating large three-phase electrolyte/ electrode/gas interfaces. Electrochemical Performance of PGEAs. The present inkjet printing technique is able to produce PGEAs on MCE on a large scale with high efficiency and low cost. As shown in Figure 3A, more than 200 patterns of electrode arrays are printed within half an hour on a 100 mm MCE membrane, which can be readily converted to usable gold electrode arrays
Figure 3. Photos of the printed GNP patterns (A) and the gold electrode arrays on MCE membranes (B). Part C shows the different detection modes (upper) and the corresponding cyclic voltammograms (lower) of PGEAs using different working solutions containing 0.1 M KCl and 5.0 mM K3Fe(CN)6: (a−d) 10.0 mL of solution in an electrochemical cell, (e) a drop of 2.0 μL of solution on the front surface of PGEAs. The reference electrodes of the voltammograms are indicated in the detection modes.
within 2 h by self-catalytic growth,24 at a cost of less than $0.1 for each electrode array using no special apparatus. Moreover, the size, shape, and composition of the electrode arrays can be easily modified on computers according to practical requirements. The printed PGEAs possess a well-defined shape, excellent flexibility, and mechanical strength as good as the substrate membranes (Figure 3B). To evaluate the electrochemical performance of the PGEAs, the cyclic voltammograms of an individual array under different three-electrode working modes were examined (Figure 3C). Clearly, when a saturated calomel electrode (SCE) was employed as the reference electrode, the gold electrode array produced a pair of welldefined redox waves in 5.0 mM K3Fe (CN)6 using either a Pt wire counter electrode (curve a) or the gold counter electrode of the array (curve b). As expected, the replacement of a SCE reference electrode by the short strip of the gold arrays led to a 257 mV negative shift of the formal potential of K3Fe(CN)6 (defined as the average potential of the redox peaks) (curves c and d), similar to the potential shift by changing the reference electrode from a Ag/AgCl electrode to a pseudoreference unmodified gold.25 Moreover, the replacement of the Pt wire counter electrode by the counter strip of the array hardly influenced the voltammetric responses (curves a−d). When 2.0 μL of 5.0 mM K3Fe(CN)6 solution was placed on the front gold surface of a PGEA, a couple of well-shaped peaks were also observed (curve e). The roughness factor of PGEAs estimated by integration of the gold oxide reduction peak according to Hoogvliet et al.26 is about 7.3 (Figure S-6 in the Supporting Information). Therefore, the PGEAs with configurations similar to traditional screen-printed electrodes (SPEs) can act as a disposable and environment-friendly SPE platform with high 3748
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result showed that the highest reduction current of O2 was obtained for 1.2 μL of BMIMPF6 when the volume of BMIMPF6 changed from 0.4 to 2.0 μL. Therefore, the thickness of IL layers on the surface of the porous electrode array may be finely tuned by simply changing the volume of the added ILs (Figure S-8 in the Supporting Information), which establishes an “ideal” three-phase electrolyte/electrode/gas interface10 for the electrochemical sensing of O2. No liquid was observed on the surface of the PGEA within this IL volume range, creating a chance for constructing paper-based housing/solution-free electrochemical gas sensors with high integration and low cost. Amperometric Response of Oxygen at PGEAs Using IL Electrolytes. For the electrochemical sensing of trace O2 in a nitrogen atmosphere, a piece of the O2 sensor was placed in the channel of a homemade gas mixer (Figure 5A). The sensor
surface area for electrochemical sensors. Meanwhile, as both the supporting MCE membrane and the conducting gold layer are porous, the PGEAs may work as a highly integrated platform for developing solution-free thin-film electrochemical sensors when suitable nonvolatile liquid or solid electrolytes (e.g., ionic liquids3a and Nafion27) are employed. Electrochemical Behaviors of Oxygen at PGEAs Using IL Electrolytes. The electrochemical behavior and sensitive sensing of O2 in ionic liquids have been extensively studied by Compton3a,b,28 and Ohsaka14,29 because of its importance in clinical diagnosis, environmental monitoring, fuel cell technology, etc.5b Their works indicated that the use of ionic liquid as an electrolyte eliminates the need for a membrane and added supporting electrolyte, but the slower diffusion of analyte within the more viscous medium results in slower time responses.3a Here, a drop of 1.0 μL of BMIMPF6 containing 50.0 mM Fc as an internal reference3b was placed onto the back MCE side of a PGEA, which is supposed to form a uniform thin layer on the surface of both MCE and the gold nanoparticles. The resulting PGEA-based oxygen sensor exhibits a highly sensitive response at negative potentials for oxygen in air as compared with that in a nitrogen atmosphere (Figure 4A). The
Figure 5. (A) Schematic structure of a homemade gas mixing setup for the electrochemical sensing of oxygen. (B) Amperometric responses of oxygen at the sensor using 1.0 μL of BMIMPF6 electrolyte. Applied potential, −1.4 V vs Au.
exhibited a sensitive and fast response for O2 with good reproducibility and stability (Figure 5B). The reduction current of O 2 possessed a good linear relationship with its concentration in the range of 0.054−0.177% (i (μA) = 6.056[%O2] − 0.028, R = 0.9976) and a low detection limit of 0.0075% (Figure S-9 in the Supporting Information). Moreover, the response time is less than 10 s (Figure S-10 in the Supporting Information), which is apparently shorter than either membrane-dependent14 or membrane-free3b ionic liquidbased electrochemical gas sensors. Besides, the sensor possessed good reproducibility, reflected by a low relative standard deviation (RSD) of 3.22% for the response of 0.0275% O2 on three different electrodes. Rogers et al. have proved the insolubility of cellulose materials in a “noncoordinating” anion-based ionic liquid like BMIMPF6.31 This, in combination with the nonvolatile nature of ionic liquid-based electrolytes and the good electrochemical stability of the gold electrode arrays in BMIMPF6 (Figure S-11 in the Supporting Information), ensures the good stability of this paper-based electrochemical gas sensor. Actually, the signal variation of 0.0275% O2 for four measurements within 40 h was about 4.6%. The selectivity of the oxygen sensor toward several typical gaseous species was examined (Figure S-12 in the
Figure 4. (A) Cyclic voltammograms of the oxygen sensor in air and in a nitrogen atmosphere using 1.0 μL of BMIMPF6 containing 50.0 mM Fc as the electrolyte. (B) Influence of IL volume on cyclic voltammograms of the oxygen sensor in air. The inset shows the variation of the reduction current of oxygen at −1.4 V vs Au with IL volume. Scan rate, 100 mV/s.
apparent difference of voltammograms in IL electrolytes with and without degassing by dry N2, i.e., the great decrease of the background and the redox currents as well as the disappearance of the reduction peak at −0.5 V likely associated with O2,29 has been proven to arise from the removal of trace water and O2 in the IL electrolyte during degassing.30 Moreover, the type of ILs was found to apparently influence the response of O2, reflected by the greatly repressed reduction current by increasing the side chain of the cations in ILs (Figure S-7 in the Supporting Information). A similar result has been reported by Zeng et al. for changing the cation type of ILs.5b The influence of electrolyte volume on the voltammetric response of the sensor in air was examined (Figure 4B). The 3749
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(6) Nadherna, M.; Opekar, F.; Reiter, J. Electrochim. Acta 2011, 56, 5650−5655. (7) Ji, X. B.; Banks, C. E.; Silvester, D. S.; Aldous, L.; Hardacre, C.; Compton, R. G. Electroanalysis 2007, 19, 2194−2201. (8) Zevenbergen, M. A. G.; Wouters, D.; Dam, V. A. T.; Brongersma, S. H.; Crego-Calama, M.. Anal. Chem. 2011, 83, 6300−6307. (9) Jin, H.; Baker, G. A.; Arzhantsev, S.; Dong, J.; Maroncelli, M. J. Phys. Chem. B 2007, 111, 7291−7302. (10) Winther-Jensen, B.; Winther-Jensen, O.; Forsyth, M.; MacFarlane, D. R. Science 2008, 321, 671−674. (11) Simmonds, M. C.; Hitchman, M. L.; Kheyrandish, H.; Colligon, J. S.; Cade, N. J.; Iredale, P. J. Electrochim. Acta 1998, 43, 3285−3291. (12) Dungchai, W.; Chailapakul, O.; Henry, C. S. Anal. Chem. 2009, 81, 5821−5826. (13) (a) Nie, Z. H.; Nijhuis, C. A.; Gong, J. L.; Chen, X.; Kumachev, A.; Martinez, A. W.; Narovlyansky, M.; Whitesides, G. M. Lab Chip 2010, 10, 477−483. (b) Carvalhal, R. F.; Kfouri, M. S.; Piazetta, M. H. D.; Gobbi, A. L.; Kubota, L. T. Anal. Chem. 2010, 82, 1162−1165. (c) Apilux, A.; Dungchai, W.; Siangproh, W.; Praphairaksit, N.; Henry, C. S.; Chailapakul, O. Anal. Chem. 2010, 82, 1727−1732. (14) Wang, R.; Okajima, T.; Kitamura, F.; Ohsaka, T. Electroanalysis 2004, 16, 66−72. (15) Hodgson, A. W. E.; Jacquinot, P.; Hauser, P. C. Anal. Chem. 1999, 71, 2831−2837. (16) Liang, Z.; Zhang, J.; Wang, L.; Song, S.; Fan, C.; Li, G. Int. J. Mol. Sci. 2007, 8, 526−532. (17) Layani, M.; Gruchko, M.; Milo, O.; Balberg, I.; Azulay, D.; Magdassi, S. ACS Nano 2009, 3, 3537−3542. (18) (a) Abe, K.; Suzuki, K.; Citterio, D. Anal. Chem. 2008, 80, 6928−6934. (b) Shin, K. Y.; Hong, J. Y.; Jang, J. Adv. Mater. 2011, 23, 2113−2118. (19) Li, Y. C.; Li, P. C. H.; Parameswaran, M.; Yu, H. Z. Anal. Chem. 2008, 80, 8814−8821. (20) Grabar, K. C.; Freeman, R. G.; Hommer, M. B.; Natan, M. J. Anal. Chem. 1995, 67, 735−743. (21) Kwon, K.; Lee, K. Y.; Lee, Y. W.; Kim, M.; Heo, J.; Ahn, S. J.; Han, S. W. J. Phys. Chem. C 2006, 111, 1161−1165. (22) Kim, F.; Connor, S.; Song, H.; Kuykendall, T.; Yang, P. Angew. Chem. 2004, 116, 3759−3763. (23) Magdassi, S.; Grouchko, M.; Berezin, O.; Kamyshny, A. ACS Nano 2010, 4, 1943−1948. (24) Xu, J. H.; Hu, C. G.; Ji, Y. P.; Hu, S. S. Electrochem. Commun. 2009, 11, 764−767. (25) Parker, C. O.; Lanyon, Y. H.; Manning, M.; Arrigan, D. W. M.; Tothill, I. E. Anal. Chem. 2009, 81, 5291−5298. (26) Hoogvliet, J. C.; Dijksma, M.; Kamp, B.; van Bennekom, W. P. Anal. Chem. 2000, 72, 2016−2021. (27) Opekar, F.; Stulík, K. Anal. Chim. Acta 1999, 385, 151−162. (28) (a) Huang, X.-J.; Rogers, E. I.; Hardacre, C.; Compton, R. G. J. Phys. Chem. B 2009, 113, 8953−8959. (b) Barnes, A. S.; Rogers, E. I.; Streeter, I.; Aldous, L.; Hardacre, C.; Wildgoose, G. G.; Compton, R. G. J. Phys. Chem. C 2008, 112, 13709−13715. (29) Islam, M. M.; Ohsaka, T. J. Phys. Chem. C 2008, 112, 1269− 1275. (30) Zhao, C.; Bond, A. M.; Compton, R. G.; O’Mahony, A. M.; Rogers, E. I. Anal. Chem. 2010, 82, 3856−3861. (31) Swatloski, R. P.; Spear, S. K.; Holbrey, J. D.; Rogers, R. D. J. Am. Chem. Soc. 2002, 124, 4974−4975.
Supporting Information). The results indicated that CO2, H2, and NH3 had sensitivity of about 16.5%, 4.7%, and 28.8% compared with oxygen in air. The employment of suitable electrocatalysts5a or IL electrolytes5b may help further improve selectivity of the sensor. Considering the low concentration of CO2 and NH3 in expiratory gas and the serious interference from H2O,30 this sensor was applied to the detection of O2 content in dry expiratory gas using a homemade gas collection system (Figure S-13 in the Supporting Information). The result indicated that the sensor possessed a sensitive, rapid, and reproducible response for the real time monitoring of O2 in dry gases.
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CONCLUSIONS In summary, a simple approach to the mass production of nanoporous gold electrode arrays on porous cellulose membranes was established. The approach, taking advantage of inkjet printing, was able to produce paper-based gold electrode arrays (PGEAs) in large scale using only inexpensive inkjet printers. The resulting PGEAs possessed several unique properties for developing thin-film electrochemical gas sensors, e.g., good conductivity, excellent flexibility, simple component, and low cost. The use of ionic liquids as electrolytes for PGEAs produced a paper-based solid-state electrochemical oxygen sensor, which looked like a piece of paper but possessed analytical performance better than previous IL-based electrochemical oxygen sensors. The present work thus demonstrates the promising applications of paper-based porous electrode arrays in electrochemical gas sensing.
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ASSOCIATED CONTENT
S Supporting Information *
Additional information as noted in text. This material is available free of charge via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*Phone: +86-27-87881642. Fax: +86-27-68754067. E-mail:
[email protected] (C.H.);
[email protected] (S.H.). Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS We thank the financial support of the National Nature Science Foundation of China (Grant Nos. 20805035, 31070885, and 90817103).
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