Inkjet Printing of Nanoporous Gold Electrode Arrays on Cellulose. Membranes for High-Sensitive Paper-Like Electrochemical Oxygen

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1 Supporting Information 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, Shengshui Hu*,, Key Laboratory of Analytical Chemistry for Biology and Medicine (Ministry of Education), College of Chemistry and Molecular Sciences, Wuhan University, Wuhan , PR China State Key Laboratory of Transducer Technology, Chinese Academy of Sciences, Beijing , PR China Preparation of GNP inks. Briefly, 160 ml of doubly distilled water was added to a 250-mL round flask and heated to 90 C, followed by adding 1.6 ml of 1.0 wt% HAuCl 4 and heating to 96 C. Then, 5.6 ml of 1.0 wt% cit was added within 1 min and the resulting mixture was stirred for 15 min at 96 C. During this period, the color of the solution gradually changed from light yellow to dark wine red, which was naturally cooled to room temperature. Then, 400 ml of the original GNP solution was stored in a freezer at 4 C for more than an hour and immediately centrifuged at rpm for 20 min. The red blackish slurry at the bottom was collected and redissolved in 10 ml of 1.0 mm SDS aqueous solution with mild sonication, which was passed through a 0.22-μm cellulose membrane to remove any large particles and stored under darkness at room temperature. Inkjet printing of GNP patterns on MCE membranes. The printer and its continuous ink supply system were thoroughly washed with distilled water before use, in order to completely remove any possible contaminants that may cause precipitation of the high-concentration GNP ink. Then, the GNP ink was placed into the corresponding ink cartridge related to the color of the designed pattern (Figure S-1). The rest of the ink cartridges were either empty or filled with distilled water. S1

2 Repeated printing was performed on a disposable white paper fixed on the CD tray to eliminate any residual water in the printing system until the pink GNP ink was printed out. Then, the white paper was replaced by a target MCE membrane for printing the desired GNP patterns (Figure S-1). When the printing process was finished, the whole printing system was thoroughly washed by repeated printing, firstly with water and then ethanol, using other clean ink supply systems. This step was carried out to remove residual GNP solutions and to avoid the possible clogging of the nozzles by dry GNPs. Figure S-1. Procedures for fabricating self-designed and inkjet-printed gold patterns on MCE membranes: (1) introduce/design a desired pattern in a file of Photoshop 7.0; pick up the selection area of the pattern by the Magic Wand Tool and transfer the selection to a new file; (2) fill the selection patterns with the color corresponding to the cartridge containing the GNP inks using the Color Picker tool, e.g., filling with magenta by setting cyan (C) 0%, magenta (M) 100%, yellow (Y) 0% and black (K) 0% if the GNP ink was placed in the magenta cartridge; (3) save the file of the magenta pattern as a jpg formatted file by Photoshop 7.0 and convert the file into the format of the EPSONCD software; then, carry out inkjet printing using EPSONCD. Figure S-2. Photos of inkjet-printed gold patterns on plastics (A) and glass (B). S2

3 Figure S-3. XRD spectra of MCE (a), the GNP-MCE composite (b) and the gold-mce composite with 8 cycles of growth (c). Insets show the TEM image of a single GNP from the gold-mce sample (left) and its icosahedron-shaped mode indicated by the XRD spectra (right). Figure S-4. Influences of printing (A, C) and growth cycles (B, D) on width (A, B) and resistance (C, D) of the inkjet-printed gold strips. Detailed information about the test samples is as follows: A. designed line width, 2px; print cycle, 1-28; growth cycle, 1; B. designed line width, 2px; print cycle, 15; growth cycle, 1-10; C. gold strip size, 0.28mm 20mm after print and growth; print cycle, 9-16; growth cycle, 10; D. gold strip size, 0.5mm 17.5mm after print and growth; print cycle, 7; growth cycle, The electric resistivity (ρ) of a gold strip (0.5 mm 17.5 mm) with seven printing cycles and eight growth cycles can be estimated according to its 0.5-μm thickness indicated by the SEM image: ρ = RA/l = 16.6Ω ( m) ( m) / m = Ω m S3

4 Figure S-5. Photos of inkjet-printed narrow gold electrode arrays on MCE. The width of the conducting lines and the intervals is about 0.3 mm and 0.25mm, respectively. Figure S-6. Cyclic voltammograms of the working electrode of a PGEA in 0.1 M phosphate buffer (ph 7.4) in the potential range of -0.1 ~ 1.2 V at scan rate of 50 mv/s. A SCE and a Pt wire were used as the reference and the counter electrodes, respectively. The roughness factor of PGEAs estimated by the integration of the gold oxide reduction peak is about 7.3 when a value of 482 μc/cm 2 was employed for the surface charge of a monolayer of chemisorbed oxygen on polycrystalline gold (see Anal. Chem. 2000, 72, ). Figure S-7. Cyclic voltammograms of PGEAs in air using 1.0 μl BMIMPF 6 and 1-octyl-3-methylimidazolium hexafluophosphate (OMIMPF 6 ) as electrolytes. Scan rate, 100 mv/s. S4

5 Figure S-8. Schematic representations on finely tuning the three-phase electrolyte/electrode/gas interface by IL volume: (A) 0.4 μl; (B) 1.2 μl; (C) 2.0 μl. Figure S-9. Calibration plot and detection limit of amperometric responses for trace O 2 in nitrogen atmosphere. Figure S-10. Response time of O 2 at the sensor using 1.0 μl BMIMPF 6 electrolyte for O 2 concentrations from 0.054% to 0.177% in N 2 carrier gas at a flow rate of 0.1 m 3 /h. Applied potential, -1.4 V vs. Au. Figure S-11. Successive voltammograms of PGEAs in air using 1 μl BMIMPF 6 with and without 50 mm Fc as electrolytes in the potential ranges of -1.0 ~ 1.0 V (A) and -2.0 ~ 2.0 V (B). S5

6 Figure S-12. The setup of selectivity test (A) and the amperometric responses of 1.0 ml different gases at the oxygen sensor in N 2 atmosphere at a flow rate of 0.1 m 3 /h (B). Electrolyte, 1.0 μl BMIMPF 6 ; applied potential, -1.4 V vs. Au. Figure S-13. The setup of breathing test (A) and the amperometric responses of different gases at the oxygen sensor in N 2 atmosphere at a flow rate of 0.1 m 3 /h (B). Electrolyte, 1.0 μl BMIMPF 6 ; applied potential, -1.4 V vs. Au. The responses indicated by air suggest the block of connection f of valve 2 and the free diffusion of air from the atmosphere to the sensor. The decrease of O 2 content by about 23% in expiratory gas detected by the sensor as compared that in air is slightly larger the physiological value, i.e., a decrease by 21.8% for the general content of O 2 in expiratory gas (about 16.4%) and in air (20.97%), probably due to the relative long-term continuous breathing out (20s) for the test in each step. S6

7 Table S-1. Analytical performance of different IL-based electrochemical oxygen sensors. Working electrodes IL electrolytes Detection potential Calibration range (v/v) Detection limit (v/v) Response time Reference QPGNP/SPCE [C 4 dmim][ntf 2 ] V (vs. Ag) 20~100% NA ~ 75 s 5a Platinum gauze [C 4 mim][ntf 2 ] -1.2 V (vs. Pt) 0~20% 0.28% ~ 2 min 9a Microdisc gold array [P 6,6,6,14 ][FAP] -1.5 V (vs. Au) 2~13% NA ~ 20 s 3b GCE EMIBF V (vs. Ag) 10~100% NA ~ 2.5 min 14 PGEA BMIMPF V (vs. Au) 0.054~ 0.177% % < 10 s this work S7