7/27/2019 ac3003243_si_001.pdf

1/7

S1

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

430072, PR China

State Key Laboratory of Transducer Technology, Chinese Academy of Sciences,Beijing 100080, 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%

HAuCl4 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

12000 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-m 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.

7/27/2019 ac3003243_si_001.pdf

2/7

S2

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).

7/27/2019 ac3003243_si_001.pdf

3/7

S3

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; growthcycle, 6-12.

The electric resistivity () of a gold strip (0.5 mm17.5 mm) with seven printing

cycles and eight growth cycles can be estimated according to its 0.5-m thickness

indicated by the SEM image:

= RA/l= 16.6 (0.510-3m) (0.510-6m) /17.510-3m = 2.3710-7m

7/27/2019 ac3003243_si_001.pdf

4/7

S4

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 goldoxide reduction peak is about 7.3 when a value of 482 C/cm2 was employed for the

surface charge of a monolayer of chemisorbed oxygen on polycrystalline gold (see

Anal. Chem. 2000, 72, 2016-2021).

Figure S-7. Cyclic voltammograms of PGEAs in air using 1.0 L BMIMPF6 and

1-octyl-3-methylimidazolium hexafluophosphate (OMIMPF6) as electrolytes. Scan rate,

100 mV/s.

7/27/2019 ac3003243_si_001.pdf

5/7

S5

Figure S-8. Schematic representations on finely tuning the three-phase

electrolyte/electrode/gas interface by IL volume: (A) 0.4 L; (B) 1.2 L; (C) 2.0 L.

Figure S-9. Calibration plot and detection limit of amperometric responses for trace

O2 in nitrogen atmosphere.

Figure S-10. Response time of O2 at the sensor using 1.0 L BMIMPF6 electrolyte for

O2 concentrations from 0.054% to 0.177% in N2 carrier gas at a flow rate of 0.1 m3/h.

Applied potential, -1.4 V vs. Au.

Figure S-11. Successive voltammograms of PGEAs in air using 1 L BMIMPF6 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).

7/27/2019 ac3003243_si_001.pdf

6/7

S6

Figure S-12. The setup of selectivity test (A) and the amperometric responses of 1.0

mL different gases at the oxygen sensor in N2 atmosphere at a flow rate of 0.1 m3/h

(B). Electrolyte, 1.0 L BMIMPF6; 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 N2 atmosphere at a flow rate of 0.1 m3/h (B).

Electrolyte, 1.0 L BMIMPF6; applied potential, -1.4 V vs. Au. The responses

indicated by air suggest the block ofconnection fofvalve 2 and the free diffusion of

air from the atmosphere to the sensor. The decrease of O2 content by about 23% in

expiratory gas detected by the sensor as compared that in air is slightly larger thephysiological value, i.e., a decrease by 21.8% for the general content of O2 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.

7/27/2019 ac3003243_si_001.pdf

7/7

S7

Table S-1. Analytical performance of different IL-based electrochemical oxygen

sensors.

Working electrodes IL electrolytesDetection

potential

Calibration

range (v/v)

Detection

limit (v/v)

Response

timeReference

QPGNP/SPCE [C4dmim][NTf2] -0.72 V (vs. Ag) 20~100% NA ~ 75 s 5a

Platinum gauze [C4mim][NTf2] -1.2 V (vs. Pt) 0~20% 0.28% ~ 2 min 9a

Microdisc gold array [P6,6,6,14][FAP] -1.5 V (vs. Au) 2~13% NA ~ 20 s 3b

GCE EMIBF4 -0.8 V (vs. Ag) 10~100% NA ~ 2.5 min 14

PGEA BMIMPF6 -1.4 V (vs. Au) 0.054~ 0.177% 0.0075% < 10 s this work