Paper electronics hold great potential that could replace conventional plastic electronics. Paper electronics are disposable and cost-effective, two distinct advantages for developing broadly accessible devices. However, the approach for functionalizing paper with electronic materials has not been sufficiently characterized from a chemical point of view. As a result, most paper-based electronic devices have an inferior electrical performance compared with plastic-based devices, which largely constrains their practical use. The design and fabrication of electronic materials on paper needs refinement to make paper electronics a valid, practical option. Here, we report a high-performance, paper-based, wearable ammonia sensor comprising composite poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and iron(III) compounds. We combined different printing and coating methods to develop the ammonia-sensitive, composite substance PEDOT:PSS:Fe3+ on paper. Our sensor achieves 10-times smaller size than the conventional sensor on Kapton film and high tolerance for humidity without impairing practical sensor response. We demonstrate the utility of our device toward wearable ammonia-sensing in a facial mask and a nasal filter; wireless battery-free monitoring of food spoilage; and wireless battery-free monitoring of the ammonia level in a paper diaper. All the comprising materials—cellulose paper, PEDOT:PSS, and iron(III) compounds—are abundant and eco-friendly, a further benefit for applications in which biological tissues or disposable wearable products are eventually discarded with the sensor attached. Our approach may open the door to advanced healthcare based on ubiquitous wearable sensing.

1. Paper-based wearable ammonia gas sensor
using organic–inorganic composite
PEDOT:PSS with iron(III) compounds
Hajime Fujita, Meiting Hao, Shinji Takeoka,
Yuji Miyahara, Tatsuro Goda, Toshinori Fujie
Advanced Materials Technologies (2022)
DOI: 10.1002/admt.202101486
Fe
OH
Fe
O
O O
S SO3
-
+
PEDOT:PSS Iron(III) compounds
Summary report
Paper
+
Ammonia gas sensing
based on resistive response
Wearable application

2. 1
Introduction – Ammonia sensors toward advanced healthcare
Ammonia sensors with high disposability, responsiveness and humidity tolerance
have been demanded in order to tackle unmet biomedical needs.
Wireless
utility
+α
H. Fujita et al., Adv. Mater. Technol. (2022).

3. 2
Ammonia
molecule
PEDOT:PSS:Iron(III) compounds
Paper substrate
We aimed to fabricate paper-based ammonia sensors
with high disposability, responsiveness and humidity tolerance.
Fe
OH
Fe
O
O O
S SO3
-
Sensing material
+
PEDOT:PSS Iron(III) compounds
Additive to enhance
the sensitivity*
Overview of this study
*Lv et al., Sens. Actuators B, 298, 126890 (2019).
5 mm
H. Fujita et al., Adv. Mater. Technol. (2022).

4. Fabrication process of PEDOT:PSS:Fe3+ on paper
3
We combined different fabrication methods to develop the composite substance
PEDOT:PSS:Fe3+ for wearable ammonia gas sensing on paper.
H. Fujita et al., Adv. Mater. Technol. (2022).

5. 4
We confirmed the distribution of PEDOT:PSS and iron(III) compounds
all over the paper substrate.
Surface analysis of PEDOT:PSS:Fe3+ on paper
O O
S SO3
-
PEDOT:PSS
Fe
OH
Fe
O
Iron(III) compounds
Elemental Distribution
(Electron Micro Probe Analyzer)
H. Fujita et al., Adv. Mater. Technol. (2022).

6. 5
Evaluation of sensor response to ammonia and tolerance for humidity
Sensor response in 5 min
13-times enhanced
response
We achieved about 13-times enhanced responsiveness to ammonia gas
by adding iron(III) compounds to PEDOT:PSS as well as humidity tolerance.
Tolerance for humidity
*Lv et al., Sens. Actuators B, 298, 126890 (2019). H. Fujita et al., Adv. Mater. Technol. (2022).

7. 6
Our sensors indicated selective response to ammonia
while showing moderate response to amine groups.
Evaluation of sensor response to other gases
H. Fujita et al., Adv. Mater. Technol. (2022).

8. Demonstration of ammonia sensing on wearable products
7
Sensor embedded in non-woven facial mask
5 mm
We demonstrated the rapid detection of the elevated ammonia level in model breath
by flowing ammonia to the sensor embedded in a facial mask.
H. Fujita et al., Adv. Mater. Technol. (2022).

9. 8
Sensor embedded in a plastic nasal filter
5 mm
Demonstration of ammonia sensing on wearable products
We demonstrated the rapid detection of the elevated ammonia level in model breath
by flowing ammonia to the sensor embedded in a nasal filter.
H. Fujita et al., Adv. Mater. Technol. (2022).

10. 9
We developed a battery-free, wearable system
for detecting the increased ammonia level during the spoilage of squid.
Wireless monitoring of ammonia levels on a rotten squid
H. Fujita et al., Adv. Mater. Technol. (2022).

11. 10
We developed a battery-free, wearable system
for detecting the increased ammonia level during the spoilage of squid.
Wireless monitoring of ammonia levels on a rotten squid
H. Fujita et al., Adv. Mater. Technol. (2022).

12. 11
We developed a battery-free, wearable system
for detecting the increased ammonia level in a paper diaper.
Wireless monitoring of ammonia levels in a paper diaper
H. Fujita et al., Adv. Mater. Technol. (2022).

13. 12
Our sensors can detect excrement contamination in a diaper
and send the notification based on the brightness of LED.
(3 wt%, 30 mL)
Wireless monitoring of ammonia levels in a paper diaper
H. Fujita et al., Adv. Mater. Technol. (2022).

14. 13
Conclusion
Our approach of this study may open the door to advanced healthcare
based on ubiquitous wearable sensing.
H. Fujita et al., Adv. Mater. Technol. (2022).

15. Paper-based wearable ammonia gas sensor
using organic–inorganic composite PEDOT:PSS
with iron(III) compounds
Hajime Fujita†#, Meiting Hao‡#, Shinji Takeoka‡, Yuji Miyahara¶,
Tatsuro Goda§*, Toshinori Fujie†* [#
equal contribution]
†School of Life Science and Technology, Tokyo Institute of Technology, B-50, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8501 (Japan), ‡Department of
Life Science and Medical Bioscience, Graduate School of Advanced Science and Engineering, Waseda University, 2-2 Wakamatsu-cho, Shinjuku, Tokyo,
162-8480 (Japan), ¶
Institute of Biomaterials and Bioengineering, Tokyo Medical and Dental University (TMDU), 2-3-10 Kanda-Surugadai, Chiyoda, Tokyo
101-0062, Japan, §
Department of Biomedical Engineering, Faculty of Science and Engineering, Toyo University, 2100 Kujirai, Kawagoe, Saitama 350-8585,
Japan.
Advanced Materials Technologies (2022)
DOI: 10.1002/admt.202101486