Highly sensitive and chemically stable NH3 sensors based on an organic acid-sensitized cross-linked hydrogel for exhaled breath analysis
Abstract
Due to interference by the high moisture content and complicated compositions of human exhaled breath, the trace-level detection of ammonia (NH 3) with desirable selectivity and stability is a large challenge for exhaled breath analysis. Carboxyl-sensitized hydrogels can be activated by moisture to exhibit a significant response and excellent selectivity to NH 3. However, the high activity of carboxyl groups in hydrogels is a double-edged sword, resulting in poor chemical stability during NH 3 detection. Herein, organic acids were embedded into a cross-linked poly(ethylene glycol) diacrylate (PEGDA) hydrogel via thiol-ene photochemistry to form stable hydrogels for NH 3 detection in a humid atmosphere. As a result, under high humidity conditions (80% RH), the optimal sensors exhibited superior selectivity to NH 3 among various interfering gas species, a remarkably high NH 3 response (Z a/Z g=6.20) towards 20 ppm NH 3, and an extremely low actual detection limit (50 ppb) at room temperature. Moreover, the sensors exhibited excellent chemical stability due to the moderate equilibrium water content of the hydrogel composites and acid dissociation constant of the acid groups. The moisture-activated NH 3 sensing mechanism was thoroughly investigated by complex impedance spectroscopy (CIS), quartz crystal microbalance (QCM) measurements, Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). To explore the application prospects of cross-linked hydrogel sensors for detecting NH 3 in exhaled breath, a simulated exhaled breath test was also performed.
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Several studies reported the direct use of hydrogel-based vapor sensors for practical applications such as smart masks, electronic skin, respiratory analysis, and wireless monitoring, demonstrating their great prospects for applications in environmental monitoring, medical health, and other fields.
“Several studies reported the direct use of hydrogel-based vapor sensors for practical applications, such as smart masks, electronic skin, respiratory analysis, and wireless monitoring, demonstrating their great prospects for applications in environmental monitoring, medical health, and other fields”
From Functionalized Hydrogel-Based Wearable Gas and Humidity Sensors. (2023) · cites this paper as [76]
The sensor exhibited a high response (6.20) to 20 ppm NH3 at room temperature, as well as a low LOD (50 ppb).
“The sensor exhibited a high response (6.20) to 20 ppm NH3 at room temperature, as well as a low LOD (50 ppb).”
From Functionalized Hydrogel-Based Wearable Gas and Humidity Sensors. (2023) · cites this paper as [76]
Zhang and her team [76] used thiol-ene photochemistry to encapsulate citric acid (CA) into crosslinked PEGDA hydrogels to prepare a highly sensitive and selective CA/PEGDA hydrogel-based NH3 gas sensor working at high humidity (80% RH).
“Zhang and her team [76] used thiol-ene photochemistry to encapsulate citric acid (CA) into crosslinked polyethylene glycol diacrylate (PEGDA) hydrogels to prepare a highly sensitive and selective CA/PEGDA hydrogel-based NH3 gas sensor working at high humidity (80% RH).”
From Functionalized Hydrogel-Based Wearable Gas and Humidity Sensors. (2023) · cites this paper as [76]
This is due to the equilibrium water content of the hydrogel composite and the moderate acid dissociation constants of the acid groups.
“This is due to the equilibrium water content of the hydrogel composite and the moderate acid dissociation constants of the acid groups.”
From Functionalized Hydrogel-Based Wearable Gas and Humidity Sensors. (2023) · cites this paper as [76]
At 80% RH, the large amount of adsorbed water enhances the activity of the carboxyl group, which causes the carboxyl group to react with a large amount of adsorbed NH3 to form ammonium salts.
“At 80% RH, the large amount of adsorbed water enhances the activity of the carboxyl group, which causes the carboxyl group to react with a large amount of adsorbed NH3 to form ammonium salts.”
From Functionalized Hydrogel-Based Wearable Gas and Humidity Sensors. (2023) · cites this paper as [76]
Compounding CA with PEGDA allows the hydrogel to maintain a good NH3 adsorption capacity while still possessing an appropriate hydrophilicity.
“Compounding CA with PEGDA allows the hydrogel to maintain a good NH3 adsorption capacity while still possessing an appropriate hydrophilicity.”
From Functionalized Hydrogel-Based Wearable Gas and Humidity Sensors. (2023) · cites this paper as [76]
The sensor exhibits good chemical stability, while the stable hydrogel structure facilitates the detection of NH3 in humid environments.
“This sensor exhibits good chemical stability, while the stable hydrogel structure facilitates the detection of NH3 in humid environments.”
From Functionalized Hydrogel-Based Wearable Gas and Humidity Sensors. (2023) · cites this paper as [76]
The ammonium salt has stronger hydrophilicity than the carboxyl group, and the adsorption of water increases, leading to CA membrane deliquescence.
“The ammonium salt has stronger hydrophilicity than the carboxyl group, and the adsorption of water increases, leading to CA membrane deliquescence.”
From Functionalized Hydrogel-Based Wearable Gas and Humidity Sensors. (2023) · cites this paper as [76]
The carboxyl group in the CA structure can provide more adsorption sites for NH3, thus, the CA/PEGDA composite has good response properties to NH3 at 80% RH.
“In addition, the carboxyl group in the CA structure can provide more adsorption sites for NH3, thus, the CA/PEGDA composite has good response properties to NH3 at 80% RH.”
From Functionalized Hydrogel-Based Wearable Gas and Humidity Sensors. (2023) · cites this paper as [76]
Unlike CA, PEGDA exhibits relatively poor hydrophilicity, and the amount of NH3 adsorbed is relatively small even at higher moderate environments, blocking the formation of carboxylates.
“Unlike CA, PEGDA exhibits relatively poor hydrophilicity, and the amount of NH3 adsorbed is relatively small even at higher moderate environments, blocking the formation of carboxylates.”
From Functionalized Hydrogel-Based Wearable Gas and Humidity Sensors. (2023) · cites this paper as [76]
The sensor can accurately identify different concentrations of NH3 in exhaled breath, demonstrating the potential for clinical application.
“They also tested for the presence of NH3 in human exhalation, the sensor can accurately identify different concentrations of NH3 in the exhaled breath, as shown in Fig. 9e-f, demonstrating the potential for clinical application of the sensor.”
From Functionalized Hydrogel-Based Wearable Gas and Humidity Sensors. (2023) · cites this paper as [76]
CA has an extremely strong hydrophilicity and NH3 adsorption ability.
“Specifically, CA has an extremely strong hydrophilicity and NH3 adsorption ability.”
From Functionalized Hydrogel-Based Wearable Gas and Humidity Sensors. (2023) · cites this paper as [76]
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Functionalized Hydrogel-Based Wearable Gas and Humidity Sensors.
Luo, Y., Li, J., Ding, Q., Wang, H., Liu, C., & Wu, J. (2023) · Nano-Micro Letters · doi:10.1007/s40820-023-01109-2 · Cited by 236 · see citing works
“1007/s40820-023-01109-2 © The authors Zhang and her team [76] used thiol-ene photochemistry to encapsulate citric acid (CA) into crosslinked polyethylene glycol diacrylate (PEGDA) hydrogels to prepare a highly sensitive and selective CA/PEGDA hydrogel-based NH3 gas sensor working at high humidity (80% RH).”
Background
- Authors
- Liu, L., Fei, T., Guan, X., Zhao, H., & Zhang, T.
- Affiliations
- Jilin University (CN)
- Corresponding author
- Zhao, Hongran
- Zhang, Tong
- Venue
- Biosensors and Bioelectronics
- Publisher
- Elsevier BV
- Published
- 2021-11
- Volume
- 191
- Pages
- 113459
- ISSN
- 0956-5663 (ISSN-L)
- OpenAlex
- W3173790210
- Cited by
- 60
- References
- 2
- Citations by year
- 2026: 6 · 2025: 11 · 2024: 14 · 2023: 14 · 2022: 12 · 2021: 3
- FWCI
- 3.10
- Type
- journal article
- Language
- en
- Open access
- closed
- Licence
- Locations
- Biosensors and Bioelectronics (publishedVersion)
- PubMed (publishedVersion)
- Funders
- Jilin Province People's Government Department of Education
- Jilin Provincial Science and Technology Department
- National Natural Science Foundation of China
- China Postdoctoral Science Foundation
- Topics
- Physical Sciences › Engineering › Electrical and Electronic Engineering › Gas Sensing Nanomaterials and Sensors
- Physical Sciences › Engineering › Biomedical Engineering › Advanced Chemical Sensor Technologies
- Physical Sciences › Materials Science › Polymers and Plastics › Conducting polymers and applications
- Keywords
- ammonia gas sensor, breath analysis, crosslinked hydrogels, poly(ethylene glycol) diacrylate, chemical stability, humidity interference, trace gas detection
- MeSH terms
- Breath Tests, Humans, Biosensing Techniques, Spectroscopy, Fourier Transform Infrared, Hydrogels, Exhalation
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