Construction of a Paper-based Sensor Based on Dual-mode pH-responsive Carbon Dots and Its Application in Visual Detection of Ammonia

WU Yifeng; LIAO Tianle; LI Roubing; YUN Xueyan; DONG Tungalag

doi:10.19554/j.cnki.1001-3563.2026.05.001

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Packaging Engineering ›› 2026, Vol. 47 ›› Issue (5) : 1-9. DOI: 10.19554/j.cnki.1001-3563.2026.05.001

Construction of a Paper-based Sensor Based on Dual-mode pH-responsive Carbon Dots and Its Application in Visual Detection of Ammonia

WU Yifeng¹, LIAO Tianle¹, LI Roubing¹, YUN Xueyan^1,2, DONG Tungalag^1,2,*

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Abstract

To address the issues of expensive equipment, complex operation, and difficulty in on-site application present in current ammonia detection technology, the work aims to develop a portable paper-based sensor based on ratio fluorescent carbon dots. With 4-chloro-o-phenylenediamine (ClOPD) and cysteine (Cys) as precursors, carbon dots (Cys-CDs) with pH responsiveness were successfully prepared. These carbon dots exhibited unique ratio fluorescence emission behavior across a wide pH range. When pH ranged from 1 to 4, the fluorescence intensity ratio of two characteristic emission peaks, I_{611 nm}/I_{659 nm}, showed a nonlinear relationship with pH (R²=0.999 81). However, when pH ranged from 4 to 7, I_{611 nm}/I_{659 nm} exhibited a linear relationship with pH (R²=0.996 09), and when pH ranged from 7 to 12, I_{611 nm}/I_{659 nm} also showed a linear relationship with pH (R²=0.980 92), accompanied by a significant color change, providing the possibility of dual-mode signal output. Zeta potential analysis indicated that the aforementioned response was attributed to the protonation and deprotonation processes of functional groups on the surface of the carbon dots. Based on the mechanism of microenvironment pH changes induced by ammonia, Cys-CDs were loaded onto filter paper to prepare a portable paper-based sensor. This sensor exhibited good fluorescence and colorimetric responses to ammonia, with the lowest detection limits (LOD) for fluorescence and colorimetric responses being 7.80 and 7.61 mg/L, respectively. In this study, a carbon dot paper-based sensor with the advantage of visual detection is successfully constructed, providing a feasible solution for real-time monitoring of ammonia in the environment.

Key words

ammonia detection / carbon dots / pH response / paper-based sensor / visual inspection

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WU Yifeng, LIAO Tianle, LI Roubing, YUN Xueyan, DONG Tungalag. Construction of a Paper-based Sensor Based on Dual-mode pH-responsive Carbon Dots and Its Application in Visual Detection of Ammonia[J]. Packaging Engineering. 2026, 47(5): 1-9 https://doi.org/10.19554/j.cnki.1001-3563.2026.05.001

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