Carbon dots (CDs) have emerged as promising fluorescent probes for environmental monitoring; however, most reported systems rely on single-emission responses and solution-phase operation, limiting their discriminative capability and practical deployability. Herein, dual-emission CDs with characteristic emission peaks at 420 nm and 520 nm were synthesized and integrated into a flexible PVA/alginate composite film for simultaneous, selective solid-state detection of nitrite (<InlineEquation ID="IEq3"> <EquationSource Format="TEX">${{NO}}_{2}^{-}$</EquationSource> <EquationSource Format="MATHML"><math> <msubsup> <mrow> <mi mathvariant="italic">NO</mi> </mrow> <mrow> <mn>2</mn> </mrow> <mo>-</mo> </msubsup> </math></EquationSource> </InlineEquation>) and ferric ions (Fe3+) in water. The CDs exhibited excellent linearity with low detection limits of 0.12 ppm (2.61 µM) for <InlineEquation ID="IEq4"> <EquationSource Format="TEX">${{NO}}_{2}^{-}$</EquationSource> <EquationSource Format="MATHML"><math> <msubsup> <mrow> <mi mathvariant="italic">NO</mi> </mrow> <mrow> <mn>2</mn> </mrow> <mo>-</mo> </msubsup> </math></EquationSource> </InlineEquation> and 0.17 ppm (3.04 µM) for Fe3+, both well below the WHO drinking water guideline. The PVA/alginate matrix provided strong CD confinement with good optical stability across a wide pH range, and intrinsic ion-gating selectivity that effectively prevents Fe3+ from penetrating the film interior. Owing to the high and uniform fluorescence of the composite film, concentration-dependent changes upon <InlineEquation ID="IEq5"> <EquationSource Format="TEX">${{NO}}_{2}^{-}$</EquationSource> <EquationSource Format="MATHML"><math> <msubsup> <mrow> <mi mathvariant="italic">NO</mi> </mrow> <mrow> <mn>2</mn> </mrow> <mo>-</mo> </msubsup> </math></EquationSource> </InlineEquation> exposure can be directly visualized by the naked eye and quantitatively evaluated through smartphone-assisted RGB image analysis, generating linear calibration curves with coefficients of determination exceeding 0.93. These findings demonstrate that the PVA/Alg/CDs film offers a stable and portable solid-state platform for on-site water quality monitoring, bridging the gap between laboratory-based fluorescence sensing and practical environmental detection. Graphical Abstract

Facile synthesis of dual-emission carbon dots and fabrication of Poly(vinyl alcohol)/Alginate/carbon dots films for selective fluorescence detection and smartphone-assisted monitoring of ${{NO}}_{2}^{-}$ and Fe³⁺ in water

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发表日期：

2026年6月25日

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Nguyen Ba Hung,
Duong Duy Son,
Le Thu Phuong,
Vu Tan Phat,
Do Anh Viet,
Tran Thi Bich Lan,
Luu Thi Van,
Ban Dieu Linh,
Nguyen Tri Nghia,
Nguyen Minh Hoang

摘要

Carbon dots (CDs) have emerged as promising fluorescent probes for environmental monitoring; however, most reported systems rely on single-emission responses and solution-phase operation, limiting their discriminative capability and practical deployability. Herein, dual-emission CDs with characteristic emission peaks at 420 nm and 520 nm were synthesized and integrated into a flexible PVA/alginate composite film for simultaneous, selective solid-state detection of nitrite ( ${{NO}}_{2}^{-}$ ${NO}_{2}^{-}$ ) and ferric ions (Fe³⁺) in water. The CDs exhibited excellent linearity with low detection limits of 0.12 ppm (2.61 µM) for ${{NO}}_{2}^{-}$ ${NO}_{2}^{-}$ and 0.17 ppm (3.04 µM) for Fe³⁺, both well below the WHO drinking water guideline. The PVA/alginate matrix provided strong CD confinement with good optical stability across a wide pH range, and intrinsic ion-gating selectivity that effectively prevents Fe³⁺ from penetrating the film interior. Owing to the high and uniform fluorescence of the composite film, concentration-dependent changes upon ${{NO}}_{2}^{-}$ ${NO}_{2}^{-}$ exposure can be directly visualized by the naked eye and quantitatively evaluated through smartphone-assisted RGB image analysis, generating linear calibration curves with coefficients of determination exceeding 0.93. These findings demonstrate that the PVA/Alg/CDs film offers a stable and portable solid-state platform for on-site water quality monitoring, bridging the gap between laboratory-based fluorescence sensing and practical environmental detection.

Graphical Abstract

Facile synthesis of dual-emission carbon dots and fabrication of Poly(vinyl alcohol)/Alginate/carbon dots films for selective fluorescence detection and smartphone-assisted monitoring of \({{NO}}_{2}^{-}\) and Fe3+ in water

摘要

Facile synthesis of dual-emission carbon dots and fabrication of Poly(vinyl alcohol)/Alginate/carbon dots films for selective fluorescence detection and smartphone-assisted monitoring of \({{NO}}_{2}^{-}\) and Fe³⁺ in water