A fluorescent nanohybrid sensor based on carbon dots encapsulated in a metal organic framework for highly selective and sensitive detection of mercury

Abstract

The accurate and sensitive detection of toxic heavy metals, particularly mercury ions, in aquatic environments is crucial due to their severe environmental persistence and detrimental health effects. In this study, we report the synthesis and application of a novel fluorescent sensor based on carbon dots encapsulated within a zeolitic imidazolate framework (CDs@ZIF-8) for the selective and sensitive detection of Hg²⁺ in aqueous media. The carbon dots were synthesized via a hydrothermal method using m-phenylenediamine and L-ascorbic acid, followed by in situ encapsulation into the ZIF-8 matrix through a one-pot solvothermal strategy. Structural and morphological characterization confirmed the successful formation and integration of CDs within the ZIF-8 framework without compromising its crystallinity or thermal stability. The resulting CDs@ZIF-8 sensor exhibited strong blue fluorescence with excellent photostability, environmental tolerance, and dispersibility in water. Notably, the sensor demonstrated high sensitivity toward Hg²⁺ ions, with a wide linear detection range of 0.01–1.0 μM, having a low detection limit of 83 nM and a quenching constant of 6.17 × 10⁶ M⁻¹. The fluorescence quenching followed a concentration-dependent Stern–Volmer relationship and was visually detectable under UV light. Real water sample analysis revealed recovery rates between 95.54% and 99.01%, confirming the practical applicability of the sensor. These findings suggest that the CDs@ZIF-8 platform holds significant promise as a cost-effective, portable, and environmentally friendly fluorescent probe for real-time Hg²⁺ monitoring in environmental samples.