A novel dual-excitation ratiometric fluorescence sensor based on nitrogen-doped carbon dots for simultaneous detection and discrimination of chloramphenicol and malachite green in fish

First simultaneous detection and discrimination of CAP and MG. • Ratiometric detection of CAP and MG using dual excitation N-CDs. • CAP and MG exhibit distinct quenching mechanisms (IFE vs IFE/FRET). • A handheld smartphone platform with N-CDs/PVA film enables visual detection. • Satisfactory recovery is achieved in aquatic product samples. The expanding aquaculture industry, driven by growing demand for aquatic products, has raised serious concerns about residual chloramphenicol (CAP) and malachite green (MG) due to their detrimental impact on human health and the environment. Herein, a dual-excitation ratiometric fluorescence probe based on nitrogen-doped carbon dots (N-CDs) is developed for simultaneously detecting and discriminating CAP and MG. Employing a hydrothermal approach with 5-aminoisophthalic acid and biuret as precursors, the synthesized N-CDs possess two excitation peaks (286 nm and 348 nm) and corresponding emission maximum at 404 nm. The presence of CAP significantly quenches the 286 nm excitation peak of N-CDs via the internal filtering effect (IFE), while leaving the 348 nm peak largely unaffected. This selective quenching yields a linear range of 0.045–100 μM with a limit of detection (LOD) as low as 45 nM. In contrast, the fluorescence quenching by MG is mediated principally by fluorescence resonance energy transfer and IFE, leading to a pronounced quenching efficacy at two excitation wavelengths, thus achieving a low LOD (73 nM) within 0.073–125 μM. Furthermore, the ability to differentiate between CAP and MG in mixed samples is achieved through linear discriminant analysis and hierarchical cluster analysis, leveraging the differential quenching responses of N-CDs. Additionally, a smartphone-integrated sensing platform is constructed for the detection of CAP and MG, achieving satisfactory recovery rates in aquatic environments. In summary, this research establishes a dual-analyte ratiometric sensing approach for CAP and MG, offering a practical tool for food safety and environmental surveillance. Download: Download high-res image (186KB) Download: Download full-size image