Synthesis and Characterization of Novel Luminol-Based Carbon Dots for Dual-Mode Chemiluminescence and Fluorescence Detection of Nitrite in Water Samples

A green hydrothermal method was used to synthesize luminol-based carbon dots (Lu-CDs) for chemiluminescence (CL) and fluorescence (FL) detection of nitrite ions in water samples. Lu-CDs were characterized by using different techniques. The morphology indicates a spherical shape and an amorphous crystalline structure. A reversed flow injection analysis (rFIA) CL detection method was developed based on the Lu-CDs-N-bromosuccinimide-NaOH system, where the CL signal was quenched by nitrite ions. For FL analysis, Lu-CDs exhibited blue fluorescence at 425 nm (quantum yield: 56.42%) upon 350 nm excitation, which was quenched by nitrite ions at pH 6.5. Reaction conditions and parameters were optimized for both methods. The CL and FL methods showed linearity for nitrite concentrations of 1.5–20.0 μg mL⁻¹ and 0.85–50.0 μg mL⁻¹, with detection limits of 0.75 and 0.55 μg mL⁻¹, respectively. Applicability was validated through tap and groundwater analysis, showing agreement with a standard spectrophotometric method (Student's t-test, F-test). The greenness of the developed methods was evaluated using the AGREE and GAPI tools, while their applicability was assessed with the BAGI tool, highlighting their eco-friendly and reliable nature for nitrite detection in water.