Nitrogen-doped carbon dot-based dual-emission ratiometric probe for smartphone-assisted ultrasensitive detection of moxifloxacin

Moxifloxacin (MOX), a widely prescribed fourth-generation fluoroquinolone antibiotic, poses significant environmental and health risks due to misuse, including the development of antibiotic resistance. Herein, we developed a smartphone-integrated, dual-emission ratiometric fluorescent probe for the ultrasensitive detection of MOX. The probe utilizes the intrinsic cyan fluorescence of MOX as the detection signal and blue-emitting nitrogen-doped carbon dots (N-CDs) as an internal reference. The N-CDs were synthesized via a facile one-pot hydrothermal method from citric acid (CA) and 4-aminoantipyrine (4AA). Comprehensive characterization (FTIR, 1H-NMR, 13C-NMR, XPS, Raman, XRD, TEM) confirmed their quasi-spherical morphology with an average diameter of 5.1 nm, successful nitrogen doping (12.56%), a quantum yield of 10%, and an abundance of surface functional groups (-OH, -NH2, -COOH). The ratiometric probe’s sensing mechanism relies on the stable blue emission of the N-CDs at 418 nm (reference signal) and the MOX-induced increase in cyan emission at 463 nm. The ratiometric signal (I463/I418) demonstrated exceptional analytical performance with a detection limit of 57 nmol L–1, a wide linear range (0.4–20 μmol L–1), and a rapid response within 3 min. A smartphone-based platform was also developed for on-site analysis, achieving an LOD of 2.8 μmol L–1 (linear range: 0–200 μmol L–1). The probe exhibited excellent selectivity against 15 common interferents and was successfully applied to commercial MOX tablets with high recovery rates (93–112%). Greenness assessment using AGREE (0.8) and Complex-MoGAPI (0.89) metrics confirmed the method’s outstanding environmental friendliness, characterized by minimal solvent use, absence of toxic substances, low energy consumption, and negligible waste generation. This integrated strategy provides a portable, cost-effective, and reliable platform for MOX monitoring in pharmaceutical, environmental, and point-of-care diagnostics.