Nitrogen-Doped Carbon Dot-Based Dual-Emission Ratiometric Probe for Smartphone-Assisted Ultrasensitive Detection of Moxifloxacin

Abstract 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 green 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 using a simple one-pot hydrothermal method involving citric acid (CA) and 4-aminoantipyrine (4AA) (180°C, 21 h), resulting in a high quantum yield of 10% due to successful nitrogen doping. The N-CDs exhibited excellent water dispersibility, attributed to surface functional groups (-OH, -NH₂, -COOH), and were thoroughly characterized (FTIR, ¹H-NMR, ¹³C-NMR, XPS, Raman, XRD, and TEM). Upon introducing MOX, a distinct blue-green fluorescence emerged, enabling ratiometric quantification. This was successfully leveraged in a smartphone-based sensing platform using the RGB color model. The probe demonstrated a low detection limit of 57 nmol L⁻ ¹, a wide linear range from 0.4 to 20 µmol L⁻ ¹, and a rapid response within 3 min. The high accuracy and precision of the method were confirmed through successful application in the analysis of pharmaceutical formulations.