Ultrasound-assisted synthesis of surface state engineered BN-carbon quantum dots for fluoroquinolone sensing: DFT insights

The development of ultrasound-assisted strategies for synthesizing carbon-based nanomaterials has attracted increasing attention owing to the unique physicochemical properties and broad environmental applications. In this study, highly fluorescent surface-state-engineered boron- and nitrogen-co-doped carbon quantum dots (BN-CQDs) were synthesized via an ultrasound-assisted hydrothermal approach using an ultrasonic bath operating at 160 W and a fixed frequency of 37 kHz. The ultrasound-assisted process, together with boron and nitrogen, influenced the physicochemical and optical properties of the resulting BN-CQDs, yielding well-dispersed nanodots with surface-active functional groups and suitable optical properties for the detection of fluoroquinolone antibiotics. The synthesized BN-CQDs were systematically characterized using UV–vis spectroscopy, PL, FTIR, XRD, and XPS. The BN-CQDs exhibited intense blue fluorescence with maximum excitation and emission wavelengths of 380 and 440 nm, respectively, and a high fluorescent quantum yield of 56.8%, highlighting their favorable optical properties for sensing. The fluorescence intensity decreased gradually with increasing concentrations of ciprofloxacin (CIP) and levofloxacin (LVX), primarily attributed to photoinduced electron-transfer and charge-transfer interactions between antibiotic molecules and the surface-active functional groups of the BN-CQDs. Under optimized conditions, the developed fluorescent nanoprobe exhibited a linear response over the concentration range of 0 to 50μmol L −1 , with low detection limits of 0.286μmol L −1 for CIP and 0.320μmol L −1 for LVX. Moreover, the sensing platform exhibited excellent selectivity against common metal ions, biomolecules, and interfering antibiotics. Its practical applicability was validated by satisfactory recoveries of 98.0 to 102.0% for CIP and LVX in drinking and tap water samples. DFT calculations provided further insights into the charge-transfer interactions responsible for fluorescence quenching. The ultrasound-assisted synthesis of BN-CQDs provides a promising sonochemical route for developing fluorescent nanoprobes for the sensitive detection of fluoroquinolone antibiotics.