In this work, highly fluorescent blue-emissive carbon quantum dots (CQDs) were synthesized successfully via a facile hydrothermal method using ortho-aminophenol and citric acid as precursors. The as-prepared CQDs exhibited an outstanding quantum yield of 89.7%, which is among the highest values reported for blue-emissive CQDs. Extensive characterization using techniques such as High resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy revealed the formation of small-sized CQDs of average diameter 2.1 nm and surface functionalization with hydroxyl, amine, and carboxyl groups.
Utilizing the excellent optical properties of the synthesized CQDs, we further explored their application as a fluorescent probe for the detection of ciprofloxacin, a widely used fluoroquinolone antibiotic. The CQD-based fluorescent probe demonstrated a linear response to ciprofloxacin concentrations in the range of 0 – 40 μM, with a remarkable limit of detection as low as 36 nM. The designed sensor's performance was validated through successful quantification of ciprofloxacin in real samples of urine and blood serum, showing its practical applicability with an excellent recovery rate of 98.65% - 105.06%. The high quantum yield, facile synthesis, and effective sensing capabilities of the CQDs developed in this study make them a promising candidate for various optoelectronic and analytical applications.

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