A sensitive fluorescence probe based on 3-mercaptopropionic acid (MPA) capped cadmiumsulfide quantum dots (CdS QDs) was prepared for determination of ciprofloxacin (CIP) in real samples Ciprofloxacin (CIP) [1-cyclopropyl-6-fluoro-1,4-dihydro-4- oxo-7-(piperazinyl)quinolone-3-carboxylic acid], belongs to the quinolones class. The quinolones are synthetic antibiotics chemically related to nalidixic acid. These drugs form a group of antimicrobial agents with different chemical structures and spectra of activity [1] Quantum dots (QDs), as a new class of fluorescent probes, have attracted considerable attentions in recent years. Compared with conventional organic fluorescent dyes, QDs have many unique optical properties, like strong signal intensity, high quantum yield, tunable size-dependent photoluminescence and narrow emission peaks, which gained them increased attention in many fields [2]. QDs are used as a fluorescence probe for high-sensitive analysis of protein, detection of some inorganic cations, construction of biosensor and imaging of cells and tissues [3]. The synthesized MPA-capped CdS QDs was characterized using Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and transmission electron microscopy (TEM) measurements. Based on the results, the fluorescence of MPA-capped CdS QDs was quenched in the presence of Cu2+ that it could have occurred because of the nonradiative electron hole recombination annihilation through an effective electron transfer process. Subsequently, the fluorescence of MPA-capped CdS QDs mixed with the Cu2+ could be recovered after the addition of CIP due to its strong affinities for Cu2+ [4-5]. The recovered fluorescence intensity of capped CdS QDs was proportional to the concentration of CIP in the ranges of 0.13 -1 -1. The established method showed a good selectivity for CIP among several kinds of ions and biomolecules. The fluorescent probe was successfully applied to the determination of CIP in pharmaceutical
