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Ketoprofen (KTP), 2-(3-benzoylphenyl) propionic acid, is a potent nonsteroidal anti-inflammatory drug used for the treatment of inflammatory diseases and musculoskeletal injuries. KTP also presents analgesic and antipyretic activity [1,2] and relieves pain associated with both rheumatic and nonrheumatic inflammatory disorders, vascular headaches, and dysmenorrhea. Taking into account the increased use of KTP and new formulations entering the market, it is important to have simple, accurate, and rapid methods for quality control analyses. Various methods have been described in scientific literatures for the determination of KTP, including gas [3] and liquid [4,5] chromatography, capillary electrophoresis [6], potentiometry [7], spectrophotometry [8], terbium-sensitized luminescence [1], and chemiluminescence [2,9]. However, due to the nonfluorescent nature of KTP, its fluorometric determination has not been reported up to date, even after derivatization.
Colloidal nanocrystals, also known as quantum dots (QDs), are nanometer-scale semiconductor crystals, defined as particles with physical dimensions smaller than the exciton Bohr radius. These monodispersed nanoparticles are made of a core of semiconductor material, elements from the IIB–VIB (e.g., CdSe, CdTe, CdS, and ZnSe), IIIB–VB (e.g., InP and InAs), or IVB–VIB (e.g., PbSe) groups, surrounded by an organic capping layer of passivating molecules, with a diameter typically ranging from 1 nm to 10 nm [10,11]. QDs display superior luminescent properties, including high quantum yield of fluorescence, broad excitation spectrum, narrow/symmetric emission spectrum, size- and composition-tunable emission wavelength, high photobleaching threshold, and excellent photostability. Therefore, thanks to recent advances in nanotechnology and nanomaterials, QDs are replacing traditional organic fluorophores in various fluorescence systems. They can be prepared readily in aqueous media or made water soluble by appropriate capping with hydrophilic ligands [12]. Compared to the traditional organic metallic method used in the aqueous synthesis, QDs are stabilized by some functional ligands, such as mercaptopropionic acid (MPA), thioglycolic acid, and glutathione, and exhibit some unique properties such as lower cost, less toxicity, water solubility, and biocompatibility [13].
In this work, MPA-capped CdTe QDs of different particle sizes were synthesized in an aqueous medium and applied to the quantitative determination of KTP. The described procedure is based on the quenching provoked by the analyte over the fluorescence of QDs. To the best of our knowledge, this is the first strategy based...