Hybrid systems consisting of core/shell semiconductor quantum dots (QDs) and organic rylene dyes have been prepared and characterized. Complex formation is mediated by bidentate carboxylate moieties covalently linked to the dye molecules. The complexes were very stable with respect to time (at least months), dilution (sub nM), and precipitation. After preparation in organic solvent, complexes could be easily transferred into water. The strong quenching of QD emission by the dye molecules (transfer efficiencies up to 95%) was satisfactorily modeled by an FRET process. Single complexes immobilized in thin polymer films were imaged by confocal fluorescence microscopy.

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The dynamics of the photoinduced Forster resonance energy transfer (FRET) in a perylene diimide−quantum dot organic−inorganic hybrid system has been investigated by femtosecond time-resolved absorption spectroscopy. The bidentate binding of the dye acceptor molecules to the surface of CdSe/CdS/ZnS multishell quantum dots provides a well-defined dye-QD geometry for which the efficiency of the energy transfer reaction can be easily tuned by the acceptor concentration. In the experiments, the spectral characteristics of the chosen FRET pair facilitate a selective photoexcitation of the quantum dot donor. Moreover, the acceptor related transient absorption change that occurs solely after energy transfer is utilized for the determination of the energy transfer dynamics. Our time-resolved measurements demonstrate that an increase of the acceptor concentration accelerates the donor−acceptor energy transfer. Considering a Poisson distribution of acceptor molecules per quantum dot, the dependence of the energy transfer rate on its mean value is linear. The results of the presented spectroscopic experiments allow for determining the relative and absolute acceptor/donor ratio in the investigated FRET system without any parameters intrinsic to Forster theory. ■ INTRODUCTIONSemiconductor quantum dots (QD) are nanometer sized luminescent particles with remarkable optical properties. Since the QD dimension is in the range of the Bohr exciton radius, the electronic transition energies become size dependent which leads to a tunability of the absorption and emission properties. 1 QD have received broad and multidisciplinary research interest which ranges from the elucidation of their fundamental photophysical properties such as blinking, 2−5 homogeneous line width, 6−8 and exciton relaxation dynamics 9−12 to the implementation as light absorbers or emitters in photovoltaic devices, 13−16 LEDs, 17−19 and lasers. 20−22 The reduced size of QD inevitably leads to a high surface to volume ratio and consequently to a strong impact of the surface composition on the QD properties. The QD fluorescence quantum yield can be significantly increased by growing an inorganic shell on the core nanoparticles. The stronger fluorescence of core/shell particles is explained by the saturation of surface associated trap states, and fluorescence quantum yields as high as 85% have been observed. 23,24 High photostability together with strong and narrow emission has motivated the application of QD in biological sensing 25−29 and imaging. 30,31 Sensing applications are typically based on the modulation of the QD emission as response to the presence of a target molecule. 28 The modulation can be achieved by quenching mechanisms such as Forster resonance energy transfer (FRET) 25−28,32,33 or charge transfer (CT). 34−38 In QD-based FRET systems the inorganic nanoparticles are predominantly applied as energy donors. Yet, in some recent reports QD have been successfully utilized as acceptors in conjugation with naphthalimide dyes 39 as well as with light harves...

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This study aimed to evaluate the hypoglycemic effect of Zanthoxylum alkylamides and explore the potential mechanism in streptozotocin (STZ)-induced diabetic rats. Diabetic rats were orally treated with 3, 6, and 9 mg per kg bw alkylamides daily for 28 days. As the alkylamide dose increased, the relative weights of the liver and kidney, fasting blood glucose, and fructosamine levels were significantly decreased. The alkylamides also significantly increased the body weight and improved the oral glucose tolerance of the rats. Likewise, the alkylamides significantly increased the levels of liver and muscle glycogen and plasma insulin. These substances further alleviated the histopathological changes in the pancreas of the diabetic rats. The beneficial effects of high-dose alkylamides showed a comparable activity to the anti-diabetic drug glibenclamide. Western blot and real-time PCR results revealed that the alkylamide treatment significantly decreased the expression levels of the key enzymes (phosphoenolpyruvate caboxykinase and glucose-6-phosphatase) involved in gluconeogenesis and increased the glycolysis enzyme (glucokinase) in the liver, and enhanced the expression levels of pancreatic duodenal homeobox-1, glucokinase, and glucose transporter 2 in the pancreas. In addition, it was also observed that the alkylamides, unlike glibenclamide, increased the transient receptor potential cation channel subfamily V member 1 and decreased cannabinoid receptor 1 expressions in the liver and pancreas. Therefore, alkylamides can prevent STZ-induced hyperglycemia by altering the expression levels of the genes related to glucose metabolism and by ameliorating pancreatic dysfunction.