Red-emission carbon dots-quercetin systems as ratiometric fluorescent nanoprobes towards Zn2+ and adenosine triphosphate.

Carbon dots (CDs) emitting red fluorescence (610 nm) were synthesized by solvent thermal treatment of p-phenylenediamine in toluene. Upon 440 nm excitation, quercetin (QCT) alone endowed slight effects on the red fluorescence of CDs. Once Zn2+ was further introduced, the QCT-Zn2+ complex was quickly formed. This complex absorbs excitation light and emits bright green fluorescence at 480 nm. The red fluorescence of CDs was greatly quenched owing to the inner-filter effect. The ratio of fluorescence intensity at 480 nm and 610 nm (I480/I610) gradually increases with increasing concentration (c) of Zn2+. Al3+ exhibits the same phenomen like Zn2+. Fluoride ions form a more stable complex with Al3+ than QCT-Al3+ complex but have a negligible effect on the QCT-Zn2+ complex. The possible interference of Al3+ on Zn2+ can thus be avoided by adding certain amount of F-. The CD-QCT-F- system was constructed as a ratio-metric fluorescent nanoprobe toward Zn2+ with determination range of 0.14-30 µM and limit of detection (LOD) of 0.14 µM. Due to the stronger affinity of adenosine triphosphate (ATP) to Zn2+ than QCT, the I480/I610 value of CD-QCT-F--Zn2+ system gradually decreases with increasing cATP. The ratiometric fluorescent nanoprobe toward ATP was established with detection ranges of 0.55-10 and 10-35 µM and a LOD of 0.55 µM. The above two probes enable the quantitative determination of Zn2+ and ATP in tap and lake water samples with satisfactory recoveries. Graphical abstract Schematic representation of the ratiometric fluorescent nanoprobes based on the carbon dots (CDs)-quercetin (QCT) system towards Zn2+ and adenosine triphosphate (ATP) with high selectivity and sensitivity.

One pot synthesis of water-soluble quercetin derived multifunctional nanoparticles with photothermal and antioxidation capabilities.

As a member of flavonoids, the application of quercetin has been mainly focused on antioxidation study. Fabrication of multifunctional nanoplatforms with quercetin is limited. In the present study, water-soluble quercetin derived nanoparticles (QFNPs) were fabricated through the one pot synthesis strategy with Fe3+, quercetin and poly (vinyl pyrrolidone) (PVP). The raw materials were dissolved in absolute ethanol and the mixed together. After stirring at room temperature for 6 h, the QFNPs could be simply harvested by centrifugation without the need of time-consuming dialysis procedure. Due to the protective effect of PVP, the synthesized nanoparticles could be well dispersed in water with the hydrodynamic size about 23 nm. DPPH free radical scavenging capacity assay showed QFNPs could act as efficient antioxidant. Besides antioxidation activity, the QFNPs also exhibited good photothermal capacity. Temperature stability result suggested the good stability of QFNPs between 35 and 95 °C. MTT and hemolysis assay showed the good biocompatibility of QFNPs. What's more, the QFNPs showed good cellular antioxidation activity and efficient photothermal killing effect to cancer cells (4T1 cells). The QFNPs could be promising nanoplatform for biomedical application.

UVA and UVB radiation-induced oxidation products of quercetin.

The flavonol quercetin is believed to provide protection against ultraviolet (UV) radiation-induced damage in plants. As part of our investigations into the potential for quercetin to protect skin against UV radiation-induced damage we have investigated the products of quercetin exposed to UV radiation in vitro. UVA (740 microW cm(-2) at 365 nm) or UVB (1300 microW cm(-2) at 310 nm) irradiation of quercetin in methanol results in a small conversion (less than 20%) to C-ring breakdown products over 11 h. When the triplet sensitizer benzophenone is added, greater than 90% conversion by UVA or UVB occurs within 1h. The major photoproducts from either UVA or UVB radiation are 2,4,6-trihydroxybenzaldehyde (1), 2-(3',4'-dihydroxybenzoyloxy)-4,6-dihydroxybenzoic acid (2) and 3,4-dihydroxyphenylethanol (3). Product 2 has previously been observed as a product of oxidative metabolism of quercetin, however products 1 and 3 appear to be the result of a unique UV-dependent pathway. In conclusion we have determined that quercetin undergoes slow decomposition to a mixture of C-ring-opened products, two of which to our knowledge have not been previously observed for quercetin decomposition, and that the presence of a triplet sensitizer greatly increases UV radiation-mediated quercetin decomposition. The presence of endogenous photosensitizers in the skin could potentially affect the UV stability of quercetin, suggesting that further study of quercetin for both its photoprotective properties and photostabilty in skin are warranted.

Radioresistance of Salmonella species and Listeria monocytogenes on minimally processed arugula (Eruca sativa Mill.): effect of irradiation on flavonoid content and acceptability of irradiated produce.

This work studied the radiation resistance of Listeria monocytogenes and Salmonella species and the effect of irradiation on leaf flavonoid content and sensory acceptability of minimally processed arugula. Immersion in ozone-treated water reduced the analyzed microorganisms by 1 log. L. monocytogenes and Salmonella were not isolated from samples. Samples of this vegetable were inoculated with a cocktail of Salmonella spp. and L. monocytogenes and exposed to gamma irradiation. D10 values for Salmonella ranged from 0.16 to 0.19 kGy and for L. monocytogenes from 0.37 to 0.48 kGy. Kaempferol glycoside levels were 4 and ca. 3 times higher in samples exposed to 1 and 2 kGy, respectively, than in control samples. An increase in quercetin glycoside was also observed mainly in samples exposed to 1 kGy. In sensory evaluation, arugula had good acceptability, even after exposure to 2 and 4 kGy. These results indicate that irradiation has potential as a practical processing step to improve the safety of arugula.