On-off-on fluorescent carbon dots from waste tea: Their properties, antioxidant and selective detection of CrO(4)(2-), Fe(3+), ascorbic acid and L-cysteine in real samples.

In this work, we reported an economical plant-based hydrothermal method for one-pot green synthesis of water-soluble carbon dots (Tea-CDs) by using waste tea extract as a carbon source. The synthesized Tea-CDs were characterized by UV-visible, fluorescence, FT-IR, TEM, XPS and XRD. The Tea-CDs were found to remove hydroxyl and superoxide anion radical in vitro. In addition, the Tea-CDs exhibited bright blue fluorescence under UV-light (λex = 365 nm), and the fluorescence could be effectively quenched by CrO42- and Fe3+ ions. Meanwhile, the fluorescence of Tea-CDs-CrO42- and Tea-CDs-Fe3+ systems could be again easily recovered by ascorbic acid (AA) and L-cysteine (L-Cys). As an on-off-on fluorescent nano-sensor of the Tea-CDs, the sensitive detection of CrO42-, Fe3+, AA and L-Cys were all performed, showing that the good linear relationships between fluorescence intensity of Tea-CDs and concentration of all testing samples. Finally, the sensors successfully detected CrO42-, Fe3+, AA and L-Cys in commercially available real samples with satisfactory recovery ranges. The prepared sensors offer distinct advantages including low cost, simple handling, good sensitivity and high selectivity.

Chen K ，Qing W ，Hu W ，Lu M ，Wang Y ，Liu X ... -  《-》

Facile preparation and characterization of new green emitting carbon dots for sensitive and selective off/on detection of Fe(3+) ion and ascorbic acid in water and urine samples and intracellular imaging in living cells.

Carbon dots (CDs) have gained great attention as multifunctional materials because of their interesting properties and general applicability. However, there are some reports for the preparation of highly luminescent green-emitting CDs (G-CDs), although these reports seem not to be extensible. Herein, new G-CDs (quantum yield: 27.2%) were synthesized from a facile hydrothermal treatment of p-aminosalicylic acid and ethylene glycol dimethacrylate as both carbon and nitrogen source and cross-linking agent, respectively. The chemical composition and optical properties of the as-prepared G-CDs were successfully investigated using transmission electron microscopy, atomic force microscopy, dynamic light scattering, X-ray diffraction, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy and fluorescence and UV-vis spectroscopies. Interestingly, the fluorescence intensity of G-CDs was selectivity quenched by Fe3+ in the range of 0.05-10.0 µmol L-1, with a detection limit of 13.7 nmol L-1. Meanwhile, ascorbic acid found to reduce Fe3+ to Fe2+, thereby causing restoration of the fluorescence of G-CDs. The detection limit for ascorbic acid detection was estimated as 82.0 nmol L-1 over a linear range from 0.2 to 11.0 µmol L-1. Furthermore, the designed sensing platform was successfully utilized to the detection of Fe3+ and ascorbic acid in water and urine samples and to intracellular imaging without surface modification.

Shamsipur M ，Molaei K ，Molaabasi F ，Alipour M ，Alizadeh N ，Hosseinkhani S ，Hosseini M ... -  《-》

Facile synthesis of fluorescent carbon dots from Prunus cerasifera fruits for fluorescent ink, Fe(3+) ion detection and cell imaging.

Carbon dots (CDs) synthesized from natural products have drawn numerous attentions due to some unique properties. Here, Prunus cerasifera fruits were used as carbon source to synthesize high luminescent CDs by hydrothermal method. The obtained CDs were characterized by TEM, FTIR and XPS methods, founding the CDs were near-spherical and contained abundant nitrogen element. The CDs aqueous solution exhibited bright blue fluorescence under ultraviolet illumination, with the maximum emission at 450 nm. They could be potentially used as invisible fluorescent ink by written on the paper and irradiated by UV light, due to their fluorescent properties. Moreover, the CDs were found being selectively quenched by Fe3+ ion. The quench of CDs was linearly related to the concentration of Fe3+ ion in the range of 0-0.5 mM, meaning they could be developed as fluorescent probe of Fe3+ ion. At last, the CDs were used for cell imaging, founding they were low toxicity to HepG2 cells and exhibited blue and green fluorescence under a fluorescence microscope. In summary, the CDs prepared from Prunus cerasifera fruits exhibited excellent fluorescence properties, and could be potentially applied in the field of fluorescent ink, Fe3+ ion detection and cell imaging.

Ma H ，Sun C ，Xue G ，Wu G ，Zhang X ，Han X ，Qi X ，Lv X ，Sun H ，Zhang J ... -  《-》

Green synthesis of carbon dots originated from Lycii Fructus for effective fluorescent sensing of ferric ion and multicolor cell imaging.

Green, economical and effective method was developed for synthesis of fluorescent carbon dots (CDs), using one-pot hydrothermal treatment of Lycii Fructus. Optical and structural properties of the CDs have been extensively studied by UV-visible and fluorescence spectroscopic, x-ray diffraction (XRD) techniques, transmission electron microscopy (TEM) and high resolution TEM (HRTEM). Surface functionality and composition of CDs has been illustrated by Fourier transform infrared spectroscopy (FTIR), x-ray photoelectron spectroscopy (XPS) spectra and elemental analysis. The fabricated CDs possess stable fluorescent properties. The fluorescent quantum yield of the CDs can reach 17.2%. The prepared CDs emitted a broad fluorescence between 415 and 545nm and their fluorescence was tuned by changing excitation wavelength. Meanwhile, the fluorescence intensity of the CDs could be significantly quenched by Fe3+ (turn-off). The CDs exhibit captivating sensitivity and selectivity toward Fe3+ with a linear range from 0 to 30μM and a detection limit of 21nM. The prepared CDs were successfully applied to the determination of Fe3+ in the urine samples, the water samples from the from the Yellow River and living HeLa (Henrietta Lacks) cells. Moreover, the low-toxicity and excellent biocompatibility of the CDs were evaluated through MTT assay on HeLa cells. The CDs were also employed as fluorescent probes for multicolor imaging of HeLa cells successfully.

Sun X ，He J ，Yang S ，Zheng M ，Wang Y ，Ma S ，Zheng H ... -  《-》

Bright-green-emissive nitrogen-doped carbon dots as a nanoprobe for bifunctional sensing, its logic gate operation and cellular imaging.

A fluorescent nanoprobe based on nitrogen-doped carbon dots (N-CDs) with green fluorescent emission have been fabricated through a facile one-step hydrothermal treatment using catechol and triethylene tetramine as precursors. The obtained N-CDs with excellent luminescent properties and superior biocompatibility have been applied for the development of a bifunctional sensor for the detection of Fe3+ and ascorbic acid (AA). Fe3+ that are tightly chelating the surface of N-CDs can induce fluorescence (FL) quenching of N-CDs through photo-induced electron transfer (PET). Meanwhile, the addition of AA serves to shelter the CDs effectively from being quenched by Fe3+ due to AA, as an antioxidant, enable easy-conversion of Fe3+ to reduced states (i.e. Fe3+ and Fe2+). The N-CDs are used as a facile and label-free "on-off-on" fluorescent nanoprobe for the determination of Fe3+ and AA with detection limits of 58.82nM and 0.236µM with the corresponding linear ranges of 25-200µM and 25-300µM, respectively. According to this phenomenon, an "AND" logic gate based on the novel N-CDs has been constructed. As-prepared N-CDs with negligible toxicity and perfect biocompatibility were expanded for cellular imaging and sensing Fe3+ and AA in living cell, which enlarges the application range of the N-CDs. Most importantly, the as-constructed fluorescent sensing system was successfully applied to detection of Fe3+ in tap water and the analyses of AA in fresh fruits with satisfactory results.

Du F ，Gong X ，Lu W ，Liu Y ，Gao Y ，Shuang S ，Xian M ，Dong C ... -  《-》