Synthesis of metal ion-tolerant Mn-doped fluorescence silicon quantum dots with green emission and its application for selective imaging of ·OH in living cells.

Monitoring hydroxyl radical (·OH) in living cells remains a big challenge on account of its high reactivity and short half-life. In this work, we designed a fluorescent probe based on manganese-doped silicon quantum dots (Mn-SiQDs) for detecting and imaging of ·OH with good water solubility. The manganese was doped in its ethylene diamine tetra-acetic acid (EDTA) complex form and effectively improved the metal ion tolerance of fluorescence of SiQDs. And m-dihydroxybenzene was used as the reductant to extend the emission of SiQDs to the green region at 515 nm when the excitation wavelength was 424 nm. Basing on the fluorescence quenching of Mn-SiQDs, a linear response of ·OH was observed in the range 0.8-50 µM with a limit of detection (LOD) of 88.4 nM, which is lower than those reported with SiQDs. The interference from other ROS or RNS has been assessed and no impact was found. In fully aqueous systems, the Mn-SiQDs have been applied to monitor and image the endogenous ·OH in HeLa cells. Our work provided a new strategy for designing SiQDs with good biocompatibility, high selectivity and long monitoring wavelength. Synthesis of green-emitting silicon quantum dots with N-[3 -(trimethoxysilyl) propyl] ethylenediamine (DAMO), Ethylenediamine tetraacetic acid disodium salt dehydrate (EDTA-2Na·2H2O), manganese acetate tetrahydrate (Mn(CH3COO)2·4H20) and m-dihydroxybenzene. The green fluorescence of the silicon quantum dots can be selectively quenched by hydroxyl radicals.

Red emissive boron and nitrogen co-doped "on-off-on" carbon dots for detecting and imaging of mercury(II) and biothiols.

Red emissive B,N co-doped carbon dots (BN-CDs) were hydrothermally synthesized from cresyl violet and boric acid. The BN-CDs exhibited excellent photostability, low cytotoxicity, excitation/emission maxima at 520/616 nm, and a relatively high quantum yield of 18%. The BN-CDs can binded to mercury(II), and this results in quenching of the red-colored fluorescence. However, on subsequent addition of the biothiol (such as cysteine, homocysteine or glutathione), fluorescence recovers. Therefore, the BN-CDs can be used as a multifunctional probe based on "on-off-on" fluorescence response for the detection of Hg(II) and biothiols. The following detection limits were accomplished: (a) Hg(II): 2.8 µM; (b) glutathione: 1.7 µM; (c) cysteine: 2.3 µM; (d) homocysteine: 3.0 µM. The BN-CDs also have been successfully applied for the imaging of Hg(II) and biothiols in HepG2 cells with excellent bio-compatibility. Graphical abstract Red emissive B,N co-doped carbon dots (BN-CDs) were synthesized through hydrothermal treatment of cresyl violet and boric acid. The BN-CDs can be used as a multifunctional probe based on "on-off-on" fluorescence response for detecting mercury(II) and biothiols in aqueous solution and living cells.

Synthesis of non-modified near-infrared carbon dots for hypochlorite detection and cell membrane imaging.

Devising carbon dots with long wavelength emission (red light or near infrared), high selectivity and good bio-compatibility is critical in fluorescence detection and imaging, but achieving this goal remains a great challenge. Herein, near-infrared emissive carbon dots (NIR-CDs) with obvious emission characteristic of 653 nm were synthesized through hydrothermally treatment of toluidine bule and gallic acid. Noticeably, the NIR-CDs exhibited excellent selectivity and sensitivity to hypochlorite (ClO-), and the limit of detection is as low as 42.7 nM. The selective recognition reaction between ClO- and the surface functional groups of NIR-CDs inhibits the fluorescence from NIR-CDs. The quenching mechanism was confirmed by fluorescence lifetime decays, FT-IR spectroscopy and UV-vis absorption spectra. More remarkably, the NIR-CDs have rich hydrophilic groups showed lower cytotoxicity, excellent bio-compatibility and specific cell membrane localization ability. The established spectrofluorometric method based on NIR-CDs has been used to determination of ClO- level in tap water sample, the recoveries were 97.7 %-103.3 %. In addition, the NIR-CDs also has been successfully applied for the imaging of cell membrane. The study provides a novel idea for developing NIR ClO- probe as well as cell membrane localization probe based on CDs, which present bright prospects in real water samples monitoring and cell membrane imaging.

Cu(II)-assisted orange/green dual-emissive carbon dots for the detection and imaging of anthrax biomarker.

The spores of Bacillus anthracis are highly deadly to human beings and animals, and are concurrently potential biological warfare agents. Hence, the rapid and sensitive monitoring Bacillus anthracis biomarker, dipicolinic acid (DPA), is very desirable. Herein, orange/green dual-emissive carbon dots (OG-CDs) were synthesized via the hydrothermal approach. The OG-CDs not only emitted dual fluorescence at 527 and 590 nm under the single 503 nm excitation, but also exhibited excellent water solubility, good photostability and great salt tolerance. The fluorescence of the OG-CDs at 527 nm can be completely quenched when chelated with Cu(II). However, because of the stronger chelation between DPA and Cu(II), the fluorescence restored rapidly on subsequent addition of DPA. As such, the CD-Cu(II) system can be used for determination of DPA based on the fluorescence "off-on" response. Under optimum conditions, the detection limit for DPA was 56 nM, with a linear range of 0.5-12.5 µM. The established CD-Cu(II) based spectrofluorometric method has been applied to the analysis of DPA in real water samples with recoveries of 93.6%-104.3%. More remarkably, the CD-Cu(II) probe also has been successfully applied for the imaging of DPA in Escherichia coli with excellent bio-compatibility.

Boron and nitrogen codoped carbon dots as fluorescence sensor for Fe3+ with improved selectivity.

Carbon dots (CDs) are popular as fluorescence sensors, and metal ions are typical analytes. However, CDs used as fluorescent sensors for Fe3+ have some interferences coming from co-existed ions. In this study, we suspect that sp3 boron atom in phenylboronic acid group will be more compatible with Fe3+ to form coordination bonds, thereby increasing the selectivity to Fe3+. Hence, we designed and synthesized boron and nitrogen codoped carbon dots (BN-CDs) for detection of Fe3+ via a hydrothermal method using o-phenylenediamine (OPA) and 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzylchloroformate as precursors. From the results, we found that BN-CDs had superior selectivity to Fe3+ in the presence of the other common interfering metal ions like Cu2+, Fe2+ and Pb2+. Besides, the obtained BN-CDs exhibited good water solubility, favorable photostability, excellent pH stability between pH 2-11, and strong fluorescence intensity with quantum yield up to 31.5 %. These excellent properties of carbon dots validate that our idea is feasible, and can be used for design CDs for Fe3+ detection. Quenching mechanism study showed the fluorescence intensity of BN-CDs could be dramatically quenched by Fe3+ through dynamic and static synergy process. Finally, the as prepared BN-CDs were successfully applied to the determination of Fe3+ in fetal bovine serum and lake water.