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Tubular structured composites have attracted great interest in catalysis research owing to their void-confinement effects. In this work, we synthesized a pair of hollow N-doped carbon microtubes (NCMTs) with Fe 3 O 4 nanoparticles (NPs) encapsulated inside NCMTs (Fe 3 O 4 @NCMTs) and supported outside NCMTs (NCMTs@Fe 3 O 4 ) while keeping other structural features the same. The impact of structural effects on the catalytic activities was investigated by comparing a pair of hollow-structured nanocomposites. It was found that the Fe 3 O 4 @NCMTs possessed a higher peroxidase-like activity when compared with NCMTs@Fe 3 O 4 , demonstrating structural superiority of Fe 3 O 4 @NCMTs. Based on the excellent peroxidase-like catalytic activity and stability of Fe 3 O 4 @NCMTs, an ultra-sensitive colorimetric method was developed for the detection of H 2 O 2 and GSH with detection limits of 0.15 μM and 0.49 μM, respectively, which has potential application value in biological sciences and biotechnology.

Biomolecule-mimicking nitrogen-doped carbon dots (N-Cdots) were synthesized from dopamine by a neutralization heat strategy. Fluorescence imaging of various cells validated their nucleus-staining efficiency. The dopamine-mimicking N-Cdots "trick" nuclear membranes to achieve nuclear localization and imaging.

Magnetic resonance imaging (MRI) is used extensively for clinical diagnoses. It is critical to design and develop highly efficient MR contrast agents with simple preparation procedure, low toxicity, and high biocompatibility. Here, we report a carbon quantum dots (CQDs)-stabilized gadolinium hybrid nanoprobe (Gd-CQDs) prepared via a one-pot hydrothermal treatment of the mixture of citrate acid, ethanediamine, and GdCl3 at 200 °C for 4 h. In vitro and in vivo tests confirmed their low toxicity and high biocompatibility. Gd-CQDs were observed to have a higher MR response than gadopentetic acid dimeglumine (Gd-DTPA) because of their high Gd content and hydrophilicity. Moreover, the fluorescence of CQDs was remained in Gd-CQDs. The in vivo MR and fluorescence dual-modality imaging of Gd-CQDs was confirmed with zebrafish embryo and mice as models. The modification of Gd-CQDs with arginine-glycine-aspartic acid (RGD) tripeptide provided a high affinity to U87 cancer cells for targeted imaging. Whereas the MR response showed a depth penetration and spatial visualization, fluorescence revealed the fine distribution of Gd-CQDs in tissues because of its high resolution and sensitivity. We found that Gd-CQDs distributed in the tissues in a heterogeneous mode: they entered into the tissue cells but were observed less in the extracellular matrix. The MR and fluorescence dual-modality imaging of Gd-CQDs makes them a potential contrast agent for clinic applications because of their simple preparation procedure, ease of functionalization, high contrast efficiency, low toxicity, and high biocompatibility.

The study of the composition, morphology, and surface structure of carbon dots (Cdots) is critical to understanding their effect on the photo- and electrochemiluminescence (PL and ECL) of Cdots in selected applications. Herein, two kinds of Cdots were prepared with 3-(3,4-dihydroxyphenyl)-L-alanine (L-DOPA) as precursor. The Cdots prepared by using a carbonization-extraction strategy have a low oxidation level and are denoted as reduced Cdots (r-Cdots). The Cdots obtained with a carbonization-oxidation process are highly oxidized and are denoted as oxidized Cdots (o-Cdots). The o-Cdots have a carbon core and oxygen-containing loose shell, but the r-Cdots consist mainly of the carbon core. Whereas r-Cdots have a strong blue PL but no apparent ECL response, o-Cdots exhibit a relatively weak PL and strong ECL emission. These properties allow for selected applications of the Cdots. The r-Cdots were used in cell imaging with their high PL emission. The o-Cdots, with their high ECL efficiencies, were selected to sense Cu(2+) with Cu(2+) -inducing ECL quenching in the o-Cdots/K2 S2 O8 system. This work provides the possibility to control the composition of Cdots for selected applications and shows a good way to characterize surface traps of Cdots because ECL is characterized by the surface-state and PL is mainly related to the core-state in Cdots., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Carbon dots (Cdots) are an important probe for imaging and sensing applications because of their fluorescence property, good biocompatibility, and low toxicity. However, complex procedures and strong acid treatment are often required and Cdots suffer from low photoluminescence (PL) emission. Herein, a facile and general strategy using carbonization of precursors and then extraction with solvents is proposed for the preparation of nitrogen-doped Cdots (N-Cdots) with 3-(3,4-dihydroxyphenyl)-L-alanine (L-DOPA), L-histidine, and L-arginine as precursor models. After they are heated, the precursors become carbonized. Nitrogen-doped Cdots are subsequently extracted into N,N'-dimethylformamide (DMF) from the carbogenic solid. A core-shell structure of Cdots with a carbon core and the oxygen-containing shell was observed. Nitrogen has different forms in N-Cdots and oxidized N-Cdots. The doped nitrogen and low oxidation level in N-Cdots improve their emission significantly. The N-Cdots show an emission with a nitrogen-content-dependent intensity and Cdot-size-dependent emission-peak wavelength. Imaging of HeLa cells, a human cervical cancer cell line, and HepG2 cells, a human hepatocellular liver carcinoma line, was observed with high resolution using N-Cdots as a probe and validates their use in imaging applications and their multicolor property in the living cell system., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The excitation-dependent emission properties of carbon dots (Cdots) are extensively reported, but their red emission is often weak, limiting their wider application. Here we introduce ethidium bromide, as a functional precursor with red emission, to enhance the red emission for Cdots, with comparable intensity at a broad wavelength range to multi-emission Cdots (M-Cdots). We found that Cdots prepared with ethidium bromide/ethylenediamine exhibited strong blue and red emission at 440 and 615 nm, with optimal excitation at 360 and 470 nm as M-Cdots, respectively, but the Cdots from single ethidium bromide (EB-Cdots) possessed weak red emission. M-Cdots exhibited a broad absorption band at 478 nm, but a band blue-shifted to 425 nm was observed for EB-Cdots, while no absorption was observed at 478–425 nm for the Cdots prepared with citric acid and ethylenediamine. Thus, we proposed that C=O and C=N formed a π-conjugation structure as the absorption band at 478 nm for the red emission of M-Cdots, as also confirmed with the excitation at 470 nm. Moreover, the π-conjugation structure is fragile and sensitive to harsh conditions, so red emission was difficult to observe for the Cdots prepared with citric acid/ethylenediamine or single ethidium bromide. M-Cdots possess two centers for blue and red emission with different structures. The dual emission was therefore used for ratiometric sensing with dichromate (Cr2O72−) and formaldehyde (HCHO) as the targets using the intensity ratio of the emissions at 615 and 440 nm. Due to the comparable intensity at a broad wavelength range, we designed encryption codes with five excitations at 360, 400, 420, 450, and 470 nm as the inputs, and the emission colors were used for information decoding. Thus, we determined why red emission was difficult to realize for Cdots, and our results could motivate the design of red-emission Cdots for extensive applications. [ABSTRACT FROM AUTHOR]

Anchoring bimetallic alloys in a one-dimensional(1D) heteroatom-doped carbon matrix with excellent electro-conductibility is a powerful strategy for the reduction of 4-nitrophenol (4-NP). Herein, we report the design and fabrication of CoNi bimetallic nanoparticles (NPs) decorated on N, P, and S-doped carbon/MnO nanowires (NWs) as an active catalyst for the reduction of 4-NP. The CoNi bimetallic NPs enable the full utilization of accessible edge sites, and the unique 1D framework creates a large surface area, exposing abundant active sites and providing a fast charge/ionic diffusion pathway. Moreover, the synergistic electronic interaction between the CoNi NPs and N, P and S co-doped carbon layer leads to optimal electronic structures and good adhesion ability, thus facilitating the catalytic performance. As a result, the obtained CoNi decorated on N, P, and S-doped carbon/MnO NWs exhibited superior catalytic activities in the reduction of 4-NP as well as robust stability in catalyst recycling. This work highlights the effect of rationally constructing a 1D bimetallic catalyst. [ABSTRACT FROM AUTHOR]

Engineering a tube-like architecture with bimetallic nanoparticles (NPs) has been considered an effective strategy for enhancing catalytic performance. Herein, we report a simple method for preparing one-dimensional (1D) carbon-based tubular composites incorporated with bimetallic active CoNi alloy NPs. CoNi alloy NPs were produced from the co-reduction of Co and Ni ions existing within a zeolitic imidazolate framework (ZIF)-based precursor and polydopamine (PDA) layer after N2-protected thermal treatment. Moreover, the coated PDA outer layer was preserved for constructing a tubular structure, which eventually resulted in a composite of N-doped carbon microtubes (NCMTs) and CoNi NPs (CoNi@NCMTs). The resultant CoNi@NCMTs exhibited excellent catalytic activity for reducing 4-nitrophenol to 4-aminophenol. The synergy between the N-doped carbon microtubes and the well-dispersed bimetallic CoNi NPs provided outstanding catalytic performance, constructing inexpensive transition metal nanocatalysts. Moreover, the catalytic activity of the CoNi@NCMTs was well conserved even after five consecutive cyclic reactions. Importantly, hierarchical MoO3@CoNi-LDH can be a good precursor to obtain tube-like structured CoNi-LDH, CoNi-LDH@SiO2 and CoNi-LDH@NiMoO4 composites. [ABSTRACT FROM AUTHOR]

13C-engineered carbon quantum dots (13C-QDs) were used as magnetic resonance (MR) and fluorescence dual-response probe. The enhanced 13C-MR signal was observed at 171 ppm from carboxylic and carboxyl carbons in 13C-QDs with 160-fold improvement on signal-to-noise ratio even when no hyperpolarization was applied, whereas the intrinsic fluorescence of C-QDs was still maintained. The stable MR and fluorescence dual-response was successfully used for long-term observation of zebrafish embryonic development. Cross-validation between MR and fluorescence confirmed the distribution of 13C-QD in zebrafish. 13C-MR provides specific information about the presence, magnitude, and progression of 13C-QDs by defining MR intensity, whereas fluorescence reveals the location of 13C-QDs with its high sensitivity. 13C-MR and fluorescence was simultaneously observed within 13C-QDs, and this work may expand the applications of isotope-engineered nanomaterials. [ABSTRACT FROM AUTHOR]

The study of the composition, morphology, and surface structure of carbon dots (Cdots) is critical to understanding their effect on the photo- and electrochemiluminescence (PL and ECL) of Cdots in selected applications. Herein, two kinds of Cdots were prepared with 3-(3,4-dihydroxyphenyl)- L-alanine ( L-DOPA) as precursor. The Cdots prepared by using a carbonization-extraction strategy have a low oxidation level and are denoted as reduced Cdots (r-Cdots). The Cdots obtained with a carbonization-oxidation process are highly oxidized and are denoted as oxidized Cdots (o-Cdots). The o-Cdots have a carbon core and oxygen-containing loose shell, but the r-Cdots consist mainly of the carbon core. Whereas r-Cdots have a strong blue PL but no apparent ECL response, o-Cdots exhibit a relatively weak PL and strong ECL emission. These properties allow for selected applications of the Cdots. The r-Cdots were used in cell imaging with their high PL emission. The o-Cdots, with their high ECL efficiencies, were selected to sense Cu2+ with Cu2+-inducing ECL quenching in the o-Cdots/K2S2O8 system. This work provides the possibility to control the composition of Cdots for selected applications and shows a good way to characterize surface traps of Cdots because ECL is characterized by the surface-state and PL is mainly related to the core-state in Cdots. [ABSTRACT FROM AUTHOR]