Huihui Lin

Colloidal synthesis of MoS2 quantum dots: size-dependent tunable photoluminescence and bioimaging

Although the synthesis of two-dimensional (2D) layered MoS2 nanomaterials has been developing rapidly, there are many technical issues in preparing MoS2 quantum dots (QDs) with photoluminescence properties. Herein, we design a facile colloidal chemical route to prepare photoluminescent MoS2 QDs using ammonium tetrathiomolybdate ((NH4)2MoS4) as a precursor and oleyl amine as a reducing agent. The optical properties and structure of as-prepared MoS2 QDs are investigated systematically. The resultant MoS2 QDs exhibit fluorescence (λmax = 575 nm; quantum yield, 4.4%), spherical morphology with a uniform thickness of ∼3 nm and an excitation-dependent PL phenomenon. Moreover, the resultant MoS2 QDs show size-dependent tunable photoluminescence in the wide visible region. With the help of amphiphilic compounds, the resultant MoS2 QDs could be transferred from an organic to an aqueous phase. MoS2 QDs in aqueous solution have many advantages, such as good dispersion, low toxicity and photoluminescent properties, which make them promising materials for application in optoelectronic and biological fields. In this study, the 293T cells are used as a model to evaluate the fluorescence imaging of MoS2 QDs. The results confirm that the fluorescent signal appears in the cytoplasm which demonstrates that as-prepared MoS2 QDs could be used as a probe for real-time optical cellular imaging.

One-step hydrothermal synthesis of flowerlike MoS2/CdS heterostructures for enhanced visible-light photocatalytic activities

Herein, we report flowerlike MoS2/CdS heterostructures prepared by a simple hydrothermal method. The structure and morphology of products are characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The experimental results indicate that the as-prepared products show a flowerlike nanostructure with size at 800 nm. This flowerlike nanostructure has a large surface area and may provide a better anchoring surface for adsorbing molecules. Very importantly, as-prepared flowerlike MoS2/CdS heterostructures exhibit excellent performance in adsorption and a higher photocatalytic activity for degrading methylene blue under the excitation of visible light than pure CdS or pure MoS2. These characteristics enable this novel flowerlike heterostructural nanomaterial to perform potential applications in water treatment, degradation of dye pollutants, and environmental cleaning.

Glutathione modified carbon-dots: from aggregation-induced emission enhancement properties to a “turn-on” sensing of temperature/Fe3+ ions in cells

In this paper, a novel “turn-on” chemosensor for detecting temperature and Fe3+ has been designed. This nanosensor is based on the aggregation-induced emission enhancement (AIEE) properties of fluorescent carbon dots (CDs). The CDs prepared by a facile hydrothermal route show blue emission (λem = 505 nm) with a quantum yield of 4.7%. The resultant CDs are modified by glutathione (GSH) on the surface through the carbodiimide-activated coupling reaction. The as-prepared GSH-CDs show good dispersion, high fluorescence and AIEE phenomenon. Resultant GSH-CDs would be aggregated by Fe3+ ions in aqueous solution which results in enhanced fluorescence. Therefore, such GSH-CDs would be excellent candidates as fluorescent probes for the label-free detection of Fe3+ ions with a limit of detection of 0.1 μM. Moreover, the PL intensity of GSH-CDs increases progressively with increasing temperature and they could be used in optical thermometry over a wide temperature range (25–80 °C) with small temperature resolution (∼0.5 °C). Using MC3T3-E1 cells as the model, the resultant nanosensor is demonstrated to monitor temperature and Fe3+ ions in cells. Thus, resultant GSH-CDs could be used as a “turn-on” sensor for highly sensitive and selective detection of temperature and Fe3+ ions in aqueous solution and biosystems.

Gold nanoparticle-enhanced near infrared fluorescent nanocomposites for targeted bio-imaging

Low toxicity and near infrared (NIR) fluorescent nanomaterials have many advantages in biological imaging. Herein, based on metal-enhanced fluorescence (MEF), novel NIR fluorescent nanocomposites (Au/SiO2/Ag2S core–shell microspheres) are designed and investigated. Characterization with UV, PL, TEM, FTIR and XPS confirms the fact that NIR Au/SiO2/Ag2S nanocomposites were prepared. The effects on the MEF including the metal core size (gold nanoparticles), and the distance between the fluorescent molecules (Ag2S nanoclusters (NCs)) and the metal core are systematically studied. The results show that the developed nanocomposites can effectively enhance the NIR fluorescence signal of the Ag2S NCs. A maximum enhancement is obtained when the nanocomposites contain a 25 nm gold nanoparticle core and a 34 ± 2 nm silica spacer. SiO2 as an important scaffold which could prevent NC aggregation and can be easily modified with functional groups (thiol, carboxyl and amine). These characteristics are beneficial for the further conjugation with folic acid (FA). FA-conjugated Au/SiO2/Ag2S nanocomposites show specific targeting of HeLa cells compared with 293T cells. With these properties provided, these nanocomposites have potential applications in distinguishing folate receptor-positive cancer cells from normal cells.

Gold nanoclusters based dual-emission hollow TiO2 microsphere for ratiometric optical thermometry

In this work, we develop a novel dual-emitting hollow TiO2 microsphere with high stability and attractive thermal sensitivity, which could work as nanosensor for accurately measuring temperature. This nanosensor is prepared through coating gold nanocluster (AuNCs) on the surface of carbon dots-doped hollow TiO2 microsphere. As-prepared nanosensor shows characteristic dual-emitting property of carbon dots (CDs, blue fluorescence) and AuNCs (red fluorescence) under a single excitation wavelength. Moreover, upon increasing the temperature, the intensity of red emission from the AuNCs continuously quenched, whereas that of blue emission from the CDs remained nearly constant. The different response results in a continuous fluorescence color change from red to purple that can be clearly observed by the naked eyes. Thus, as-prepared dual-emitting hollow TiO2 microsphere could be used as optical thermometry by taking the advantage of the temperature sensitivity of their fluorescence intensity ratio (red/blue) with high reliability and accuracy, which change considerably over the wide temperature range (20–80 °C) with small temperature resolution (∼0.5 °C). Additionally, this nanosensor is successfully applied in 10 mM buffered saline (PBS) solution with physiological temperature ranging from 20 to 45 °C, which suggests as-prepared dual-emitting microspheres have promising applications in vivo temperature sensing.

A facile strategy for the synthesis of ferroferric oxide/titanium dioxide/molybdenum disulfide heterostructures as a magnetically separable photocatalyst under visible-light

Semiconductor photocatalysts is a promising approach to combat both environmental pollution and global energy shortage despite the challenges of recycling and stability. In this paper, magnetic Fe3O4 particle is introduced in the system and Fe3O4/TiO2/MoS2 heterostructures can be formed in a facile strategy. The morphology and structure of Fe3O4/TiO2/MoS2 can be controlled by adjusting the hydrolysis rate of the titanium source. MoS2 is designed to fill in the mesoporous of TiO2 core, forming heterojunction on the surface and near-surface of TiO2 under solvothermal conditions. With respect to the decomposition of a rhodamine B (RhB) solution under visible light, the Fe3O4/TiO2/MoS2 heterostructures display highly photocatalytic activities in aqueous solutions, and they can be easily recovered to realize cyclic utilization by applying an external magnetic field. Thus, the effective magnetic recycle of the catalyst is achieved, and high visible light catalytic activity is ensured simultaneously. Since the current method is simple and flexible to create recyclable catalysts with high stability in this way, it could promote the practicability of semiconductor photocatalysts in water treatment, degradation of dye pollutants, and environmental cleaning.

Morphology-controlled synthesis of TiO2/MoS2 nanocomposites with enhanced visible-light photocatalytic activity

The development of photocatalysts that utilize sunlight is very important for solving the energy crisis and reducing environmental pollution. In this report, two kinds of TiO2/MoS2 cocatalyst with novel morphologies (hollow and yolk–shell structure) are prepared via a polymer assisted targeted-etching method. MoS2, as a typical two-dimensional (2D) layered transition metal sulfide, can accept electrons and provide active sites for photocatalytic reactions. Besides, with the assistance of MoS2, the absorption band of the resultant heterostructures becomes broader and covers the entire visible region. Thus the photocatalytic activity of TiO2 in the visible light region can be improved. Moreover, the hollow and yolk–shell heterostructures of TiO2/MoS2 possess a high specific surface area, and the excellent interface of the heterostructures enables the easy separation of holes and electrons, which can enhance the photodegradation of dye. The results demonstrate that the as-prepared TiO2/MoS2 nanocomposites with hollow and yolk–shell structures show outstanding catalytic activity which is tested through the degradation of methylene blue and rhodamine B under visible light. Our design provides a new strategy to acquire novel photocatalysts, with various nanostructures, that have remarkable potential applications in environmental protection, e.g. water treatment and dye pollutant degradation.