Chuanxi Wang

Tunable near-infrared fluorescent gold nanoclusters: temperature sensor and targeted bioimaging

Near-infrared (NIR) fluorescence nanomaterials with low toxicity and long wavelength emission play an important role in bioapplications. Herein, a simple and rapid microwave heating method is designed to synthesize fluorescent gold nanoclusters (AuNCs) by using glutathione (GSH) as a reducing agent and stabilizing agent simultaneously. By adjusting the microwave heating time, the as-prepared GSH–AuNCs can show size-dependent tunable fluorescence from the visible region to the NIR region, and even to 800 nm wavelength. Besides, the as-prepared GSH–AuNCs are water-soluble, low toxicity and highly stable, and exhibit multifunctional surface chemistry based on GSH as the protective surface layer. Another attractive feature of the resultant NIR GSH–AuNCs is temperature-dependent fluorescence and they could be used as a nanoprobe to measure the temperature in the range from 0 to 80 °C. Moreover, this process is reversible, which means that the fluorescence intensity of the GSH–AuNCs can be recovered to the initial intensity when the temperature changes reversibly. Finally, the resultant NIR GSH–AuNCs are further conjugated with folic acids (FAs) which helps the AuNCs target HeLa cells. These properties provide FA-conjugated GSH–AuNCs with potential applications as a platform for cancer diagnosis studies in various biological systems.

Yellow-emitting carbon-dots-impregnated carboxy methyl cellulose/poly-vinyl-alcohol and chitosan: stable, freestanding, enhanced-quenching Cu2+-ions sensor

Carbon dots (CDs) have a combination of desirable fluorescence and chemical properties, which makes them relevant for sensing in aqueous environments. However, CDs suffer from aggregation-induced instabilities in their sensing performance. In this study, we attempted to address this problem by focusing on Cu2+-ions detection compliant with US Environment Protection Agencys (EPA) standards (i.e. requiring detection as low as 1.3 ppm). The as-prepared yellow-emitting carbon dots (y-CDs) prepared via a one-step hydrothermal process had high water dispersivity and prominent fluorescence properties. However there were two contrary mechanisms (aggregation-caused quenching vs. the chelation-enhanced fluorescence effect) for y-CDs with the addition of Cu2+ ions. The y-CDs/polymer composite sensor reported here comes in two forms: y-CDs impregnated with: (a) carboxy methyl cellulose/poly-vinyl-alcohol or (b) chitosan. Although selectivity existed in both (a) and (b), the sensor response of (b) films was remarkably more sensitive than that of (a) films, due to the chelation mechanism of chitosan with Cu2+ ions. Through an optimized sample of system (b), a 10 nM/1.3 ppm detection limit for Cu2+ ions was achieved, which shows it was EPA compliant.

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.

Concentration-dependent color tunability of nitrogen-doped carbon dots and their application for iron(III) detection and multicolor bioimaging

Nitrogen doping can effectly adjust the compositions and structures of carbon dots and hence enhance their fluorescence. In this work, we report a fast and low-cost route for synthesis of nitrogen-doped carbon dots (N-CDs) by microwave pyrolysis of citric acid and ammonium within 7 min. The as-prepared N-CDs contain plentiful oxygen and nitrogen functional groups, and dispaly intense fluorescence with high quantum yield of ca. 44.3% and have an average size of 1.8 nm. The obtained N-CDs exhibit highly stable against photobleaching, ionic strengths, and can be used for selective and sensitive detection of Fe(III). It is postulated that the Fe3+-mediated fluorescence quenching is attributed to the charge transfer between N-CDs and Fe3+. In particular, the emission peaks from blue to red region can be tuned by interparticle distance of N-CDs, simply by increasing the concentration of N-CDs in aqueous solution, which indicates its potential applications as a promising optical image probe in multicolor cellular imaging.

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.

Facile fabrication of PS/Fe3O4@PANi nanocomposite particles and their application for the effective removal of Cu2+

This work presents a simple and straightforward approach to fabricating multifunctional nanocomposite particles which possess a core of a polystyrene (PS) particle, a transition layer of magnetic Fe3O4 nanoparticles (NPs), and an outer shell of adsorbable polyaniline (PANi). In detail, the positively charged Fe3O4 NPs synthesized via the chemical co-precipitation method are directly loaded onto the negatively charged surfaces of the PS particles obtained by emulsifier-free emulsion polymerization through electrostatic self-assembly; subsequently, the coating of the resultant PS/Fe3O4 nanocomposite particles with PANi was successfully achieved by virtue of the “swelling–diffusion–interfacial-polymerization method” (SDIPM). Furthermore, the adsorption of Cu2+ by PS/Fe3O4@PANi nanocomposite particles was investigated by changing the initial pH value, adsorption time, and initial concentration of the adsorbate. The adsorption data in our work follow a pseudo-second-order kinetics model and fit the Langmuir isotherm model. The PS/Fe3O4@PANi nanocomposite particles show that the maximum adsorption capacity is up to 181.5 mg g−1 at pH 5. More importantly, these nanocomposite particles can be easily recovered using an external magnetic field owing to the presence of Fe3O4 NPs, and the regenerated nanocomposite particles can be repeatedly used for eight cycles without significant loss of their adsorption capacity.

A simple and general approach for the decoration of interior surfaces of silica hollow microspheres with noble metal nanoparticles and their application in catalysis

Precise control of the size, composition, and assembly process of each component is expected to play a key role in the construction of integrated functional nanostructures. Herein we report a unique sacrificial template method for the fabrication of noble metal@silica hollow microspheres with noble metal (Au, Pt, and Pd) nanoparticles uniformly immobilized on the inner surfaces of silica hollow microspheres. A polystyrene microsphere as a sacrificial template is used to play dual roles, creating a cavity inside the silica microsphere and introducing noble metal nanoparticles into the silica microsphere. Distinct from the reported sacrificial template methods, this method takes advantage of a thermodynamic effect to easily deposit the noble metal nanoparticles with different sizes and compositions onto the template microspheres. In addition, taking Au@silica hollow microspheres for example, they exhibit excellent catalytic activity and recyclability for the reduction of p-nitrophenol (4-NP) by NaBH4.

Polycation-functionalized gold nanodots with tunable near-infrared fluorescence for simultaneous gene delivery and cell imaging

Near-infrared (NIR) fluorescent metal nanodots may have significant advantages in biological detection and bioimaging. Herein, we introduce tunable near-infrared fluorescent gold nanodots (AuNDs) protected by branched polyethylenimine (PEI) modified by surface segmental attachment of sulfhydryl groups (PEI-SH), abbreviated as PEI-SH-AuNDs, for simultaneous gene delivery and cell imaging. The modified PEI endows the resultant PEI-SH-AuNDs with the following excellent advantages. Sulfhydryl groups of PEI-SH anchor to the surface of AuNDs, and such polycations with amine groups give PEI-SH-AuNDs remarkable stability. The cationic polymer PEI-SH with positive charges enables PEI-SH-AuNDs to perform gene delivery, and the gene transfection efficiency can reach 22.8%. Moreover, the fluorescence of PEI-SH-AuNDs is tunable from visible red light (wavelength 609 nm) to NIR light (wavelength 811 nm) via an increase in the size of AuNDs. PEI-SH-AuNDs yielded gene transfection efficiency similar to that of commercial PEI, but showed much lower cytotoxicity and much greater red-shift fluorescence. With excellent photoluminescent properties, such multifunctional fluorescent PEI-SH-AuNDs hold promise in applications to bioimaging and as ideal fluorescent probes for tracking gene transfection behavior.

Simple surface-assisted formation of palladium nanoparticles on polystyrene microspheres and their application in catalysis

A facile and green approach has been developed for fabricating well-dispersed palladium nanoparticles (Pd NPs) supported on the surface of poly(N-vinylpyrrolidone) (PVP)-stabilized polystyrene (PS) microspheres. The strategy harnesses the reducing ability of PVP and the affinity between PVP and Pd NPs to achieve in situ surface-assisted growth of small noble metal NPs on the PS microspheres, without involving any additional stabilizer or reducing agent. The stabilizer-free formation contributes to the superior availability and accessibility of active sites for catalysis. The resulting PS/Pd composite particles have demonstrated excellent catalytic performance in the probe reaction of 4-nitrophenol reduction. As far as we know, this approach has been the first straightforward in situ deposition of Pd NPs on the PS microspheres, obviating surface treatment and the use of an exogenous reducing agent or a stabilizer. Furthermore, it is extendable to the fabrication of other composite systems, PS/Ag composite particles for example.