Yecheng Li

Graphene and g-C3N4 nanosheets cowrapped elemental α-sulfur as a novel metal-free heterojunction photocatalyst for bacterial inactivation under visible-light.

A new class of metal-free heterojunction photocatalysts was prepared by wrapping reduced graphene oxide (RGO) and g-C3N4 (CN) sheets on crystals of cyclooctasulfur (α-S8). Two distinctive structures were fabricated by wrapping RGO and CN sheets in different orders. The first was RGO sheets sandwiched in heterojunction of CN sheets and α-S8 (i.e., CNRGOS8), while the second structure was the other way around (i.e., RGOCNS8). Both structures exhibited antibacterial activity under visible-light irradiation. CNRGOS8 showed stronger bacterial inactivation than RGOCNS8 in aerobic conditions. However, RGOCNS8 was more active than CNRGOS8 under anaerobic condition. A possible mechanism was proposed to explain the differences between photocatalytic oxidative inactivation and reductive inactivation. As a proof-of-concept, this work could offer new inroads into exploration and utilization of graphene sheets and g-C3N4 sheets cowrapped nanocomposites for environmental applications.

Chemical modification of inorganic nanostructures for targeted and controlled drug delivery in cancer treatment

Chemically modified inorganic nanoparticles (NPs) hold great promise for biomedical applications. In this review, we examine the recent advances in nanotechnology for targeted drug delivery and controlled drug release. The development of an effective drug delivery system requires good understanding of the chemical and physical properties that affect the interaction of nanoparticles with the biological environment. A robust drug carrier should have an appropriate circulation time and should not exert any harmful effect on normal cells. The nanostructures involved must satisfy the requirements of no pre-release of drugs, stability and biocompatibility in vivo, targeted delivery to cancer cells/inflammation area, and on-demand release of drugs. Herein we summarize the surface modifications of nanostructures to achieve systematic targeting to intended sites and controlled release by different stimuli, including pH, redox, light, enzyme and so on. The use of DNA, proteins and other biomolecules opens a new gate to create smart nanocarriers for anti-cancer drugs.

Porous TiO2 Materials through Pickering High-Internal Phase Emulsion Templating

We report a facile method for preparing porous structured TiO2 materials by templating from Pickering high-internal phase emulsions (HIPEs). A Pickering HIPE with an internal phase of up to 80 vol %, stabilized by poly(N-isopropylacrylamide)-based microgels and TiO2 solid nanoparticles, was first formulated and employed as a template to prepare the porous TiO2 materials with an interconnected structure. The resultant materials were characterized by scanning electron microscopy, X-ray diffraction, and mercury intrusion. Our results showed that the parent emulsion droplets promoted the formation of macropores and interconnecting throats with sizes of ~50 and ~10 μm, respectively, while the interfacially adsorbed microgel stabilizers drove the formation of smaller pores (~100 nm) throughout the macroporous walls after drying and sintering. The interconnected structured network with the bimodal pores could be well preserved after calcinations at 800 °C. In addition, the photocatalytic activity of the fabricated TiO2 was evaluated by measuring the photodegradation of Rhodamine B in water. Our results revealed that the fabricated TiO2 materials are good photocatalysts, showing enhanced activity and stability in photodegrading organic molecules.

Mesoporous carbon/CuS nanocomposites for pH-dependent drug delivery and near-infrared chemo-photothermal therapy

Spurred by the recent development in nanotechnology, multi-functional therapeutic platforms have emerged as promising anti-cancer treatments for their combinational effects. In this paper, we report a novel drug delivery system composed of mesoporous carbon nanospheres (MCN) of 150 to 200 nm in diameter capped with copper sulfide (CuS) nanoparticles (NPs). MCNs can efficiently load doxorubicin (DOX, an anti-cancer drug) due to their hollow and porous structures as well as the π–π stacking interactions between MCN and DOX. DOX is retained in MCN under a basic and physiological environment, but releases rapidly under an acidic environment in its ionized state. Due to the intrinsic near-infrared (NIR) absorption and photothermal conversion ability of copper sulfide nanoparticles, heat is generated for killing tumor cells as well as stimulating DOX release upon NIR irradiation. Thus, this complex (MCN–CuS) exhibits efficient drug loading, low pre-release, temperature-, NIR- and pH-responsive DOX release, and combined antitumor activity.

Assembly of polyethylenimine-functionalized iron oxide nanoparticles as agents for DNA transfection with magnetofection technique

Various kinds of inorganic nanoparticles have been used as non-viral gene carriers. Two fundamental roles of gene carriers are to bind the DNA molecules and to protect them from enzymatic attack after internalization into the cells. Therefore, all nanoparticles that are used as gene carriers must be functionalized. Lately, magnetic gene carriers incorporating PEI have been adopted to improve DNA transfection efficiency. Researchers have used PEI-coated MNPs for DNA entrapment, and they have found that this complex was not able to achieve an efficient DNA transfection, but needed an extra free PEI to deliver the DNA to the cell nucleus. In this study, magnetic gene carriers with small sizes and surface modifications were prepared to explore the magnetofection process. Different methods for PEI immobilization on smaller MNPs were adopted to compare DNA binding abilities, transfection and transient gene expression efficiencies. Finally, the magnetofection process was studied with confocal microscopy and flow cytometry. These results provide details regarding the mechanism of DNA magnetofection, which has not been yet fully understood.

Redox-responsive controlled DNA transfection and gene silencing based on polymer-conjugated magnetic nanoparticles

Gene or DNA transfection is a non-viral tool for therapy on gene-based diseases by delivering nucleic acids into the target cells and change gene functions or protein expressions. The efficiency of gene transfection may be enhanced by magnetofection, which uses magnetic fields to concentrate magnetic nano-particles (MNPs) containing nucleic acid into the target cells. To protect from degradation after cellular uptake, MNPs are usually modified with cationic compounds such as polyethylenimine (PEI). After adsorption of plasmid DNAs onto the surface of positively charged MNPs, addition of extra free PEI is often required to form a ternary complex for magnetofection. It is because only the cationic compound could escape from the endosomes and transfers the nucleic acids into the cell nucleus, while the MNPs stay only in the perinuclear region. In this study, a redox-responsive disulfide bond was used to link 25 kDa PEI to MNPs, generating detachable PEIs for DNA protection, endosomal escape and nuclear entry. The as-synthesized MNPs were first wrapped in silica with thiol groups on the surface. After thiol exchange with 2-carboxyethyl-2-pyridyl disulfide, PEI was linked to the carboxyl groups with EDC/NHS chemistry. The magnetic gene carrier exhibited not only efficient DNA transfection but also a gene silencing effect as tested in both HeLa and HepG2 cells. After adding glutathione (GSH) as a trigger, plasmid DNA was released from the nanoparticles, confirming the redox-responsive property of the modified magnetic nanoparticles. The confocal microscopy images showed the labeled plasmid DNA located in the nucleus 3 h post-transfection, which was more obvious in 24 h after transfection. The co-localization of PEI and plasmid DNA in the nucleus confirmed the nucleic acids were taken in with the help of PEI, while nanoparticles remained in the perinuclear region. Our results demonstrate that the polymer-conjugated magnetic nanoparticles are effective DNA and siRNA carriers in vitro.

A metal-free composite photocatalyst of graphene quantum dots deposited on red phosphorus

A simple approach to enhance the photocatalytic activity of red phosphorus (P) was developed. A mechanical ball milling method was applied to reduce the size of red P and to deposit graphene quantum dots onto red P. The product was characterized by scanning electron microscopy, transmission electron microscopy, contact angle measurements, zeta-potential measurements, X-ray diffraction and UV-vis absorption spectroscopy. The product exhibited high visible-light-driven photocatalytic performance in the photodegradation of rhodamine B.

Free-standing red phosphorous/silver sponge monolith as an efficient and easily recyclable macroscale photocatalyst for organic pollutant degradation under visible light irradiation

Traditional nano-sized photocatalysts in powdery form suffer from difficulties in recyclability, and have to be immobilized before practical applications. In this study, red phosphorous/silver (red P/Ag) sponge monolith was discovered to be a new free-standing macroscale photocatalyst, which was fabricated by a one-pot hydrothermal method without using any organic surfactants or templates for the first time. The elemental red P not only functioned as a reducing agent in the formation of Ag sponge monolith during the synthesis processes, but also as the active photocatalyst in-situ immobilized onto the Ag sponge. The as-prepared red P/Ag sponge monolith showed enhanced photocatalytic activity than that of traditional pure powdery red P by a factor of 3.1 times for organic pollutants (i.e. Rhodamine 6G, phenol) degradation under visible light irradiation. The enhancement was mainly attributed to the function of Ag sponge served as good electron sink to trap photo-generated electrons. More importantly, such free-standing macroscale photocatalyst can be easily recycled without activity deterioration. As a proof of concept, this work provides new insights into not only for the development of red P-based elemental photocatalysts, but also for the one-pot fabrication of novel free-standing macroscale materials with excellent photocatalytic activity for practical environmental applications.