Yapeng Li

Layer-by-Layer Assembled Fe3O4@C@CdTe Core/Shell Microspheres as Separable Luminescent Probe for Sensitive Sensing of Cu2+ Ions

A novel multifunctional microsphere with a fluorescent CdTe quantum dots (QDs) shell and a magnetic core (Fe(3)O(4)) has been successfully developed and prepared by a combination of the hydrothermal method and layer-by-layer (LBL) self-assembly technique. The resulting fluorescent Fe(3)O(4)@C@CdTe core/shell microspheres are utilized as a chemosensor for ultrasensitive Cu(2+) ion detection. The fluorescence of the obtained chemosensor could be quenched effectively by Cu(2+) ions. The quenching mechanism was studied and the results showed the existence of both static and dynamic quenching processes. However, static quenching is the more prominent of the two. The modified Stern-Volmer equation showed a good linear response (R(2) = 0.9957) in the range 1-10 μM with a quenching constant (K(sv)) of 4.9 × 10(4) M(-1). Most importantly, magnetic measurements showed that the Fe(3)O(4)@C@CdTe core/shell microspheres were superparamagnetic and they could be separated and collected easily using a commercial magnet in 10 s. These results obtained not only provide a way to solve the embarrassments in practical sensing applications of QDs, but also enable the fabrication of other multifunctional nanostructure-based hybrid nanomaterials.

Preparation of a durable superhydrophobic membrane by electrospinning poly (vinylidene fluoride) (PVDF) mixed with epoxy–siloxane modified SiO2 nanoparticles: A possible route to superhydrophobic surfaces with low water sliding angle and high water contact angle

A durable superhydrophobic surface with low water sliding angle (SA) and high water contact angle (CA) was obtained by electrospinning poly (vinylidene fluoride) (PVDF) which was mixed with epoxy-siloxane modified SiO(2) nanoparticles. To increase the roughness, modified SiO(2) nanoparticles were introduced into PVDF precursor solution. Then in the electrospinning process, nano-sized SiO(2) particles irregularly inlayed (it could also be regard as self-assembly) in the surface of the micro-sized PVDF mini-islands so as to form a dual-scale structure. This structure was responsible for the superhydrophobicity and self-cleaning property. In addition, epoxy-siloxane copolymer was used to modify the surface of SiO(2) nanoparticles so that the SiO(2) nanoparticles could stick to the surface of the micro-sized PVDF mini-islands. Through the underwater immersion test, the SiO(2) nanoparticles cannot be separated from PVDF easily so as to achieve the effect of durability. We chiefly explore the surface wettability and the relationship between the mass ratio of modified SiO(2) nanoparticles/PVDF and the CA, SA of electrospun mat. As the content of modified SiO(2) nanoparticles increased, the value of CA increased, ranging from 145.6° to 161.2°, and the water SA decreased to 2.17°, apparently indicating that the membrane we fabricated has a perfect effect of superhydrophobicity.

Novel water-soluble and pH-responsive anticancer drug nanocarriers: Doxorubicin–PAMAM dendrimer conjugates attached to superparamagnetic iron oxide nanoparticles (IONPs)

PH-responsive drug release system based on the conjugates of PAMAM dendrimers-doxorubicin (PAMAM-DOX) and superparamagnetic iron oxide (Fe(3)O(4)) nanoparticles (IONPs) has been constructed and characterized. The IONPs were stabilized by mPEG-G2.5 PAMAM dendrimers. The anticancer drug DOX was conjugated to the dendrimer segments of amino-stabilized IONPs using hydrazine as the linker via hydrazone bonds, which is acid cleavable and can be used as an ideal pH-responsive drug release system. The drug release profiles of DOX-PAMAM dendrimer conjugates were studied at pH 5.0 and 7.4. The results showed that the hydrolytic release profile can be obtained only at the condition of lysosomal pH (pH=5.0), and IONPs participated in carrying DOX to the tumor by the Enhanced Permeability and Retention (EPR) effect. These novel DOX-conjugated IONPs have the potential to enhance the effect of MRI contrast and cancer therapy in the course of delivering anticancer drugs to their target sites. Although the dendrimer-DOX-coated IONPs do not have any targeting ligands attached on their surface, they are potentially useful for cancer diagnosis in vivo.

Synthesis and grafting of folate–PEG–PAMAM conjugates onto quantum dots for selective targeting of folate-receptor-positive tumor cells

We report the design and synthesis of folate-poly(ethylene glycol)-polyamidoamine (FPP)-functionalized CdSe/ZnS quantum dots (QDs), in which the QD plays a key role in imaging, whereas the folate-poly(ethylene glycol) (PEG) conjugates of the polyamidoamine (PAMAM) dendrimer serve as a system targeted to folate receptors in tumor cells. Dendrimer ligands such as folate-PEG grafted PAMAM of generation 3.5 are found to encapsulate and solubilize luminescent QDs through direct ligand-exchange reactions. Because of membrane expression of FA receptors in tumor cells, this class of ligand-exchanged QDs is able to target tumor cells. We have evaluated FPP-coated QDs and QDs without folate in HeLa cells and shown that cellular uptake of FPP-coated QDs is more significant than that non folate QDs in vivo imaging experiment. In particular, QDs coated with FPP are initially bound to tumor cell surfaces, followed by slow endosomal escape and release into the tumor cells. These insights are important for the design and development of nanoparticle agents for optical detection of tumor cells and bio-imaging.

Synthesis and characterization of DOX-conjugated dendrimer-modified magnetic iron oxide conjugates for magnetic resonance imaging, targeting, and drug delivery

A tumor targeted and pH-responsive drug release system that is based on folic acid (FA) conjugated to poly(ethylene glycol) (PEG)-modified dendrimers (PAMAM) with doxorubicin (DOX) and superparamagnetic iron oxide (Fe3O4) (FA-PEG-PAMAM-DOX@IONPs) has been constructed and characterized. IONPs were stabilized by FA-PEG-G3.5 PAMAM dendrimers. The anticancer drug DOX was conjugated to the dendrimer segments of amino-stabilized IONPs using hydrazine as the linker via hydrazone bonds, which are acid cleavable and can be used as an ideal pH-responsive drug release system. The PEG moiety attached to the PAMAM@IONPs provides the conjugates with excellent solubility and stability in an aqueous medium, which may increase the circulation time. The attached FA could target the conjugates to the folate receptor (FR). These novel DOX-loaded conjugates have the potential to enhance the effect of MRI contrast and cancer therapy in the course of delivering drugs to the target sites.

A new colorimetric fluorescent sensor for ratiometric detection of cyanide in solution, test strips, and in cells

A new high selective and sensitive fluorescent sensor for the detection of cyanide was developed based on the nucleophilic attack of CN− with a color change from purple to colourless. The chemosensor was used for fabrication of test strips that can detect cyanide in aqueous samples. The living animal fluorescence experiment demonstrated the practical value of the sensor in tracing the CN− in biological systems.

Architecture of stable and water-soluble CdSe/ZnS core–shell dendron nanocrystals via ligand exchange

We describe a process for transferring octadecylamine-stabilized CdSe/ZnS core-shell semiconductor nanocrystals (ODA-QDs) from chloroform into water through a ligand exchange process with a dendron ligand which has two primary amine anchoring groups at its focal point and hydroxyl groups as its terminal groups. In this dendron ligand, two primary amine anchoring groups serve as bidentate ligands for the QD, while we expected the protruding hydroxyl groups to enhance the water-solubility of the dendron nanocrystals. The resulting dendron nanocrystals dissolved in water exhibit the same fluorescence and absorption spectra as the ODA-CdSe/ZnS core-shell nanocrystals dissolved in organic solvents such as chloroform. Furthermore, the stability of dendron nanocrystals were quantitatively examined against sintering, acid etching, oxidation with H(2)O(2) and photo-oxidation using the methods reported previously. These stable and bright dendron nanocrystals were soluble in various aqueous media, including all common biological buffer solutions tested. In addition to their superior performance, the synthetic chemistry of dendron ligands and the corresponding dendron nanocrystals is relatively simple and with high yield.

Magnetically separable iron oxide nanostructures-TiO2 nanofibers hierarchical heterostructures: controlled fabrication and photocatalytic activity

Novel hierarchical heterostructures of TiO2 nanofibers separately decorated with hematite (α-Fe2O3) or magnetite (Fe3O4) were prepared by combining the electrospinning technique and the hydrothermal method. Extensive characterizations of the resulting hierarchical heterostructures revealed that the secondary α-Fe2O3 or Fe3O4 nanostructures successfully grew on the surface of the primary TiO2 nanofibers substrates, thus integrating the magnetic and photocatalytic properties into the α-Fe2O3/TiO2 and Fe3O4/TiO2 hierarchical heterostructures. The component as well as morphology of the secondary α-Fe2O3 or Fe3O4 nanostructures could be further controlled by simply tuning the experimental parameters. Moreover, the magnetic properties and photocatalytic activities of the hierarchical heterostructures were systematically investigated. Electronic interactions between two semiconductors are the major contributing factor for the changed photoactivity. Most importantly, magnetic measurements showed that the Fe3O4/TiO2 hierarchical heterostructures were ferromagnetic and they could be separated and collected easily using a commercial magnet.

Dendrimer functionalized water soluble magnetic iron oxide conjugates as dual imaging probe for tumor targeting and drug delivery

A tumor targeted and drug-loaded system that is based on folic acid (FA) conjugated to poly(ethylene glycol) (PEG)-modified dendrimers (PAMAM) with paclitaxel (PTX), Cy5.5 fluorophore and superparamagnetic iron oxide (IONPs) (FA-PEG-G3.5-PTX-Cy5.5@IONPs) has been constructed and characterized. The IONPs were stabilized by FA-PEG-G3.5 PAMAM dendrimers. The anticancer drug PTX was conjugated to the dendrimer segments of the amino-stabilized IONPs using biocleavable ester bonds as the linkers, which are acid cleavable and can be used as an ideal drug delivery system. The PEG moiety attached to the PAMAM@IONPs provides the conjugates with excellent solubility and stability in aqueous medium, and the attached FA could facilitate the use of the conjugates as a folate receptor-targeted drug delivery system. These novel PTX-loaded conjugates have the potential to enhance the effect of fluorescence imaging, MRI contrast and cancer therapy in the course of delivering drugs to target sites.

Synthesis and characterization of pH-sensitive poly(itaconic acid)-poly(ethylene glycol)-folate-poly(l-histidine) micelles for enhancing tumor therapy and tunable drug release.

pH responsive intracellular tumor targeting is increasingly investigated as a pathway to trigger the release of anti-tumor drugs once the drug carrier reached the unique acidic environment of the solid tumors or after the drug carrier has been taken up by cells, resulting in the localization of the micelles in the acidic endosomes and lysosomes. Poly(itaconic acid)-poly(ethylene glycol)-folate-poly(l-histidine) (PIA-PEG-FA-PHIS) was synthesized as a carrier for tumor-targeted drug delivery. The micelles were internalized by receptor-mediated endocytosis, and the combination of active targeting and triggered release resulted in apparent cytotoxicity and antitumor activity. The MTT assay showed DOX-loaded micelles had higher and obvious cytotoxicity against Hela cells at pH 5.0 than that at pH 7.4. Cellular uptake experiments revealed that these pH-responsive PIA-PEG-FA-PHIS micelles were taken up in great amounts by receptor-mediated endocytosis and delivered to lysosomes, triggering release of DOX into the cytoplasm. These indicated that the PIA-PEG-FA-PHIS micelles could be a promising drug delivery system with preeminent stability for targeting the hydrophobic drugs to cancer cells and releasing DOX in to the cells by sensing the acidic environment of the endosomes for cancer therapy.