Hai-Sheng Qian

Multiplex Templating Process in One-Dimensional Nanoscale: Controllable Synthesis, Macroscopic Assemblies, and Applications

Since their detection 20 years ago, carbon nanotubes (CNTs) have captured the interest of scientists, because one-dimensional (1D) nanostructures (nanowires, nanotubes, and nanoribbons) have fascinating physical properties and many potential technological applications. These are materials with structural features limited to the range of 1-100 nm in one dimension, and unlimited in the others. When their size goes down to certain characteristic lengths, such as the Bohr radius, the wavelength of incandescent light, and the phonon mean-free path, quantum mechanical effects can occur. This results in novel optical, magnetic, and electronic characteristics. These physical properties, along with unique transport features in the longitudinal direction and large surface-to-volume ratio, make 1D nanostructures attract extensive attention in both fundamental research and engineering applications. From a synthetic point of view, it is highly desirable to develop a simple route for fabricating 1D nanostructures in large scale at low cost. On the other hand, in order to transfer the intrinsic features of individual 1D nanostructures into macroscopic scale and realize practical applications, we need to explore highly efficient and scalable assembly methods to integrate 1D nanostructures into functional macroscopic architectures. In 2006, our group developed a simple hydrothermal method for synthesizing ultrathin Te nanowires (TeNWs) using conventional chemicals. As we found through systematic study over the past several years, we can use the ultrathin TeNWs as a versatile templating material to fabricate a series of high-quality 1D nanostructures by taking the unique advantages of TeNWs, such as large-scale synthesis, high processability, and high reactivity. The obtained 1D products inherit the dimensional (high aspect ratio) and mechanical (high flexibility) features of the original TeNW templates, thus allowing us to construct macroscopic architectures by using them as nanoscale building blocks. In this Account, we describe on our recent developments in the multiplex templating synthesis of 1D nanostructures, their macroscopic assemblies, and applications. We first introduce ultrathin TeNWs and their advantages as a templating material. Through the multiplex templating process, we can prepare a family of 1D nanostructures that covers a wide range of materials, including noble metals, metal oxides, semiconductors, carbon, polymers, and their binary and multiple hybrids. We emphasize the reactivity of templating materials and the versatility of templating processes in this Account. On the basis of the templated 1D products, we then describe a series of macroscopic assemblies of 1D nanostructures, including free-standing membranes, films, hydrogels, and aerogels. These exhibit enormous potential for attractive applications, such as liquid filtration and separation, continuous-flow catalysis, electrocatalysis, polymer-based nanocomposites, and superadsorbents, and elastomeric conductors. We believe that the great versatility of templating synthesis, a scalable assembling process, and large-scale synthesis can significantly enhance the application reliability of the 1D nanostructures.

Titanium Dioxide/Upconversion Nanoparticles/Cadmium Sulfide Nanofibers Enable Enhanced Full-Spectrum Absorption for Superior Solar Light Driven Photocatalysis.

In this work, we demonstrate an electrospinning technique to fabricate TiO2 /upconversion nanoparticles (UCNPs)/CdS nanofibers on large scale. In addition, the as-prepared TiO2 nanofibers are incorporated with a high population of UCNPs and CdS nanospheres; this results in Förster resonance energy-transfer configurations of the UCNPs, TiO2 , and CdS nanospheres that are in close proximity. Hence, strong fluorescent emissions for the Tm(3+) ions including the (1) G4 →(3) H6 transition are efficiently transferred to TiO2 and the CdS nanoparticles through an energy-transfer process. The as-prepared TiO2 /UCNPs/CdS nanofibers exhibit full-spectrum solar-energy absorption and enable the efficient degradation of organic dyes by fluorescence resonance energy transfer between the UCNPs and TiO2 (or CdS). The UCNPs/TiO2 /CdS nanofibers may also have enhanced energy-transfer efficiency for wide applications in solar cells, bioimaging, photodynamics, and chemotherapy.

A Donor-Acceptor Conjugated Polymer with Alternating Isoindigo Derivative and Bithiophene Units for Near-Infrared Modulated Cancer Thermo-Chemotherapy.

Conjugated polymers containing alternating donor/acceptor units have strong and sharp absorbance peaks in near-infrared (NIR) region, which could be suitable for photothermal therapy. However, these polymers as photothermal transducers are rarely reported because of their water insolubility, which limits their applications for cancer therapy. Herein, we report the donor-acceptor conjugated polymer PBIBDF-BT with alternating isoindigo derivative (BIBDF) and bithiophene (BT) units as a novel photothermal transducer, which exhibited strong near-infrared (NIR) absorbance due to its low band gap (1.52 eV). To stabilize the conjugated polymer physiological environments, we utilized an amphiphilic copolymer, poly(ethylene glycol)-block-poly(hexyl ethylene phosphate) (mPEG-b-PHEP), to stabilize PBIBDF-BT-based nanoparticles (PBIBDF-BT@NPPPE) through a single emulsion method. The obtained nanoparticles PBIBDF-BT@NPPPE showed great stability in physiological environments and excellent photostability. Moreover, the PBIBDF-BT@NPPPE exhibited high photothermal conversion efficiency, reaching 46.7%, which is relatively high compared with those of commonly used materials for photothermal therapy. Accordingly, in vivo and in vitro experiments demonstrated that PBIBDF-BT@NPPPE exhibits efficient photothermal anticancer efficacy. More importantly, PBIBDF-BT@NPPPE could simultaneously encapsulate other types of therapeutic agents though hydrophobic interactions with the PHEP core and achieve NIR-triggered intracellular drug release and a synergistic combination therapy of thermo-chemotherapy for the treatment of cancer.

Silica/ultrasmall Ag composite microspheres: facile synthesis, characterization and antibacterial and catalytic performance

Uniform silica/ultrasmall silver composite microspheres have been prepared from [Ag(NH3)2]+ in the presence of silica microspheres via a hydrothermal process. The reaction temperature plays a critical role in the formation of the as-prepared SiO2/ultrasmall Ag composite microspheres. The as-prepared product was investigated by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM, JEOL-6700F) and transmission electron microscopy (TEM, JEOL 3010). The silica/ultrasmall silver composite microspheres are 200 nm in diameter and the silica microspheres decorated with ultrasmall Ag nanoparticles have an average diameter of 4 nm. As expected, the as-prepared silica/ultrasmall silver composite microspheres exhibit superior bacteriostatic and bactericidal activities and excellent photodecomposition towards Rhodamine 6G (R6G) dyes.

Polyphosphoester-based nanoparticles with viscous flow core enhanced therapeutic efficacy by improved intracellular drug release.

The intracellular drug release rate from the hydrophobic core of self-assembled nanoparticles can significantly affect the therapeutic efficacy. Currently, the hydrophobic core of many polymeric nanoparticles which are usually composed of poly(ε-caprolactone) (PCL), polylactide (PLA), or poly(D, L-lactide-co-glycolide) (PLGA) may hinder the diffusion of drug from the core because of their glassy state at room temperature. To investigate the effect of the hydrophobic core state on therapeutic efficacy, we synthesized an amphiphilic diblock copolymers of hydrophilic poly(ethylene glycol) (PEG) and hydrophobic polyphosphoester, which were in a viscous flow state at room temperature. The obtained copolymers self-assembled into core-shell nanoparticles, which efficiently encapsulate doxorubicin (DOX) in the hydrophobic polyphosphoester core (NP(PPE)/DOX). As speculated, compared with the nanoparticles bearing glassy core (hydrophobic PLA core, NP(PLA)/DOX), the encapsulated DOX was more rapidly released from NP(PPE)/DOX with viscous flow core, resulting in significantly increased cytotoxicity. Accordingly, the improved intracellular drug release from viscous flow core enhances the inhibition of tumor growth, suggesting the nanoparticles bearing viscous flow core show great potential in cancer therapy.

Design of Tumor Acidity-Responsive Sheddable Nanoparticles for Fluorescence/Magnetic Resonance Imaging-Guided Photodynamic Therapy

Imaging-guided cancer therapy, which integrates diagnostic and therapeutic functionalities into a single system, holds great promise to enhance the accuracy of diagnosis and improve the efficacy of therapy. Specifically, for photodynamic therapy (PDT), it is highly desirable to precisely focus laser light onto the tumor areas to generate reactive oxygen species (ROS) that are cytotoxic tumor cells and avoid light-associated side effects. Herein, a distinct three-layer nanostructured particle with tumor acidity-responsiveness (S-NP) that encapsulates the photosensitizer chlorin e6 (Ce6) and chelates Gd3+ is successfully developed for fluorescence/magnetic resonance (MR) dual-model imaging-guided precision PDT. We show clear evidence that the outer PEG layer significantly prolongs circulation time, and the inner poly(ε-caprolactone) (PCL) core can physically encapsulate Ce6. More interestingly, the middle layer of the S-NP, acting as a molecular fence to keep Ce6 in the circulation system, was dismantled by the slightly acidic tumor microenvironment. Afterwards, the PEG shell is deshielded from the S-NP at the tumor tissue, resulting in improved cell uptake, enlarged MR signal intensity, rapid release of Ce6 within tumor cells, and elevated PDT efficacy. Our results suggest that tumor-acidity-responsive nanoparticles with fine design could serve as a theranostic platform with great potential in imaging-guided PDT treatment of cancer.

Redox-Responsive Polyphosphoester-Based Micellar Nanomedicines for Overriding Chemoresistance in Breast Cancer Cells.

Multidrug resistance (MDR) has been recognized as a key factor contributing to the failure of chemotherapy for cancer in the clinic, often due to insufficient delivery of anticancer drugs to target cells. For addressing this issue, a redox-responsive polyphosphoester-based micellar nanomedicine, which can be triggered to release transported drugs in tumor cells, has been developed. The micelles are composed of diblock copolymers with a hydrophilic PEG block and a hydrophobic polyphosphoester (PPE) block bearing a disulfide bond in a side group. After incubating the redox-responsive micelles with drug-resistant tumor cells, the intracellular accumulation and retention of DOX were significantly enhanced. Moreover, after internalization by MDR cancer cells, the disulfide bond in the side group was cleaved by the high intracellular glutathione levels, resulting in a hydrophobic to hydrophilic transition of the PPE block and subsequent disassembly of the micelles. Thus, the encapsulated DOX was rapidly released, and abrogation of drug resistance in the cancer cells was observed in vitro. Moreover, the DOX-loaded redox-responsive micelles exhibited significantly enhanced inhibition of tumor growth in nude mice bearing MCF-7/ADR xenograft tumors via tail vein injection, indicating that such micelles have great potential in overcoming MDR for cancer therapy.

Sequential Growth of NaYF4:Yb/Er@NaGdF4 Nanodumbbells for Dual-Modality Fluorescence and Magnetic Resonance Imaging

Upconversional core-shell nanostructures have gained considerable attention due to their distinct enhanced fluorescence efficiency, multifunctionality, and specific applications. Recently, we have developed a sequential growth process to fabricate unique upconversion core-shell nanoparticles. Time evolution of morphology for the NaYF4:Yb/Er@NaGdF4 nanodumbbells has been extensively investigated. An Ostwald ripening growth mechanism has been proposed to illustrate the formation of NaYF4:Yb/Er@NaGdF4 nanodumbbells. The hydrophilic NaYF4:Yb/Er@NaGdF4 core-shell nanodumbbells exhibited strong upconversion fluorescence and showed higher magnetic resonance longitudinal relaxivity (r1 = 7.81 mM-1 s-1) than commercial contrast agents (Gd-DTPA). NaYF4:Yb/Er@NaGdF4 nanodumbbells can serve as good candidates for high efficiency fluorescence and magnetic resonance imaging.

Silica-based hybrid microspheres: synthesis, characterization and wastewater treatment

Silica hybrid microspheres with diameter of 280 nm have been synthesized from 1 mL tetraethyl orthosilicate (TEOS) and 0.4 mL octadecyltrimethoxysilane (C18TMS) in 20 mL of ethanol solution at room temperature for 24 h. The morphology and size of the samples were investigated by field-emission scanning electron microscopy (FESEM, JEOL-6700F) and transmission electron microscopy (TEM, JEOL 3010). The silica microspheres exhibit excellent adsorption abilities towards organic pollutants, for instance, dyes, oils, etc. Furthermore, the hydrophobic silica microspheres could be used as versatile templates for the controlled synthesis of mesoporous silica hybrid materials for wastewater treatment.

Decoration of upconversion nanoparticles@mSiO2 core–shell nanostructures with CdS nanocrystals for excellent infrared light triggered photocatalysis

In this work, we demonstrate a facile process to synthesize upconversion nanoparticles (UCNPs)@mesoporous SiO2 (mSiO2) core–shell nanoparticles decorated with CdS nanoparticles. The size and morphology of the as-prepared products have been investigated carefully; which show that the UCNPs and CdS nanoparticles are ca. 50 and 5 nm in diameter, respectively, and the mesoporous silica layer is 10 nm in thickness. The fluorescence spectra of the as-prepared UCNPs@mSiO2/CdS nanoparticles show that the fluorescence emissions (380, 451 and 470 nm) have been greatly quenched via energy transitions from the UCNPs nanoparticles (donors) to the CdS nanoparticles (acceptors). CdS nanoparticles were activated by the UCNPs to produce photo-generated ˙OH radicals under irradiation of infrared (IR) light. Photodegradation towards RhB dyes was studied to demonstrate the photocatalytic properties for the as-prepared UCNPs@mSiO2/CdS nanoparticles under irradiation of near infrared light. The as-designed nanostructures of UCNPs@mSiO2/CdS nanoparticles show excellent photocatalytic performance on photodegradation towards RhB under irradiation of infrared light. This kind of nanostructure may find potential applications in photodynamic therapy of cancer cells, for use as nanotransducers, in dyed sensitized solar cells etc.