Guoqiang Guan

Design and Functionalization of the NIR-Responsive Photothermal Semiconductor Nanomaterials for Cancer Theranostics

Despite the development of medical technology, cancer still remains a great threat to the survival of people all over the world. Photothermal therapy (PTT) is a minimally invasive method for selective photothermal ablation of cancer cells without damages to normal cells. Recently, copper chalcogenide semiconductors have emerged as a promising photothermal agent attributed to strong absorbance in the near-infrared (NIR) region and high photothermal conversion efficiency. An earlier study witnessed a rapid increase in their development for cancer therapy, including CuS, Cu2-xSe and CuTe nanocrystals. However, a barrier is that the minimum laser power intensity for effective PTT is still significantly higher than the conservative limit for human skin exposure. Improving the photothermal conversion efficiency and reducing the laser power density has become a direction for the development of PTT. Furthermore, in an effort to improve the therapeutic efficacy, many multimode therapeutic nanostuctures have been formulated by integrating the photothermal agents with antitumor drugs, photosensitizers, or radiosensitizers, resulting in a synergistic effect. Various functional materials also have been absorbed, attached, encapsulated, or coated on the photothermal nanostructures, including fluorescence, computed tomography, magnetic resonance imaging, realizing cancer diagnosis, tumor location, site-specific therapy, and evaluation of therapeutic responses via incorporation of diagnosis and treatment. In this Account, we present an overview of the NIR-responsive photothermal semiconductor nanomaterials for cancer theranostics with a focus on their design and functionalization based on our own work. Our group has developed a series of chalcogenides with greatly improved NIR photoabsorption as photothermal agents, allowing laser exposure within regulatory limits. We also investigated the photothermal bioapplications of hypotoxic oxides including WO3-x, MoO3-x, and RuO2, expanding their applications into a new field of photothermal materials. Furthermore, considering a much more enhanced therapeutic effect of multifunctional nanoagents, our group elaborately designed many nanocomposites, such as core-shell nanoparticles of Fe3O4@Cu2-xS and Cu9S5@mSiO2, based on the integration of photothermal agents with contrast agents or other anticancer medicines, achieving cancer theranostic and synergistic treatment. Ternary compound nanocrystals were also prepared with synthetic simplicity for multimodal imaging-guided therapy for cancer. This Account summarizes our past work, including the design and concept, synthesis, and characterization for in vitro and in vivo applications. Then, we analyzed the tendencies of the NIR-responsive photothermal semiconductor nanomaterials for clinical applications, highlighting their prospects and challenges. We believe that the photothermal technology from the NIR-responsive photothermal semiconductor nanomaterials would promote cancer theranostics to result in giant strides forward in the future.

In situ transmission electron microscopy study of individual nanostructures during lithiation and delithiation processes

Direct observation of the nanostructural evolution of electrode materials is critical to understanding lithiation and delithiation processes during cycling of batteries. Due to its real-time monitoring and high spatial resolution, in situ transmission electron microscopy (TEM) plays an important role in understanding the reaction mechanism and dynamic processes in battery materials. This paper reviews the recent progress in using in situ TEM to study individual nanostructures in battery materials using an open-cell design, including for anode materials and cathode materials in lithium ion batteries, and Li–S batteries. Through in situ TEM, the fundamental science and reaction mechanisms, including phase transformations, electrode degradation, size effects, evolution of a solid electrolyte interphase (SEI) and nanostructures, and electrolyte decomposition of nanomaterial-based electrodes were observed during lithiation and delithiation processes. These characteristics will be very useful to the development of basic guidelines for the rational design of high-performance batteries. Finally, the challenges and perspectives of observing individual nanostructures using in situ TEM during electrochemical processes still need to be discussed and addressed.

SnS nanosheets for efficient photothermal therapy

A novel photothermal agent based on PEGylated SnS nanosheets is developed via a simple solvothermal route and the subsequent exfoliation is carried out using an ultrasonication method. The PEGylated SnS nanosheets exhibit much higher extinction coefficient and photothermal conversion efficiency than bulk SnS. With the irradiation of the NIR light, cancer cells in vitro can be efficiently killed by the photothermal effects of the SnS nanosheets. The findings reported here show promising potential for further exploration of 2D nanomaterials as a nanoplatform for cancer therapy.

Degradable rhenium trioxide nanocubes with high localized surface plasmon resonance absorbance like gold for photothermal theranostics

The applications of inorganic theranostic agents in clinical trials are generally limited to their innate non-biodegradability and potential long-term biotoxicity. To address this problem, herein via a straightforward and tailored space-confined on-substrate route, we obtained rhenium trioxide (ReO3) nanocubes (NCs) that display a good biocompatibility and biosafety. Importantly, their aqueous dispersion has high localized surface plasmon resonance (LSPR) absorbance in near-infrared (NIR) region different from previous report, which possibly associates with the charge transfer and structural distortion in hydrogen rhenium bronze (HxReO3), as well as ReO3s cubic shape. Such a high LSPR absorbance in the NIR region endows them with photoacoustic (PA)/infrared (IR) thermal imaging, and high photothermal conversion efficiency (∼57.0%) for efficient ablation of cancer cells. Also, ReO3 NCs show X-ray computed tomography (CT) imaging derived from the high-Z element Re. More attractively, those ReO3 NCs, with pH-dependent oxidized degradation behaviors, are revealed to be relatively stable in hypoxic and weakly acidic microenvironment of tumor for imaging and treatment whilst degradable in normal physiological environments of organs to enable effective clearance. In spite of their degradability, ReO3 NCs still possess tumor targeting capabilities. We thus develop a simple but powerful, safe and biodegradable inorganic theranostic platform to achieve PA/CT/IR imaging-guided cancer photothermal therapy (PTT) for improved therapeutic efficacy and decreased toxic side effects.

Stabilizing Lithium–Sulfur Batteries through Control of Sulfur Aggregation and Polysulfide Dissolution

Lithium-sulfur (Li-S) batteries are investigated intensively as a promising large-scale energy storage system owing to their high theoretical energy density. However, the application of Li-S batteries is prevented by a series of primary problems, including low electronic conductivity, volumetric fluctuation, poor loading of sulfur, and shuttle effect caused by soluble lithium polysulfides. Here, a novel composite structure of sulfur nanoparticles attached to porous-carbon nanotube (p-CNT) encapsulated by hollow MnO2 nanoflakes film to form p-CNT@Void@MnO2 /S composite structures is reported. Benefiting from p-CNTs and sponge-like MnO2 nanoflake film, p-CNT@Void@MnO2 /S provides highly efficient pathways for the fast electron/ion transfer, fixes sulfur and Li2 S aggregation efficiently, and prevents polysulfide dissolution during cycling. Besides, the additional void inside p-CNT@Void@MnO2 /S composite structure provides sufficient free space for the expansion of encapsulated sulfur nanoparticles. The special material composition and structural design of p-CNT@Void@MnO2 /S composite structure with a high sulfur content endow the composite high capacity, high Coulombic efficiency, and an excellent cycling stability. The capacity of p-CNT@Void@MnO2 /S electrode is ≈599.1 mA h g-1 for the fourth cycle and ≈526.1 mA h g-1 after 100 cycles, corresponding to a capacity retention of ≈87.8% at a high current density of 1.0 C.

Hydrophilic K2Mn4O8 nanoflowers as a sensitive photothermal theragnosis synergistic platform for the ablation of cancer

Achieving cancer diagnosis and treatment simultaneously, multifunctional nanomaterials lead the trend in the development of nanomedicine. Manganese-based compounds have been well developed as excellent magnetic resonance (MR) imaging contrast agents, while they have not been demonstrated as photothermal agents (PTAs) due to their unsatisfactory near-infrared photoabsorption. Herein, we report a hydrophilic flower-like K2Mn4O8 superstructure self-assembled by ultrathin nanosheets that can work simultaneously as a PTA and an ultrasensitive T1-weighted magnetic resonance imaging (T1-MRI) enhancing agent. These K2Mn4O8 nanoflowers are efficient vehicles transforming 808 nm laser energy into thermal energy and then leading to the effective ablation of cancer cells in vitro and in vivo. Importantly, with a high longitudinal relaxivity (r1) of 4.6 mM−1 s−1, they also act as quite impressive T1-MRI enhancing agents. Both in vitro and in vivo experiments confirmed their great biocompatibility, low toxicity and high photothermal conversion capability. This is the first application of K2Mn4O8 as a PTA and would hopefully promote other Mn-based theranostics.

A self-powered broadband photodetector based on an n-Si(111)/p-NiO heterojunction with high photosensitivity and enhanced external quantum efficiency

A self-powered high-performance broadband photodetector was fabricated, based on n-Si(111)/p-NiO heterojunctions consisting of single-crystal NiO nanosheets, via a facile hydrothermal method. The device exhibited broadband detection capabilities (350–600 nm) and excellent self-powered performance, with an external quantum efficiency (EQE) as high as ∼20% under zero bias. Under a low reverse bias of −0.2 V, the highest photosensitivity (photo-dark current ratio) values of 938% and 2249% were achieved under illumination from 350 nm and 600 nm light (0.5 mW cm−2), respectively, which was several orders of magnitude higher than for previously reported Si/NiO heterojunction photodetectors. Under a high reverse bias of −2 V, the excellent EQE of the device was found to be between 62.5% and 89.5% upon illumination from 350–600 nm light. In addition, the fast response speed of the as-fabricated device was less than 30 ms. The results indicate that n-Si(111)/p-NiO heterojunction photodetectors made of single-crystal NiO nanosheets have obvious advantages for application in high-performance and energy-saving optoelectronic devices.