Electrically Insulating Thermal Nano-Oils Using 2D Fillers

Different nanoscale fillers have been used to create composite fluids for applications such as thermal management. The ever increasing thermal loads in applications now require advanced operational fluids, for example, high thermal conductivity dielectric oils in transformers. These oils require excellent filler dispersion, high thermal conduction, but also electrical insulation. Such thermal oils that conform to this thermal/electrical requirement, and yet remain in highly suspended stable state, have not yet been synthesized. We report here the synthesis and characterization of stable high thermal conductivity Newtonian nanofluids using exfoliated layers of hexagonal boron nitride in oil without compromising its electrically insulating property. Two-dimensional nanosheets of hexagonal boron nitride are liquid exfoliated in isopropyl alcohol and redispersed in mineral oil, used as standard transformer oil, forming stable nanosuspensions with high shelf life. A high electrical resistivity, even higher than that of the base oil, is maintained for the nano-oil containing small weight fraction of the filler (0.01 wt %), whereas the thermal conductivity was enhanced. The low dissipation factor and high pour point for this nano-oil suggests several applications in thermal management

Smart Human Serum Albumin-Indocyanine Green Nanoparticles Generated by Programmed Assembly for Dual-Modal Imaging-Guided Cancer Synergistic Phototherapy

Phototherapy, including photodynamic therapy (PDT) and photothermal therapy (PTT), is a light-activated local treatment modality that is under intensive preclinical and clinical investigations for cancer. To enhance the treatment efficiency of phototherapy and reduce the light-associated side effects, it is highly desirable to improve drug accumulation and precision guided phototherapy for efficient conversion of the absorbed light energy to reactive oxygen species (ROS) and local hyperthermia. In the present study, a programmed assembly strategy was developed for the preparation of human serum albumin (HSA)-indocyanine green (ICG) nanoparticles (HSA-ICG NPs) by intermolecular disulfide conjugations. This study indicated that HSA-ICG NPs had a high accumulation with tumor-to-normal tissue ratio of 36.12 ± 5.12 at 24 h and a long-term retention with more than 7 days in 4T1 tumor-bearing mice, where the tumor and its margin, normal tissue were clearly identified <i>via</i> ICG-based <i>in vivo</i> near-infrared (NIR) fluorescence and photoacoustic dual-modal imaging and spectrum-resolved technology. Meanwhile, HSA-ICG NPs efficiently induced ROS and local hyperthermia simultaneously for synergetic PDT/PTT treatments under a single NIR laser irradiation. After an intravenous injection of HSA-ICG NPs followed by imaging-guided precision phototherapy (808 nm, 0.8 W/cm² for 5 min), the tumor was completely suppressed, no tumor recurrence and treatments-induced toxicity were observed. The results suggest that HSA-ICG NPs generated by programmed assembly as smart theranostic nanoplatforms are highly potential for imaging-guided cancer phototherapy with PDT/PTT synergistic effects

Smac Therapeutic Peptide Nanoparticles Inducing Apoptosis of Cancer Cells for Combination Chemotherapy with Doxorubicin

Smac-conjugated nanoparticle (Smac-NP) was designed to induce the apoptosis of cancer cells and as a drug carrier for combination therapy. It contained three parts, a SmacN7 peptide which could induce apoptosis of cancer cells by interacting with XIAPs, the cell penetrating domain rich in arginine, and four hydrophobic tails for self-assembled Smac-NP. We demonstrated that Smac-NPs exerted an antitumor effect in breast cancer cell MDA-MB-231 and nonsmall lung cancer (NSCLC) cell H460, which efficiently inhibited cancer cells proliferation without influencing normal liver cell lines LO2. Smac-NPs also significantly induced apoptosis of MDA-MB-231 and H460 cells through activating pro-caspase-3, down-regulating the expression of antiapoptotic protein Bcl-2 and up-regulating the pro-apoptotic protein Bax. Furthermore, Smac-NPs could be explored as a drug delivery system to load hydrophobic drug such as DOX for combination therapy. The DOX-loaded nanoparticles (DOX-Smac-NPs) exhibited higher cellular uptake efficiency and antitumor effect. Our work provided a new insight into therapeutic peptides integrated with drug simultaneously in one system for cancer combination treatment

Artificially Stacked Atomic Layers: Toward New van der Waals Solids

Strong in-plane bonding and weak van der Waals interplanar interactions characterize a large number of layered materials, as epitomized by graphite. The advent of graphene (G), individual layers from graphite, and atomic layers isolated from a few other van der Waals bonded layered compounds has enabled the ability to pick, place, and stack atomic layers of arbitrary compositions and build unique layered materials, which would be otherwise impossible to synthesize via other known techniques. Here we demonstrate this concept for solids consisting of randomly stacked layers of graphene and hexagonal boron nitride (h-BN). Dispersions of exfoliated h-BN layers and graphene have been prepared by liquid phase exfoliation methods and mixed, in various concentrations, to create artificially stacked h-BN/G solids. These van der Waals stacked hybrid solid materials show interesting electrical, mechanical, and optical properties distinctly different from their starting parent layers. From extensive first principle calculations we identify (i) a novel approach to control the dipole at the h-BN/G interface by properly sandwiching or sliding layers of h-BN and graphene, and (ii) a way to inject carriers in graphene upon UV excitations of the Frenkell-like excitons of the h-BN layer(s). Our combined approach could be used to create artificial materials, made predominantly from inter planar van der Waals stacking of robust bond saturated atomic layers of different solids with vastly different properties

Cancer Cell Membrane–Biomimetic Nanoparticles for Homologous-Targeting Dual-Modal Imaging and Photothermal Therapy

An active cell membrane–camouflaged nanoparticle, owning to membrane antigens and membrane structure, can achieve special properties such as specific recognition, long blood circulation, and immune escaping. Herein, we reported a cancer cell membrane–cloaked nanoparticle system as a theranostic nanoplatform. The biomimetic nanoparticles (indocyanine green (ICG)-loaded and cancer cell membrane-coated nanoparticles, ICNPs) exhibit a core–shell nanostructure consisting of an ICG-polymeric core and cancer cell membrane shell. ICNPs demonstrated specific homologous targeting to cancer cells with good monodispersity, preferable photothermal response, and excellent fluorescence/photoacoustic (FL/PA) imaging properties. Benefited from the functionalization of the homologous binding adhesion molecules from cancer cell membranes, ICNPs significantly promoted cell endocytosis and homologous-targeting tumor accumulation <i>in vivo</i>. Moreover, ICNPs were also good at disguising as cells to decrease interception by the liver and kidney. Through near-infrared (NIR)-FL/PA dual-modal imaging, ICNPs could realize real-time monitored <i>in vivo</i> dynamic distribution with high spatial resolution and deep penetration. Under NIR laser irradiation, ICNPs exhibited highly efficient photothermal therapy to eradicate xenografted tumor. The robust ICNPs with homologous properties of cancer cell membranes can serve as a bionic nanoplatform for cancer-targeted imaging and phototherapy

Crystal-Phase Quantum Wires: One-Dimensional Heterostructures with Atomically Flat Interfaces

In semiconductor quantum-wire heterostructures, interface roughness leads to exciton localization and to a radiative decay rate much smaller than that expected for structures with flat interfaces. Here, we uncover the electronic and optical properties of the one-dimensional extended defects that form at the intersection between stacking faults and inversion domain boundaries in GaN nanowires. We show that they act as crystal-phase quantum wires, a novel one-dimensional quantum system with atomically flat interfaces. These quantum wires efficiently capture excitons whose radiative decay gives rise to an optical doublet at 3.36 eV at 4.2 K. The binding energy of excitons confined in crystal-phase quantum wires is measured to be more than twice larger than that of the bulk. As a result of their unprecedented interface quality, these crystal-phase quantum wires constitute a model system for the study of one-dimensional excitons

Molecular Beam Epitaxy of GaN Nanowires on Epitaxial Graphene

We demonstrate an all-epitaxial and scalable growth approach to fabricate single-crystalline GaN nanowires on graphene by plasma-assisted molecular beam epitaxy. As substrate, we explore several types of epitaxial graphene layer structures synthesized on SiC. The different structures differ mainly in their total number of graphene layers. Because graphene is found to be etched under active N exposure, the direct growth of GaN nanowires on graphene is only achieved on multilayer graphene structures. The analysis of the nanowire ensembles prepared on multilayer graphene by Raman spectroscopy and transmission electron microscopy reveals the presence of graphene underneath as well as in between nanowires, as desired for the use of this material as contact layer in nanowire-based devices. The nanowires nucleate preferentially at step edges, are vertical, well aligned, epitaxial, and of comparable structural quality as similar structures fabricated on conventional substrates

Structure−activity relationships in Ni-carboxylate-type metal−organic frameworks’ metamorphosis for the oxygen evolution reaction

Metal−organic frameworks (MOFs) have been reported to catalyze the oxygen evolution reaction (OER). Despite the established links between the pristine MOFs and their derived metal hydroxide electrocatalysts, several limitations still preclude understanding of the critical factors determining the OER performance. Of prime importance appears the choice of MOF and how its compositions relate to the catalyst stability and in turn to the reconstruction or metamorphosis mechanisms into the active species under OER conditions. An isoreticular series of Ni-carboxylate-type MOFs [Ni2(OH)2L] was chosen to elucidate the effects of the carboxylate linker length expansion and modulation of the linker−linker π−π interactions (L = 1,4-benzodicarboxylate, 2,6-napthalenedicarboxylate, biphenyl-4,4′-dicarboxylate, and pterphenyl-4,4″-dicarboxylate). Degradation and reconstruction of MOFs were systematically investigated. The linker controls the transformation of Ni-MOF into distinct nickel hydroxide phases, and the conversion from α-Ni(OH)2 to β-Ni(OH)2, thus correlating the Ni-MOF composition with the OER activity of the Ni-MOF-derived metastable nickel hydroxide phase mixture</p

Graphene Quantum Dots Derived from Carbon Fibers

Graphene quantum dots (GQDs), which are edge-bound nanometer-size graphene pieces, have fascinating optical and electronic properties. These have been synthesized either by nanolithography or from starting materials such as graphene oxide (GO) by the chemical breakdown of their extended planar structure, both of which are multistep tedious processes. Here, we report that during the acid treatment and chemical exfoliation of traditional pitch-based carbon fibers, that are both cheap and commercially available, the stacked graphitic submicrometer domains of the fibers are easily broken down, leading to the creation of GQDs with different size distribution in scalable amounts. The as-produced GQDs, in the size range of 1–4 nm, show two-dimensional morphology, most of which present zigzag edge structure, and are 1–3 atomic layers thick. The photoluminescence of the GQDs can be tailored through varying the size of the GQDs by changing process parameters. Due to the luminescence stability, nanosecond lifetime, biocompatibility, low toxicity, and high water solubility, these GQDs are demonstrated to be excellent probes for high contrast bioimaging and biosensing applications