Tuning the Electronic Structure of Graphite Oxide through Ammonia Treatment for Photocatalytic Generation of H₂ and O₂ from Water Splitting

Graphite oxide (GO) synthesized from the oxidation of graphite powders exhibits p-type conductivity and is active in photocatalytic H₂ evolution from water decomposition. The p-type conductivity hinders hole transfer for water oxidation and suppresses O₂ evolution. Treating GO with NH₃ gas at room temperature tunes the electronic structure by introducing amino and amide groups to its surface. The ammonia-modified GO (NGO) exhibits n-type conductivity in photoelectrochemical analysis and has a narrower optical band gap than GO. Electrochemical analysis attributes the band gap reduction to a negative shift of the valence band. An NGO-film electrode exhibits a substantially higher incident photo-to-current efficiency in the visible light region than a GO electrode. Photoluminescence analyses demonstrate the above-edge emission characteristic of GO and NGO. NH₃ treatment enhances the emission by removing nonirradiative epoxy and carboxyl sites on the GO. In half-reaction tests of water decomposition, NGO effectively catalyzes O₂ evolution in an aqueous AgNO₃ solution under mercury-lamp irradiation, whereas GO is inactive. NGO also effectively catalyzes H₂ evolution in an aqueous methanol solution but shows less activity than GO. Under illumination with visible light (λ > 420 nm), NGO simultaneously catalyzes H₂ and O₂ evolutions, but with a H₂/O₂ molar ratio below 2. The n-type conductivity of NGO may hinder electron transfer and form peroxide species instead of H₂ molecules. This study demonstrates that the functionality engineering of GO is a promising technique to synthesize an industrially scalable photocatalyst for overall water splitting

Sonochemical Synthesis of Well-Dispersed Gold Nanoparticles at the Ice Temperature

A newly modified sonochemical approach was demonstrated to synthesize stable Au suspensions. The formation of Au nanoparticles with diameters of ∼20 nm was accomplished through the ultrasonic irradiation of aqueous HAuCl4 solutions containing trisodium citrate at 4 °C. The efficient generation in gold particles only occurred when the sufficient citrate concentrations (1.9, 2.9, and 3.9 mM) were reached. At low citrate concentrations ranging from 0.49 to 1.5 mM, large aggregates of coalesced Au particles were observed as sonication time increased. It is proposed that citrate could transform as the reducing radicals, 1,2,3-tricarboxy-2-propyl radicals, for the AuCl4- reduction and might also act as the stabilizer during particles formation

One-Pot Synthesis of Hollow Au₃Cu₁ Spherical-like and Biomineral Botallackite Cu₂(OH)₃Cl Flowerlike Architectures Exhibiting Antimicrobial Activity

A new form of Au3Cu1 hollow nanostructure was prepared by the reaction of Cu nanoparticles with HAuCl4. Following a course of aging, the biomineral botallackite Cu2(OH)3Cl nanoflowers were developed with the aid of Au3Cu1 hollow nanostructures at room temperature. It was proposed that the hollow nanospheres could serve as active centers for heterogeneous nucleation and mediated a mineralization process. Scanning electron microscopy and high-resolution transmission electron microscopy indicated that the nanoflowers are three-dimensional in appearance with a range of 500 nm − to 1 μm in size and made of several nanopetals with about 25 nm in thickness. In addition, we found that the shape separation could be achieved by using cationic cetyltrimethylammonium bromide to filter the different morphology spherical- and flowerlike structures due to the negative charge of hollow nanospheres. Both hollow nanospheres and nanoflowers presented antimicrobial activity toward Streptococcus aureus with MIC50 at 39.6 and 127.2 μg/mL, respectively

Bacteria-Mediated Hypoxia-Specific Delivery of Nanoparticles for Tumors Imaging and Therapy

The hypoxia region in a solid tumor has been recognized as a complex microenvironment revealing very low oxygen concentration and deficient nutrients. The hypoxic environment reduces the susceptibility of the cancer cells to anticancer drugs, low response of free radicals, and less proliferation of cancer cells in the center of the solid tumors. However, the reduced oxygen surroundings provide an appreciable habitat for anaerobic bacteria to colonize. Here, we present the bacteria-mediated targeting hypoxia to offer the expandable spectra for diagnosis and therapy in cancer diseases. Two delivery approaches involving a cargo-carrying method and an antibody-directed method were designed to deliver upconversion nanorods for imaging and Au nanorods for photothermal ablation upon near-infrared light excitation for two forms of the anaerobic Bifidobacterium breve and Clostridium difficile. The antibody-directed strategy shows the most effective treatment giving stronger imaging and longer retention period and effective therapy to completely remove tumors

Formation of Oligonucleotide-Gated Silica Shell-Coated Fe₃O₄‑Au Core–Shell Nanotrisoctahedra for Magnetically Targeted and Near-Infrared Light-Responsive Theranostic Platform

A new multifunctional nanoparticle to perform a near-infrared (NIR)-responsive remote control drug release behavior was designed for applications in the biomedical field. Different from the previous studies in formation of Fe₃O₄-Au core–shell nanoparticles resulting in a spherical morphology, the heterostructure with polyhedral core and shell was presented with the truncated octahedral Fe₃O₄ nanoparticle as the core over a layer of trisoctahedral Au shell. The strategy of Fe₃O₄@polymer@Au was adopted using poly-l-lysine as the mediate layer, followed by the subsequent seeded growth of Au nanoparticles to form a Au trisoctahedral shell. Fe₃O₄@Au trisoctahedra possess high-index facets of {441}. To combine photothermal and chemotherapy in a remote-control manner, the trisoctahedral core–shell Fe₃O₄@Au nanoparticles were further covered with a mesoporous silica shell, yielding Fe₃O₄@Au@mSiO₂. The bondable oligonucleotides (referred as dsDNA) were used as pore blockers of the mesoporous silica shell that allowed the controlled release, resulting in a NIR-responsive DNA-gated Fe₃O₄@Au@mSiO₂ nanocarrier. Taking advantage of the magnetism, remotely triggered drug release was facilitated by magnetic attraction accompanied by the introduction of NIR radiation. DNA-gated Fe₃O₄@Au@mSiO₂ serves as a drug control and release carrier that features functions of magnetic target, MRI diagnosis, and combination therapy through the manipulation of a magnet and a NIR laser. The results verified the significant therapeutic effects on tumors with the assistance of combination therapy consisting of magnetic guidance and remote NIR control

Singlet Oxygen Generation Using Thiolated Gold Nanoclusters under Photo- and Ultrasonic Excitation: Size and Ligand Effect

Ultrasonic irradiation of liquids can induce catalytic activity in semiconductor nanoparticles (sonocatalysis/sonosensitization) similar to light-induced photocatalysis/photosensitization. However, due to the complexity of the acoustic cavitation processes involved in sonocatalysis/sonosensitization, an ideal nanoparticle design has not been identified for them. Herein, the size- and ligand-dependent ultrasonic activation of thiolate gold nanoclusters (Au NCs) and their photosensitizing and sonosensitizing abilities for singlet oxygen (1O2) generation were investigated. The difference between Au NC-based photosensitization and sonosensitization was also elucidated, along with a mechanism for the latter. For Au25 NC-based sonosensitization and photosensitization, the ligand effect on the 1O2-generation efficiency was in the order of glutathione < captopril 1O2 production and quenching reactions using sono-/photo-excited Au25 NCs determined the net 1O2 production. The size effects on the 1O2-generation efficiency were in the order of Au144 ≫ Au25 > plasmonic Au nanoparticle for sonosensitization, as opposed to the case of photosensitization: Au25 ≫ Au144 ∼ plasmonic Au nanoparticle. The 1O2 generation via ultrasonically excited Au144 NCs correlated with high-energy ultrasonic cavitation depending on the ultrasonication power and frequency. Therefore, high-energy ultrasonic cavitation-mediated Au144 NC-based sonosensitizers could be effectively used in the production of 1O2 for various chemical and biomedical applications

Graphite-Shelled Si Nanoparticles and Their Au/Si Heterodimers: Preparation, Photoluminescence, and Second Harmonic Generation

New structured graphite-shelled Si nanocrystals were prepared by laser ablation in various solvents including H2O, ethanol, 2-propanol, hexane, octane, octadecene, trioctylamine, toluene, trioctylamine/toluene, and oleylamine/toluene. With the aromatic debris, containing hexagonal carbon rings, from organic media seems to facilitate graphitization process to build up graphitic carbon layers on Si. The luminescent feature was strongly related to the presence of graphite shells. Excited by infrared femtosecond lasers, the graphite-shelled Si nanocrystals showed extraordinarily strong second harmonic generation (SHG). Both fluorescence and SHG signals were growing with the aging days. The single photon-excited fluorescence and quantum yield were increased from as-prepared graphite-shelled Si quantum dots (QDs) (8%) to 30-day aged samples (13.0%). Because of oxidation upon aging, it is suggested that the possible increase of the Si–O bonds on Si surface could have diminished nonradiative centers resulting in enhancing fluorescence. The SHG signal was also up to 32 times higher than that of as-prepared graphite-shelled Si QDs after the aging process. Such an oxidative aging process likely created strain at the Si/SiO2 interface, breaking the central symmetry, and allowed the SHG. Additionally, the poling of SiO2 on the surface of graphite-shelled Si QDs and the transition states of quantum-confined excitons have been addressed for the SHG observation as well. The enhancements of fluorescence and SHG signals have opened an avenue for the applications of graphite-shelled Si QDs as cell biolabeling agents and contrast agents in deep tissue microscopy and tomography. The blue emission of graphite-shelled Si QDs integrated with Rhodamine 610 dye has allowed us to tune luminous spectra giving white light luminescence. The first synthesis of the Au/Si heterodimer nanostructures were formed through replacement reaction between graphite-shelled Si nanocrystals and tetraoctylammonium–Au3+ complexes in organic solvent

Iron Oxide Nanopropellers Prepared by a Low-Temperature Solution Approach

The α-Fe2O3 (hematite) nanopropellers were synthesized via a low-temperature solution-based method using FeCl2 as a precursor in the presence of urea and glycine hydrochloride. The formation of α-Fe2O3 nanopropellers is strongly depended on the addition of glycine hydrochloride, which serves as a pH modulator and affects the oxidation rate of Fe2+. The structural evolution of the propeller-structured hematite was found to follow dissolution and recrystallization processes. For the structural conformation, each nanopropeller presents a hexagonal central column closed by six equivalent surfaces of {1̄100} and the six arrays of the nanopropeller structure are a result of growth along ±[1̄100], ±[1̄010], and ±[01̄10]. Preliminary results show that the magnetic maghemite (γ-Fe2O3) nanopropellers could also be prepared by a reduction and reoxidation process from the α-Fe2O3 (hematite) nanopropeller precursors

Ultrasound-Induced Reactive Oxygen Species Mediated Therapy and Imaging Using a Fenton Reaction Activable Polymersome

Ultrasound techniques have been extensively employed for diagnostic purposes. Because of its features of low cost, easy access, and noninvasive real-time imaging, toward clinical practice it is highly anticipated to simply use diagnostic ultrasound to concurrently perform imaging and therapy. We report a H₂O₂-filled polymersome to display echogenic reflectivity and reactive oxygen species-mediated cancer therapy simply triggered by the microultrasound diagnostic system accompanied by MR imaging. Instead of filling common perfluorocarbons, the encapsulation of H₂O₂ in H₂O₂/Fe₃O₄–PLGA polymersome provides O₂ as the echogenic source and ^•OH as the therapeutic element. On exposure to ultrasound, the polymersome can be easily disrupted to yield ^•OH through the Fenton reaction by reaction of H₂O₂ and Fe₃O₄. We showed that malignant tumors can be completely removed in a nonthermal process