Fluoride releasing photothermal responsive TiO2 matrices for antibiosis, biosealing and bone regeneration.

Peri-implantitis induced by infection leads to gingival recession, alveolar resorption and eventual dental implant failure. So, antibiosis and biosealing of abutments as well as osseointegration of roots need to be projected seriously during the whole service lifespan of dental implants. In this work, a multipurpose photothermal therapy strategy based on Si/P/F doped TiO2 matrix is proposed to address the above issues. This TiO2 matrix not only has outstanding photothermal response, but also triggers the release of F ions under near-infrared (NIR) light irradiation. Local hyperthermia assisted with the released F ions reduces adenosine triphosphate (ATP) synthesis of staphylococcus aureus (S. aureus), increases bacterial membrane permeability, and induces abundant of reactive oxygen species, resulting in the oxidation of cellular components and eventual death of bacteria. Furthermore, the synergic action of mild photothermal stimulation and Si/P/F ions of TiO2 matrix up-regulates gingival epithelial cells behavior (e.g., hemidesmosome formation) and osteoblasts response in vitro. In an infected model, this TiO2 matrix obviously eliminates bacteria, reduces inflammatory response, improves epithelial sealing and osseointegration, and reduces alveolar resorption by regulating NIR irradiation.

Alkaline "Nanoswords" Coordinate Ferroptosis-like Bacterial Death for Antibiosis and Osseointegration.

Ferroptosis is an iron-dependent cell death and is associated with cancer therapy. Can it play a role in resistance of postoperative infection of implants, especially with an extracellular supplement of Fe ions in a non-cytotoxic dose? To answer this, "nanoswords" of Fe-doped titanite are fabricated on a Ti implant surface to resist bacterial invasion by a synergistic action of ferroptosis-like bacteria killing, proton disturbance, and physical puncture. The related antibiosis mechanism is explored by atomic force microscopy and genome sequencing. The nanoswords induce an increased local pH value, which not only weakens the proton motive force, reducing adenosine triphosphate synthesis of Staphylococcus aureus, but also decreases the membrane modulus, making the nanoswords distort and even puncture a bacterial membrane easily. Simultaneously, more Fe ions are taken by bacteria due to increased bacterial membrane permeability, resulting in ferroptosis-like death of bacteria, and this is demonstrated by intracellular iron enrichment, lipid peroxidation, and glutathione depletion. Interestingly, a microenvironment constructed by these nanoswords improves osteoblast behavior in vitro and bone regeneration in vivo. Overall, the nanoswords can induce ferroptosis-like bacterial death without cytotoxicity and have great promise in applications with clinical implants for outstanding antibiosis and biointegration performance.

Atomic Layer Deposition of TiO2 Thin Films on the Inner Walls of Steel Tubes Increases Anti-coking Properties.

To suppress catalytic coking, TiO2 passivation films were deposited on the inner walls of SS316 stainless steel tubes by atomic layer deposition (ALD). Indentation test results showed a platform on the indentation curve of TiO2 films grown over 2000 ALD cycles due to internal stress-induced microcracks. In coking experiments, the TiO2-coated tubes exhibited a higher heat flux and lower pressure difference than bare ones. Analysis of the coking surface revealed that TiO2 thin film passivation can reduce the size and number of particulate deposits. At the same time, passivation treatment inhibits the formation of filamentous carbon and improves anti-coking performance by reducing the ability of the tube to adsorb amorphous deposition products. The coking surfaces of TiO2-coated tubes had less graphitization, indicating that the coking products had fewer defects and lower activated carbon contents.

Nanostructured Bi Grown on Epitaxial Graphene/SiC.

Controllable growth of metal nanostructures on epitaxial graphene (EG) is particularly interesting and important for the applications in electric devices. Bi nanostructures on EG/SiC are fabricated through thermal decomposition of SiC and subsequent low-flux evaporation of Bi. The orientation, atomic structure, and thickness-dependent electronic states of Bi are investigated by scanning tunneling microscopy/spectroscopy. It is found that metallic Bi nanoflakes and nanorods prefer to grow on the SiC buffer layer region with higher diffusion barrier, but Bi nanoribbons are formed on regularly ordered EG. Although the thicker Bi nanoribbons of 11 monolayers on EG are still metallic, the thinner ones become semiconducting owing to the interfacial effect. This indicates that the electronic states and physical properties of Bi are substrate-dependent. The results are helpful for the design of Bi- and graphene-based electronic and spintronic devices.

Thickness dependent Raman spectra and interfacial interaction between Ag and epitaxial graphene on 6H-SiC(0001).

Graphene as the thinnest material has an extremely large specific surface area, and thus the physical properties of graphene based devices should be sensitively dependent on the contacted metals. Moreover, the interfacial interaction between graphene and metals is complicated and it is difficult to probe. In this paper, epitaxial graphene is prepared by thermal decomposition of 6H-SiC(0001), and then Ag is deposited on it. It is found that the morphology and distribution of Ag particles on graphene domains are independent of the graphene thickness. The Ag particles induce the surface enhanced Raman scattering (SERS) effect and the doping effect in epitaxial graphene. The enhancement factor of SERS as well as the splitting of the G band and the shift of the 2D band decreases with increasing graphene thickness, which can be ascribed to the weakened interaction between Ag and EG. This is confirmed by the charge transfer between the Ag atom and epitaxial graphene on 6H-SiC predicted by first-principles calculations. The results are helpful to the design and development of graphene-based composites and devices.

Green in Situ Synthesis of Clean 3D Chestnutlike Ag/WO3-x Nanostructures for Highly Efficient, Recyclable and Sensitive SERS Sensing.

Surface-enhanced Raman scattering (SERS) has proven to be an effective technique for identifying and providing fingerprint structural information on various analytes in low concentration. However, this analytical technique has been plagued by the ubiquitous presence of organic contaminants on roughened SERS substrate surfaces, which not only often result in poorer detection sensitivity but also significantly affect the reproducibility and accuracy of SERS analysis. Herein, we developed a clean, stable, and recyclable three-dimensional (3D) chestnutlike Ag/WO3-x (0 < x < 0.28) SERS substrate by simple hydrothermal reaction and subsequent green in situ decoration of silver nanoparticles. None of the organic additives were used in synthesis, which ensures the substrate surfaces are completely clean and free of interferences from impurities. The innovative design combines the SERS enhancement effect and self-cleaning property, making it a multifunctional and reusable SERS platform for highly sensitive SERS detection. Using malachite green as a model target, the as-prepared SERS substrates exhibited good reproducibility (relative standard deviation of 7.5%) and pushed the detection limit down to 0.29 pM. The enhancement factor was found to be as high as 1.4 × 107 based on the analysis of 4-aminothiophenol. The excellent regeneration performance indicated that the 3D biomimetic SERS substrates can be reused many times. In addition, the fabricated substrate was successfully employed for detecting thiram in water with a detection limit of 0.32 nM, and a good linear relationship was obtained between the logarithmic intensities and the logarithmic concentrations of thiram ranging from 1 nM to 1 µM. More importantly, the resultant SERS-active colloid can be used for accurate and reliable determination of thiram in real fruit peels. These results predict that the proposed SERS system have great potential toward rapid, reliable, and on-site analysis, especially for food safety and environmental supervision.

Fabrication of Bi2Te3-x Se x nanowires with tunable chemical compositions and enhanced thermoelectric properties.

Uniform Bi2Te3-x Se x nanowires (NWs) with tunable components are synthesized by a modified solution method free of any template, and inter-diffusion mechanism is proposed for the growth and transformation of ternary nanowires. Spark plasma sintering is adopted to fabricate the pellets of Bi2Te3-x Se x NWs and thermoelectric transport properties are measured. As compared to Bi2Te3 pellets, Se doping results in lowered electrical conductivity because of the reduced carrier concentration, both the Seebeck coefficient and the power factor are enhanced substantially. The Bi2Te2.7Se0.3 pellet exhibits the highest power factor at room temperature as a result of optimized carrier concentration (4.37 × 1019 cm-3) and mobility (60.22 cm2 V-1 s-1). As compared to Bi2Te3, the thermal conductivity of Bi2Te3-x Se x is lowered owing to the enhanced phonon scattering by dopants and grain boundaries. As a result, the ZT value at 300 K is substantially improved from 0.045 of Bi2Te3 to 0.42 of Bi2Te2.7Se0.3. It is suggested that Se doping is an effective way to enhance the thermoelectric performance of Bi2Te3 based materials.

Ag Nanoparticles Decorated Cactus-Like Ag Dendrites/Si Nanoneedles as Highly Efficient 3D Surface-Enhanced Raman Scattering Substrates toward Sensitive Sensing.

Surface-enhanced Raman scattering (SERS) has been considered as a promising sensing technique to detect low-level analytes. However, its practical application was hindered owing to the lack of uniform SERS substrates for ultrasensitive and reproducible assay. Herein, inspired by the natural cactus structure, we developed a cactus-like 3D nanostructure with uniform and high-density hotspots for highly efficient SERS sensing by both grafting the silicon nanoneedles onto Ag dendrites and subsequent decoration with Ag nanoparticles. The hierarchical scaffolds and high-density hotspots throughout the whole substrate result in great amplification of SERS signal. A high Raman enhancement factor of crystal violet up to 6.6 × 10(7) was achieved. Using malachite green (MG) as a model target, the fabricated SERS substrates exhibited good reproducibility (RSD ∼ 9.3%) and pushed the detection limit down to 10(-13) M with a wide linear range of 10(-12) M to 10(-7) M. Excellent selectivity was also demonstrated by facilely distinguishing MG from its derivative, some organics, and coexistent metal ions. Finally, the practicality and reliability of the 3D SERS substrates were confirmed by the quantitative analysis of spiked MG in environmental water with high recoveries (91.2% to 109.6%). By virtue of the excellent performance (good reproducibility, high sensitivity, and selectivity), the cactus-like 3D SERS substrate has great potential to become a versatile sensing platform in environmental monitoring, food safety, and medical diagnostics.

3D silver nanoparticles decorated zinc oxide/silicon heterostructured nanomace arrays as high-performance surface-enhanced Raman scattering substrates.

Three-dimensional (3D) hierarchical nanostructures have been considered as one of the most promising surface-enhanced Raman spectroscopy (SERS) substrates because of the ordered arrangement of high-density hotspots along the third dimension direction. Herein, we reported a unique 3D nanostructure for SERS detection based on silver nanoparticles (AgNPs) decorated zinc oxide/silicon (ZnO/Si) heterostructured nanomace arrays. They were prepared by two steps: (1) Si nanoneedles were grafted onto ZnO nanorod arrays via a catalyst-assisted vapor-liquid-solid (VLS) growth mechanism. (2) AgNPs were rapidly immobilized on the surface of nanomaces by a facile galvanic displacement reaction. The fabricated substrates were employed to detect rhodamine 6G (R6G) with a detection limit down to 10(-16) M, and exhibited a high-enhanced performance (enhancement factor (EF) as high as 8.7 × 10(7)). To illustrate the potential value of the prepared substrates, the different concentrations of melamine aqueous solution (from 10(-4) to 10(-10) M) were detected, and a quantitative relationship between the SERS spectrum intensity and the melamine concentration had been established. In addition, the measure of melamine residual in pure milk was carried out successfully, and the results indicated that the prepared 3D nanomace substrates had great potential in food inspection, environment protection, and a few other technologically important fields.

Synthesis and stress relaxation of ZnO/Al-doped ZnO core-shell nanowires.

Doping nanostructures is an effective method to tune their electrical and photoelectric properties. Taking ZnO nanowires (NWs) as a model system, we demonstrate that atomic layer deposition (ALD) can be adopted for the realization of a doping process by the homo-epitaxial growth of a doped shell on the NW core. The Al-doped ZnO NWs have a layered superlattice structure with dopants mainly occupying the interstitial positions. After annealing, Al(3+) ions diffuse into the ZnO matrix and occupy substitutional locations, which is desirable for dopant activation. The stress accumulated during epitaxial growth is relaxed by the nucleation of dislocations, dislocation dipoles and anti-phase boundaries. We note that the proposed method can be easily adopted for doping different types of nanostructures, and fabricating superlattices and multiple quantum wells on NWs in a controllable way.

Fabrication and characterization of silicon quantum dots in Si-rich silicon carbide films.

Amorphous Si-rich silicon carbide films were prepared by magnetron co-sputtering and subsequently annealed at 900-1100 degrees C. After annealing at 1100 degrees C, this configuration of silicon quantum dots embedded in amorphous silicon carbide formed. X-ray photoelectron spectroscopy was used to study the chemical modulation of the films. The formation and orientation of silicon quantum dots were characterized by glancing angle X-ray diffraction, which shows that the ratio of silicon and carbon significantly influences the species of quantum dots. High-resolution transmission electron microscopy investigations directly demonstrated that the formation of silicon quantum dots is heavily dependent on the annealing temperatures and the ratio of silicon and carbide. Only the temperature of about 1100 degrees C is enough for the formation of high-density and small-size silicon quantum dots due to phase separation and thermal crystallization. Deconvolution of the first order Raman spectra shows the existence of a lower frequency peak in the range 500-505 cm(-1) corresponding to silicon quantum dots with different atom ratio of silicon and carbon.

Multi-band silicon quantum dots embedded in an amorphous matrix of silicon carbide.

Silicon quantum dots embedded in an amorphous matrix of silicon carbide were realized by a magnetron co-sputtering process and post-annealing. X-ray photoelectron spectroscopy, glancing x-ray diffraction, Raman spectroscopy and high-resolution transmission electron microscopy were used to characterize the chemical composition and the microstructural properties. The results show that the sizes and size distribution of silicon quantum dots can be tuned by changing the annealing atmosphere and the atom ratio of silicon and carbon in the matrix. A physicochemical mechanism is proposed to demonstrate this formation process. Photoluminescence measurements indicate a multi-band configuration due to the quantum confinement effect of silicon quantum dots with different sizes. The PL spectra are further widened as a result of the existence of amorphous silicon quantum dots. This multi-band configuration would be extremely advantageous in improving the photoelectric conversion efficiency of photovoltaic solar cells.

Bistability of nanoscaleAg islands on a Si(111)-(4 x 1)-in surface induced by anisotropic stress.

We demonstrate experimentally the existence of two stability regimes of Ag nanoislands grown on a Si(111)-(4 x 1)-In surface: a conventional regime at low temperature where only one island shape is stable, and an unconventional regime at room temperature (RT) where isotropic compact islands coexist with anisotropic elongated ones. First-principles calculations show the unusual bistability at RT arises from the fact that the Ag nanoislands are under anisotropic stress, supporting a recent theoretical prediction by Zandvliet and van Gastel [Phys. Rev. Lett. 99, 136103 (2007)10.1103/PhysRevLett.99.136103].