Catalyst Droplet-Based Puncturable Nanostructures with Mechano-Bactericidal Properties Against Bioaerosols

Bioaerosol contamination problems have led to the need for new technologies that effectively collect and inactivate airborne microorganisms. Typical nanomaterial-based filter membranes are usually sterilized using photocatalysts, electrical stimulation, and thermal treatment, which are expensive and require additional devices and cumbersome manufacturing. In this study, a membrane with nanotopographical features is manufactured via a catalyst droplet-based procedure to mechanically damage airborne bacteria. The catalyst droplets are used as templates for in situ novel puncturable nanopillar growth on the membrane surface. Numerical simulations and microscopic observations show that puncturable nanopillars with a thin and rough nano-edge are advantageous for rupturing the bacterial cell compared to flat nanopillars without a thin edge. A puncturable nanostructured air filter (PNAF) is compared to a bare air filter and exhibits higher bioaerosol collection efficiencies (>98% and 89.3–95.7%, respectively). PNAF is tested under breathing conditions as part of a face mask, where it effectively captures and deactivates E. coli aerosols through a mechano-bactericidal effect, resulting in the inhibition of bacterial proliferation and finally death. Thus, PNAF can be applied as an air purifier or face mask filter for bioaerosol collection presenting antibacterial effects without external stimulation.     

Answer to comments on “Fabrication and photovoltaic conversion enhancement of graphene/n-Si Schottky barrier solar cells by electrophoretic deposition”

Here, we reply to comments by Valentic et al. on our paper published in Electrochimica Acta (2014, 130: 279). They commented that Au nanoparticles played the dominant role on the whole cell''s performances in our improved graphene/Si solar cell. We argued that our devices are Au-doped graphene/n-Si Schottky barrier devices, not Au nanoparticles (film)/n-Si Schottky barrier devices. During the doping process, most of the Au nanopatricles covered the surfaces of the graphene. Schottky barriers between doped graphene and n-Si dominate the total cells properties. Through doping, by adjusting and tailoring the Fermi level of the graphene, the Fermi level of n-Si can be shifted down in the graphene/Si Schottky barrier cell. They also argued that the instability of our devices were related to variation in series resistance reduced at the beginning due to slightly lowered Fermi level and increased at the end by the self-compensation by deep in-diffusion of Au nanoparticles. But for our fabricated devices, we know that an oxide layer covered the Si surface, which makes it difficult for the Au ions to diffuse into the Si layer, due to the continuous growth of SiO₂ layer on the Si surface which resulted in series resistance decreasing at first and increasing in the end.     

Fabrication of Frog-Skin-Inspired Slippery Antibiofouling Coatings Through Degradable Block Copolymer Wrinkling

Marine biofouling is a severe problem with a wide-reaching impact on ship maintenance, the economy, and ecosystem safety, among others. Inspired by complex multifunctional frogskins, wrinkled slippery coatings are created that exhibit remarkable antifouling, anti-icing, and self-cleaning properties through a combination of degradable di-block copolymer self-assembly [i.e., polystyrene-b-polylactide (PS-b-PLA)] and hydrolysis-driven dynamic release-induced surface wrinkling. Microwrinkled patterns can generate curved surfaces that are resistant to biofouling. Gyroid-forming PS-b-PLA can be used to produce nanoporous templates with cocontinuous nanochannels, which generate strong capillary forces for trapping and storing infiltrated lubricants. In this study, block-copolymer-derived hierarchically wrinkled slippery liquid-infused nanoporous surfaces (i.e., micro wrinkles with nanochannels infused with slippery fluids) are successfully fabricated after silicone oil infiltration. The antibiofouling performance of these surfaces is examined against different foulers under various conditions. The produced coatings exhibited flexible, stable, transparent, and easily tunable antibiofouling characteristics. In particular, the formation of an eco-friendly silicon-based lubricant layer without the use of fluorinated compounds and costly material precursors is an advantage in industrial practice that can be adopted in various applications, such as fuel transport, self-cleaning windows, anticorrosion protection, nontoxic coatings for medical devices, and optical instruments.     

Distinguishing between activated and nonactivated eosinophils by ACimpedance measurements

A cellular electrical impedance device which can detect the activated state of eosinophils has been developed and tested. This impedance device consists of a small gold electrode (50 μm×50 μm) and a large gold electrode (1.5 cm×0.5 cm) on a glass substrate, and it was fabricated by standard photolithographic techniques. Eosinophils, which belong to the granulocytic class of white blood cells, exhibit different physical properties when they change from the nonactivated state to the activated state. Hypothetically, these changes should correspond to a change in the measured electrical impedance. In this paper, data from the measured electrical impedance of eosinophils is presented. The measurements show that the average impedance of the activated eosinophils is 26% lower than the average impedance of the nonactivated eosinophils. Statistical analysis of the measured data shows that there is a significant difference between the measured impedances of activated and nonactivated eosinophils     

Surface passivation of crystalline silicon solar cells: a review

In the 1980s, advances in the passivation of both cell surfaces led to the first crystalline silicon solar cells with conversion efficiencies above 20%. With today's industry trend towards thinner wafers and higher cell efficiency, the passivation of the front and rear surfaces is now also becoming vitally important for commercial silicon cells. This paper presents a review of the surface passivation methods used since the 1970s, both on laboratory‐type as well as industrial cells. Given the trend towards lower‐cost (but also lower‐quality) Si materials such as block‐cast multicrystalline Si, ribbon Si or thin‐film polycrystalline Si, the most promising surface passivation methods identified to date are the fabrication of a p–n junction and the subsequent passivation of the resulting silicon surface with plasma silicon nitride as this material, besides reducing surface recombination and reflection losses, additionally provides a very efficient passivation of bulk defects. Copyright © 2000 John Wiley & Sons, Ltd.     

Nanostructured Si/Organic Heterojunction Solar Cells with High Open‐Circuit Voltage via Improving Junction Quality

Nanostructured silicon (Si) can provide improved light harvest efficiencies in organic‐Si heterojunction solar cells due to its low light reflection ratio compared with planar one. However, the associated large surface/volume ratio of nanostructured Si suffers from serious surface recombination as well as poor adhesion with organics in organic‐Si heterojunction solar cells, which leads to an inferior open‐circuit voltage (V_oc). Here, we develop a simple and effective method to suppress charge recombination as well as enhancing adhesion force between nanostructured Si and organics by incorporating a silane chemical, namely 3‐glycidoxypropyltrimethoxydsilane (GOPS). GOPS can chemically graft onto nanostructured Si and improve the aqueous organic wetting properties, suppressing surface charge recombination velocity dramatically. In addition, this chemically grafted layer can enhance adhesion force between organics and Si. In such a way, a record V_oc of 640 mV associated with a power conversion efficiency of 14.1% is obtained for organic‐nanostructured Si heterojunction devices. These findings suggest a promising approach to low‐cost and simple fabrication for high‐performance organic‐Si solar cells.     

Ultraviolet, visible, and infrared response of PtSiSchottky-barrier detectors operated in the front-illuminated mode

The quantum efficiency of PtSi Schottky-barrier detectors has been measured as a function of wavelength from 0.23 to 7 μm. For front-illuminated PtSi/p-Si devices operated at low temperatures, quantum efficiencies of 40 to 70% are obtained in the ultraviolet (UV) and visible regions with little loss of the infrared (IR) photoresponse that is obtained for operation in the conventional back-illumination mode. For room-temperature operation of front-illumination PtSi/n-Si devices, the quantum efficiencies are approximately the same in the UV and visible regions, but the IR response decreases abruptly beyond the Si absorption edge. Room-temperature transmission and reflection measurements have been used to determine the values of the real and imaginary parts of the complex dielectric constant for PtSi at wavelengths from 0.2 to 3 μm. A simple model, used with these values and published values of the dielectric constant for Si, yields calculated quantum efficiencies in the UV and visible regions that agree quite well with the measured efficiencies. The temporal response of front-illuminated PtSi/p-Si detectors in the visible and IR regions is found to be fast enough for operation at video frame rates     

Peptides for the Biofunctionalization of Silicon for Use in Optical Sensing with Porous Silicon Microcavities

Addressing the surface chemistry of silicon is of fundamental scientific and technical significance due to the wide use of this material in electronics and optics. A novel method of functionalizing silicon (Si) via short peptides with binding specificity for Si is presented. The peptide presenting the highest affinity for Si is identified via phage display technology, and the 12‐mer LLADTTHHRPWT and SPGLSLVSHMQT peptides were found to be specific for the n⁺‐Si and p⁺‐Si surfaces, respectively. In our sensing application, the obtained peptides are used as functionalizing linkers to allow porous silicon microcavities to bind biotin and then capture streptavidin. Molecular detection is monitored via reflectometric interference spectra as shifts in the resonance peaks of the cavity structure. An improved streptavidin sensing (21 times lower detection limit) with peptide‐functionalized porous silicon microcavities is demonstrated, compared to sensing performed with devices functionalized with the commonly used silanization method, suggesting that the modification of Si via Si‐specific peptides provides better interface layers for molecular detection. High‐resolution atomic force microscopy images corroborate this result and reveal the formation of ordered nanometer‐sized molecular layers when peptide‐route functionalization is performed.     

Model Organic Surfaces to Probe Marine Bacterial Adhesion Kinetics by Surface Plasmon Resonance

Understanding how bacteria adhere to a surface is a critical step in the development of novel materials and coatings to prevent bacteria forming biofilms. Here, surface plasmon resonance (SPR) spectroscopy, in combination with self‐assembled monolayers (SAMs) that have different backbone structures and/or functional groups, is used for the first time to study the initial stages of bacterial adhesion to surfaces (i.e., initial interaction of cells with a surface, a process governed by van der Waals, electrostatic, and hydrophobic interactions). The work highlights SPR spectroscopy as a powerful and unique approach to probe bacterial adhesion in real time. SPR spectral data reveal different kinetics of adhesion for the interaction of two marine bacterial species (Marinobacter hydrocarbonoclasticus and Cobetia marina) to a range of organosulfur SAMs. Furthermore, the extent of adhesion is dependent on the backbone structures and functional groups of the SAMs. The role of extracellular polymeric substances (EPS) in bacterial adhesion is also investigated. Pre‐conditioning experiments with cell‐free culture supernatants, containing planktonic EPS, allow quantification of the amount adsorbed onto surfaces and directly account for the impact of EPS adsorption on bacterial adhesion in the assay. While the physicochemical characteristics of the surfaces play a significant role in determining bacterial cell adhesion for low levels of conditioning by planktonic EPS, greater levels of conditioning by EPS reduce the difference between surfaces.     

Microstructure and mechanical properties of ceramic/self-assembled monolayer bilayer coatings

Thin ceramic coatings/films find their applications in various electronic devices, sensors, and microelectromechanical systems (MEMS) as a protection/barrier layer as well as functional films. Ceramics are, however, susceptible to catastrophic failure due to their inherent brittleness. We have developed a strain-tolerant, bilayer coating consisting of a ceramic layer and a self-assembled monolayer (SAM). The top ceramic coating offers an inert, protective layer, while the underlying SAM acts as a “template” for the subsequent growth of a hard ceramic coating. In this study, we explore the ZrO₂/SAM coatings on Si substrates prepared in situ at 80°C in solution. The coatings exhibited good coverage on the silicon surface, but the hardness was rather low. Characterization tools including x-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), and nanoindentation were employed to achieve a better understanding of the synthesis and processing of the coatings and their relation to the mechanical properties.     

GaAs Shallow-homojunction solar cells on Ge-coated Si substrates

Solar cells with conversion efficiencies of 12% (AM1) have been fabricated from single-crystal GaAs epilayers grown by CVD on Ge-coated Si substrates. The cells utilize an n⁺/p/p⁺shallow-homo junction GaAs structure on a thin (<0.2 µm) epitaxial Ge layer. These solar cells are the first reported GaAs devices fabricated on Si substrates.     

Antibacterial Surface Coatings from Zinc Oxide Nanoparticles Embedded in Poly(N‐isopropylacrylamide) Hydrogel Surface Layers

Despite multiple research approaches to prevent bacterial colonization on surfaces, device‐associated infections are currently responsible for about 50% of nosocomial infections in Europe and significantly increase health care costs, which demands development of advanced antibacterial surface coatings. Here, novel antimicrobial composite materials incorporating zinc oxide nanoparticles (ZnO NP) into biocompatible poly(N‐isopropylacrylamide) (PNIPAAm) hydrogel layers are prepared by mixing the PNIPAAm prepolymer with ZnO NP, followed by spin‐coating and photocrosslinking. Scanning electron microscopy (SEM) characterization of the composite film morphology reveals a homogeneous distribution of the ZnO NP throughout the film for every applied NP/polymer ratio. The optical properties of the embedded NP are not affected by the matrix as confirmed by UV‐vis spectroscopy. The nanocomposite films exhibit bactericidal behavior towards Escherichia coli (E. coli) for a ZnO concentration as low as ≈0.74 μg cm^?2 (1.33 mmol cm^?3), which is determined by inductively coupled plasma optical emission spectrometry. In contrast, the coatings are found to be non‐cytotoxic towards a mammalian cell line (NIH/3T3) at bactericidal loadings of ZnO over an extended period of seven days. The differential toxicity of the ZnO/hydrogel nanocomposite thin films between bacterial and cellular species qualifies them as promising candidates for novel biomedical device coatings.     

Silicon solar cells

The key attributes for achieving high-efficiency crystalline silicon solar cells are identified and historical developments leading to their realization discussed. Despite the achievement of laboratory cells with performance approaching the theoretical limit, commercial cell designs need to evolve significantly to realize their potential. In particular, the development of cell structures and processes that facilitate entirely activated device volumes in conjunction with well-passivated metal contacts a nd front and rear surfaces is essential (and yet not overly challenging) to achieve commercial devices of 20% efficiency from solar-grade substrates. The inevitable trend towards thinner substrates will force manufacturers to evolve their designs in this direction or else suffer substantial performance loss. Eventually, a thin-film technology will likely dominate, with thin-film crystalline silicon cells being a serious candidate. Present commercial techniques and processes are in general unsuitable for t hin-film fabrication, with even greater importance placed on the achievement of devices with entirely activated volumes (diffusion lengths much greater than device thicknesses), well-passivated metal contacts and surfaces and the important inclusion of li ght trapping. The recent achievement of 21.5% efficiency on a thin crystalline silicon cell (less than 50 μm thick) adds credibility to the pursuit of crystalline silicon in thin films, with a key attribute of this laboratory cell being its extremely good light trapping that nullifies the long-term criticism of crystalline silicon regarding its poor absorption properties and correspondingly perceived inability to achieve high-performance thin-film devices. For low-cost, low-quality polycrystalline sil icon material, the parallel-multijunction cell structure may provide a mechanism for achieving entirely activated cell volumes with the potential to achieve reasonable efficiencies at low cost over the next decade.     

Channelled substrate narrow stripe GaAs/(GaAl)As lasers with quarter-wavelength facet coatings

Channelled substrate narrow stripe GaAs/(GaAl)As lasers with quarter-wavelength antireflection coatings are described. These devices have low thresholds, broad spectra, high external quantum efficiencies and operate up to 10 mW in the fundamental transverse mode.     

Antibody Engineered Platelets Attracted by Bacteria-Induced Tumor-Specific Blood Coagulation for Checkpoint Inhibitor Immunotherapy

Bacteria can act as a promising anti-tumor platform due to their specific targeting capacity to the tumor microenvironment. In this study, it is discovered that intravenous administration of Escherichia coli TOP10 induces rapid and intense blood coagulation in tumor tissues instead of normal tissues. It is demonstrated that E. coli TOP10 can act as an activator of a coagulation cascade to trigger abnormal hemorrhage, blood coagulation, and inflammation with abundant macrophages recruitment in tumors. In addition, the recruited macrophages are principally polarized by lipopolysaccharide in the bacterial wall to the anti-tumor M1-like phenotype. Based on the above finding, coagulation-tropism blood platelets decorated with CD47 antibodies (Anti-CD47), which possess tropism for bacteria-treated tumors are further prepared. As a result, Anti-CD47 blocks the “don't eat me” signal from tumor cells, consequently promoting the phagocytosis of polarized M1-like phenotype macrophages for tumor cells. This manipulation of local blood coagulation in tumors may find great potential for accurately delivering immune checkpoint inhibitors and facilitating tumor immunotherapy.     

Functionalized DNA Nanomaterials Targeting Toll-Like Receptor 4 Prevent Bisphosphonate-Related Osteonecrosis of the Jaw via Regulating Mitochondrial Homeostasis in Macrophages

Imbalance of macrophage polarization characterized by an increase in the percentage of pro-inflammatory M1 macrophages and a decrease in anti-inflammatory M2 macrophages is considered a critical pathogenic mechanism of bisphosphonate-related osteonecrosis of the jaws (BRONJ). Because high levels of Toll-like receptor 4 (TLR4) mediates mitochondrial dyshomeostasis in Zoledronic Acid (ZA)-treated M1 macrophages, tetrahedral DNA nanomaterial (TDN)-modified with TLR4-siRNA on each vertex (TDN-TLR4-4siR) with excellent biocompatibility is synthesized. This novel TDN-TLR4-4siR nanomaterial reverses the polarization phenotype imbalance decreasing the percentage of M1 RAW264.7 macrophages. Mitochondrial dynamics analysis shows a shift from short rod-like ultrastructure to elongated shapes with more mitochondrial network continuity in ZA-primed M1 macrophages after treatment with TDN-TLR4-4siR, along with elevated expression of Mfn1 and Mfn2. TDN-TLR4-4siR further reduces intracellular ROS production and restored mitochondrial membrane potential. Furthermore, decreased sequestra formation and accelerated healing of the extraction wound are observed in the TDN-TLR4-4siR group, resulting in decreased incidence of rat BRONJ via reprogramming polarized macrophages. Consequently, this study establishes a novel strategy using TDN-TLR4-4siR nanomaterial to regulate mitochondrial homeostasis of polarized macrophages to prevent BRONJ.     

A Shape‐Adaptive,Antibacterial‐Coating of Immobilized Quaternary‐Ammonium Compounds Tethered on Hyperbranched Polyurea and its Mechanism of Action

Quaternary‐ammonium‐compounds are potent cationic antimicrobials used in everyday consumer products. Surface‐immobilized, quaternary‐ammonium‐compounds create an antimicrobial contact‐killing coating. We describe the preparation of a shape‐adaptive, contact‐killing coating by tethering quaternary‐ammonium‐compounds onto hyperbranched polyurea coatings, able to kill adhering bacteria by partially enveloping them. Even after extensive washing, coatings caused high contact‐killing of Staphylococcus epidermidis, both in culture‐based assays and through confocal‐laser‐scanning‐microscopic examination of the membrane‐damage of adhering bacteria. In culture‐based assays, at a challenge of 1600 CFU/cm², contact‐killing was >99.99%. The working‐mechanism of dissolved quaternary‐ammonium‐compounds is based on their interdigitation in bacterial membranes, but it is difficult to envisage how immobilized quaternary‐ammonium‐molecules can exert such a mechanism of action. Staphylococcal adhesion forces to hyperbranched quaternary‐ammonium coatings were extremely high, indicating that quaternary‐ammonium‐molecules on hyperbranched polyurea partially envelope adhering bacteria upon contact. These lethally strong adhesion forces upon adhering bacteria then cause removal of membrane lipids and eventually lead to bacterial death.     

Optimization of Si NC/P3HT Hybrid Solar Cells

Silicon nanocrystals (Si NCs) are shown to be an electron acceptor in hybrid solar cells combining Si NCs with poly(3‐hexylthiophene) (P3HT). The effects of annealing and different metal electrodes on Si NC/P3HT hybrid solar cells are studied in this paper. After annealing at 150 °C, Si NC/P3HT solar cells exhibit power conversion efficiencies as high as 1.47%. The hole mobility in the P3HT phase extracted from space‐charge‐limited current measurements of hole‐only devices increases from 2.48 × 10^?10 to 1.11 × 10^?9 m² V^?1 s^?1 after annealing, resulting in better transport in the solar cells. A quenching of the open‐circuit voltage and short‐circuit current is observed when high work function metals are deposited as the cathode on Si NC/P3HT hybrid devices.     

Microstructured ZnO coatings combined with antireflective layers for light management in photovoltaic devices

We describe microstructured ZnO coatings that improve photovoltaic (PV) device performance through their antireflective properties and their tendency to scatter incoming light at large angles. In many PV devices, reflection from the transparent conductive top contact significantly degrades performance. Traditional quarter‐wave antireflective (AR) coatings reduce surface reflection but perform optimally for only a narrow spectral range and incident illumination angle. Furthermore, in some types of devices, absorption far from the junction increases the rate of recombination, and light management strategies are required to remedy this. The randomly patterned, microstructured ZnO coatings described in this paper, formed via a simple wet etch process, serve as both an AR layer with superior performance to that of a thin film AR coating alone as well as a large angle forward scatterer. We model formation of the coatings and evaluate their AR properties. When combined with a traditional quarter‐wave MgF₂ coating, these microstructured ZnO coatings increase short circuit currents of example Cu(In,Ga)Se₂ (CIGS) devices by over 20% in comparison to those of uncoated devices at normal incidence. A similar improvement is observed for illumination angles of up to 60°. While demonstrated here for CIGS, these structures may prove useful for other PV technologies as well. Published 2016. This article is a U.S. Government work and is in the public domain in the USA. Progress in Photovoltaics: Research and Applications Published by John Wiley & Sons Ltd.     

Thermal characterization of embedded electronic features by an integrated system of CCD thermography and self-adaptive numerical modeling

This work provides a practical application of a coupled experimental-computational system devised for the full characterization of the thermal behavior of complex three-dimensional active submicron electronic devices. A thermoreflectance thermography (TRTG) technique is used to non-invasively measure the 2D surface temperature field of an activated device, with submicron spatial resolution. The measured planar temperature distribution field is then used as input for an ultra-fast inverse computational solution to derive the three-dimensional temperature distribution throughout the device. For the purposes of this investigation, test micro-heater devices were constructed on epitaxial layers of natural (Si) and isotopically pure (Si²⁸) silicon. Then, all devices were activated and measured with the TRTG technique. In order to demonstrate the coupled experimental-computational system, the measured temperature fields of the samples whose thermal properties are known (Si) were used to extract critical physical parameters (the oxide layer thickness and the effective heater length). Then, since the devices with unknown thermal properties (Si²⁸) share the same construction with the Si devices, the extracted parameters were used together with the measured planar temperature fields to derive the thermal conductivity of Si²⁸. The extracted oxide layer thickness and thermal conductivity of Si²⁸ compared very closely to values obtained by other independent direct methods.