Combinatorial materials research applied to the development of new surface coatings IV. A high-throughput bacterial biofilm retention and retraction assay for screening fouling-release performance of coatings

Abstract

A high-throughput bacterial biofilm retention screening method has been augmented to facilitate the rapid analysis and down-selection of fouling-release coatings for identification of promising candidates. Coatings were cast in modified 24-well tissue culture plates and inoculated with the marine bacterium Cytophaga lytica for attachment and biofilm growth. Biofilms retained after rinsing with deionised water were dried at ambient laboratory conditions. During the drying process, retained biofilms retracted through a surface de-wetting phenomenon on the hydrophobic silicone surfaces. The retracted biofilms were stained with crystal violet, imaged, and analysed for percentage coverage. Two sets of experimental fouling-release coatings were analysed with the high-throughput biofilm retention and retraction assay (HTBRRA). The first set consisted of a series of model polysiloxane coatings that were systematically varied with respect to ratios of low and high MW silanol-terminated PDMS, level of cross-linker, and amount of silicone oil. The second set consisted of cross-linked PDMS-polyurethane coatings varied with respect to the MW of the PDMS and end group functionality. For the model polysiloxane coatings, HTBRRA results were compared to data obtained from field immersion testing at the Indian River Lagoon at the Florida Institute of Technology. The percentage coverage calculations of retracted biofilms correlated well to barnacle adhesion strength in the field (R² = 0.82) and accurately identified the best and poorest performing coating compositions. For the cross-linked PDMS-polyurethane coatings, the HTBRRA results were compared to combinatorial pseudobarnacle pull-off adhesion data and good agreement in performance was observed. Details of the developed assay and its implications in the rapid discovery of new fouling-release coatings are discussed.     

Mechanism of bactericidal and fungicidal activities of textiles covalently modified with alkylated polyethylenimine

Our previous studies have led to a novel "nonrelease" approach to making materials bactericidal by covalently attaching certain moderately hydrophobic polycations to their surfaces. In the present work, this strategy is extended beyond the heretofore-used nonporous materials to include common woven textiles (cotton, wool, nylon, and polyester). Pieces of such cloths derivatized with N-hexylated+methylated high-molecular-weight polyethylenimine (PEI) are strongly bactericidal against several airborne Gram-positive and Gram-negative bacteria. In contrast, the immobilized and N-alkylated PEIs of low molecular weight have only a weak, if any, bactericidal activity. These findings support a mechanism of the antibacterial action whereby high-molecular-weight and hydrophobic polycationic chains penetrate bacterial cell membranes/walls and fatally damage them. The bactericidal textiles prepared herein are lethal not only to pathogenic bacteria but to fungi as well.     

Quantum Dot Based Heterostructures for Unassisted Photoelectrochemical Hydrogen Generation

TiO₂ hollow nanowires (HNWs) and nanoparticles (NPs) constitute promising architectures for QDs sensitized photoanodes for H₂ generation. We sensitize these structures with CdS/CdSe quantum dots by two different methods (chemical bath deposition, CBD and succesive ionic layer adsorption and reaction, SILAR) and evaluate the performance of these photoelectrodes. Remarkable photocurrents of 4 mA·cm and 8 mA·cm^?2 and hydrogen generation rates of 40 ml·cm^?2·day^?1 and 80 ml·cm^?2·day^?1 have been obtained in a three electrode configuration with sacrificial hole scavengers (Na₂S and Na₂SO₃), for HNWs and NPs respectively, which is confirmed through gas analysis. More importantly, autonomous generation of H₂ (20 ml·cm^?2·day^?1 corresponding to 2 mA·cm^?2 photocurrent) is obtained in a two electrode configuration at short circuit under 100 mW·cm^?2 illumination, clearly showing that these photoanodes can produce hydrogen without the assistance of any external bias. To the best of the authors' knowledge, this is the highest unbiased solar H₂ generation rate reported for these of QDs based heterostructures. Impedance spectroscopy measurements show similar electron density of trap states below the TiO₂ conduction band while the recombination resistance was higher for HNWs, consistently with the much lower surface area compared to NPs. However, the conductivity of both structures is similar, in spite of the one dimensional character of HNWs, which leaves some room for improvement of these nanowired structures. The effect of the QDs deposition method is also evaluated. Both structures show remarkable stability without any appreciable photocurrent loss after 0.5 hour of operation. The findings of this study constitute a relevant step towards the feasibility of hydrogen generation with wide bandgap semiconductors/quantum dots based heterostructures.     

Dynamic Modeling and Experiment of a Fish Robot with a Flexible Tail Fin

This paper presents the dynamic modeling of a flexible tail for a robotic fish. For this purpose firstly, the flexible tail was simplified as a slewing beam actuated by a driving moment. The governing equation of the flexible tail was derived by using the Euler-Bernoulli theory. In this equation, the resistive forces were estimated as a term analogous to viscous damping. Then, the modal analysis method was applied in order to derive an analytical solution of the governing equation, by which the relationship between the driving moment and the lateral movement of the flexible tail was described. Finally, simulations and experiments were carried out and the results were compared to verify the accuracy of the dynamic model. It was proved that the dynamic model of a fish robot with a flexible tail fin well explains the real behavior of robotic fish in underwater environment.     

Quality Control and Assurance: crucial for the sustainability of the applied phycology industry

The chemical and nutritional properties of microalgae are well known, which has led to an ever expanding industry for foods and dietary supplements both in terms of quantity and products. Little has been done to regulate or control quality and assurance in the applied phycology industry and it is known that it varies considerably. Nutritional aspects of produced biomass and consumption as dietary supplements have become issues of concern, especially since the industry is lucrative and fast growing. Various claims are made regarding dietary and food supplements that include health, nutrition, structure and functioning, many often unsubstantiated. Although quality is a subjective term many organisations are involved in testing, controlling and determining criteria. Today quality is more than just standards where it is an "integrated quality management approach" involving amongst others "hazard analyses and critical control points" (HACCP) practices. Microalgae are not recognised as a food or food supplement and they are also not categorised under herbals or botanicals, but as "other supplements". Produced microalgal biomass is subject to contamination from the entire range of contaminants and pathogens. Contamination of products by algal toxins in mixed culture populations also occurs. The industry has largely regulated itself, but there is considerable scope for improvement. There is a need for support and dissemination of information in the industry.     

The Influence of Nanocrystal Aggregates on Photovoltaic Performance in Nanocrystal–Polymer Bulk Heterojunction Solar Cells

CdSe nanocrystals (NCs) can be used as an electron acceptor in solar cells, employing organic ligands to passivate their surface and make them processable from solution. The nature and abundance of impurities present after NC ligand exchange from oleic acid to n‐butylamine are identified. A further purification step using hexane as a selective solvent is described, which excludes NC aggregates from solution. The influence of NC aggregates on photovoltaic device performance is studied in a CdSe:poly[2‐methoxy‐5‐(3′,7′‐dimethyloctyloxy)‐1,4‐phenylene vinylene] (MDMO‐PPV) bulk heterojunction solar cell. The exclusion of NC aggregates leads to a four‐fold increase in device power conversion efficiency (PCE) in optimized devices. A superior blend morphology leading to improved charge generation and a better NC percolation network is identified as the main causes of this increased solar cell performance.     

糖芯片制备技术研究进展

糖芯片是一种分析糖-蛋白质相互作用最直接有效的方法.对目前糖芯片的各种制备方法进行了综述,并分析了影响糖芯片质量的一些关键因素及其对底片材料和固定方法的整体要求,进而对该领域发展方向和广阔的应用前景进行了展望.     

Thin Film Co3O4/TiO2 Heterojunction Solar Cells

Co₃O₄ is investigated as a light absorber for all‐oxide thin‐film photovoltaic cells because of its nearly ideal optical bandgap of around 1.5 eV. Thin film TiO₂/Co₃O₄ heterojunctions are produced by spray pyrolysis of TiO₂ as a window layer, followed by pulsed laser deposition of Co₃O₄ as a light absorbing layer. The photovoltaic performance is investigated as a function of the Co₃O₄ deposition temperature and a direct correlation is found. The deposition temperature seems to affect both the crystallinity and the morphology of the absorber, which affects device performance. A maximum power of 22.7 μW cm^?2 is obtained at the highest deposition temperature (600 °C) with an open circuit photovoltage of 430 mV and a short circuit photocurrent density of 0.2 mA cm^?2. Performing deposition at 600 °C instead of room temperature improves power by an order of magnitude and reduces the tail states (Urbach edge energy). These phenomena can be explained by larger grains that grows at high temperature, as opposed to many nucleation events that occur at lower temperature.     

Synthesis of Partially Graphitic Ordered Mesoporous Carbons with High Surface Areas

Graphitic carbons with ordered mesostructure and high surface areas (of great interest in applications such as energy storage) have been synthesized by a direct triblock‐copolymer‐templating method. Pluronic F127 is used as a structure‐directing agent, with a low‐molecular‐weight phenolic resol as a carbon source, ferric oxide as a catalyst, and silica as an additive. Inorganic oxides can be completely eliminated from the carbon. Small‐angle XRD and N₂ sorption analysis show that the resultant carbon materials possess an ordered 2D hexagonal mesostructure, uniform bimodal mesopores (about 1.5 and 6 nm), high surface area (～1300 m²/g), and large pore volumes (～1.50 cm³/g) after low‐temperature pyrolysis (900 °C). All surface areas come from mesopores. Wide‐angle XRD patterns demonstrate that the presence of the ferric oxide catalyst and the silica additive lead to a marked enhancement of graphitic ordering in the framework. Raman spectra provide evidence of the increased content of graphitic sp² carbon structures. Transmission electron microscopy images confirm that numerous domains in the ordered mesostructures are composed of characteristic graphitic carbon nanostructures. The evolution of the graphitic structure is dependent on the temperature and the concentrations of the silica additive, and ferric oxide catalyst. Electrochemical measurements performed on this graphitic mesoporous carbon when used as an electrode material for an electrochemical double layer capacitor shows rectangular‐shaped cyclic voltammetry curves over a wide range of scan rates, even up to 200 mV/s, with a large capacitance of 155 F/g in KOH electrolyte. This method can be widely applied to the synthesis of graphitized carbon nanostructures.     

固定化微生物在生物膜式生化需氧量传感器中的应用现状

生化需氧量(Biochemical oxygen demand,BOD)微生物传感器是一种快速检测水样中有机污染物含量的设备,固定化微生物是其核心部件之一,对其稳定性、响应时间、使用寿命及实际应用范围等性能有着重要影响。生物膜式BOD传感器较其他类型的BOD微生物传感器具有结构简单、灵敏度高、响应时间短等优点,受到广泛的研究和应用。本文主要针对固定化微生物在生物膜式BOD传感器中的应用情况,概述较典型的微生物固定化方式的原理、特点及应用;总结几类应用较多或具有较好前景的载体材料,并讨论载体特性与传感器性能之间的关系;综述微生物在该领域的应用现状;简要介绍生物膜式BOD传感器的实际应用及商业化现状,比较其与另外几种BOD微生物传感器的优缺点;分析生物膜式BOD传感器中固定化微生物现存的一些问题及其发展趋势。