David E. Mainwaring

Bactericidal activity of black silicon

Black silicon is a synthetic nanomaterial that contains high aspect ratio nanoprotrusions on its surface, produced through a simple reactive-ion etching technique for use in photovoltaic applications. Surfaces with high aspect-ratio nanofeatures are also common in the natural world, for example, the wings of the dragonfly Diplacodes bipunctata. Here we show that the nanoprotrusions on the surfaces of both black silicon and D. bipunctata wings form hierarchical structures through the formation of clusters of adjacent nanoprotrusions. These structures generate a mechanical bactericidal effect, independent of chemical composition. Both surfaces are highly bactericidal against all tested Gram-negative and Gram-positive bacteria, and endospores, and exhibit estimated average killing rates of up to ~450,000 cells min−1 cm−2. This represents the first reported physical bactericidal activity of black silicon or indeed for any hydrophilic surface. This biomimetic analogue represents an excellent prospect for the development of a new generation of mechano-responsive, antibacterial nanomaterials.

Transformation and degradation of the disazo dye Chicago Sky Blue by a purified laccase from Pycnoporus cinnabarinus

The degradation of the disazo dye Chicago Sky Blue 6B by a purified laccase from Pycnoporus cinnabarinus was investigated. Laccase was purified to homogeneity and characterized. The enzyme had a molecular size of 63 kDa as determined by SDS-PAGE and an isoelectric point at pH 3. Amino acid composition and N-terminal amino acid sequence was shown to be similar to other fungal laccases. The purified laccase was stable for 1 h at 60 degrees C and was irreversibly inactivated by sodium azide at 0.1 mM. Laccase was shown to initiate destruction of the chromophore of the disazo dye Chicago Sky Blue, resulting in the formation of two intermediate products with absorption intensities about one order of magnitude lower than the parent molecule. The rate at which the dye was transformed by purified laccase was shown to increase with increasing concentrations of the enzyme.

Dielectric enhancement in polymer-nanoparticle composites through interphase polarizability

Dielectric measurements on polyimide-oxide nanoparticle composite thin films show a composite dielectric constant (ecomposite) that increased monotonically with increasing oxide content well above the value predicted by Maxwell’s rule for dielectric mixtures below the percolation threshold. Above certain volume fractions, the measured ecomposite values were found to exceed the corresponding nanoparticle e such that epolymer<eparticle<ecomposite contrasted to conventional composites where epolymer<ecomposite<eparticle. The ecomposite was independent of frequency to 10MHz with dielectric loss of <0.005 throughout this range, indicating that the observed enhancement in e does not originate from space-charge related contributions and hence should be due to dipolar contributions. The observed e enhancement (ecomposite−eMaxwell) showed a correlation with the total surface area of the nanoparticles. The dielectric model of Vo and Shi [Microelectron. J. 33, 409 (2002), and references therein] showed that the enha...

The influence of surfactant adsorption on the surface characterisation of Australian coals

The surfaces of three Australian coals varying widely in coal type (Collie, Wongawilli and Norwich Park) have been modified by adsorption of three surfactants (sodium dodecyl sulphate, cetyl trimethylammonium bromide and Teric G12A8). The mechanism and impact of the surfactant adsorption has been explored by correlating three chemical characterisation techniques. Changes in coal surface hydrophobicity were assessed using contact angle measurements at the coal/water interface. Adsorption of surfactants did not increase the surface hydrophobicity for the lowest rank coal, however appreciable changes in contact angle were measured as the rank of the coal increased. As the coal rank decreased, the surfactant adsorption densities increased for all three surfactants under investigation. The largest variation in zeta potential resulting from addition of surfactants was seen for the higher rank coals. The results from this study have allowed a possible surfactant adsorption model to be postulated.

Practical precooling: Effect on cycling time trial performance in warm conditions

Abstract The purpose of this study was to compare the effects of two practical precooling techniques (skin cooling vs. skin + core cooling) on cycling time trial performance in warm conditions. Six trained cyclists completed one maximal graded exercise test ([Vdot]O2peak 71.4 ± 3.2 ml · kg−1 · min−1) and four ∼40 min laboratory cycling time trials in a heat chamber (34.3°C ± 1.1°C; 41.2% ± 3.0% rh) using a fixed-power/variable-power format. Cyclists prepared for the time trial using three techniques administered in a randomised order prior to the warm-up: (1) no cooling (control), (2) cooling jacket for 40 min (jacket) or (3) 30-min water immersion followed by a cooling jacket application for 40 min (combined). Rectal temperature prior to the time trial was 37.8°C ± 0.1°C in control, similar in jacket (37.8°C ± 0.3°C) and lower in combined (37.1°C ± 0.2°C, P < 0.01). Compared with the control trial, time trial performance was not different for jacket precooling (−16 ± 36 s, −0.7%; P = 0.35) but was faster for combined precooling (−42 ± 25 s, −1.8%; P = 0.009). In conclusion, a practical combined precooling strategy that involves immersion in cool water followed by the use of a cooling jacket can produce decrease in rectal temperature that persist throughout a warm-up and improve laboratory cycling time trial performance in warm conditions.

Chitosan Microparticles and Nanoparticles as Biocompatible Delivery Vehicles for Peptide and Protein-Based Immunocontraceptive Vaccines

It has become increasingly recognized that polymer particle size can have a profound effect on the interactions of particle-based vaccines with antigen presenting cells (APCs) thereby influencing and modulating ensuing immune responses. With the aim of developing chitosan particle-based immunocontraceptive vaccines, we have compared the use of chitosan-based nanoparticles and chitosan-based microparticles as vaccine delivery vehicles for vaccine candidates based on luteinizing hormone-releasing hormone (LHRH). Particles, functionalized with chloroacetyl groups, which allows the covalent attachment of thiol-containing antigens, were able to adsorb ~60-70% of their weight of peptide-based antigen and 10-20% of their weight of protein-based antigen. Quantitation by amino acid analysis of antigen associated with particles demonstrated a correlation between associated antigen and the degree of chloracetylation of particles. Visualization of fluorescently labeled antigen-loaded particles by confocal microscopy indicated that the majority of antigen was localized at the particle surface with a smaller amount located in the interior. We also found that uptake of both fluoresceinated nanoparticles and microparticles by dendritic cells occurred in a manner dependent on particle concentration. Nanoparticles trafficked from the injection site to draining lymph nodes faster than microparticles; high numbers of nanoparticle-bearing cells appeared in draining lymph nodes on day 3 and microparticles on day 4. This difference in trafficking rate did not, however, appear to have any significant impact on the ensuing immune response because inoculation with both peptide-conjugated and protein-conjugated particles induced high levels of LHRH-specific antibodies. In the case of protein-conjugated particles, the levels of antibodies elicited were similar to those elicited following inoculation with antigen emulsified with complete Freunds adjuvant. The approach to vaccine design that we have described here could represent another useful method for inducing immune responses against microbial, viral and tumorigenic protein antigens.

Micropore size distributions and specific interactions in coals

Abstract Micropore surface areas, pore size distributions and pore volumes were determined for four brown coals, one medium-volatile subbituminous coal, one high-volatile subbituminous coal, and one low-volatile bituminous coal by carbon dioxide adsorption at 273 K. For comparison, BET surface areas were determined for two of the brown coals by nitrogen adsorption at 77 K. Surface areas were consistent with published values. The micropore size distributions obtained using the Dubinin-Medek approach were found to be independent of coal rank and functional groups.

The detection of influenza A and B viruses in clinical specimens using a quartz crystal microbalance.

Abstract Current methods for the accurate diagnosis of influenza based on culture of the virus or PCR are highly sensitive and specific but require specialised laboratory facilities and highly trained personnel and, in the case of viral culture, can take up to 14 days to obtain a definitive result. In this study, a quartz crystal microbalance-based immunosensor (QCM) has been developed and its potential evaluated for the rapid and sensitive detection of both influenza A and B viruses in laboratory-cultured preparations and clinical samples. The effective limit for detection by QCM for stock preparations of both A/PR/8/34 and B/Lee/40 viruses was 1×104 pfu/mL, associated with observed frequency shifts of 30 (±5) and 37 (±6.5)Hz, respectively. Conjugation of 13nm gold nanoparticles to the detecting antibody improved the mass sensitivity of the immunosensor, resulting in a 10-fold increase in sensitivity and a detection limit of 1×103 pfu/mL for both preparations, with resulting frequency shifts of 102 (±11) and 115 (±5)Hz, respectively. Detection of virus in nasal washes with this technique was achieved by overnight passage in MDCK cultures prior to analysis. A comparison of results obtained from 67 clinical samples using existing RT-PCR, shell vial, cell culture and ELISA methods showed that QCM techniques were comparable in sensitivity and specificity to cell culture methods.

Decolourisation of a pigment plant effluent by Pycnoporus cinnabarinus in a packed-bed bioreactor

SummaryThe decolourisation of wastewater from a pigment plant by the white-rot fungus Pycnoporus cinnabarinus was studied in a packed-bed bioreactor. Decolourisation was first observed 48 to 72 h after inoculation and was followed using UV/VIS spectrophotometry. An assessment of the inhibitory properties of the effluent on the growth of Pycnoporus cinnabarinus showed that this fungus can tolerate high levels of potentially toxic waste.

The wetting behaviour of several organic liquids in water on coal surfaces

Abstract Several organic liquids were used to probe the surface chemical characteristics of five coal types ranging in rank from brown to low-volatile bituminous in the presence of water. The liquids were hexane, cyclohexane, diiodomethane, toluene, o-xylene, chloroform, dichloromethane, oleic acid, chloroform and hexan-1-ol. The advancing and receding contact angles formed at the coal-water-liquid junction were measured and it was found that a critical interfacial tension existed, below which the organic liquid wetting properties were equivalent. Above the critical interfacial tension, the wettability of the coal by the organic liquid increased as the polarity of the liquid increased, giving a measure of the efficiency with which the water wetting film could be expelled from the coal surface. At a fixed interfacial tension, the advancing and receding contact angles decreased as the rank of the coal increased.