Effects of surface topography and chemistry of Rumex obtusifolius leaves on the attachment of the beetle Gastrophysa viridula

Broad-leaved dock, Rumex obtusifolius L. (Polygonaceae), is the main host plant of the green dock beetle, Gastrophysa viridula Degeer (Coleoptera: Chrysomelidae). Adult beetles are able to attach and walk on leaves of this plant. Leaf surface is rather uneven, because of irregularly shaped prominent epidermal cells with a maximum height of about 9 µm. The surface is covered with a smooth epicuticular wax layer having relatively low free surface energy (FSE). The aim of this study was to measure beetle attachment force applying a 'centrifugal technique' on adult insects on the leaf surface and other substrates, in order to understand the effect of surface architecture and its physicochemical properties on insect attachment. We compared forces on an adaxial leaf surface with forces on a smooth silanized glass plate having low FSE, and on a polishing paper having slightly lower FSE and similar surface roughness (asperities' size = 9 µm). Smooth plate made of normal untreated clean glass with high FSE was used as a reference substrate. On the leaf surface and the polishing paper, attachment forces were lower compared to both glass samples. There was no significant difference between force values on leaves and the polishing paper, but on both glass surfaces they were significantly higher than on the other substrates. Hydrophobicity alone explains a decrease in attachment force of the beetle, but when combined with roughness the decrease in force is four times greater.     

Quantifying the cleanliness of glass capillaries

I used capillary rise methods to investigate the lumenal surface properties of quartz (fused silica, Amersil T-08), borosilicate (Corning 7800), and high-lead glass (Corning 0010) capillaries commonly used to make patch pipets. I calculated the capillary rise and contact angle for water and methanol from weight measurements. The capillary rise was compared with the theoretical maximum value calculated by assuming each fluid perfectly wetted the lumenal surface of the glass (i.e., zero contact angle, which reflects the absence of surface contamination). For borosilicate, high-lead, and quartz capillaries, the rise for water was substantially less than the theoretical maximum rise. Exposure of the borosilicate, lead, and quartz capillaries to several cleaning methods resulted in substantially better—but not perfect—agreement between the theoretical maximum rise and calculated capillary rise. By contrast, the capillary rise for methanol was almost identical in untreated and cleaned capillaries, but less than its theoretical maximum rise. The residual discrepancy between the observed and theoretical rise for water could not be improved on by trying a variety of cleaning procedures, but some cleaning methods were superior to others. The water solubility of the surface contaminants, deduced from the effectiveness of repeated rinsing, was different for each of the three types of capillaries examined: Corning 7800>quartz>Corning 0010. A surface film was also detected in quartz tubing with an internal filament. I conclude that these borosilicate, quartz, and high-lead glass capillaries have a film on the lumenal surface, which can be removed using appropriate cleaning methods. The surface contaminants may be unique to each type of capillary and may also be hydrophobic. Two simple methods are presented to quantitate the cleanliness of glass capillary tubing commonly used to make pipets for studies of biological membranes. It is not known if the surface film is of importance in electrophysiological studies of biological membranes.     

Covalent attachment of synthetic DNA to self-assembled monolayer films.

The covalent attachment of thiol-modified DNA oligomers; to self-assembled monolayer silane films on fused silica and oxidized silicon substrates is described. A heterobifunctional crosslinking molecule bearing both thiol- and amino-reactive moieties was used to tether a DNA oligomer (modified at its terminus with a thiol group) to an aminosilane film formed on silica surfaces. A variety of aminosilanes, crosslinkers and treatment conditions have been tested to identify optimal conditions for DNA immobilization using this approach. The DNA films which result have been characterized using UV spectroscopy, water contact angle measurement, radiolabeling and hybridization methods.     

Nonlinear variation in clinging performance with surface roughness in geckos

Understanding the challenges faced by organisms moving within their environment is essential to comprehending the evolution of locomotor morphology and habitat use. Geckos have developed adhesive toe pads that enable exploitation of a wide range of microhabitats. These toe pads, and their adhesive mechanisms, have typically been studied using a range of artificial substrates, usually significantly smoother than those available in nature. Although these studies have been fundamental in understanding the mechanisms of attachment in geckos, it is unclear whether gecko attachment simply gradually declines with increased roughness as some researchers have suggested, or whether the interaction between the gekkotan adhesive system and surface roughness produces nonlinear relationships. To understand ecological challenges faced in their natural habitats, it is essential to use test surfaces that are more like surfaces used by geckos in nature. We tested gecko shear force (i.e., frictional force) generation as a measure of clinging performance on three artificial substrates. We selected substrates that exhibit microtopographies with peak‐to‐valley heights similar to those of substrates used in nature, to investigate performance on a range of smooth surfaces (glass), and fine‐grained (fine sandpaper) to rough (coarse sandpaper). We found that shear force did not decline monotonically with roughness, but varied nonlinearly among substrates. Clinging performance was greater on glass and coarse sandpaper than on fine sandpaper, and clinging performance was not significantly different between glass and coarse sandpaper. Our results demonstrate that performance on different substrates varies, probably depending on the underlying mechanisms of the adhesive apparatus in geckos.     

Novel Covellite CuS Single-Crystal Thin Films for Optoelectronic Applications

Copper sulfide (CuS) thin films have been used in many applications such as solar cells, photo-thermal, electro-conductive, and microwave shielding. In this work, copper sulfide thin films were deposited on glass and silicon substrates by thermal evaporation of in situ synthesized CuS powder. XRD analysis of these films revealed a single-crystal structure, AFM measurements indicated the films have a surface roughness (14.1 nm) and agglomerates of multiple monocrystalline particles with average size (66 nm), and the optical properties were investigated by UV-Vis spectrophotometer showing the films have high transmission (>80%) in the visible region and low absorbance with wide energy gap (3.813 eV). This novel structure with outstanding optical properties makes it very promising optical materials in optoelectronics.

     

Laboratory studies on adhesion of microalgae to hard substrates

Adhesion of Chlorella vulgaris(chlorophyceae), Nitzschia amphibia(bacillariophceae) and Chroococcus minutus(cyanobacteria) to hydrophobic (perspex, titanium and stainless steel 316-L), hydrophilic (glass) and toxic (copper, aluminium brass and admiralty brass) substrata were studied in the laboratory. The influence of surface wettability, surface roughness, pH of the medium, culture age, culture density, cell viability and presence of organic and bacterial films on the adhesion of Nitzschia amphibia was also studied using titanium, stainless steel and glass surfaces. All three organisms attached more on titanium and stainless steel and less on copper and its alloys. The attachment varied significantly with respect to exposure time and different materials. The attachment was higher on rough surfaces when compared to smooth surfaces. Attachment was higher on pH 7 and above. The presence of organic film increased the attachment significantly when compared to control. The number of attached cells was found to be directly proportional to the culture density. Attachment by log phase cells was significantly higher when compared to stationary phase cells. Live cells attached more when compared to heat killed and formalin killed cells. Bacterial films of Pseudomonas putida increased the algal attachment significantly. %     

Immobilisation of oligo-peptidic probes for microarray implementation: characterisation by FTIR, atomic force microscopy and 2D fluorescence

Proteomic microarrays show a wide range of applications for the investigation of DNA-protein, enzyme-substrate as well as protein-protein interactions. Among many challenges to build a viable "protein microarray", the surface chemistry that will allow to immobilised various proteins to retain their biological activity is of paramount importance. Here we report a chemical functionalisation method allowing immobilisation of oligo-peptides onto silica surface (porous silica, glass, thermal silicon dioxide). Substrates were first derivatised with a monofunctional silane allowing the elaboration of dense and uniform monolayers in highly reproducible way. Prior to the oligo-peptides grafting, this organic layer was functionalised with an amino-polyethyleneglycol. The coupling step of oligo-peptides onto functionalised supports is achieved through activation of the C-terminal function of the oligo-peptides. Chemical surface modifications were followed by FTIR spectroscopy, AFM measurements and fluorescence scanning microscopy. A systematic study of the oligo-peptide grafting conditions (time, concentration, solvent) was carried out to optimise this step. The oligo-peptides grafting strategy implemented in this work ensure a covalent and oriented grafting of the oligo-peptides. This orientation is ensured through the use of fully protected peptide except the terminal primary amine. The immobilized peptides will be then deprotected before biological recognition. This strategy is crucial to retain the biological activity of thousands of oligo-probes assessed on a microarray.     

Understanding enzyme action on immobilised substrates

With increasing interest in automated synthesis and screening protocols, solid supported chemistry and biochemistry are attractive technologies. Studies with surface-immobilised substrates have been carried out to analyse enzyme accessibility, kinetics and thermodynamics. Several interesting new methods have been developed to monitor enzyme action on substrates attached to a solid phase such as polymer beads glass or gold surfaces. These include fluorescence measurements, MALDI-TOF mass spectrometry, and the use of quartz crystal microbalances to measure weight changes of immobilised molecules directly on the surface. Approaches that allow spatial resolution in single beads have also been reported. The ability of enzymes to reach the inside of beads is becoming better characterised and new supports have been developed that allow improved accessibility. The equilibrium position of reactions on the solid surface can be substantially shifted compared with reactions in solution, and this can be usefully exploited using hydrolases in reverse. Research is also starting to tackle the way in which kinetics are modified when the substrates are surface immobilised.     

Effects of adsorbed organic and primary fouling films on bryozoan settlement

Marine primary fouling films, which consist of molecular organic and microbial components, have been reported to facilitate colonization of immersed surfaces by marine fouling organisms. Larvae of the cosmopolitan fouling bryozoan Bugula neritina (Linnaeus) were offered various substrata for attachment and metamorphosis. The materials were offered (a) after detergent washing, (b) after sorption of dissolved organic molecular films, and (c) after formation of primary films consisting of both microbial and adsorbed organic material. Wettability of the substrata by sea water was determined by contact angle measurements for each substratum. On washed substrata, attachment was favored with contact angles greater than ≈45° (cos contact angle <0.7). Adsorbed surface films had no effect on the low settlement of larvae on glass and high settlement on plastics. Microbial primary films, however, made glass attractive and plastics unattractive. These settlement preference changes did not correlate with the changes in wettability observed on these substrata. Dispersion of larvae over the settlement surface was random except on wettable surfaces coated with bacterial films, where settlement was strongly clustered (contagious).     

Impact of nano-topography on bacterial attachment

The adhesion of bacteria to surfaces is an important biological process, but one that has resisted simple categorization due to the number and complexity of parameters involved. The roughness of the substrate is known to play a significant role in the attachment process, particularly when the surface irregularities are comparable to the size of the bacteria and can provide shelter from unfavorable environmental factors. According to this scenario, roughness on a scale much smaller than the bacteria would not be expected to influence the initial attachment. To test this hypothesis, the impact of nanometer-scale roughness on bacterial attachment has been investigated using as-received and chemically etched glass surfaces. The surface modification by etching resulted in a 70% reduction in the nanoscale roughness of the glass surface with no significant alteration of its chemical composition or charge. Nevertheless, the number of bacteria adhering to the etched surface was observed to increase by a factor of three. The increase in attachment was also associated with an alteration in cellular metabolic activity as demonstrated by changes in characteristic cell morphologies and increased production of extracellular polymeric substances. The results indicate that bacteria may be more sensitive to nanoscale surface roughness than was previously believed.     

Efficiency Enhancement of Organic Solar Cells Using Hydrophobic Antireflective Inverted Moth‐Eye Nanopatterned PDMS Films

Poly‐dimethylsiloxane (PDMS) films with 2D periodic inverted moth‐eye nanopatterns on one surface are implemented as antireflection (AR) layers on a glass substrate for efficient light capture in encapsulated organic solar cells (OSCs). The inverted moth‐eye nanopatterned PDMS (IMN PDMS) films are fabricated by a soft imprint lithographic method using conical subwavelength grating patterns formed by laser interference lithography/dry etching. Their optical characteristics, together with theoretical analysis using rigorous coupled‐wave analysis simulation, and wetting behaviors are investigated. For a period of 380 nm, IMN PDMS films laminated on glass substrates exhibit a hydrophobic surface with a water contact angle (θ_CA) of ≈120° and solar weighted transmittance (SWT) of ≈94.2%, both significantly higher than those (θ_CA≈ 36° and SWT ≈ 90.3%) of bare glass substrates. By employing IMN PDMS films with a period of 380 nm on glass substrates for OSCs, an enhanced power conversion efficiency (PCE) of 6.19% is obtained mainly due to the increased short‐circuit current density (J_sc) of 19.74 mA cm^‐2 compared to the OSCs with the bare glass substrates (PCE = 5.16% and J_sc = 17.25 mA cm^‐2). For the OSCs, the device stability is also studied.     

Enhanced sensitivity detection of protein immobilization by fluorescent interference on oxidized silicon

We present a silicon chip-based approach for the enhanced sensitivity detection of surface-immobilized fluorescent molecules. Green fluorescent protein (GFP) is bound to the silicon substrate by a disuccinimidyl terephtalate-aminosilane immobilization procedure. The immobilized organic layers are characterized by surface analysis techniques, like ellipsometry, atomic force microscopy (AFM) and X-ray induced photoelectron spectroscopy. We obtain a 20-fold enhancement of the fluorescent signal, using constructive interference effects in a fused silica dielectric layer, deposited before immobilization onto the silicon. Our method opens perspectives to increase by an order of magnitude the fluorescent response of surface immobilized DNA- or protein-based layers for a variety of biosensor applications.     

Effect of substrate on the responsive behaviour of functionalised surfaces: insights from molecular simulation

Abstract

Responsive surfaces have been suggested to enhance longevity and antifouling performance of materials in many applications from industrial coatings to tissue engineering and drug delivery. We present a molecular dynamics study investigating de-swelling and swelling of some of the most commonly used responsive materials – PEG-functionalised silica and polymer surfaces – as a function of hydration and temperature. We show that PEG chains grafted onto the hard silica substrates exhibit a dehydration-induced collapse that is far more pronounced compared to chains grafted onto the soft polyester surface. The difference between the hard and soft substrates is particularly notable at low coverage densities where the chains are sufficiently separated from one another. We also show that inter-molecular hydrogen bonding responsible for the conformational state of the tethered chains in water can be temperature controlled. It can be suggested that the hard substrates with the intermediate-to-high coverage densities of low molecular weight hydrophilic grafts may be more appropriate for anti-fouling applications due to their ability to trap greater amount of water molecules. Soft substrates may be detrimental for the efficient response of the functionalised surfaces to changes in hydration and enhancement of the surface hardness must be considered when designing responsive surfaces for solution-based applications, such as antimicrobial coatings for industry and biomedicine.     

Genetic diversity of gamma-hexachlorocyclohexane-degrading sphingomonads isolated from a single experimental field

Aim:  To determine the effect of the surface roughness of denture acrylic on the attachment of Streptococcus oralis .
Methods and Results:  Roughened denture acrylic samples were assessed for bacterial attachment, over time, using microscopy. The area of the image covered by bacteria was calculated and converted into a percentage of the total area sampled. The results showed an increasing bacterial coverage with time of incubation and increasing roughness. Differences were seen between heat cured acrylic and cold cured acrylic.
Conclusion:  This study successfully demonstrated a system for the assessment of the amount of attached bacteria on denture acrylic varying roughness. The system was able to discern the difference in surface area coverage by attached bacteria over a roughness range relevant to brushing dentures with dentifrices.
Significance and Impact of Study:  This study provides strong support for the scratches caused by brushing dentures with dentifrice encouraging bacterial attachment. This is likely to have a significant effect on efficacy of denture cleaning, general hygiene and biofilm re-formation between cleaning regimens and may indicate that alternative low abrasive cleaners, such as antimicrobial denture-cleaning tablets, offer a more appropriate regimen.     

Properties of free and immobilised lipase from Burkholderia cepacia in organic media

The purified lipase from Burkholderia cepacia was immobilised on a porous polypropylene support and its biocatalytic properties were compared with those of the free enzyme in organic media. For both lipase preparations, the rate of p-nitrophenyl ester hydrolysis in n-heptane was not restricted by mass transfer limitations. The immobilisation changed neither the temperature at which the reaction rate was maximal, nor the activation energy of the reaction. The enzyme stability was slightly decreased (1.3-fold) upon immobilisation. Moreover, the immobilised enzyme displayed fewer variations of activity with fatty acid chain length. Interestingly, for all the different p-nitrophenyl esters used, the immobilised enzyme was more active (from 5.8- to 18.9-fold) than the free enzyme. Therefore, it would be very useful to use B. cepacia lipase immobilised onto porous polypropylene for applications in organic media, as it displayed high activities on a larger range of substrates. Received: 8 February 1999 / Received revision: 19 March 1999 / Accepted: 20 March 1999     

Determination of the Optical Thickness of sub 10-nm Thin Metal Films by SPR Experiments

We discuss the experimental data of surface plasmon resonance (SPR) occurring at the interface between air and single and bimetallic thin layers of Au and Ag prepared on glass substrates. The bilayer configuration allowed for the measurements of the optical constants of metallic films that are ultra thin; e.g., below 10 nm of thickness since SPR modes on such thin films in a single-layer configuration are shallow. We also discuss the effect of film thickness on SPR coupling. Thickness and refractive index of the films were determined by matching experimental SPR curves to the theoretical ones. Thickness and roughness of the films were also measured by atomic force microscopy. The results obtained by experimental measurements are in good agreement with AFM analysis.     

High capacity substrates as a platform for a DNA probe array genotyping assay

Colloidal silica particles were deposited on a glass substrate to produce high-capacity porous supports for high-density DNA probe arrays. Porous surfaces were used to increase the addressable surface area and number of probes available for hybridization. Surfaces derived from 70-100 nm size particles deposited in films from 0.15 to 2 microns thick exhibited excellent performance in light-directed oligonucleotide synthesis. Evaluation of these substrates in a genotyping assay is reported.     

Enhanced cell attachment using a novel cell culture surface presenting functional domains from extracellular matrix proteins

Many factors contribute to the creation and maintenance of a realistic environment for cell growth in vitro, e.g. the consistency of the growth medium, the addition of supplements, and the surface on which the cells grow. The nature of the surface on which cells are cultured plays an important role in their ability to attach, proliferate, migrate and function. Components of the extracellular matrix (ECM) are often used to coat glass or plastic surfaces to enhance cell attachment in vitro. Fragments of ECM molecules can be immobilised on surfaces in order to mimic the effects seen by whole molecules. In this study we evaluate the application of a novel technology for the immobilisation of functional domains of known ECM proteins in a controlled manner on a surface. By examining the adherence of cultured PC12 cells to alternative growth surfaces, we show that surfaces coated with motifs from collagen I, collagen IV, fibronectin and laminin can mimic surfaces coated with the corresponding whole molecules. Furthermore, we show that the adherence of cells can be controlled by modifying the hydropathic properties of the surface to either enhance or inhibit cell attachment. Collectively, these data demonstrate the application of a new technology to enable optimisation of cell growth in the tissue culture laboratory.     

Light-induced immobilisation of biomolecules as an attractive alternative to microdroplet dispensing-based arraying technologies

The present work shows how UV 'light-induced molecular immobilisation' (LIMI) of biomolecules onto thiol reactive surfaces can be used to make biosensors, without the need for traditional microdispensing technologies. Using 'LIMI,' arrays of biomolecules can be created with a high degree of reproducibility. This technology can be used to circumvent the need for often expensive nano/microdispensing technologies. The ultimate size of the immobilised spots is defined by the focal area of the UV beam, which for a diffraction-limited beam can be less than 1 microm in diameter. LIMI has the added benefit that the immobilised molecules will be spatially oriented and covalently bound to the surface. The activity of the sensor molecules is retained. Antibody sensor arrays made using LIMI demonstrated successful antigen binding. In addition, the pattern of immobilised molecules on the surface is not restricted to conventional array formats. The ultimate consequence of the LIMI is that it is possible to write complex protein patterns using bitmaps at high resolution onto substrates. Thus, LIMI of biomolecules provides a new technological platform for biomolecular immobilisation and the potential for replacing present microdispensing arraying technologies.     

Differences in colonisation of five marine bacteria on two types of glass surfaces

The retention patterns of five taxonomically different marine bacteria after attachment on two types of glass surfaces, as-received and chemically etched, have been investigated. Contact angle measurements, atomic force microscopy (AFM), scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), X-ray fluorescence spectroscopy (XRF) and X-ray photoelectron spectrometry (XPS) were employed to investigate the impact of nanometer scale surface roughness on bacterial attachment. Chemical modification of glass surfaces resulted in a ～1 nm decrease in the average surface roughness (R _a) and the root-mean-squared roughness (R_q ) and in a ～8 nm decrease in the surface height and the peak-to-peak (R _max) and the 10-point average roughness (R_z ). The study revealed amplified bacterial attachment on the chemically etched, nano-smoother glass surfaces. This was a consistent response, notwithstanding the taxonomic affiliation of the selected bacteria. Enhanced bacterial attachment was accompanied by elevated levels of secreted extracellular polymeric substances (EPS). An expected correlation between cell surface wettability and the density of the bacterial attachment on both types of glass surfaces was also reported, while no correlation could be established between cell surface charge and the bacterial retention pattern.