Biological water pollution, including organic pollutants and their possible transportation, via biofouling and ballast water, has the potential to cause severe economic and health impacts on society and environment. Current water pollution monitoring methods are limited by transportation of samples to the laboratory for analysis, which could take weeks. There is an urgent need for a water quality monitoring technique that generates real-time data. The study aims to assess the feasibility of three sensing techniques to detect and monitor the concentrations of the model species Tetraselmis suecica in real-time using eleven samples for each method. Results showed UV-Vis spectrophotometer detected increasing concentration of Tetraselmis suecica with R2 = 0.9627 and R2 = 0.9672, at 450 nm and 650 nm wavelengths, respectively. Secondly, low-frequency capacitance measurements showed a linear relationship with increasing concentration of Tetraselmis suecica at 150 Hz (R2 = 0.8463) and 180 Hz (R2 = 0.8391). Finally, a planar electromagnetic wave sensor measuring the reflected power S11 amplitude detected increasing cell density at 4 GHz (R2 = 0.8019).

A number of organisms is routinely used in laboratory assays (i) to enable the down-selection of coating libraries and (ii) to test hypotheses in relation to settlement/adhesion on model/practical surfaces. Settlement and fouling-release assays are described for bacteria, algae (Ulva sp. and diatoms) and barnacles.

Amphibalanus (=Balanus) amphitrite is a tropical/sub-tropical barnacle species which is naturally exposed to sea temperatures of 16-27 degrees C throughout its larval development. An established technique widely employed by investigators of A. amphitrite settlement involves the storage of cyprids at 4-6 degrees C prior to their use in bioassays. Our study focuses on the effects on ageing temperature on settlement and discrimination of A. amphitrite larvae. Using cyprids aged at 2 temperatures, 6 and 23 degrees C, we confirmed the general trend in the literature that young d0 cyprids of this species do not appear competent to settle. Performing cyprid settlement assays at 20, 25 or 28 degrees C, we observed that the proportion of settled cyprids when incubated at 28 degrees C was greater than that of cyprid incubated at 25 degrees C and 20 degrees C. Settlement rates of cyprids aged at 6 degrees C and 23 C increased relative to age from d1 to d10 irrespective of temperature. Cyprids lost the ability to undergo attachment and metamorphosis at d14 or d15 when aged at 6 degrees C or 23 degrees C respectively.In the choice assays executed in this study, cyprids generally chose to settle on adult extract-treated areas. But localised settlement on adult extract-treated areas decreased with time. Choice settlement assays at set age intervals during the cypris larval stage showed that cyprids were able to discriminate between con- and allospecific adult extracts. The duration and the temperature of cyprids storage influenced selectivity. (C) 2012 Elsevier Ltd. All rights reserved.

Amphiphilic copolymers containing different amounts of poly(ethylene glycol)-fluoroalkyl acrylate and polysiloxane methacrylate units were blended with a poly(dimethyl siloxane) (PDMS) matrix in different proportions to investigate the effect of both copolymer composition and loading on the biological performance of the coatings. Laboratory bioassays revealed optimal compositions for the release of sporelings of Ulva linza, and the settlement of cypris larvae of Balanus amphitrite. The best-performing coatings were subjected to field immersion tests. Experimental coatings containing copolymer showed significantly reduced levels of hard fouling compared to the control coatings (PDMS without copolymer), their performance being equivalent to a coating based on Intersleek 700™. XPS analysis showed that only small amounts of fluorine at the coating surface were sufficient for good antifouling/fouling-release properties. AFM analyses of coatings under immersion showed that the presence of a regular surface structure with nanosized domains correlated with biological performance.

Balanus amphitrite cyprids produce complex adhesive substances that enable their attachment to surfaces and impart a strong detachment resistance from most immersed substrata. The colonization of man-made structures by barnacle cyprids and other marine organisms is a troublesome and costly phenomenon, for which controlling strategies are actively sought. In this work, we expand previous investigations about the susceptibility of cyprid adhesives to unpurified proteases in solution by evaluating the interplay between these secreted biomolecules and a surface-confined purified protease. The strategy involved the covalent immobilization of the enzyme Subtilisin A to maleic anhydride copolymer thin films through the spontaneous reaction of anhydride moieties with lysine side chains. This enabled the production of bioactive layers of tunable enzyme surface concentration and activity, which were utilized to systematically evaluate the effect of the immobilized enzyme on cyprid settlement and exploratory behavior. Surfaces of increasing enzyme activity displayed a gradual decrease in cyprid settlement levels (approaching inhibition) as well as an increase in post-settlement adhesion failure (evidenced by significant numbers of detached metamorphosed individuals). High activities of the bound enzyme also affected pre-settlement behavior of cyprids, reducing the velocity and total distance moved while increasing the amount and speed of meander compared to the controls. The here-reported low enzyme surface concentrations found to be remarkably effective at reducing cyprid settlement hold promise for the use of immobilized enzymes in the control of marine biofouling.

We describe the synthesis of a series of mono-, di-, and trisaccharide-functionalized alkanethiols as well as the formation of fouling-resistant self-assembled monolayers (SAMs) from these. The SAMs were characterized using ellipsometry, wetting measurements, and infrared reflection-absorption spectroscopy (IRAS). We show that the structure of the carbohydrate moiety affects the packing density and that this also alters the alkane chain organization. Upon increasing the size of the sugar moieties (from mono- to di- and trisaccharides), the structural qualities of the monolayers deteriorated with increasing disorder, and for the trisaccharide, slow reorganization dynamics in response to changes in the environmental polarity were observed. The antifouling properties of these SAMs were investigated through protein adsorption experiments from buffer solutions as well as settlement (attachment) tests using two common marine fouling species, zoospores of the green macroalga Ulva linza and cypris larvae of the barnacle Balanus amphitrite. The SAMs showed overall good resistance to fouling by both the proteins and the tested marine organisms. To improve the packing density of the SAMs with bulky headgroups, we employed mixed SAMs where the saccharide-thiols are diluted with a filler molecule having a small 2-hydroxyethyl headgroup. This method also provides a means by which the steric availability of sugar moieties can be varied, which is of interest for specific interaction studies with surface-bound sugars. The results of the surface dilution study and the low nonspecific adsorption onto the SAMs both indicate the feasibility of this approach.

Self-assembled monolayers (SAMs) of galactoside-terminated alkanethiols have protein-resistance properties which can be tuned via the degree of methylation [Langmuir 2005, 21, 2971-2980]. Specifically, a partially methylated compound was more resistant to nonspecific protein adsorption than the hydroxylated or fully methylated counterparts. We investigate whether this also holds true for resistance to the attachment and adhesion of a range of marine species, in order to clarify to what extent resistance to protein adsorption correlates with the more complex adhesion of fouling organisms. The partially methylated galactoside-terminated SAM was further compared to a mixed monolayer of ω-substituted methyl- and hydroxyl-terminated alkanethiols with wetting properties and surface ratio of hydroxyl to methyl groups matching that of the galactoside. The settlement (initial attachment) and adhesion strength of four model marine fouling organisms were investigated, representing both micro- and macrofoulers; two bacteria (Cobetia marina and Marinobacter hydrocarbonoclasticus), barnacle cypris larvae (Balanus amphitrite), and algal zoospores (Ulva linza). The minimum in protein adsorption onto the partially methylated galactoside surface was partly reproduced in the marine fouling assays, providing some support for a relationship between protein resistance and adhesion of marine fouling organisms. The mixed alkanethiol SAM, which was matched in wettability to the partially methylated galactoside SAM, consistently showed higher settlement (initial attachment) of test organisms than the galactoside, implying that both wettability and surface chemistry are insufficient to explain differences in fouling resistance. We suggest that differences in the structure of interfacial water may explain the variation in adhesion to these SAMs.

The interaction of covalently coupled hyaluronic acid, alginic acid, and pectic acid with proteins, cells (hematopoietic KG1a and Jurkat cells), and marine organisms (algal zoospores and barnacle cypris larvae) is compared. In contrast to cells and proteins for which such polysaccharide coatings are known for their antiadhesive properties, marine algal spores and barnacle cyprids were able to colonize the surfaces. Of the three polysaccharides, hyaluronic acid showed the lowest settlement of both Ulva zoopores and barnacles. Photoelectron spectroscopy reveals that the polysaccharide coatings tend to bind bivalent ions, such as calcium, from salt water. Such pretreatment with a high salinity medium significantly changes the protein and hematopoietic cell resistance of the surfaces. Complexation of bivalent ions is therefore considered as one reason for the decreased resistance of polysaccharide coatings when applied in the marine environment.

Fouling-release coatings were prepared from blends of a fluorinated/siloxane copolymer with a poly(dimethyl siloxane) (PDMS) matrix in order to couple the low modulus character of PDMS with the low surface tension typical for fluorinated polymers. The content of the surface-active copolymer was varied in the blend over a broad range (0.15-10 wt % with respect to PDMS). X-ray photoelectron spectroscopy depth profiling analyses were performed on the coatings to establish the distribution of specific chemical constituents throughout the coatings, and proved enrichment in fluorine of the outermost layers of the coating surface. Addition of the fluorinated/siloxane copolymer to the PDMS matrix resulted in a concentration-dependent decrease in settlement of barnacle, Balanus amphitrite, cyprids. The release of young plants of Ulva, a soft fouling species, and young barnacles showed that adhesion strength on the fluorinated/siloxane copolymer was significantly lower than the siloxane control. However, differences in adhesion strength were not directly correlated with the concentration of copolymer in the blends.

Barnacles are a persistent fouling problem in the marine environment, although their effects (eg reduced fuel efficiency, increased corrosion) can be reduced through the application of antifouling or fouling-release coatings to marine structures. However, the developments of fouling-resistant coatings that are cost-effective and that are not deleterious to the marine environment are continually being sought. The incorporation of proteolytic enzymes into coatings has been suggested as one potential option. In this study, the efficacy of a commercially available serine endopeptidase, Alcalase® as an antifoulant is assessed and its mode of action on barnacle cypris larvae investigated. In situ atomic force microscopy (AFM) of barnacle cyprid adhesives during exposure to Alcalase supported the hypothesis that Alcalase reduces the effectiveness of the cyprid adhesives, rather than deterring the organisms from settling. Quantitative behavioural tracking of cyprids, using Ethovision™ 3.1, further supported this observation. Alcalase removed cyprid ‘footprint’ deposits from glass surfaces within 26 min, but cyprid permanent cement became resistant to attack by Alcalase within 15 h of expression, acquiring a crystalline appearance in its cured state. It is concluded that Alcalase has antifouling potential on the basis of its effects on cyprid footprints, un-cured permanent cement and its non-toxic mode of action, providing that it can be successfully incorporated into a coating.

With the recent ban an organotin-containing antifouling coatings by the International Maritime Organisation and doubts about paints containing copper, there is a pressing need for environmentally benign antifoulants. In the current study, we investigated the use of opoponax essential oil (scented myrrh Commiphora guidotti), its constituent terpenes/oids: ocimene, beta-bisabolene, alpha-bisabolol and farnesol, and sandalwood essential oil in this role. Assays using cypris larvae of the barnacle Balanus amphitrite revealed that coatings of the sesquiterpenoid alcohols (farnesol and alpha-bisabolol) and sandalwood essential oil (determined by a gas chromatograph-flame ionisation detector to consist of 78.1% santolol, another sesquiterpenoid alcohol) were the most larvicidal. The LC(50) values after 48 h were 18 (farnesol), 88 (alpha-bisabolol) and 1.65 mu g well(-1) (sandalwood essential oil). No anti-settlement was observed without accompanying larvicidal activity and no synergistic effects were seen when oils were used in combination. Farnesol and a-bisabolol exhibited very low leaching rates into assay water, suggesting that cyprid mortality may have resulted from direct contact with the coatings. Extending the duration of these assays from 48 to 120 h increased settlement in controls but did not reveal additional anti-settlement activity in the presence of oils. Inclusion of the settlement inducer, 3-isobutyl-1-methylxanthine (IBMX, 10(-5) M) increased settlement in controls and demonstrated anti-settlement activity in opoponax essential oil without any significant cyprid mortality. Field trials that incorporated opoponax essential oil or the terpenes/oids into marine paint either individually or in 1:1 mixtures did not show clear evidence of antifouling activity at the concentrations tested.

This work describes the fabrication, characterization, and biological evaluation of a thin protein-resistant poly(ethylene glycol) (PEG)-based hydrogel coating for antifouling applications. The coating was fabricated by free-radical polymerization on silanized glass and silicon and on polystyrene-covered silicon and gold. The physicochemical properties of the coating were characterized by infrared spectroscopy, ellipsometry, and contact angle measurements. In particular, the chemical stability of the coating in artificial seawater was evaluated over a six-month period. These measurements indicated that the degradation process was slow under the test conditions chosen, with the coating thickness and composition changing only marginally over the period. The settlement behavior of a broad and diverse group of marine and freshwater fouling organisms was evaluated. The tested organisms were barnacle larvae (Balanus amphitrite), algal zoospores (Ulva linza), diatoms (Navicula perminuta), and three bacteria species (Cobetia marina, Marinobacter hydrocarbonoclasticus, and Pseudomonas fluorescens). The biological results showed that the hydrogel coating exhibited excellent antifouling properties with respect to settlement and removal.

A computer-controlled force gauge designed to measure the adhesive strength of barnacles on test substrata is described. The instrument was evaluated with adult barnacles grown in situ on Silastic T2 (R)-coated microscope slides and epoxy replicas adhered to the same substratum with synthetic adhesive. The force per unit area required to detach the barnacles (critical removal stress) using the new automated system was comparable to that obtained with ASTM D5618 (1994) (0.19 and 0.28 MPa compared with 0.18 and 0.27 MPa for two batches of barnacles). The automated method showed a faster rate of force development compared with the manual spring force gauge used for ASTM D5618 (1994). The new instrument was as accurate and precise at determining surface area as manual delineation used with ASTM D5618 (1994). The method provided significant advantages such as higher throughput speed, the ability to test smaller barnacles (which took less time to grow) and to control the force application angle and speed. The variability in measurements was lower than previously reported, suggesting an improved ability to compare the results obtained by different researchers.

This article reports on the preparation and partial characterisation of silicone-based coatings filled with low levels of either synthetic multiwall carbon nanotubes (MWCNTs) or natural sepiolite (NS). The antifouling and fouling-release properties of these coatings were explored through laboratory assays involving representative soft-fouling (Ulva) and hard-fouling (Balanus) organisms. The bulk mechanical properties of the coatings appeared unchanged by the addition of low amounts of filler, in contrast to the surface properties, which were modified on exposure to water. The release of Ulva sporelings (young plants) was improved by the addition of low amounts of both NS and MWCNTs. The most profound effect recorded was the significant reduction of adhesion strength of adult barnacles growing on a silicone elastomer containing a small amount (0.05%) of MWCNTs. All the data indicate that independent of the bulk properties, the surface properties affect settlement, and more particularly, the fouling-release behaviour, of the filled materials.