Formation of underbrushes on thiolated poly(ethylene glycol) PEG monolayers by oligoethylene glycol (OEG) terminated alkane thiols on gold

Adding underbrushes of oligoethylene glycol (OEG) to monolayers of long chain PEG molecules on a surface is one of the strategies in designing a suitable platform for antifouling purpose, where it is possible to have high graft density and molecular conformational freedom simultaneously, there by maximal retention of activity of covalently immobilised antifouling enzyme on PEG surfaces along with resistance to protein adsorption. Here we present some our studies on the addition of OEG thiol molecules over a self assembled monolayer of PEG thiol on gold. The kinetics of addition of OEG thiol to monolayers of PEG thiol was followed using X- ray photoelectron spectroscopy (XPS), which indicated the time point of maximum graft density and beyond this time point there was predominant desorption of OEG thiol as indicated by the C/O ratio. The initial increase in graft density was reflected in the superior resistance towards non specific adsorption of proteins as shown by N 1s signal. We also performed protein adsorption studies using quartz crystal microbalance (QCM-D). Studies involving addition of alkane thiol instead of OEG terminating alkane thiol showed the importance of OEG part of the molecule in superior resistance towards protein adsorption. The surfaces with underbrushes were imaged using atomic force microscopy (AFM) to detect any changes in mechanical properties of PEG thiol covered surfaces upon addition of OEG thiol

Grafting poly ethylene glycol chains for antifouling purposes using supercritical CO2

Poly (ethylene glycol) (PEG) brushes are widely used for making antifouling surfaces. High graft density, which is desirable for optimal antifouling activity can be achieved using techniques such as atom transfer radical polymerisation (ATRP), cloud point grafting, and underbrushes formation. Here we demonstrate that PEG grafting using supercritical carbon dioxide (scCO2) results in higher PEG thickness (figure 2) relative to ethanol or toluene based grafting in thiol or silane based grafting respectively. Adsorption of bovine serum albumin (BSA), lysozyme, casein and lactoglobulin (Lacto-G) on PEG grafted surfaces were quantified using quartz crystal microbalance (QCM-D) (figure 4) and x-ray photoelectron spectroscopy (XPS) (figure 3). In conclusion scCO2 based PEG grafting resulted in surfaces that could significantly lower the adsorption of proteins and hence can be used as an efficient solvent in processes involving PEG grafting for antifouling purposes. Significant chemical efficiency and extremely low surface tension makes scCO2 an apt solvent for Grafting PEG brushes into three dimensional micro or nano porous scaffolds related to tissue engineering

Surface physicochemistry and ionic strength affects eDNA's role in bacterial adhesion to abiotic surfaces

Extracellular DNA (eDNA) is an important structural component of biofilms formed by many bacteria, but few reports have focused on its role in initial cell adhesion. The aim of this study was to investigate the role of eDNA in bacterial adhesion to abiotic surfaces, and determine to which extent eDNA-mediated adhesion depends on the physicochemical properties of the surface and surrounding liquid. We investigated eDNA alteration of cell surface hydrophobicity and zeta potential, and subsequently quantified the effect of eDNA on the adhesion of Staphylococcus xylosus to glass surfaces functionalised with different chemistries resulting in variable hydrophobicity and charge. Cell adhesion experiments were carried out at three different ionic strengths. Removal of eDNA from S. xylosus cells by DNase treatment did not alter the zeta potential, but rendered the cells more hydrophilic. DNase treatment impaired adhesion of cells to glass surfaces, but the adhesive properties of S. xylosus were regained within 30 minutes if DNase was not continuously present, implying a continuous release of eDNA in the culture. Removal of eDNA lowered the adhesion of S. xylosus to all surfaces chemistries tested, but not at all ionic strengths. No effect was seen on glass surfaces and carboxyl-functionalised surfaces at high ionic strength, and a reverse effect occurred on amine-functionalised surfaces at low ionic strength. However, eDNA promoted adhesion of cells to hydrophobic surfaces irrespective of the ionic strength. The adhesive properties of eDNA in mediating initial adhesion of S. xylosus is thus highly versatile, but also dependent on the physicochemical properties of the surface and ionic strength of the surrounding medium.Peer reviewe

Effect of ionic strength and surface chemistries on eDNA mediated adhesion of <i>S. xylosus</i>.

<p>Black bars indicate untreated cells. White bars indicate cells treated with DNase. Experiments were carried out at low (I = 0.015 M), medium (I = 0.19 M) and high (I = 0.70 M) ionic strength. Values are average of 3 replicates (error bars  =  S.D.) Asterisk indicates statistically significant differences between samples with and without eDNA (t-test, *p<0.05, **p<0.01).</p

Mixed poly (ethylene glycol) (PEG) and oligo (ethylene glycol) (OEG) layers on gold as non fouling surfaces created by backfilling

Backfilling a self-assembled monolayer (SAM) of long poly (ethylene glycol) (PEG) with short PEG is a well-known strategy to improve its potential to resist fouling. Here it is shown, using x-ray photoelectron spectroscopy, contact angle, and atomic force microscopy, that backfilling PEG thiol with oligo (ethylene glycol) (OEG) terminated alkane thiol molecules results in underbrush formation. The authors also confirm the absence of phase separated arrangement, which is commonly observed with backfilling experiments involving SAMs of short chain alkane thiol with long chain alkane thiol. Furthermore, it was found that OEG addition caused less PEG desorption when compared to alkane thiol. The ability of surface to resist fouling was tested through serum adsorption and bacterial adhesion studies. The authors demonstrate that the mixed monolayer with PEG and OEG is better than PEG at resisting protein adsorption and bacterial adhesion, and conclude that backfilling PEG with OEG resulting in the underbrush formation enhances the ability of PEG to resist fouling

Effect of DNase on the adhesion of <i>S. xylosus</i> to glass surface in flow cell.

<p>Black bars indicate untreated cells. Crossed bars indicate cells treated with DNase (50 µg/ml), washed and resuspended in PBS. White bars indicate cells resuspended in PBS containing DNase (50 µg/ml). Asterisk indicates statistically significant differences between samples with and without eDNA (t-test, *p<0.05, **p<0.01).</p

Cell surface properties with and without eDNA.

<p>Water contact angle and zeta potential measurements of <i>S. xylosus</i> cells with and without eDNA.</p><p>*indicates statistically significant difference (t-test, p<0.05).</p

Identity and antibiotic sensitivity pattern of the bacterial strains isolated from the PETL WWTP against 39 antibiotics.

<p>Source of strains: Strains ER1 to ER-5 and ET-1 to ET-7 were isolated from the equilibratior tank; A1R-2 to A1R-10 and A1T2 to A1T8 were isolated from aeration tank No. 1; A2R4 to A2R-8 and A2T-3 to A2T-8 were isolated from aeration tank No. 2; SR-1 to SR-14 and ST-1 to ST-8 were isolated from the settling tank; SSR-1 to SSR-6 and SST-1 to SST-8 were isolated from secondary sludge; DSR-1 to DSR-6 and DST-1 to DST-8 were isolated from dewatered sludge; OSR-1 to OSR-4 and OST-1 to OST-14 were isolated from old dried sludge.</p

Multi-drug resistance observed among 93 bacterial strains isolated from the PETL WWTP.

<p>The X-axis indicates the number of antibiotics (of 39 tested) to which the strains are resistant; the Y-axis indicates the percentage of resistant strains of 93 strains. The resistant and intermediately-resistant phenotypes are grouped together and denoted as resistant.</p

PCR-primers used in the present study.

<p>PCR-primers used in the present study.</p