New Evidence for Ag-Sputtered Materials Inactivating Bacteria by Surface Contact without the Release of Ag Ions: End of a Long Controversy?

The study provides new evidence for Ag-coated polyester (PES) mediating Escherichia coli inactivation by way of genetically engineered E. coli (without porins, from now denoted porinless bacteria). This allows the quantification of the bactericidal kinetics induced by the Ag surface without the intervention of Ag ions. Bacterial inactivation mediated by Ag-PES was seen to be completed within 60 min. The samples were prepared by high-power impulse magnetron sputtering (HiPIMS) at different sputter powers. In anaerobic media, this process required 120 min. The amounts of ions (Ar+, Ag+, and Ag2+) generated during the deposition by direct current magnetron sputtering (DCMS) and HiPIMS were determined by mass spectrometry. The thickness of the Ag films sputtered on PES by DCMS (0.28 A) during 100 s was found to be 340 nm. Thicknesses of 250, 230, and 200 nm were found when sputtering with HiPIMS was tuned at 8, 17, and 30 A, respectively. By scanning transmission electron microscopy (STEM-HAADF), the atomic distribution of Ag and oxygen was detected. By X-ray photoelectron spectroscopy (XPS), a shift in the Ag oxidation state was observed within the bacterial inactivation period. This reveals redox catalysis within the time required for the total bacterial inactivation due to the interaction between the bacterial suspension and Ag-PES. Surface properties of the Ag-coated PES samples were additionally investigated by X-ray diffraction (XRD). The formation of Ag plasmon was detected by diffuse reflectance spectroscopy (DRS) and was a function of the applied sputtering energy. The indoor sunlight irradiation dose required to induce an accelerated bacterial inactivation was found to be 5-10 mW/cm2.

Femtosecond Spectroscopy of Au Hot-Electron Injection into TiO2: Evidence for Au/TiO2 Plasmon Photocatalysis by Bactericidal Au Ions and Related Phenomena.

In the present work, we provide evidence for visible light irradiation of the Au/TiO2 nanoparticles' surface plasmon resonance band (SPR) leading to electron injection from the Au nanoparticles to the conduction band of TiO2. The Au/TiO2 SPR band is shown to greatly enhance the light absorption of TiO2 in the visible region. Evidence is presented for the light absorption by the Au/TiO2 plasmon bands leading to the dissolution of Au nanoparticles. This dissolution occurs concomitantly with the injection of the hot electrons generated by the Au plasmon into the conduction band of TiO2. The electron injection from the Au nanoparticles into TiO2 was followed by femtosecond spectroscopy. The formation of Au ions was further confirmed by the spectral shift of the transient absorption spectra of Au/TiO2. The spectral changes of the SPR band of Au/TiO2 nanoparticles induced by visible light were detected by spectrophotometer, and the morphological transformation of Au/TiO2 was revealed by electron microscopy techniques as well. Subsequently, the fate of the Au ions was sorted out during the growth and biofilm formation for some selected Gram-negative bacteria. This study compares the bactericidal mechanism of Au ions and Ag ions, which were found to be substantially different depending on the selected cell used as a probe.

Innovative Ti1- xNb xN-Ag Films Inducing Bacterial Disinfection by Visible Light/Thermal Treatment.

This study presents innovative Ti1- xNb xN-Ag films obtained by a suitable combination of low-energy and high-energy sputtering leading to bacterial inactivation. The bacterial inactivation kinetics by the TiNbN layers was drastically enhanced by the addition of 6-7% Ag and proceeded to completion within 3 h after the film autoclaving. By X-ray photoelectron spectroscopy (XPS), the samples after autoclaving presented in their upper layers TiO2, Nb2O5 and Ag2O with a surface composition of Ti0.81Nb0.19N0.99Ag0.068. Surface potential/pH changes in the Ti1- xNb xN-Ag films were monitored during bacterial inactivation. Surface redox processes during the bacterial inactivation were detected by XPS. The diffusion of Ag in the Ti1- xNb xN-Ag films was followed at 50 and 70 °C pointing. The beneficial thermal treatment points out to the bifunctional bacterial inactivation properties of these films and their potential application in healthcare facilities. Interfacial charge transfer (IFCT) under light irradiation between Ag2O, Nb2O5 and TiO2 is suggested consistent with the data found during the course of this study. The TiO2/Nb2O5 lattice mechanism is discussed in the framework of the Verwey's controlled valence model. The surface properties of the Ti1- xNb xN-Ag films were investigated by X-ray diffraction, atomic force microscopy, and scanning electron microscopy.

Evidence for differentiated ionic and surface contact effects driving bacterial inactivation by way of genetically modified bacteria.

New evidence is presented for the bacterial inactivation of E. coli presenting normal porins on sputtered Ag-Cu surfaces compared with similar E. coli porinless bacteria. Inactivation at a reduced rate was observed on the genetically modified porinless bacteria interacting via surface contact with metal/oxides without the intervention of metal-ions.

Fungicidal activity of copper-sputtered flexible surfaces under dark and actinic light against azole-resistant Candida albicans and Candida glabrata.

Candida spp. are able to survive on hospital surfaces and causes healthcare-associated infections (HCAIs). Since surface cleaning and disinfecting interventions are not totally effective to eliminate Candida spp., new approaches should be devised. Copper (Cu) has widely recognized antifungal activity and the use of Cu-sputtered surfaces has recently been proposed to curb the spread of HCAIs. Moreover, the activity of Cu under the action of actinic light remains underexplored. We investigated the antifungal activity of Cu-sputtered polyester surfaces (Cu-PES) against azole-resistant Candida albicans and Candida glabrata under dark and low intensity visible light irradiation (4.65mW/cm2). The surface properties of Cu-PES photocatalysts were characterized by diffuse reflectance spectroscopy (DRS) and X-ray fluorescence (XRF). Under dark, Cu-PES showed a fungicidal activity (≥3log10CFU reduction of the initial inoculum) against both C. albicans DSY296 and C. glabrata DSY565 leading to a reduction of the starting inoculum of 3.1 and 3.0log10CFU, respectively, within 60min of exposure. Under low intensity visible light irradiation, Cu-PES exhibited an accelerated fungicidal activity against both strains with a reduction of 3.0 and 3.4log10CFU, respectively, within 30min of exposure. This effect was likely due to the semiconductor Cu2O/CuO charge separation. The decrease in cell viability of the two Candida strains under dark and light conditions correlated with the progressive loss of membrane integrity. These results indicate that Cu-PES represent a promising strategy for decreasing the colonization of surfaces by yeasts and that actinic light can improve its self-disinfecting activity.

VUV/UV light inducing accelerated phenol degradation with a low electric input.

This study presents the first evidence for the accelerated degradation of phenol by Fenton's reagent in a mini-fluidic VUV/UV photoreaction system (MVPS). A low-pressure mercury lamp used in the MVPS led to a complete degradation of phenol within 4-6 min. The HO˙ and HO2˙ originating from both Fenton's reagent and VUV photolysis of water were identified with suitable radical scavengers. The effects of initial concentrations of phenol, H2O2 and Fe3+ as well as solution pH on phenol degradation kinetics were examined. Increasing the initial phenol concentration slowed down the phenol degradation, whereas increasing the initial H2O2 or Fe3+ concentration accelerated the phenol degradation. The optimal solution pH was 3.7. At both 254 and 185 nm, increasing phenol concentration enhanced its absorption for the incident photons. The reaction mechanism for the degradation of phenol was suggested consistent with the results obtained. This study indicates that the VUV/UV photo-Fenton process has potential applications in the treatment of industrial wastewater containing phenol and related aromatic pollutants.

Beneficial effect of Cu on Ti-Nb-Ta-Zr sputtered uniform/adhesive gum films accelerating bacterial inactivation under indoor visible light.

This article presents the evidence for the significant effect of copper accelerating the bacterial inactivation on Ti-Nb-Ta-Zr (TNTZ) sputtered films on glass up to a Cu content of 8.3 at.%. These films were deposited by dc magnetron co-sputtering of an alloy target Ti-23Nb-0.7Ta-2Zr (at.%) and a Cu target. The fastest bacterial inactivation of E. coli on this later TNTZ-Cu surface proceeded within ∼75min. The films deposited by magnetron sputtering are chemically homogenous. The film roughness evaluated by atomic force spectroscopy (AFM) on the TNTZ-Cu 8.3 at.% Cu sample presented an RMS-value of 20.1nm being the highest RMS of any Cu-sputtered TNTZ sample. The implication of the RMS value found for this sample leading to the fastest interfacial bacterial inactivation kinetics is also discussed. Values for the Young's modulus and hardness are reported for the TNTZ films in the presence of various Cu-contents. Evaluation of the bacterial inactivation kinetics of E. coli under low intensity actinic hospital light and in the dark was carried out. The stable repetitive bacterial inactivation was consistent with the extremely low Cu-ion release from the samples of 0.4 ppb. Evidence is presented by the bacterial inactivation dependence on the applied light intensity for the intervention of Cu as semiconductor CuO during the bacterial inactivation at the TNTZ-Cu interface. The mechanism of CuO-intervention under light is suggested based on the pH/and potential changes registered during bacterial disinfection.

FeOx-TiO2 Film with Different Microstructures Leading to Femtosecond Transients with Different Properties: Biological Implications under Visible Light.

This study presents the first report addressing the effect of FeOx-TiO2 films microstructure on the transients detected by fast spectroscopy related to the long-range bacterial inactivation performance. The different fast kinetic femtosecond transient spectroscopy is reported for each FeOx+TiO2 microstructure. The lifetime of the short transient-species and the oxidative intermediate radicals generated under light were identified. Co-sputtered FeOx-TiO2 on polyethylene films presenting random distribution for both oxides were compared with sequentially sputtered FeOx/TiO2 films made up only by FeOx in the topmost layers. The ratio FeOx:TiO2 was optimized to attain the highest photo-conversion. By X-ray fluorescence, the Fe:Ti ration was found to be ~1.4 in the film bulk and by XPS-etching a ratio of 4:1 was found on the photocatalyst top-most layers. For co-sputtered FeOx-TiO2-PE films, the FeOx-TiO2 heterojunction led to electron injection from the FeOx to lower-lying TiO2 trapping states. The film optical properties, particle size, roughness, hydrophobic-hydrophilic shift and temporal evolution of the transient redox states were characterized in detail. Films with different microstructure led to different antibacterial activity. This suggests that the FeOx-TiO2-PE microstructure and not the position of the potential energy level of the semiconductors FeOx and TiO2 control the charge transfer under light irradiation.

In Vitro and In Vivo Effectiveness of an Innovative Silver-Copper Nanoparticle Coating of Catheters To Prevent Methicillin-Resistant Staphylococcus aureus Infection.

In this study, silver/copper (Ag/Cu)-coated catheters were investigated for their efficacy in preventing methicillin-resistant Staphylococcus aureus (MRSA) infection in vitro and in vivo Ag and Cu were sputtered (67/33% atomic ratio) on polyurethane catheters by direct-current magnetron sputtering. In vitro, Ag/Cu-coated and uncoated catheters were immersed in phosphate-buffered saline (PBS) or rat plasma and exposed to MRSA ATCC 43300 at 10(4) to 10(8) CFU/ml. In vivo, Ag/Cu-coated and uncoated catheters were placed in the jugular vein of rats. Directly after, MRSA (10(7) CFU/ml) was inoculated in the tail vein. Catheters were removed 48 h later and cultured. In vitro, Ag/Cu-coated catheters preincubated in PBS and exposed to 10(4) to 10(7) CFU/ml prevented the adherence of MRSA (0 to 12% colonization) compared to uncoated catheters (50 to 100% colonization; P < 0.005) and Ag/Cu-coated catheters retained their activity (0 to 20% colonization) when preincubated in rat plasma, whereas colonization of uncoated catheters increased (83 to 100%; P < 0.005). Ag/Cu-coating protection diminished with 10(8) CFU/ml in both PBS and plasma (50 to 100% colonization). In vivo, Ag/Cu-coated catheters reduced the incidence of catheter infection compared to uncoated catheters (57% versus 79%, respectively; P = 0.16) and bacteremia (31% versus 68%, respectively; P < 0.05). Scanning electron microscopy of explanted catheters suggests that the suboptimal activity of Ag/Cu catheters in vivo was due to the formation of a dense fibrin sheath over their surface. Ag/Cu-coated catheters thus may be able to prevent MRSA infections. Their activity might be improved by limiting plasma protein adsorption on their surfaces.

Bactericidal activity and mechanism of action of copper-sputtered flexible surfaces against multidrug-resistant pathogens.

Using direct current magnetron sputtering (DCMS), we generated flexible copper polyester surfaces (Cu-PES) and investigated their antimicrobial activity against a range of multidrug-resistant (MDR) pathogens including eight Gram-positive isolates (three methicillin-resistant Staphylococcus aureus [MRSA], four vancomycin-resistant enterococci, one methicillin-resistant Staphylococcus epidermidis) and four Gram-negative strains (one extended-spectrum ß-lactamase-producing [ESBL] Escherichia coli, one ESBL Klebsiella pneumoniae, one imipenem-resistant Pseudomonas aeruginosa, and one ciprofloxacin-resistant Acinetobacter baumannii). Bactericidal activity (≥3 log10 CFU reduction of the starting inoculum) was reached within 15-30 min exposure to Cu-PES. Antimicrobial activity of Cu-PES persisted in the absence of oxygen and against both Gram-positive and Gram-negative bacteria containing elevated levels of catalases, indicating that reactive oxygen species (ROS) do not play a primary role in the killing process. The decrease in cell viability of MRSA ATCC 43300 and Enterococcus faecalis V583 correlated with the progressive loss of cytoplasmic membrane integrity both under aerobic and anaerobic conditions, suggesting that Cu-PES mediated killing is primarily induced by disruption of the cytoplasmic membrane function. Overall, we here present novel antimicrobial copper surfaces with improved stability and sustainability and provide further insights into their mechanism of killing.

Quasi-Instantaneous Bacterial Inactivation on Cu-Ag Nanoparticulate 3D Catheters in the Dark and Under Light: Mechanism and Dynamics.

The first evidence for Cu-Ag (50%/50%) nanoparticulate hybrid coatings is presented leading to a complete and almost instantaneous bacterial inactivation in the dark (≤5 min). Dark bacterial inactivation times on Cu-Ag (50%/50%) were observed to coincide with the times required by actinic light irradiation. This provides the evidence that the bimetal Cu-Ag driven inactivation predominates over a CuO/Cu2O and Ag2O oxides inducing a semiconductor driven behavior. Cu- or Ag-coated polyurethane (PU) catheters led to bacterial inactivation needing about ∼30 min. The accelerated bacterial inactivation by Cu-Ag coated on 3D catheters sputtered was investigated in a detailed way. The release of Cu/Ag ions during bacterial inactivation was followed by inductively coupled plasma mass-spectrometry (ICP-MS) and the amount of Cu and Ag-ions released were below the cytotoxicity levels permitted by the sanitary regulations. By stereomicroscopy the amount of live/dead cells were followed during the bacterial inactivation time. By Fourier transform infrared spectroscopy (FTIR), the systematic shift of the -(CH2) band stretching of the outer lipo-polysaccharide bilayer (LPS) was followed to monitor the changes leading to cell lysis. A hydrophobic to hydrophilic transformation of the Cu-Ag PU catheter surface under light was observed within 30 min followed concomitantly to a longer back transformation to the hydrophobic initial state in the dark. Physical insight is provided for the superior performance of Cu-Ag films compared to Cu or Ag films in view of the drastic acceleration of the bacterial inactivation observed on bimetal Cu-Ag films coating PU catheters. A mechanism of bacterial inactivation is suggested that is consistent with the findings reported in this study.

Microstructure of Cu-Ag Uniform Nanoparticulate Films on Polyurethane 3D Catheters: Surface Properties.

The preparation, characterization, and antibacterial testing of Cu-Ag sputtered polyurethane (PU) catheters are addressed in this study. PU catheters with different atomic ratios Cu:Ag have been sputtered and led to different optical properties as followed by diffuse reflectance spectroscopy (DRS) and the surface redox properties were also different for different Cu-Ag ratios as observed by X-ray photoelectron spectroscopy (XPS). The surface atomic percentage concentration of the oxidized/reduced C-species originating from bacterial cultures before and after bacterial inactivation were determined on the Cu-Ag PU catheters. The crystallographic properties were determined by X-ray diffraction (XRD). The XRD-diffractogram showed the presence of Cu2O (111), Cu (200), CuO (020), and Ag (111) indicating that Cu nanoparticles present a more crystalline character compared to Ag nanoparticles. Increasing the percentage of Ag in the Cu-Ag films, bigger Ag-particle agglomerates were detected by scanning transmission electron microscopy (STEM) microanalysis confirming the results obtained by AFM. The bacterial inactivation kinetics of the sputtered Cu-Ag films on PU catheters was investigated in detail. Quasi-instantaneous bacterial inactivation kinetics was induced by the sputtered films on PU catheters after optimization of the Cu-Ag film thickness.

New evidence for hybrid acrylic/TiO2 films inducing bacterial inactivation under low intensity simulated sunlight.

This study addresses the preparation and characterization of hybrid films prepared from Titanium dioxide (TiO2) Pickering stabilized acrylic polymeric dispersion as well as their bacterial inactivation efficiency under sunlight irradiation. Complete bacterial inactivation under low intensity simulated solar light irradiation (55 mW/cm(2)) was observed within 240 min for the films containing 10 weight based on monomers (wbm) % of TiO2, whereas 360 min were needed for the films containing 20 wbm% of TiO2. The hybrid films showed repetitive Escherichia coli (E. coli) inactivation under light irradiation. TiO2 released from the films surfaces was measured by inductively coupled plasma mass spectrometry (IPC-MS), obtaining values of ∼ 0.5 and 1 ppb/cm(2) for the films containing 10 wbm% and 20 wbm% of TiO2, respectively, far below the allowed cytotoxicity level for TiO2 (200 ppb). Transmission electron microscopy (TEM) of the hybrid films showed that TiO2 nanoparticles (NPs) were located at the polymer particle's surface forming a continuous inorganic network inside the film matrix. Atomic force microscopy (AFM) images showed differences in the TiO2 dispersion between the air-film and film-substrate interfaces. Films containing 10 wbm% of TiO2 had higher roughness (Rg) at both interfaces than the one containing 20 wbm% of TiO2 inducing an increase in the bacterial adhesion as well as the bacterial inactivation kinetics. The highly oxidative OH-radicals participating in the bacterial inactivation were determined by fluorescence.

Preparation and Mechanism of Cu-Decorated TiO2-ZrO2 Films Showing Accelerated Bacterial Inactivation.

Antibacterial robust, uniform TiO2-ZrO2 films on polyester (PES) under low intensity sunlight irradiation made up by equal amounts of TiO2 and ZrO2 exhibited a much higher bacterial inactivation kinetics compared to pure TiO2 or ZrO2. The TiO2-ZrO2 matrix was found to introduce a drastic increase in the Cu-dopant promoter enhancing bacterial inactivation compared to Cu sputtered in the same amount on PES. Furthermore, the bacterial inactivation was accelerated by a factor close to three, by Cu- on TiO2-ZrO2 at extremely low levels ∼0.01%. Evidence is presented by X-ray photoelectron spectroscopy for redox catalysis taking place during bacterial inactivation. The TiO2-ZrO2-Cu band gap is estimated and the film properties were fully characterized. Evidence is provided for the photogenerated radicals intervening in the bacterial inactivation. The photoinduced TiO2-ZrO2-Cu interfacial charge transfer is discussed in term of the electronic band positions of the binary oxide and the Cu TiO2 intragap state.

Effect of surface pretreatment of TiO2 films on interfacial processes leading to bacterial inactivation in the dark and under light irradiation.

Evidence is presented for radio-frequency plasma pretreatment enhancing the amount and adhesion of TiO2 sputtered on polyester (PES) and on polyethylene (PE) films. Pretreatment is necessary to attain a suitable TiO2 loading leading to an acceptable Escherichia coli reduction kinetics in the dark or under light irradiation for PES-TiO2 and PE-TiO2 samples. The amount of TiO2 on the films was monitored by diffuse reflectance spectroscopy and X-ray fluorescence. X-ray electron spectroscopy shows the lack of accumulation of bacterial residues such as C, N and S during bacterial inactivation since they seem to be rapidly destroyed by TiO2 photocatalysis. Evidence was found for Ti(4+)/Ti(3+) redox catalysis occurring on PES-TiO2 and PE-TiO2 during the bacterial inactivation process. On PE-TiO2 surfaces, Fourier transform infrared spectroscopy (ATR-FTIR) provides evidence for a systematic shift of the na(CH2) stretching vibrations preceding bacterial inactivation within 60 min. The discontinuous IR-peak shifts reflect the increase in the C-H inter-bond distance leading to bond scission. The mechanism leading to E. coli loss of viability on PES-TiO2 was investigated in the dark up to complete bacterial inactivation by monitoring the damage in the bacterial outer cell by transmission electron microscopy. After 30 min, the critical step during the E. coli inactivation commences for dark disinfection on 0.1-5% wt PES-TiO2 samples. The interactions between the TiO2 aggregates and the outer lipopolysaccharide cell wall involve electrostatic effects competing with the van der Waals forces.

New evidence for TiO2 uniform surfaces leading to complete bacterial reduction in the dark: critical issues.

This study presents new evidence for the events leading to Escherichia coli reduction in the absence of light irradiation on TiO2-polyester (from now on TiO2-PES. By transmission electron microscopy (TEM) the diffusion of TiO2 NP's aggregates with the E. coli outer lipo-polyssacharide (LPS) layer is shown to be a prerequisite for the loss of bacterial cultivability. Within 30 min in the dark the TiO2 aggregates interact with E. coli cell wall leading within 120 min to the complete loss of bacterial cultivability on a TiO2-PES 5% TiO2 sample. The bacterial reduction was observed to increase with a higher TiO2 loading on the PES up to 5%. Bacterial disinfection on TiO2-PES in the dark was slower compared to the runs under low intensity simulated sunlight light irradiation. The interaction between the TiO2 aggregates and the E. coli cell wall is discussed in terms of the competition between the TiO2 units collapsing to form TiO2-aggregates at a physiologic pH-value followed by the electrostatic interaction with the bacteria surface. TiO2-PES samples were able to carry repetitive bacterial inactivation. This presents a potential for practical applications. X-ray photoelectron spectroscopy (XPS) evidence was found for the reduction of Ti4+ to Ti3+ contributing to redox interactions between TiO2-PES and the bacterial cell wall. Insight is provided into the mechanism of interaction between the E. coli cell wall and TiO2 NP's. The properties of the TiO2-PES surface like percentage atomic concentration, TiO2-loading, optical absorption, surface charge and crystallographic phases are reported in this study.

Accelerated Escherichia coli inactivation in the dark on uniform copper flexible surfaces.

The bacterial inactivation of Escherichia coli on Cu/CuO-polyester surfaces prepared by direct current magnetron sputtering was investigated in the dark and under actinic light (360 nm≤ λ ≤ 720 nm; 4.1 mW/cm(2)) as used commonly in hospital facilities. In the dark, complete bacterial inactivation (6log10 reduction) was observed within 150 min and under actinic light within 45 min. Sputtered samples led to nanoparticulate uniform Cu/CuO films ~70 nm thick. The deposition rate used was 2.2×10(15) atoms/cm(2) s as determined by profilometry. X-ray fluorescence was used to determine the sample Cu-content and transmission electron microscopy determined Cu-particles ~20 ± 5 nm in size. The film optical absorption was observed to increase with Cu-content of the sample by diffuse reflection spectroscopy. The bacterial inactivation involved redox processes between Cu/CuO-polyester and the bacteria as observed by x-ray photoelectron spectroscopy. During sample recycling, the amount of Cu-release was determined by inductively coupled plasma-mass spectroscopy. The values required for E. coli inactivation were below the cytotoxicity level threshold allowed for mammalian cells. The E. coli inactivation by Cu/CuO-polyester seems to involve an oligodynamic effect since bacterial inactivation was achieved at very low Cu-concentrations.

Inactivation of bacteria under visible light and in the dark by Cu films. Advantages of Cu-HIPIMS-sputtered films.

INTRODUCTION: The Cu polyester thin-sputtered layers on textile fabrics show an acceptable bacterial inactivation kinetics using sputtering methods. MATERIALS AND METHODS: Direct current magnetron sputtering (DCMS) for 40 s of Cu on cotton inactivated Escherichia coli within 30 min under visible light and within 120 min in the dark. For a longer DCMS time of 180 s, the Cu content was 0.294% w/w, but the bacterial inactivation kinetics under light was observed within 30 min, as was the case for the 40-s sputtered sample. RESULTS AND DISCUSSION: This observation suggests that Cu ionic species play a key role in the E. coli inactivation and these species were further identified by X-ray photoelectron spectroscopy (XPS). The 40-s sputtered samples present the highest amount of Cu sites held in exposed positions interacting on the cotton with E. coli. Cu DC magnetron sputtering leads to thin metallic semi-transparent gray-brown Cu coating composed by Cu nanoparticulate in the nanometer range as found by electron microscopy (EM). Cu cotton fabrics were also functionalized by bipolar asymmetric DCMSP. CONCLUSION: Sputtering by DCMS and DCMSP for longer times lead to darker and more compact Cu films as detected by diffuse reflectance spectroscopy and EM. Cu is deposited on the polyester in the form of Cu(2)O and CuO as quantified by XPS. The redox interfacial reactions during bacterial inactivation involve changes in the Cu oxidation states and in the oxidation intermediates and were followed by XPS. High-power impulse magnetron sputtering (HIPIMS)-sputtered films show a low rugosity indicating that the texture of the Cu nanoparticulate films were smooth. The values of R (q) and R (a) were similar before and after the E. coli inactivation providing evidence for the stability of the HIPIMS-deposited Cu films. The Cu loading percentage required in the Cu films sputtered by HIPIMS to inactivate E. coli was about three times lower compared to DCMS films. This indicates a substantial Cu metal savings within the preparation of antibacterial films.

Comparison of methods for evaluation of the bactericidal activity of copper-sputtered surfaces against methicillin-resistant Staphylococcus aureus.

Bacteria can survive on hospital textiles and surfaces, from which they can be disseminated, representing a source of health care-associated infections (HCAIs). Surfaces containing copper (Cu), which is known for its bactericidal properties, could be an efficient way to lower the burden of potential pathogens. The antimicrobial activity of Cu-sputtered polyester surfaces, obtained by direct-current magnetron sputtering (DCMS), against methicillin-resistant Staphylococcus aureus (MRSA) was tested. The Cu-polyester microstructure was characterized by high-resolution transmission electron microscopy to determine the microstructure of the Cu nanoparticles and by profilometry to assess the thickness of the layers. Sputtering at 300 mA for 160 s led to a Cu film thickness of 20 nm (100 Cu layers) containing 0.209% (wt/wt) polyester. The viability of MRSA strain ATCC 43300 on Cu-sputtered polyester was evaluated by four methods: (i) mechanical detachment, (ii) microcalorimetry, (iii) direct transfer onto plates, and (iv) stereomicroscopy. The low efficacy of mechanical detachment impeded bacterial viability estimations. Microcalorimetry provided only semiquantitative results. Direct transfer onto plates and stereomicroscopy seemed to be the most suitable methods to evaluate the bacterial inactivation potential of Cu-sputtered polyester surfaces, since they presented the least experimental bias. Cu-polyester samples sputtered for 160 s by DCMS were further tested against 10 clinical MRSA isolates and showed a high level of bactericidal activity, with a 4-log(10) reduction in the initial MRSA load (10(6) CFU) within 1 h. Cu-sputtered polyester surfaces might be of use to prevent the transmission of HCAI pathogens.

TiO2 nanoparticles suppress Escherichia coli cell division in the absence of UV irradiation in acidic conditions.

TiO(2) nanoparticles (NPs) activated by UV irradiation are known to have a bactericidal effect. In this study we report the details of TiO(2) NPs influence on the colony-forming capacity of E. coli in the dark at pH 4.0-4.5. At this pH the bacterial cells are negatively charged and TiO(2) NPs present a positive charge. A 60 min contact between E. coli with TiO(2) at concentrations of 0.02-0.2 mg/mL led to a reduction of E. coli cell number from 10(8) to 10(4)CFU/mL. After the reduction the system remains unchanged during the subsequent incubation. The observed reduction was a function on the initial E. coli concentration. In the presence of 0.04 mg/mL TiO(2) the colony-forming units (CFU) reduction after 60 min was of four-five orders of magnitude when the initial concentration was 10(8) cells/mL. But when starting with an E. coli concentration of 10(7) cells/mL the cell number reduction was less than one order of magnitude. Less than one order of magnitude cell number reduction was also observed for suspensions of E. coli 10(8) cells/mL and 0.002 mg/mL of TiO(2). The bacteria number reduction was always accompanied by the formation of cell aggregates. During cell incubation with TiO(2), the pH of the suspension increased, but did not reach the TiO(2) isoelectric point (IEP). E. coli cells stained with the fluorescent dye acridine orange (AO) showed that the fluorescence of single cells remained unchanged after incubation in the presence of TiO(2). The color change of fluorescence was revealed only in aggregated cells. This suggests changes in the physiologic state of E. coli incorporated into the aggregates. Aggregates of E. coli occur due to the electrostatic interaction between TiO(2) NPs and the bacterial cell surface. A hypothesis is suggested in this study to explain the CFU reduction and the retention of a certain irreducible number of cells capable of further division in the suspension in the presence of TiO(2) in the dark.