Photobiocidal Activity of TiO2/UHMWPE Composite Activated by Reduced Graphene Oxide under White Light.

Herein, we introduce a photobiocidal surface activated by white light. The photobiocidal surface was produced through thermocompressing a mixture of titanium dioxide (TiO2), ultra-high-molecular-weight polyethylene (UHMWPE), and reduced graphene oxide (rGO) powders. A photobiocidal activity was not observed on UHMWPE-TiO2. However, UHMWPE-TiO2@rGO exhibited potent photobiocidal activity (>3-log reduction) against Staphylococcus epidermidis and Escherichia coli bacteria after a 12 h exposure to white light. The activity was even more potent against the phage phi 6 virus, a SARS-CoV-2 surrogate, with a >5-log reduction after 6 h exposure to white light. Our mechanistic studies showed that the UHMWPE-TiO2@rGO was activated only by UV light, which accounts for 0.31% of the light emitted by the white LED lamp, producing reactive oxygen species that are lethal to microbes. This indicates that adding rGO to UHMWPE-TiO2 triggered intense photobiocidal activity even at shallow UV flux levels.

Performance comparison of photodynamic antimicrobial chemotherapy with visible-light-activated organic dyes: Rose bengal, crystal violet, methylene blue, and toluidine blue O.

This study evaluated the photobiocidal performance of four widely distributed visible-light-activated (VLA) dyes against two bacteria (Staphylococcus epidermidis and Escherichia coli) and two bacteriophages (phages MS2 and phi 6): rose bengal (RB), crystal violet, methylene blue, and toluidine blue O (TBO). The photobiocidal performance of each dye depended on the relationship between the type of dye and microorganism. Gram-negative E. coli and the non-enveloped structure of phage MS2 showed more resistance to the photobiocidal reaction than Gram-positive S. epidermidis and the enveloped structure of phage phi 6. RB had the highest potential to yield reactive oxygen species. However, the photobiocidal performance of RB was dependent on the magnitude of the surface charge of the microorganisms; for example, anionic RB induced a negative surface charge and thus electrical repulsion. On the other hand, the photobiocidal performance of TBO was observed to be less affected by the microorganism type. The comparative results presented in our study have significant implications for selecting photodynamic antimicrobial chemotherapy (PACT) dyes suitable for specific situations and purposes. Furthermore, they contribute to the advancement of PACT-related technologies by enhancing their applicability and scalability.

Transparent, Robust, and Photochemical Antibacterial Surface Based on Hydrogen Bonding between a Si-Al and Cationic Dye.

Healthcare-associated infections can occur and spread through direct contact with contaminated fomites in a hospital, such as mobile phones, tablets, computer keyboards, doorknobs, and other surfaces. Herein, this study shows a transparent, robust, and visible light-activated antibacterial surface based on hydrogen bonds between a transparent silica-alumina (Si-Al) sol-gel and a visible light-activated photosensitizer, such as crystal violet (CV). The study of the bonding mechanisms revealed that hydrogen bonding predominantly occurs between the N of CV and Al-OH. Apart from CV, Si-Al can be combined with a variety of dyes, highlighting its potential for wide application. The Si-Al@CV film selectively generates singlet oxygen using ambient visible light, triggering potent photochemical antibacterial performance against Gram-positive and Gram-negative bacteria. Additionally, the Si-Al@CV film is stable even after mechanical stability tests such as tape adhesion, scratch, bending, and water immersion. In vitro cytotoxicity tests using C2C12 myoblast cells showed that the Si-Al@CV film is a biocompatible material. This work suggests a new approach for designing a transparent and robust touchscreen surface with photochemical antibacterial capability against healthcare-associated infections.

Production of an EP/PDMS/SA/AlZnO Coated Superhydrophobic Surface through an Aerosol-Assisted Chemical Vapor Deposition Process.

In this study, a superhydrophobic coating on glass has been prepared through a single-step aerosol-assisted chemical vapor deposition (AACVD) process. During the process, an aerosolized precursor containing polydimethylsiloxane, epoxy resin, and stearic acid functionalized Al-doped ZnO nanoparticles was deposited onto the glass at 350 °C. X-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy showed that the precursor was successfully coated and formed a nano/microstructure (surface roughness: 378.0 ± 46.1 nm) on the glass surface. The coated surface had a water contact angle of 159.1 ± 1.2°, contact angle hysteresis of 2.2 ± 1.7°, and rolling off-angle of 1°, indicating that it was superhydrophobic. In the self-cleaning test of the coated surface at a tilted angle of 20°, it was shown that water droplets rolled and washed out dirt on the surface. The stability tests showed that the surface remained superhydrophobic after 120 h of exposure to ultraviolet (UV) irradiation and even after heat exposure at 350 °C. In addition, the surface was highly repellent to water solutions of pH 1-13. The results showed that the addition of the functionalized nanoparticles into the precursor allowed for the control of surface roughness and provided a simplified single-step fabrication process of the superhydrophobic surface. This provides valuable information for developing the manufacturing process for superhydrophobic surfaces.

Photobiocidal-triboelectric nanolayer coating of photosensitizer/silica-alumina for reusable and visible-light-driven antibacterial/antiviral air filters.

Outbreaks of airborne pathogens pose a major threat to public health. Here we present a single-step nanocoating process to endow commercial face mask filters with photobiocidal activity, triboelectric filtration capability, and washability. These functions were successfully achieved with a composite nanolayer of silica-alumina (Si-Al) sol-gel, crystal violet (CV) photosensitizer, and hydrophobic electronegative molecules of 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane (PFOTES). The transparent Si-Al matrix strongly immobilized the photosensitizer molecules while dispersing them spatially, thus suppressing self-quenching. During nanolayer formation, PFOTES was anisotropically rearranged on the Si-Al matrix, promoting moisture resistance and triboelectric charging of the Si-Al/PFOTES-CV (SAPC)-coated filter. The SAPC nanolayer stabilized the photoexcited state of the photosensitizer and promoted redox reaction. Compared to pure-photosensitizer-coated filters, the SAPC filter showed substantially higher photobiocidal efficiency (∼99.99 % for bacteria and a virus) and photodurability (∼83 % reduction in bactericidal efficiency for the pure-photosensitizer filter but ∼0.34 % for the SAPC filter after 72 h of light irradiation). Moreover, after five washes with detergent, the SAPC filter maintained its photobiocidal and filtration performance, proving its reusability potential. Therefore, this SAPC nanolayer coating provides a practical strategy for manufacturing an antimicrobial and reusable mask filter for use during the ongoing COVID-19 pandemic.

Zn and N Codoped TiO2 Thin Films: Photocatalytic and Bactericidal Activity.

We explore a series of Zn and N codoped TiO2 thin films grown using chemical vapor deposition. Films were prepared with various concentrations of Zn (0.4-2.9 at. % Zn vs Ti), and their impact on superoxide formation, photocatalytic activity, and bactericidal properties were determined. Superoxide (O2•-) formation was assessed using a 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenylamino)carbonyl]-2H-tetrazolium sodium salt (XTT) as an indicator, photocatalytic activity was determined from the degradation of stearic acid under UVA light, and bactericidal activity was assessed using a Gram-negative bacterium E. coli under both UVA and fluorescent light (similar to what is found in a clinical environment). The 0.4% Zn,N:TiO2 thin film demonstrated the highest formal quantum efficiency in degrading stearic acid (3.3 × 10-5 molecules·photon-1), while the 1.0% Zn,N:TiO2 film showed the highest bactericidal activity under both UVA and fluorescent light conditions (>3 log kill). The enhanced efficiency of the films was correlated with increased charge carrier lifetime, supported by transient absorption spectroscopy (TAS) measurements.

Crystal Violet-Impregnated Slippery Surface to Prevent Bacterial Contamination of Surfaces.

Biofilms which are self-organized communities can contaminate various infrastructural systems. Preventing bacterial adhesion on surfaces is more desirable than cleaning or disinfection of bacteria-contaminated surfaces. In this study, a 24 h bacterial adhesion test showed that "slippery surfaces" had increased resistance to bacterial contamination compared to polydimethylsiloxane and superhydrophobic surfaces. However, it did not completely inhibit bacterial attachment, indicating that it only retards surface contamination by bacteria. Hence, a strategy of killing bacteria with minimal bacterial adhesion was developed. A crystal violet-impregnated slippery (CVIS) surface with bactericidal and slippery features was produced through a simple dipping process. The CVIS surface had a very smooth and lubricated surface that was highly repellent to water and blood contamination. Bactericidal tests against Escherichia coli and Staphylococcus aureus showed that the CVIS surface exhibited bactericidal activity in dark and also showed significantly enhanced bactericidal activity (>3 log reduction in bacteria number) in white light.

Water-Repellent TiO2-Organic Dye-Based Air Filters for Efficient Visible-Light-Activated Photochemical Inactivation against Bioaerosols.

Recently, bioaerosols, including the 2019 novel coronavirus, pose a serious threat to global public health. Herein, we introduce a visible-light-activated (VLA) antimicrobial air filter functionalized with titanium dioxide (TiO2)-crystal violet (CV) nanocomposites facilitating abandoned visible light from sunlight or indoor lights. The TiO2-CV based VLA antimicrobial air filters exhibit a potent inactivation rate of ∼99.98% and filtration efficiency of ∼99.9% against various bioaerosols. Under visible-light, the CV is involved in overall inactivation by inducing reactive oxygen species production both directly (CV itself) and indirectly (in combination with TiO2). Moreover, the susceptibility of the CV to humidity was significantly improved by forming a hydrophobic molecular layer on the TiO2 surface, highlighting its potential applicability in real environments such as exhaled or humid air. We believe this work can open a new avenue for designing and realizing practical antimicrobial technology using ubiquitous visible-light energy against the threat of infectious bioaerosols.

Continuous Single-Phase Synthesis of [Au25(Cys)18] Nanoclusters and their Photobactericidal Enhancement.

Thiolate-gold nanoclusters have various applications. However, most of the synthesis methods require prolonged synthesis times from several hours to days. In the present study, we report a rapid synthesis method for [Au25(Cys)18] nanoclusters and their application for photobactericidal enhancement. For [Au25(Cys)18] synthesis, we employed a tube-in-tube membrane reactor using CO as a reducing agent at elevated temperatures. This approach allows continuous generation of high-quality [Au25(Cys)18] within 3 min. Photobactericidal tests against Staphylococcus aureus showed that crystal violet-treated polymer did not have photobactericidal activity, but addition of [Au25(Cys)18] in the treated polymer demonstrated a potent photobactericidal activity at a low white light flux, resulting in >4.29 log reduction in viable bacteria numbers. Steady-state and time-resolved photoluminescence spectroscopies demonstrated that after light irradiation, photoexcited electrons in crystal violet flowed to [Au25(Cys)18] in the silicone, suggesting that redox reaction from [Au25(Cys)18] enhanced the photobactericidal activity. Stability tests revealed that leaching of crystal violet and [Au25(Cys)18] from the treated silicone was negligible and cyclic testing showed that the silicone maintained a strong photobactericidal activity after repeated use.

Photobactericidal activity activated by thiolated gold nanoclusters at low flux levels of white light.

The emergence of antibiotic resistant bacteria is a major threat to the practice of modern medicine. Photobactericidal agents have obtained significant attention as promising candidates to kill bacteria, and they have been extensively studied. However, to obtain photobactericidal activity, an intense white light source or UV-activation is usually required. Here we report a photobactericidal polymer containing crystal violet (CV) and thiolated gold nanocluster ([Au25(Cys)18]) activated at a low flux levels of white light. It was shown that the polymer encapsulated with CV do not have photobactericidal activity under white light illumination of an average 312 lux. However, encapsulation of [Au25(Cys)18] and CV into the polymer activates potent photobactericidal activity. The study of the photobactericidal mechanism shows that additional encapsulation of [Au25(Cys)18] into the CV treated polymer promotes redox reactions through generation of alternative electron transfer pathways, while it reduces photochemical reaction type-ІІ pathways resulting in promotion of hydrogen peroxide (H2O2) production.

Photobactericidal Activity of Dual Dyes Encapsulated in Silicone Enhanced by Silver Nanoparticles.

Crystal violet (CV) and methylene blue (MB) dyes with silver (Ag) nanoparticles (NPs) were encapsulated into silicone to produce light-activated antimicrobial surfaces. Optical microscopy and X-ray photoelectron spectroscopy showed that CV and MB were diffused throughout the silicone samples and that Ag NPs were successfully encapsulated by the swell-encapsulation-shrink process. Antimicrobial tests on Staphylococcus aureus and Escherichia coli showed that CV/MB-encapsulated silicone samples have stronger photobactericidal activity than CV or MB samples and the addition of Ag NPs significantly enhanced the antimicrobial activity under white light. The number of viable bacteria decreased below the detection limit (below <103 CFU) on the silicone-incorporating CV/MB/Ag NPs within 3 h for S. aureus and within 5 h for E. coli. In leaching tests over 216 h, the amount of dye leaching from the samples was barely detectable (<0.02 ppm). These surfaces have a potential for use in healthcare settings to decrease hospital-associated infections.

The Anti-Biofouling Properties of Superhydrophobic Surfaces are Short-Lived.

Superhydrophobic surfaces are present in nature on the leaves of many plant species. Water rolls on these surfaces, and the rolling motion picks up particles including bacteria and viruses. Man-made superhydrophobic surfaces have been made in an effort to reduce biofouling. We show here that the anti-biofouling property of a superhydrophobic surface is due to an entrapped air-bubble layer that reduces contact between the bacteria and the surface. Further, we showed that prolonged immersion of superhydrophobic surfaces in water led to loss of the bubble-layer and subsequent bacterial adhesion that unexpectedly exceeded that of the control materials. This behavior was not restricted to one particular type of material but was evident on different types of superhydrophobic surfaces. This work is important in that it suggests that superhydrophobic surfaces may actually encourage bacterial adhesion during longer term exposure.

Covalently Attached Antimicrobial Surfaces Using BODIPY: Improving Efficiency and Effectiveness.

The development of photoactivated antimicrobial surfaces that kill pathogens through the production of singlet oxygen has proved very effective in recent years, with applications in medical devices and hospital touch surfaces, to improve patient safety and well being. However, many of these surfaces require a swell-encapsulation-shrink strategy to incorporate the photoactive agents in a polymer matrix, and this is resource intensive, given that only the surface fraction of the agent is active against bacteria. Furthermore, there is a risk that the agent will leach from the polymer and thus raises issues of biocompatibility and patient safety. Here, we describe a more efficient method of fabricating a silicone material with a covalently attached monolayer of photoactivating agent that uses heavy-atom triplet sensitization for improved singlet oxygen generation and corresponding antimicrobial activity. We use boron-dipyrromethane with a reactive end group and incorporated Br atoms, covalently attached to poly(dimethylsiloxane). We demonstrate the efficacy of this material in producing singlet oxygen and killing Staphylococcus aureus and suggest how it might be easily modifiable for future antimicrobial surface development.

Superhydrophobic and White Light-Activated Bactericidal Surface through a Simple Coating.

Bacterial adhesion and proliferation on surfaces are a challenge in medical and industrial fields. Here, a simple one-step technique is reported to fabricate self-cleaning and bactericidal surfaces. White, blue, and violet paints were produced using titanium dioxide nanoparticles, 1H,1H,2H,2H-perfluorooctyltriethoxysilane, crystal violet, toluidine Blue O, and ethanol solution. All of the painted surfaces showed superhydrophobicity in air, and even after hexadecane oil contamination, they retained water repellency and self-cleaning properties. In an assay of bacterial adhesion, significant reductions (>99.8%) in the number of adherent bacteria were observed for all the painted surfaces. In bactericidal tests, the painted surfaces not only demonstrated bactericidal activity against Staphylococcus aureus and Escherichia coli in the dark but also induced very potent photosensitization (>4.4 log reduction in the number of viable bacteria on the violet painted surface) under white light illumination. The technique that we developed here is general and can be used on a wide range of substrates such as paper, glass, polymers, and others.

Buoyancy increase and drag-reduction through a simple superhydrophobic coating.

A superhydrophobic paint was fabricated using 1H,1H,2H,2H-perfluorooctyltriethoxysilane (PFOTES), TiO2 nanoparticles and ethanol. The paint has potential for aquatic application of a superhydrophobic coating as it induces increased buoyancy and drag reduction. Buoyance testing showed that the reduction of surface energy by superhydrophobic coating made it feasible that glass, a high density material, was supported by the surface tension of water. In a miniature boat sailing test, it was shown that the low energy surface treatment decreased the adhesion of water molecules to the surface of the boat resulting in a reduction of the drag force. Additionally, a robust superhydrophobic surface was fabricated through layer-by-layer coating using adhesive double side tape and the paint, and after a 100 cm abrasion test with sand paper, the surface still retained its water repellency, enhanced buoyancy and drag reduction.

White Light-Activated Antimicrobial Paint using Crystal Violet.

Crystal violet (CV) was incorporated into acrylic latex to produce white-light-activated antimicrobial paint (WLAAP). Measurement of the water contact angle of the WLAAP showed that the water contact angle increased with increasing CV concentration. In a leaching test over 120 h, the amount of CV that leached from the WLAAPs was close to the detection limit (<0.03%). The WLAAPs were used to coat samples of polyurethane, and these showed bactericidal activity against Escherichia coli, which is a key causative agent of healthcare-associated infections (HAIs). A reduction in the numbers of viable bacteria was observed on the painted coated polyurethane after 6 h in the dark, and the bactericidal activity increased with increasing CV concentration (P < 0.1). After 6 h of white light exposure, all of coated polyurethanes demonstrated a potent photobactericidal activity, and it was statistically confirmed that the WLAAP showed better activity in white light than in the dark (P < 0.05). At the highest CV concentration, the numbers of viable bacteria fell below the detection limit (<10(3) CFU/mL) after 6 h of white light exposure. The difference in antimicrobial activity between the materials in the light and dark was 0.48 log at CV 250 ppm, and it increased by 0.43 log at each increment of CV 250 ppm. The difference was the highest (>1.8 log) at the highest CV concentration (1000 ppm). These WLAAPs are promising candidates for use in healthcare facilities to reduce HAIs.

White light-activated antimicrobial surfaces: effect of nanoparticles type on activity.

Toluidine blue O (TBO) dye together with either silver (Ag) nanoparticles (NPs), gold (Au) NPs, or a mixture of Ag and Au NPs (Mix Ag-Au NPs) were incorporated into polyurethane to make antimicrobial surfaces using a swell-encapsulation-shrink process. Antimicrobial testing against Escherichia coli showed that inclusion of the NPs significantly enhanced the antimicrobial activities of the TBO polyurethane samples. In particular, samples containing Ag NPs exhibited potent antimicrobial activity under white light and surprisingly, also in the dark. The numbers of viable bacteria decreased below the detection limit on the TBO/Ag NPs incorporated samples within 3 h and 24 h under white light and dark conditions. A mechanistic study using furfuryl alcohol indicated that the enhanced photobactericidal activity was most likely due to a type I photochemical reaction. To the best of our knowledge, this is the first report of an antimicrobial surface comprised of a combination of Ag NPs and a light activated agent to provide a dual kill mechanism. These surfaces are promising candidates for use in healthcare environments to reduce the incidence of hospital-acquired infections.

Antimicrobial Air Filters Using Natural Euscaphis japonica Nanoparticles.

Controlling bioaerosols has become more important with increasing participation in indoor activities. Treatments using natural-product nanomaterials are a promising technique because of their relatively low toxicity compared to inorganic nanomaterials such as silver nanoparticles or carbon nanotubes. In this study, antimicrobial filters were fabricated from natural Euscaphis japonica nanoparticles, which were produced by nebulizing E. japonica extract. The coated filters were assessed in terms of pressure drop, antimicrobial activity, filtration efficiency, major chemical components, and cytotoxicity. Pressure drop and antimicrobial activity increased as a function of nanoparticle deposition time (590, 855, and 1150 µg/cm2(filter) at 3-, 6-, and 9-min depositions, respectively). In filter tests, the antimicrobial efficacy was greater against Staphylococcus epidermidis than Micrococcus luteus; ~61, ~73, and ~82% of M. luteus cells were inactivated on filters that had been coated for 3, 6, and 9 min, respectively, while the corresponding values were ~78, ~88, and ~94% with S. epidermidis. Although statistically significant differences in filtration performance were not observed between samples as a function of deposition time, the average filtration efficacy was slightly higher for S. epidermidis aerosols (~97%) than for M. luteus aerosols (~95%). High-performance liquid chromatography (HPLC) and electrospray ionization-tandem mass spectrometry (ESI/MS) analyses confirmed that the major chemical compounds in the E. japonica extract were 1(ß)-O-galloyl pedunculagin, quercetin-3-O-glucuronide, and kaempferol-3-O-glucoside. In vitro cytotoxicity and disk diffusion tests showed that E. japonica nanoparticles were less toxic and exhibited stronger antimicrobial activity toward some bacterial strains than a reference soluble nickel compound, which is classified as a human carcinogen. This study provides valuable information for the development of a bioaerosol control system that is environmental friendly and suitable for use in indoor environments.

Synthesis of hybrid carbon nanotube structures coated with Sophora flavescens nanoparticles and their application to antimicrobial air filtration.

Controlling airborne microorganisms has become increasingly important with increase in human indoor activities, epidemic disease outbreaks, and airborne pathogen transmission. Treatments using antimicrobial nanoparticles have shown promise because of the high surface-to-volume ratio of nanoparticles compared to their bulk counterparts, and their unique physical and chemical properties. In this study, hybrid nanostructures of multi-walled carbon nanotubes (MWCNTs) coated with antimicrobial, natural product (NP) nanoparticles were synthesized using a twin-head electrospray system (THES). The coated nanoparticles were then used in antimicrobial air filters to increase their antimicrobial efficiency. Electrosprayed droplets were converted to NP nanoparticles and MWCNTs through ethanol evaporation. Oppositely charged NP nanoparticles and MWCNTs were coagulated via Coulombic collisions to form hybrid nanoparticles that were deposited continuously onto an air filter medium. The size distribution and composition of the hybrid NP/MWCNT particles were characterized using a wide-range particle spectrometer (WPS) and transmission electron microscope (TEM). The concentration of hybrid NP/MWCNT nanoparticles was lower than that of NP nanoparticles but higher than that of MWCNTs and showed a bimodal size distribution with peak diameters of 21.1 and 49 nm. TEM analyses confirmed that the NP nanoparticles were attached to the MWCNT surface with a density of ~4-9 particles/MWCNT. When deposited onto the filter medium, NP/MWCNT particles formed dendrites on the filter׳s fiber surface. The filtration efficiency and pressure drop of the NP/MWCNT-coated filters were higher than those of pristine, NP nanoparticles-coated or MWCNTs-coated filters. The hybrid filter also exhibited stronger antimicrobial activity than those of NP or MWCNT-coated filters at identical deposited volumes (1.1×10-2 cm3/cm2 filter). Ninety-five percent of the tested bacterial aerosols were inactivated on the NP/MWCNTs filter while only <70% were inactivated on NP- or MWCNT-coated filters.

Development and evaluation of antimicrobial activated carbon fiber filters using Sophora flavescens nanoparticles.

Activated carbon fiber (ACF) filters have a wide range of applications, including air purification, dehumidification, and water purification, due to their large specific surface area, high adsorption capacity and rate, and specific surface reactivity. However, when airborne microorganisms such as bacteria and fungi adhere to the carbon substrate, ACF filters can become a source of microbial contamination, and their filter efficacy declines. Antimicrobial treatments are a promising means of preventing ACF bio-contamination. In this study, we demonstrate the use of Sophora flavescens in antimicrobial nanoparticles coated onto ACF filters. The particles were prepared using an aerosol process consisting of nebulization-thermal drying and particle deposition. The extract from S. flavescens is an effective, natural antimicrobial agent that exhibits antibacterial activity against various pathogens. The efficiency of Staphylococcus epidermidis inactivation increased with the concentration of S. flavescens nanoparticles in the ACF filter coating. The gas adsorption efficiency of the coated antimicrobial ACF filters was also evaluated using toluene. The toluene-removal capacity of the ACF filters remained unchanged while the antimicrobial activity was over 90% for some nanoparticle concentrations. Our results provide a scientific basis for controlling both bioaerosol and gaseous pollutants using antimicrobial ACF filters coated with S. flavescens nanoparticles.