Visible light sensitized inactivation of MS-2 bacteriophage by a cationic amine-functionalized C60 derivative

Research Progress on Inactivation of Bacteriophages by Visible-Light Photocatalytic Composite Materials: A Mini Review

Infectious diseases caused by waterborne viruses have attracted researchers' great attention. To ensure a safe water environment, it is important to advance water treatment and disinfection technology. Photocatalytic technology offers an efficient and practical approach for achieving this goal. This paper reviews the latest studies on visible-light composite catalysts for bacteriophage inactivation, with a main focus on three distinct categories: modified UV materials, direct visible-light materials and carbon-based materials. This review gives an insight into the progress in photocatalytic material development and offers a promising solution for bacteriophage inactivation.

An Overview of Diverse Strategies To Inactivate Enterobacteriaceae-Targeting Bacteriophages

Bacteriophages are viruses that infect bacteria and thus threaten industrial processes relying on the production executed by bacterial cells. Industries bear huge economic losses due to such recurring and resilient infections. Depending on the specificity of the process, there is a need for appropriate methods of bacteriophage inactivation, with an emphasis on being inexpensive and high efficiency. In this review, we summarize the reports on antiphagents, i.e., antibacteriophage agents on inactivation of bacteriophages. We focused on bacteriophages targeting the representatives of the Enterobacteriaceae family, as its representative, Escherichia coli, is most commonly used in the bio-industry. The review is divided into sections dealing with bacteriophage inactivation by physical factors, chemical factors, and nanotechnology-based solutions.

Tailored hybrid microbial water disinfection system using sequentially assembled microbial fuel cells and an ultraviolet C light-emitting diode

An integrated ultraviolet C light-emitting diode (UV-C LED) water disinfection system activated by microbial fuel cells (MFCs) was developed, and optimized via electric circuit and device voltage profiling. The intensity of the renewable energy operated, self-powered UV-C LED for E. coli inactivation was calculated by bio-dosimetry to be 2.4  × 10-2 μW cm-2 using fluence-based rate constant (k) of ∼1.03 (±0.11) cm2/mJ to obtain the reduction equivalent fluence kinetics value. Finally, the first-order rate constant for E. coli inactivation during the tailored hybrid disinfection system was found to be 0.53 (±0.1) cm2/mJ by multiplying intensity with 1.09 (±0.1) × 10-5 s-1 derived from the linear regression of E. coli inactivation as a function of time. Furthermore, selected model microbial consisting of two bacteria (Salmonella sp. and Listeria sp.) and three viruses (MS2 bacteriophage, influenza A virus, and murine norovirus-1) were treated with UV-C LED irradiation under controlled experimental conditions to validate the disinfection efficiency of the system. Consequently, the required to achieve significant removal (i.e., >3-log; 99.9%) UV fluence and dose time were calculated to be 4-7 cm2/mJ and 54-76 h and 33-53 cm2/mJ and 400-622 h for model bacterial and viral, respectively. This study expands the applicability of microbial electrochemical system (MES) for microbial disinfection and could be utilized in future MFCs implementation studies for predicting and measuring the kinetics of microbial elimination using a tailored hybrid water treatment system.

Implication of cell culture methods and biases on UV inactivation of viruses

Inactivation of human respiratory viruses in air and on surfaces is important to control their spread. Exposure to germicidal ultraviolet (UV-C) light damages viral nucleic acid rendering them non-infectious. Most of the recent viral inactivation studies have not considered potential artifacts caused by interactions between UV-C light and culture media used to suspend and deposit virus on surfaces. We show that the reactive oxygen and nitrogen species (ROS and RNS) form when commonly used virus culture media is exposed to 265 nm irradiation from light emitting diodes (LEDs) at UV-C doses (4 or 40 mJ/cm²) commonly considered to achieve multiple log-inactivation of virus. Surface viral inactivation values were enhanced from 0.49 to 2.92 log₁₀ of viruses in DMEM, EMEM or EMEM-F as compared to absence of culture media (only suspended in Tris-buffer). The mechanisms responsible for the enhanced surface inactivate is hypothesized to involve photo-activation of vitamins and dyes present in the culture media, deposited with the virus on surfaces to be disinfected, which produce ROS and RNS. Given the rapidly growing research and commercial markets for UV-C disinfecting devices, there is a need to establish surface disinfecting protocols that avoid viral inactivation enhancement artifacts associated with selection and use of common cell culture media in the presence of UV-C light. This study addresses this weak link in the literature and highlights that inadequate selection of virus suspension media may cause a bias (i.e., over-estimation) for the UV-C dosages required for virus inactivation on surfaces.

A review on disinfection methods for inactivation of waterborne viruses

Water contamination is a global health problem, and the need for safe water is ever-growing due to the public health implications of unsafe water. Contaminated water could contain pathogenic bacteria, protozoa, and viruses that are implicated in several debilitating human diseases. The prevalence and survival of waterborne viruses differ from bacteria and other waterborne microorganisms. In addition, viruses are responsible for more severe waterborne diseases such as gastroenteritis, myocarditis, and encephalitis among others, hence the need for dedicated attention to viral inactivation. Disinfection is vital to water treatment because it removes pathogens, including viruses. The commonly used methods and techniques of disinfection for viral inactivation in water comprise physical disinfection such as membrane filtration, ultraviolet (UV) irradiation, and conventional chemical processes such as chlorine, monochloramine, chlorine dioxide, and ozone among others. However, the production of disinfection by-products (DBPs) that accompanies chemical methods of disinfection is an issue of great concern due to the increase in the risks of harm to humans, for example, the development of cancer of the bladder and adverse reproductive outcomes. Therefore, this review examines the conventional disinfection approaches alongside emerging disinfection technologies, such as photocatalytic disinfection, cavitation, and electrochemical disinfection. Moreover, the merits, limitations, and log reduction values (LRVs) of the different disinfection methods discussed were compared concerning virus removal efficiency. Future research needs to merge single disinfection techniques into one to achieve improved viral disinfection, and the development of medicinal plant-based materials as disinfectants due to their antimicrobial and safety benefits to avoid toxicity is also highlighted.

The Overlooked Photochemistry of Iodine in Aqueous Suspensions of Fullerene Derivatives

Fullerene's low water solubility was a serious challenge to researchers aiming to harness their excellent photochemical properties for aqueous applications. Cationic functionalization of the fullerene cage provided the most effective approach to increase water solubility, but common synthesis practices inadvertently complicated the photochemistry of these systems by introducing iodide as a counterion. This problem was overlooked until recent work noted a potentiation effect which occurred when photosensitizers were used to inactivate microorganisms with added potassium iodide. In this work, several photochemical pathways were explored to determine the extent and underlying mechanisms of iodide's interference in the photosensitization of singlet oxygen by cationic fulleropyrrolidinium ions and rose bengal. Triplet excited state sensitizer lifetimes were measured via laser flash photolysis to probe the role of I^- in triplet sensitizer quenching. Singlet oxygen production rates were compared across sensitizers in the presence or absence of I^-, SO₄^2-, and other anions. 3,5-Dimethyl-1H-pyrazole was employed as a chemical probe for iodine radical species, such as I·, but none were observed in the photochemical systems. Molecular iodine and triiodide, however, were found in significant quantities when photosensitizers were irradiated in the presence of I^- and O₂. The formation of I₂ in these photochemical systems calls into question the interpretations of prior studies that used I^- as a counterion for photosensitizer materials. As an example, MS2 bacteriophages were inactivated here by cationic fullerenes with and without I^- present, showing that I^- moderately accelerated the MS2 deactivation, likely by producing I₂. Production of I₂ did not appear to be directly correlated with estimates of ¹O₂ concentration, suggesting that the relevant photochemical pathways are more complex than direct reactions between ¹O₂ and I^- in the bulk solution. On the basis of the results here, iodine photochemistry may be underappreciated and misunderstood in other environmental systems.

Degradation of contaminants in plasma technology: An overview

The information of plasma technologies applications for environmental clean-up on treating and degrading metals, metalloids, dyes, biomass, antibiotics, pesticides, volatile organic compounds (VOCs), bacteria, virus and fungi is compiled and organized in the review article. Different reactor configurations of plasma technology have been applied for reactive species generation, responsible for the pollutants removal, hydrogen and methane production and microorganism inactivation. Therefore, in this review article, the reactive species from discharge plasma are presented here to provide the insight into the environmental applications. The combinations of plasma technology with flux agent and photocatalytic are also given in this review paper associated with the setup of the plasma system on the removal process of metals, VOCs, and microorganisms. Furthermore, the potential of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) inactivation via plasma technology is also described in this review paper. Detailed information of plasma parameter configuration is given to support the influence of the critical process in the plasma system to deal with contaminants.

Inactivation efficacy and mechanism of pulsed corona discharge plasma on virus in water

The presence of viruses in water is a major risk for human and animal health due to their high resistance to disinfection. Pulsed corona discharge plasma (PCDP) efficiently inactivates bacteria by causing damage to biological macromolecules, but its effect on waterborne virus has not been reported. This study evaluated the inactivation efficacy of PCDP to viruses using spring viremia of carp virus (SVCV) as a model. The results showed that 4-log₁₀ reduction of SVCV infectivity in cells was reached after 120 s treatment, and there was no significant difference in survival of fish infected with SVCV inactivated by PCDP for 240 s or more longer compared to the control fish without virus challenge, thus confirming the feasibility of PCDP to waterborne virus inactivation. Moreover, the high input energy density caused by voltage significantly improved the inactivation efficiency. The further research indicated that reactive species (RS) generated by pulsed corona discharge firstly reacted with phosphoprotein (P) and polymerase complex proteins (L) through penetration into the SVCV virions, and then caused the loss of viral infectivity by damage to genome and other structural proteins. This study has significant implications for waterborne virus removal and development of novel disinfection technologies.

Photocatalytic nanoparticles - From membrane interactions to antimicrobial and antiviral effects

As a result of increasing resistance among pathogens against antibiotics and anti-viral therapeutics, nanomaterials are attracting current interest as antimicrobial agents. Such materials offer triggered functionalities to combat challenging infections, based on either direct membrane action, effects of released ions, thermal shock induced by either light or magnetic fields, or oxidative photocatalysis. In the present overview, we focus on photocatalytic antimicrobial effects, in which light exposure triggers generation of reactive oxygen species. These, in turn, cause oxidative damage to key components in bacteria and viruses, including lipid membranes, lipopolysaccharides, proteins, and DNA/RNA. While an increasing body of studies demonstrate that potent antimicrobial effects can be achieved by photocatalytic nanomaterials, understanding of the mechanistic foundation underlying such effects is still in its infancy. Addressing this, we here provide an overview of the current understanding of the interaction of photocatalytic nanomaterials with pathogen membranes and membrane components, and how this translates into antibacterial and antiviral effects.

Photocatalytic Inactivation of Viruses Using Graphitic Carbon Nitride-Based Photocatalysts: Virucidal Performance and Mechanism

The prevalence of lethal viral infections necessitates the innovation of novel disinfection techniques for contaminated surfaces, air, and wastewater as significant transmission media of disease. The instigated research has led to the development of photocatalysis as an effective renewable solar-driven technology relying on the reactive oxidative species, mainly hydroxyl (OH●) and superoxide (O2●−) radicals, for rupturing the capsid shell of the virus and loss of pathogenicity. Metal-free graphitic carbon nitride (g-C3N4), which possesses a visible light active bandgap structure, low toxicity, and high thermal stability, has recently attracted attention for viral inactivation. In addition, g-C3N4-based photocatalysts have also experienced a renaissance in many domains, including environment, energy conversion, and biomedical applications. Herein, we discuss the three aspects of the antiviral mechanism, intending to highlight the advantages of photocatalysis over traditional viral disinfection techniques. The sole agenda of the review is to summarize the significant research on g-C3N4-based photocatalysts for viral inactivation by reactive oxidative species generation. An evaluation of the photocatalysis operational parameters affecting viral inactivation kinetics is presented. An overview of the prevailing challenges and sustainable solutions is presented to fill in the existing knowledge gaps. Given the merits of graphitic carbon nitride and the heterogeneous photocatalytic viral inactivation mechanism, we hope that further research will contribute to preventing the ongoing Coronavirus pandemic and future calamities.

Virus Removal and Inactivation Mechanisms during Iron Electrocoagulation: Capsid and Genome Damages and Electro-Fenton Reactions

Virus destabilization and inactivation are critical considerations in providing safe drinking water. We demonstrate that iron electrocoagulation simultaneously removed (via sweep flocculation) and inactivated a non-enveloped virus surrogate (MS2 bacteriophage) under slightly acidic conditions, resulting in highly effective virus control (e.g., 5-logs at 20 mg Fe/L and pH 6.4 in 30 min). Electrocoagulation simultaneously generated H₂O₂ and Fe(II) that can potentially trigger electro-Fenton reactions to produce reactive oxygen species such as ^•OH and high valent oxoiron(IV) that are capable of inactivating viruses. To date, viral attenuation during water treatment has been largely probed by evaluating infective virions (as plaque forming units) or genomic damage (via the quantitative polymerase chain reaction). In addition to these existing means of assessing virus attenuation, a novel technique of correlating transmission electron micrographs of electrocoagulated MS2 with their computationally altered three-dimensional electron density maps was developed to provide direct visual evidence of capsid morphological damages during electrocoagulation. The majority of coliphages lost at least 10-60% of the capsid protein missing a minimum of one of the 5-fold and two of 3- and 2-fold regions upon electrocoagulation, revealing substantial localized capsid deformation. Attenuated total reflectance-Fourier transform infrared spectroscopy revealed potential oxidation of viral coat proteins and modification of their secondary structures that were attributed to reactive oxygen species. Iron electrocoagulation simultaneously disinfects and coagulates non-enveloped viruses (unlike conventional coagulation), adding to the robustness of multiple barriers necessary for public health protection and appears to be a promising technology for small-scale distributed water treatment.

A Comparison of Porphyrin Photosensitizers in Photodynamic Inactivation of RNA and DNA Bacteriophages

Effective broad-spectrum antiviral treatments are in dire need as disinfectants and therapeutic alternatives. One such method of disinfection is photodynamic inactivation, which involves the production of reactive oxygen species from dissolved oxygen in response to light-stimulated photosensitizers. This study evaluated the efficacy of functionalized porphyrin compounds for photodynamic inactivation of bacteriophages as human virus surrogates. A blue-light light emitting diode (LED) lamp was used to activate porphyrin compounds in aqueous solution (phosphate buffer). The DNA bacteriophages ΦX174 and P22 were more resistant to porphyrin TMPyP photodynamic inactivation than RNA bacteriophage fr, with increasing rates of inactivation in the order: ΦX174 << P22 << fr. Bacteriophage ΦX174 was therefore considered a resistant virus suitable for the evaluation of three additional porphyrins. These porphyrins were synthesized from TMPyP by inclusion of a central palladium ion (PdT4) and/or the addition of a hydrophobic C14 chain (PdC14 or C14). While the inactivation rate of bacteriophage ΦX174 via TMPyP was similar to previous reports of resistant viruses, ΦX174 inactivation increased by a factor of approximately 2.5 using the metalloporphyrins PdT4 and PdC14. The order of porphyrin effectiveness was TMPyP < C14 < PdT4 < PdC14, indicating that both Pd²⁺ ligation and C14 functionalization aided virus inactivation.

Interfacial Molecular Fractionation on Ferrihydrite Reduces the Photochemical Reactivity of Dissolved Organic Matter

The selective sorption of dissolved organic matter (DOM) on minerals is a widespread geochemical process in the natural environment. Recent studies have explored the influence of this process on the molecular fractionation of DOM at water-mineral interfaces. However, it remains unclear how molecular fractionation affects the photochemistry of DOM. Here, we demonstrate that the adsorptive fractionation of DOM on ferrihydrite greatly reduces its photoproduction of reactive oxygen species (ROS) including ¹O₂, O₂^•-, and •OH normalized to organic carbon (ROS_OC). The ROS_OC for ¹O₂, O₂^•-, and •OH were positively correlated with the abundances of polyphenols and oxygenated polycyclic aromatics, which were also observed using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis to be preferentially sequestered by ferrihydrite. The molecules that preferentially remained in the solution after adsorption displayed low levels of ROS_OC. The molecular fractionation of DOM induced by adsorption on ferrihydrite therefore influenced the molecular components and also significantly reduced the photoreactive fractions of DOM in waters. These results are very important in promoting our understanding of the effects of molecular fractionation on the biogeochemical features, behaviors, and implications of DOM in the environment.

Synthesis and characterization of gadolinium-decorated [60]fullerene for tumor imaging and radiation sensitization

PURPOSE

The excellent contrast of high atomic number (Z) elements compared to soft tissues has advanced their use as contrast agents for computed tomographic imaging and as potential radiation sensitizers. We evaluated whether gadolinium (Gd) could serve as such a theranostic agent for high-resolution magnetic resonance imaging (MRI) due to its paramagnetic properties and radiosensitization due to its high Z.

MATERIALS AND METHODS

To improve the relaxivity of Gd, we coupled it to [60]fullerene, an elemental carbon allotropic nanoparticle that seamlessly traverses physiological barriers . By adding serinol, an aliphatic alcohol derived from amino acid serine, we turned [60]fullerene, which is otherwise insoluble in water, into a highly water-soluble derivative and decorated it externally with a payload of chelated gadolinium ions.

RESULTS

When [60]fullerene was functionalized in this manner with two gadolinium ions (Gd2C60), it displayed considerably higher T1 relaxivity at 4.7 T than the commercially used MRI contrast agent, Magnevist, (18.2 mM-1s-1 vs. 4.7 mM-1s-1). Attempts to increase this even further via decoration of [60]fullerene with 12 gadolinium ions was unsuccessful due to a poor water solubility. However, the current formulation of Gd2C60 did not result in any appreciable radiosensitization.

CONCLUSION

Our results show a successful generation of a novel contrast agent via decoration of fullerene with two chelated Gd ions. Though this formulation was not successful in generating radiosensitization, other chemical modifications can be further explored to increase radiosensitization potential.

Thermal-Sprayed Photocatalytic Coatings for Biocidal Applications: A Review

There have been ever-growing demands for disinfection of water and air in recent years. Efficient, eco-friendly, and cost-effective methods of disinfection for pathogens are vital to the health of human beings. The photocatalysis route has attracted worldwide attention due to its highly efficient oxidative capabilities and sustainable recycling, which can be used to realize the disinfection purposes without secondary pollution. Though many studies have comprehensively reviewed the work about photocatalytic disinfection, including design and fabrication of photocatalytic coatings, inactivation mechanisms, or practical applications, systematic reviews about the disinfection photocatalysis coatings from fabrication to effort for practical use are still rare. Among different ways of fabricating photocatalytic materials, thermal spray is a versatile surface coating technique and competitive in constructing large-scale functional coatings, which is a most promising way for the future environmental purification, biomedical and life health applications. In this review, we briefly introduced various photocatalytic materials and corresponding inactivation mechanisms for virus, bacteria and fungus. We summarized the thermal-sprayed photocatalysts and their antimicrobial performances. Finally, we discussed the future perspectives of the photocatalytic disinfection coatings for potential applications. This review would shed light on the development and implementation of sustainable disinfection strategies that is applicable for extensive use for controlling pathogens in the near future.

Developing [60]Fullerene Nanomaterials for Better Photodynamic Treatment of Non-Melanoma Skin Cancers

Skin cancer is the most common cancer in the U.S.A. and Europe. Its subtype, squamous skin carcinoma (SCC), if allowed to grow, has the potential to metastasize and can become deadly. Currently, carbon nanomaterials are being developed to treat cancer due to their attractive physicochemical and biological properties such as an enhanced permeability effect and their ability to produce reactive oxygen species. Here, we describe the synthesis of two water-soluble aminofullerenes (MonoaminoC₆₀ and HexakisaminoC₆₀), which were evaluated as novel [60]fullerene based photosentizers exhibiting anticancer properties. Moreover, the previously described neutral glycofullerene GF1 and its peracetylated lipophilic precursor MMS48 were compared with the aminofullerenes for their ability to generate reactive oxygen species and oxidize lipids. Remarkably, the generation of singlet oxygen and a superoxide radical by HexakisaminoC₆₀ was found to be markedly elevated in the presence of bovine serum albumin and NADH, respectively. Mechanistic studies of lipid peroxidation using cholesterol as a unique reporter molecule revealed that although all four fullerene nanomaterials primarily generated singlet oxygen, superoxide anion was also formed, which suggest a mixed mechanism of action (in which Type I and Type II photochemistry is involved). The [60]fullerene derivative HexakisaminoC₆₀ was also studied for its phototoxicity in squamous skin cancer cell line (A431) using the MTT test and propidium iodide staining.

Carbon-based antiviral nanomaterials: graphene, C-dots, and fullerenes. A perspective

The appearance of new and lethal viruses and their potential threat urgently requires innovative antiviral systems. In addition to the most common and proven pharmacological methods, nanomaterials can represent alternative resources to fight viruses at different stages of infection, by selective action or in a broad spectrum. A fundamental requirement is non-toxicity. However, biocompatible nanomaterials have very often little or no antiviral activity, preventing their practical use. Carbon-based nanomaterials have displayed encouraging results and can present the required mix of biocompatibility and antiviral properties. In the present review, the main candidates for future carbon nanometric antiviral systems, namely graphene, carbon dots and fullerenes, have been critically analysed. In general, different carbon nanostructures allow several strategies to be applied. Some of the materials have peculiar antiviral properties, such as singlet oxygen emission, or the capacity to interfere with virus enzymes. In other cases, nanomaterials have been used as a platform for functional molecules able to capture and inhibit viral activity. The use of carbon-based biocompatible nanomaterials as antivirals is still an almost unexplored field, while the published results show promising prospects.

Recent Progress on Fullerene-Based Materials: Synthesis, Properties, Modifications, and Photocatalytic Applications

Solar light is an inexpensive energy source making up for energy shortage and solving serious environmental problems. For efficient utilization of solar energy, photocatalytic materials have attracted extensive attention over the last decades. As zero-dimensional carbon nanomaterials, fullerenes (C60, C70, etc.) have been extensively investigated for photocatalytic applications. Due to their unique properties, fullerenes can be used with other semiconductors as photocatalyst enhancers, and also as novel photocatalysts after being dispersed on non-semiconductors. This review summarizes fullerene-based materials (including fullerene/semiconductors and fullerene/non-semiconductors) for photocatalytic applications, such as water splitting, Cr (Ⅵ) reduction, pollutant degradation and bacterial disinfection. Firstly, the optical and electronic properties of fullerene are presented. Then, recent advances in the synthesis and photocatalytic mechanisms of fullerene-based photocatalysts are summarized. Furthermore, the effective performances of fullerene-based photocatalysts are discussed, mainly concerning photocatalytic H2 generation and pollutant removal. Finally, the current challenges and prospects of fullerene-based photocatalysts are proposed. It is expected that this review could bring a better understanding of fullerene-based photocatalysts for water treatment and environmental protection.

Trends and targets in antiviral phototherapy

Photodynamic therapy (PDT) is a well-established treatment option in the treatment of certain cancerous and pre-cancerous lesions. Though best-known for its application in tumor therapy, historically the photodynamic effect was first demonstrated against bacteria at the beginning of the 20^th century. Today, in light of spreading antibiotic resistance and the rise of new infections, this photodynamic inactivation (PDI) of microbes, such as bacteria, fungi, and viruses, is gaining considerable attention. This review focuses on the PDI of viruses as an alternative treatment in antiviral therapy, but also as a means of viral decontamination, covering mainly the literature of the last decade. The PDI of viruses shares the general action mechanism of photodynamic applications: the irradiation of a dye with light and the subsequent generation of reactive oxygen species (ROS) which are the effective phototoxic agents damaging virus targets by reacting with viral nucleic acids, lipids and proteins. Interestingly, a light-independent antiviral activity has also been found for some of these dyes. This review covers the compound classes employed in the PDI of viruses and their various areas of use. In the medical area, currently two fields stand out in which the PDI of viruses has found broader application: the purification of blood products and the treatment of human papilloma virus manifestations. However, the PDI of viruses has also found interest in such diverse areas as water and surface decontamination, and biosafety.

Differential Microbicidal Effects of Bimetallic Iron-Copper Nanoparticles on Escherichia coli and MS2 Coliphage

Bimetallic iron-copper nanoparticles (Fe/Cu-NPs) were synthesized by a single-pot surfactant-free method in aqueous solution [via the reduction of ferrous ion to zerovalent iron nanoparticles (Fe-NPs) and the subsequent copper-coating by metal ion exchange]. The produced Fe/Cu-NPs formed aggregates of spherical nanoparticles (approximately 30-70 nm) of Fe-Cu core-shell structures with 11 wt % copper content. The microbicidal effects of Fe/Cu-NPs were explored on Escherichia coli and MS2 coliphage, surrogates for bacterial and viral pathogens, respectively. Fe/Cu-NPs exhibited synergistically enhanced activity for the inactivation of E. coli and MS2, compared to single-metal nanoparticles (i.e., Fe-NPs and Cu-NPs). Various experiments (microbial inactivation tests under different conditions, fluorescence staining assays, experiments using ELISA and qRT-PCR, etc.) suggested that Fe/Cu-NPs inactivate E. coli and MS2 via dual microbicidal mechanisms. Two biocidal copper species [Cu(I) and Cu(III)] can be generated by different redox reactions of Fe/Cu-NPs. It is suggested that E. coli is strongly influenced by the cytotoxicity of Cu(I), while MS2 is inactivated mainly due to the oxidative damages of protein capsid and RNA by Cu(III).

A mechanism study on the photocatalytic inactivation ofSalmonella typhimuriumbacteria by CuxO loaded rhodium–antimony co-doped TiO2nanorods

A detailed photocatalytic inactivation mechanism forS. typhimurium, using a Cu_xO/Rh–Sb–TiO₂NR was studied under visible light.

Edible Dye-Enhanced Solar Disinfection with Safety Indication

The rural developing world faces disproportional inequity in drinking water access, where point-of-use water treatment technologies often fail to achieve adequate levels of pathogen removal, especially for viruses. Solar disinfection (SODIS) is practiced because of its universal applicability and low implementation cost, though the excessively long treatment time and lack of safety indication hinder wider implementation. This study presents an enhanced SODIS scheme that utilizes erythrosine-a common food dye-as a photosensitizer to produce singlet oxygen for virus inactivation and to indicate the completion of water disinfection through photobleaching color change. Experimental results and predictions based on global solar irradiance data suggest that over 99.99% inactivation could be achieved within 5 min in the majority of developing countries, reducing the time for SODIS by 2 orders of magnitude. Preserving the low cost of traditional SODIS, erythrosine embodies edible dye-enhanced SODIS, an efficient water disinfection method that could potentially be used by governments and non-governmental organizations to improve drinking water quality in rural developing communities.

Sunlight-mediated inactivation of health-relevant microorganisms in water: a review of mechanisms and modeling approaches

Health-relevant microorganisms present in natural surface waters and engineered treatment systems that are exposed to sunlight can be inactivated by a complex set of interacting mechanisms. The net impact of sunlight depends on the solar spectral irradiance, the susceptibility of the specific microorganism to each mechanism, and the water quality; inactivation rates can vary by orders of magnitude depending on the organism and environmental conditions. Natural organic matter (NOM) has a large influence, as it can attenuate radiation and thus decrease inactivation by endogenous mechanisms. Simultaneously NOM sensitizes the formation of reactive intermediates that can damage microorganisms via exogenous mechanisms. To accurately predict inactivation and design engineered systems that enhance solar inactivation, it is necessary to model these processes, although some details are not yet sufficiently well understood. In this critical review, we summarize the photo-physics, -chemistry, and -biology that underpin sunlight-mediated inactivation, as well as the targets of damage and cellular responses to sunlight exposure. Viruses that are not susceptible to exogenous inactivation are only inactivated if UVB wavelengths (280-320 nm) are present, such as in very clear, open waters or in containers that are transparent to UVB. Bacteria are susceptible to slightly longer wavelengths. Some viruses and bacteria (especially Gram-positive) are susceptible to exogenous inactivation, which can be initiated by visible as well as UV wavelengths. We review approaches to model sunlight-mediated inactivation and illustrate how the environmental conditions can dramatically shift the inactivation rate of organisms. The implications of this mechanistic understanding of solar inactivation are discussed for a range of applications, including recreational water quality, natural treatment systems, solar disinfection of drinking water (SODIS), and enhanced inactivation via the use of sensitizers and photocatalysts. Finally, priorities for future research are identified that will further our understanding of the key role that sunlight disinfection plays in natural systems and the potential to enhance this process in engineered systems.

Photodynamic inactivation of bacteriophage MS2: The A-protein is the target of virus inactivation

Singlet oxygen mediated oxidation has been shown to be responsible for photodynamic inactivation (PDI) of viruses in solution with photosensitisers such as 5, 10, 15, 20-tetrakis (1-methyl-4-pyridinio) porphyrin tetra p-toluenesulfonate (TMPyP). The capsids of non-enveloped viruses, such as bacteriophage MS2, are possible targets for viral inactivation by singlet oxygen oxidation. Within the capsid (predominantly composed of coat protein), the A-protein acts as the host recognition and attachment protein. The A-protein has two domains; an α-helix domain and a β-sheet domain. The α-helix domain is attached to the viral RNA genome inside the capsid while the β-sheet domain, which is on the surface of the capsid, is believed to be the site for attachment to the host bacteria pilus during infection. In this study, 4 sequence-specific antibodies were raised against 4 sites on the A-protein. Changes induced by the oxidation of singlet oxygen were compared to the rate of PDI of the virus. Using these antibodies, our results suggest that the rate of PDI is relative to loss of antigenicity of two sites on the A-protein. Our data further showed that PDI caused aggregation of MS2 particles and crosslinking of MS2 coat protein. However, these inter- and intra-capsid changes did not correlate to the rate of PDI we observed in MS2. Possible modes of action are discussed as a means to gaining insight to the targets and mechanisms of PDI of viruses.

Boosting Photocatalytic Performance of Inactive Rutile TiO2 Nanorods under Solar Light Irradiation: Synergistic Effect of Acid Treatment and Metal Oxide Co-catalysts

In the present work, we accomplish the boosting of photocatalytic performance by the synergistic effect of acid treatment and transition metal oxide co-catalysts on molten salt rutile TiO₂ nanorods. FT-IR and XPS (oxygen deconvolution) results confirmed that the amount of hydroxyl groups increased on the surface of rutile TiO₂ nanorods (TO-NRs) after acid treatment. HR-TEM analysis revealed fine dispersion of metal oxide on the surface of acid treated TiO₂ nanorods (ATO-NRs). The photocatalytic activities of as-prepared (TO-NRs), acid treated (ATO-NRs), metal oxide loaded (MTO-NRs), and both acid treated and metal oxide loaded (MATO-NRs) nanorods were compared based on the rate kinetics and dye degradation efficiencies. Cobalt oxide (1 wt %) loaded and 1.0 M acid treated TiO₂ nanorods (Co/ATO-NR) exhibited the higher photocatalytic degradation efficiency for Orange-II dye degradation and inactivation of S. typhimurium pathogen compared to other photocatalysts under solar irradiation. Photoelectrochemical analysis demonstrated that the charge transfer process in Co/ATO-NR is significantly higher than that in the untreated samples. The improved photocatalytic activity of inactive TO-NRs might be due to enhanced charge transfer of finely dispersed metal oxides on the OH-rich surface of acid treated TiO₂ nanorods.

Photochemical reactivity of aqueous fullerene clusters: C60 versus C70

Over the past few years, there has been a strong interest in exploring the potential impact of fullerenes in the environment. Despite that both C₆₀ and C₇₀ have been detected in environmental matrices, the research on the impact of higher fullerenes, such as C_70, has been largely missing. This study evaluated and compared the phototransformation of aqueous C₆₀ and C₇₀ clusters (nC₆₀ and nC₇₀) and their ¹O₂ production under sunlight and lamp light irradiation (315nm, 360nm and 420nm). The nC₆₀ and nC₇₀ samples formed by direct mixing with water adopted a face-centered cubic (FCC) crystal structure. The apparent quantum yields (AQYs) of fullerene phototransformed were relatively constant over the examined wavelengths, while ¹O₂ production AQYs decreased with increased wavelengths. The long-term fate studies with outdoor sunlight indicated that both nC₆₀ and nC₇₀ lost considerable organic carbon contents (>80%) in water after ∼8 months of irradiation and that the intermediate photoproducts of nC₆₀ and nC₇₀ exhibited a progressively increased level of oxygen-containing functionalities. Overall, the study indicates that nC₇₀ can be photochemically removed under sunlight conditions and that the photoreactivity of nC₆₀ based on AQYs is greater than that of nC₇₀.

Visible-light-driven photocatalytic inactivation of MS2 by metal-free g-C3N4: Virucidal performance and mechanism

The challenge to achieve effective water disinfection of pathogens, especially viruses, with minimized harmful disinfection byproducts calls for a cost-effective and environmentally benign technology. Here, polymeric graphitic carbon nitride (g-C₃N₄), as a metal-free robust photocatalyst, was explored for the first time for its ability to inactivate viruses under visible light irradiation. MS2 with an initial concentration of 1 × 10⁸ PFU/mL was completely inactivated by g-C₃N₄ with a loading of 150 mg/L under visible light irradiation of 360 min. g-C₃N₄ was a robust photocatalyst, and no decrease in its virucidal performance was observed over five cycles of sequential MS2 photocatalytic inactivation. The reactive oxygen species (ROSs) were measured by a range of scavengers, and photo-generated electrons and its derived ROSs (O- 2) were found to be the leading contributor for viral inactivation. TEM images indicated that the viral particle shape was distorted and the capsid shell was ruptured after photocatalysis. Viral surface proteins, particularly replicase proteins and maturation proteins, were damaged by photocatalytic oxidation. The loss of proteins would result in the leakage and rapid destruction of interior components (four main types of RNA genes), finally leading to viral death without regrowth. Our work opens a new avenue for the exploration and applications of a low-cost, high-efficient, and robust metal-free photocatalyst for green/sustainable viral disinfection.

Microbial inactivation kinetics and mechanisms of carbon-doped TiO2 (C-TiO2) under visible light

In this study, titanium dioxide nanoparticles doped with carbon (C-TiO2) were synthesized by means of sol-gel methods, and the synthesis was verified by means of X-ray photoelectron spectroscopy. The nanoparticles' photocatalytic disinfection activity of Listeria monocytogenes was tested under UV and visible light. The observed inactivation levels for 150min of visible light exposure with and without UV cutoff filters were 2.10 and 2.45 log, respectively. We also found that traditional reactive oxygen species had insignificant actions on C-TiO2 photocatalysts and that L. monocytogenes inactivation in the C-TiO2 system under visible light was induced in large part by the midgap states (hmid(+)) that was produced photochemically from the visible light response. C-TiO2 was found to accelerate bacterial inactivation (of L. monocytogenes) in the presence of visible light. Our data suggests that the C-TiO2 may be useful in the development of alternative disinfectants for environmental applications.

Singlet-Oxygen Generation in Alkaline Periodate Solution

A nonphotochemical generation of singlet oxygen ((1)O2) using potassium periodate (KIO4) in alkaline condition (pH > 8) was investigated for selective oxidation of aqueous organic pollutants. The generation of (1)O2 was initiated by the spontaneous reaction between IO4(-) and hydroxyl ions, along with a stoichiometric conversion of IO4(-) to iodate (IO3(-)). The reactivity of in-situ-generated (1)O2 was monitored by using furfuryl alcohol (FFA) as a model substrate. The formation of (1)O2 in the KIO4/KOH system was experimentally confirmed using electron spin resonance (ESR) measurements in corroboration with quenching studies using azide as a selective (1)O2 scavenger. The reaction in the KIO4/KOH solution in both oxic and anoxic conditions initiated the generation of superoxide ion as a precursor of the singlet oxygen (confirmed by using superoxide scavengers), and the presence of molecular oxygen was not required as a precursor of (1)O2. Although hydrogen peroxide had no direct influence on the FFA oxidation process, the presence of natural organic matter, such as humic and fulvic acids, enhanced the oxidation efficiency. Using the oxidation of simple organic diols as model compounds, the enhanced (1)O2 formation is attributed to periodate-mediated oxidation of vicinal hydroxyl groups present in humic and fulvic constituent moieties. The efficient and simple generation of (1)O2 using the KIO4/KOH system without any light irradiation can be employed for the selective oxidation of aqueous organic compounds under neutral and near-alkaline conditions.

Improving the Visible Light Photoactivity of Supported Fullerene Photocatalysts through the Use of [C₇₀] Fullerene

We herein present the first instance of employing [C₇₀] fullerene for photocatalytic ¹O₂ production in water, through covalent immobilization onto a mesoporous silica support via nucelophilic amine addition directly to fullerene's cage. This attachment approach prevents the aggregation of individual fullerene molecules in water, thus allowing fullerene to retain its photoactivity, yet is much less complex than other techniques commonly pursued to create such supported-fullerene materials, which typically rely on water-soluble fullerene derivatives and elaborate immobilization methods. The solid-supported C₇₀ material exhibits significantly improved aqueous visible-light photoactivity compared to previous C₆₀- and C₆₀-derivative-based supported fullerene materials. Further, this material rapidly inactivates MS2 bacteriophage under sunlight illumination, oxidizes various organic contaminants, and does not appear to be significantly fouled by natural organic matter (NOM), highlighting the potential of these materials in real-world applications. Collectively, the ease of preparation and significantly enhanced visible-light photoactivity of these materials advance fullerene-based technologies for water treatment.

Photochemical and photophysical properties of sequentially functionalized fullerenes in the aqueous phase

The vast range of C₆₀ derivatives makes it difficult to assess the potential environmental impact of this class of materials, while past environmental studies mostly focused only on pristine C₆₀. Central to derivatized C₆₀'s potential to negatively impact (micro)biological receptors upon unintended release is its unique property of mediating the transfer of light energy to ambient oxygen, producing ¹O₂. To initiate the process of establishing a thorough understanding of the photoinduced adverse biological effects of functionalized fullerenes and their aqueous dispersions, the photochemical properties relevant to ¹O₂ production were evaluated using three selected series of mono-, bis-, and tris-adducted fullerene materials. Differential ¹O₂ production of derivatives in toluene were explained by spectral variations under visible and UVA light conditions. Of the nine functionalities studied only aggregates of two positively charged derivatives showed significant photoactivity under experimental conditions. Laser flash photolysis revealed a triplet excited state in the photoactive aggregates with a sufficiently long lifetime to be quenched by ³O₂. Dynamic light scattering, transmission electron microscopy, and electron diffraction patterns revealed aggregates with sizes typical of aqueous C₆₀ colloids that varied in crystallinity based on functionality. Results raised questions about our current understanding of the photoactivity of fullerene aggregates.

Bacterial inactivation by a singlet oxygen bubbler: identifying factors controlling the toxicity of (1)O2 bubbles

A microphotoreactor device was developed to generate bubbles (1.4 mm diameter, 90 μL) containing singlet oxygen at levels toxic to bacteria and fungus. As singlet oxygen decays rapidly to triplet oxygen, the bubbles leave behind no waste or byproducts other than O(2). From a comparative study in deaerated, air saturated, and oxygenated solutions, it was reasoned that the singlet oxygen bubbles inactivate Escherichia coli and Aspergillus fumigatus, mainly by an oxygen gradient inside and outside of the bubble such that singlet oxygen is solvated and diffuses through the aqueous solution until it reacts with the target organism. Thus, singlet oxygen bubble toxicity was inversely proportional to the amount of dissolved oxygen in solution. In a second mechanism, singlet oxygen interacts directly with E. coli that accumulate at the gas-liquid interface although this mechanism operates at a rate approximately 10 times slower. Due to encapsulation in the gaseous core of the bubble and a 0.98 ms lifetime, the bubbles can traverse relatively long 0.39 mm distances carrying (1)O(2) far into the solution; by comparison the diffusion distance of (1)O(2) fully solvated in H(2)O is much shorter (~150 nm). Bubbles that reached the outer air-water interface contained no (1)O(2). The mechanism by which (1)O(2) deactivated organisms was explored through the addition of detergent molecules and Ca(2+) ions. Results indicate that the preferential accumulation of E. coli at the air-water interface of the bubble leads to enhanced toxicity of bubbles containing (1)O(2). The singlet oxygen device offers intriguing possibilities for creating new types of disinfection strategies based on photodynamic ((1)O(2)) bubble carriers.

Virucidal nanofiber textiles based on photosensitized production of singlet oxygen

Novel biomaterials based on hydrophilic polycaprolactone and polyurethane (Tecophilic®) nanofibers with an encapsulated 5,10,5,20-tetraphenylporphyrin photosensitizer were prepared by electrospinning. The doped nanofiber textiles efficiently photo-generate O₂(¹Δ_g), which oxidize external chemical and biological substrates/targets. Strong photo-virucidal effects toward non-enveloped polyomaviruses and enveloped baculoviruses were observed on the surface of these textiles. The photo-virucidal effect was confirmed by a decrease in virus infectivity. In contrast, no virucidal effect was detected in the absence of light and/or the encapsulated photosensitizer.

Bacteriophage inactivation by UV-A illuminated fullerenes: role of nanoparticle-virus association and biological targets

Inactivation rates of the MS2 bacteriophage and (1)O(2) generation rates by four different photosensitized aqueous fullerene suspensions were in the same order: aqu-nC(60) < C(60)(OH)(6) ≈ C(60)(OH)(24) < C(60)(NH(2))(6). Alterations to capsid protein secondary structures and protein oxidation were inferred by detecting changes in infrared vibrational frequencies and carbonyl groups respectively. MS2 inactivation appears to be the result of loss of capsid structural integrity (localized deformation) and the reduced ability to eject genomic RNA into its bacterial host. Evidence is also presented for possible capsid rupture in MS2 exposed to UV-A illuminated C(60)(NH(2))(6) through TEM imagery and detection of RNA infrared fingerprints in ATR-FTIR spectra. Fullerene-virus mixtures were also directly visualized in the aqueous phase using a novel enhanced darkfield transmission optical microscope fitted with a hyperspectral imaging (HSI) spectrometer. Perturbations in intermolecular extended chains, HSI, and electrostatic interactions suggest that inactivation is a function of the relative proximity between nanoparticles and viruses and (1)O(2) generation rate. MS2 log survival ratios were linearly related to CT (product of (1)O(2) concentration C and exposure time T) demonstrating the applicability of classical Chick-Watson kinetics for all fullerenes employed in this study. Results suggest that antiviral properties of fullerenes can be increased by adjusting the type of surface functionalization and extent of cage derivatization thereby increasing the (1)O(2) generation rate and facilitating closer association with biological targets.

Photosensitized oxidation of emerging organic pollutants by tetrakis C₆₀ aminofullerene-derivatized silica under visible light irradiation

We recently reported that C(60) aminofullerenes immobilized on silica support (aminoC(60)/silica) efficiently produce singlet oxygen ((1)O(2)) and inactivate virus and bacteria under visible light irradiation. (1) We herein evaluate this new photocatalyst for oxidative degradation of 11 emerging organic contaminants, including pharmaceuticals such as acetaminophen, carbamazepine, cimetidine, propranolol, ranitidine, sulfisoxazole, and trimethoprim, and endocrine disruptors such as bisphenol A and pentachlorophenol. Tetrakis aminoC(60)/silica degraded pharmaceuticals under visible light irradiation faster than common semiconductor photocatalysts such as platinized WO(3) and carbon-doped TiO(2). Furthermore, aminoC(60)/silica exhibited high target-specificity without significant interference by natural organic matter. AminoC(60)/silica was more efficient than unsupported (water-suspended) C(60) aminofullerene. This was attributed to kinetically enhanced (1)O(2) production after immobilization, which reduces agglomeration of the photocatalyst, and to adsorption of pharmaceuticals onto the silica support, which increases exposure to (1)O(2) near photocatalytic sites. Removal efficiency increased with pH for contaminants with a phenolic moiety, such as bisphenol A and acetaminophen, because the electron-rich phenolates that form at alkaline pH are more vulnerable to singlet oxygenation.

Escherichia coli Inactivation by UVC-Irradiated C60: kinetics and mechanisms

Motivated by recent studies that documented changes in fullerene toxicity after chemical transformation, C(60) aggregates (nC(60)) were subject to UVC irradiation at monochromatic 254 nm and subsequently evaluated for antibacterial and bactericidal properties against Escherichia coli. The nC(60) treated with UVC irradiation, referred to herein as UVC-irradiated C(60), did not directly inhibit bacterial growth at concentrations up to 20 mg/L. In the presence of UVA and visible light, however, UVC-irradiated C(60) rapidly inactivated E. coli, suggesting that photochemical production of reactive oxygen species (ROS) was involved. The use of ROS scavengers and probes determined that hydroxyl radicals were the primary ROS responsible for the E. coli inactivation. Results from protein release, lipid peroxidation, cell permeability, and intracellular enzyme assays suggest that the inactivation mechanism involves UVC-irradiated C(60) diffusing through E. coli cell membrane and producing hydroxyl radicals within the cell. Further study on water-soluble C(60) derivatives and possible transformative processes is, therefore, recommended based on the environmental implications of results presented herein that nC(60) exposed to UVC irradiation is more toxic than parent nC(60).

Evidence of singlet oxygen and hydroxyl radical formation in aqueous goethite suspension using spin-trapping electron paramagnetic resonance (EPR)

The generation of reactive species in an aqueous goethite suspension, under room light and aeration conditions, was investigated using the electron paramagnetic resonance (EPR) technique employing spin trap agents. The trap reagents, including 5,5-dimethylpyrroline N-oxide (DMPO) and 2,2,6,6-tetramethylpiperidine (TEMP), were used for the detection of OH radicals (OH·) and singlet oxygen (1O2), respectively. On the addition of DMPO to the goethite suspended solution, a DMPO-OH adduct was formed, which was not decreased, even in the presence of the OH· scavenger, mannitol. This result implied a false positive interpretation from the DMPO-OH EPR signal. In the presence of TEMP reagent, a TEMP-O signal was detected, which was completely inhibited in the presence of the singlet oxygen scavenger, sodium azide. With both DMPO-OH and TEMP-O radicals in the presence and absence of radical scavengers, singlet oxygen was observed to be the key species formed in the room-light sensitized goethite suspension. In the goethite/H2O2 system; however, both OH· and singlet oxygen were generated, with significant portions of DMPO-OH resulting from both OH· and singlet oxygen. In fact, the DMPO-OH resulting from OH· should be carefully calculated by correcting for the amount of DMPO-OH due to singlet oxygen. This study reports, for the first time, that the goethite suspensions may also act as a natural sensitizer, such as fulvic acids, to form singlet oxygen.

C60 aminofullerene immobilized on silica as a visible-light-activated photocatalyst

A new strategy is described to immobilize photoactive C(60) aminofullerene on silica gel (3-(2-succinic anhydride)propyl functionalized silica), thus enabling facile separation of the photocatalyst for recycling and repeated use. An organic linker moiety containing an amide group was used to anchor C(60) aminofullerene to the functionalized silica support. The linker moiety prevents aqueous C(60) aggregation/agglomeration (shown by TEM images), resulting in a remarkable enhancement of photochemical (1)O(2) production under visible light irradiation. With no loss in efficacy of (1)O(2) production plus insignificant chemical modification of the aminoC(60)/silica photocatalyst after multiple cycling, the system offers a promising new visible-light-activated photocatalyst. Under visible-light irradiation, the aminoC(60)/silica photocatalyst is capable of effective and kinetically enhanced oxidation of Ranitidine and Cimetidine (pharmaceutical pollutants) and inactivation of MS-2 bacteriophage compared to aqueous solutions of the C(60) aminofullerene alone. Thus, this photocatalyst could enable water treatment in less developed areas by alleviating dependence on major infrastructure, including the need for electricity.