Bactericidal Activity of TiO2 Photocatalyst in Aqueous Media: Toward a Solar-Assisted Water Disinfection System

NH2-MIL-125-Derived N-Doped TiO2@C Visible Light Catalyst for Wastewater Treatment

The utilization of titanium dioxide (TiO2) as a photocatalyst for the treatment of wastewater has attracted significant attention in the environmental field. Herein, we prepared an NH2-MIL-125-derived N-doped TiO2@C Visible Light Catalyst through an in situ calcination method. The nitrogen element in the organic connector was released through calcination, simultaneously doping into the sample, thereby enhancing its spectral response to cover the visible region. The as-prepared N-doped TiO2@C catalyst exhibited a preserved cage structure even after calcination, thereby alleviating the optical shielding effect and further augmenting its photocatalytic performance by increasing the reaction sites between the catalyst and pollutants. The calcination time of the N-doped TiO2@C-450 °C catalyst was optimized to achieve a balance between the TiO2 content and nitrogen doping level, ensuring efficient degradation rates for basic fuchsin (99.7%), Rhodamine B (89.9%) and tetracycline hydrochloride (93%) within 90 min. Thus, this study presents a feasible strategy for the efficient degradation of pollutants under visible light.

Selected strategies to fight pathogenic bacteria

Natural products and analogues are a source of antibacterial drug discovery. Considering drug resistance levels emerging for antibiotics, identification of bacterial metalloenzymes and the synthesis of selective inhibitors are interesting for antibacterial agent development. Peptide nucleic acids are attractive antisense and antigene agents representing a novel strategy to target pathogens due to their unique mechanism of action. Antisense inhibition and development of antisense peptide nucleic acids is a new approach to antibacterial agents. Due to the increased resistance of biofilms to antibiotics, alternative therapeutic options are necessary. To develop antimicrobial strategies, optimised in vitro and in vivo models are needed. In vivo models to study biofilm-related respiratory infections, device-related infections: ventilator-associated pneumonia, tissue-related infections: chronic infection models based on alginate or agar beads, methods to battle biofilm-related infections are discussed. Drug delivery in case of antibacterials often is a serious issue therefore this review includes overview of drug delivery nanosystems.

Kirigami Photopiezo Catalysts for Self-Sustainable Environment Remediation

Photo(electro)-piezo catalysis has emerged as one of the most effective strategies for sustainable environmental remediation. While various (nano)materials have been investigated for enhancing the intrinsic properties related to the interfacial band structure, increasing the efficiency by integration of materials with rational design for stress-strain applications has not yet been considered. Herein, we introduce kirigami strain engineering to photopiezo catalysts for enhancing efficiency by increasing the magnitude of applied strain and density of bends. Macroscale stretching motion is converted into localized bending by a pliable kirigami structure using similar or even lower input energy, which can be easily modulated by natural waves. The kirigami structure leads to a significant enhancement (∼250%) in the degradation of dyes, and we discovered the significant contribution of the oxygen reduction pathway in the charge-transfer mechanism, which corresponds to the observed enhancement. The photopiezo catalytic effects of kirigami were further highlighted by the small water reservoir test, showing its feasibility in nature for self-sustainable environmental remediation that can be modulated using motions of winds, waves, and life vibrations.

Role of Microbial Interactions across Food-Related Bacteria on Biofilm Population and Biofilm Decontamination by a TiO2-Nanoparticle-Based Surfactant

Microbial interactions play an important role in initial cell adhesion and the endurance of biofilm toward disinfectant stresses. The present study aimed to evaluate the effect of microbial interactions on biofilm formation and the disinfecting activity of an innovative photocatalytic surfactant based on TiO₂ nanoparticles. Listeria monocytogenes, Salmonella Enteritidis, Escherichia coli, Leuconostoc spp., Latilactobacillus sakei, Serratia liquefaciens, Serratia proteomaculans, Citrobacter freundii, Hafnia alvei, Proteus vulgaris, Pseudomonas fragi, and Brochothrix thermosphacta left to form mono- or dual-species biofilms on stainless steel (SS) coupons. The effectiveness of the photocatalytic disinfectant after 2 h of exposure under UV light on biofilm decontamination was evaluated. The effect of one parameter i.e., exposure to UV or disinfectant, was also determined. According to the obtained results, the microbial load of a mature biofilm depended on the different species or dual species that had adhered to the surface, while the presence of other species could affect the biofilm population of a specific microbe (p < 0.05). The disinfectant strengthened the antimicrobial activity of UV, as, in most cases, the remaining biofilm population was below the detection limit of the method. Moreover, the presence of more than one species affected the resistance of the biofilm cells to UV and the disinfectant (p < 0.05). In conclusion, this study confirms that microbial interactions affected biofilm formation and decontamination, and it demonstrates the effectiveness of the surfactant with the photocatalytic TiO₂ agent, suggesting that it could be an alternative agent with which to disinfect contaminated surfaces.

Antimicrobial effects of nano titanium dioxide and disinfectants on maxillofacial silicones

STATEMENT OF PROBLEM

Deficient hygiene of maxillofacial prostheses can be a source of infection, and various disinfectants, including nano-oxides, have been suggested for the disinfection of silicone prostheses. While maxillofacial silicones involving nano-oxides at different sizes and concentrations have been evaluated in terms of their mechanical and physical properties, reports are lacking on the antimicrobial effect of nano titanium dioxide (TiO₂) incorporated into maxillofacial silicones contaminated by different biofilms.

PURPOSE

The purpose of this in vitro study was to evaluate the antimicrobial effects of 6 different disinfectants and nano TiO₂ incorporation into maxillofacial silicone contaminated with Staphylococcus aureus, Escherichia coli, and Candida albicans biofilms.

MATERIAL AND METHODS

A total of 258 silicone specimens (129 pure silicones and 129 nano TiO₂-incorporated silicones) were fabricated. Specimens in each silicone group (with or without nano TiO₂) were divided into 7 disinfectant groups (control, 0.2% chlorhexidine gluconate, 4% chlorhexidine gluconate, 1% sodium hypochlorite, neutral soap, 100% white vinegar, and effervescent) in each biofilm group. Contaminated specimens were disinfected, and the suspension of each specimen was incubated at 37 °C for 24 hours. Proliferated colonies were recorded in colony-forming units per mL (CFU/mL). The differences in microbial levels among specimens were evaluated to test the effect of the type of silicone and the disinfectant (α=.05).

RESULTS

Significant difference was found among disinfectants regardless of the silicone type (P<.05). Nano TiO₂ incorporation showed an antimicrobial effect on S aureus, E coli, and C albicans biofilms. Nano TiO₂ incorporated silicone cleaned with 4% chlorhexidine gluconate had statistically less C albicans than pure silicone. Using white vinegar or 4% chlorhexidine gluconate led to no E coli on either silicone. Nano TiO₂ incorporated silicone cleaned with effervescent had fewer S aureus or C albicans biofilms.

CONCLUSIONS

The tested disinfectants and nano TiO₂ incorporation into silicone were effective against most of the microorganisms used in this study.

A Review on Nano Ti-Based Oxides for Dark and Photocatalysis: From Photoinduced Processes to Bioimplant Applications

Catalysis on TiO₂ nanomaterials in the presence of H₂O and oxygen plays a crucial role in the advancement of many different fields, such as clean energy technologies, catalysis, disinfection, and bioimplants. Photocatalysis on TiO₂ nanomaterials is well-established and has advanced in the last decades in terms of the understanding of its underlying principles and improvement of its efficiency. Meanwhile, the increasing complexity of modern scientific challenges in disinfection and bioimplants requires a profound mechanistic understanding of both residual and dark catalysis. Here, an overview of the progress made in TiO₂ catalysis is given both in the presence and absence of light. It begins with the mechanisms involving reactive oxygen species (ROS) in TiO₂ photocatalysis. This is followed by improvements in their photocatalytic efficiency due to their nanomorphology and states by enhancing charge separation and increasing light harvesting. A subsection on black TiO₂ nanomaterials and their interesting properties and physics is also included. Progress in residual catalysis and dark catalysis on TiO₂ are then presented. Safety, microbicidal effect, and studies on Ti-oxides for bioimplants are also presented. Finally, conclusions and future perspectives in light of disinfection and bioimplant application are given.

A mace-like heterostructural enriched injectable hydrogel composite for on-demand promotion of diabetic wound healing

Wound healing is a multifaceted process that involves hemostasis, inflammation, proliferation, and remodeling stages. Diabetic wounds affect the transition of the organized phases and result in delayed healing due to impaired angiogenesis, chronic inflammation, bacterial infection, and insufficient growth factors. Multifunctional heterostructural nanoparticles enriched minimally invasive hydrogels for on-demand procedural distribution to aid wound healing at various stages has become a promising strategy. Herein, silk fibroin-hyaluronic acid based injectable hydrogels incorporated with mace-like Au-CuS heterostructural nanoparticles (gAu-CuS HSs) were used to cure diabetic wounds. SF-HA and the rough surface of gAu-CuS HSs confer a synergistic hemostatic phase with a nano-bridge effect and rapidly close the wounds. During the inflammation stage, gAu-CuS HSs perform in-space resonance energy transfer under 808 nm laser irradiation which in return produces reactive oxygen species for bacterial destruction. The unusual mace-like rough structure of nanoparticles causes macrophage transfer to the M2 phenotype, regulates cytokine expression (interleukin 6, transforming factor-β1, interferon γ, and interleukin-10), promotes angiogenesis, and promotes cell multiplication and fibroblast emigration to the wound area during the proliferation and remodeling phase. Overall, the gAu-CuS HSs reinforced injectable hydrogel programmatically accelerates wound healing and could represent a versatile strategy for advanced diabetic wound healing.

An overview of nanomaterial-based novel disinfection technologies for harmful microorganisms: Mechanism, synthesis, devices and application

Harmful microorganism (e.g., new coronavirus) based infection is the most important security concern in life sciences and healthcare. This article aims to provide a state-of-the-art review on the development of advanced technology based on nanomaterial disinfection/sterilization techniques (NDST) for the first time including the nanomaterial types, disinfection techniques, bactericidal devices, sterilization products, and application scenarios (i.e., water, air, medical healthcare), with particular brief account of bactericidal behaviors referring to varied systems. In this emerging research area spanning the years from 1998 to 2021, total of ~200 publications selected for the type of review paper and research articles were reviewed. Four typical functional materials (namely type of metal/metal oxides, S-based, C-based, and N-based) with their development progresses in disinfection/sterilization are summarized with a list of synthesis and design. Among them, the widely used silver nanoparticles (AgNPs) are considered as the most effective bacterial agents in the type of nanomaterials at present and has been reported for inactivation of viruses, fungi, protozoa. Some methodologies against (1) disinfection by-products (DBPs) in traditional sterilization, (2) noble metal nanoparticles (NPs) agglomeration and release, (3) toxic metal leaching, (4) solar spectral response broadening, and (5) photogenerated e^-/h⁺ pairs recombination are reviewed and discussed in this field, namely (1) alternative techniques and nanomaterials, (2) supporter anchoring effect, (3) nonmetal functional nanomaterials, (4) element doping, and (5) heterojunction constructing. The feasible strategies in the perspective of NDST are proposed to involve (1) non-noble metal disinfectors, (2) multi-functional nanomaterials, (3) multi-component nanocomposite innovation, and (4) hybrid techniques for disinfection/sterilization system. It is promising to achieve 100% bactericidal efficiency for 10⁸ CFU/mL within a short time of less than 30 min.

Fighting Antibiotic-Resistant Bacterial Infections by Surface Biofunctionalization of 3D-Printed Porous Titanium Implants with Reduced Graphene Oxide and Silver Nanoparticles

Nanoparticles (NPs) have high multifunctional potential to simultaneously enhance implant osseointegration and prevent infections caused by antibiotic-resistant bacteria. Here, we present the first report on using plasma electrolytic oxidation (PEO) to incorporate different combinations of reduced graphene oxide (rGO) and silver (Ag) NPs on additively manufactured geometrically ordered volume-porous titanium implants. The rGO nanosheets were mainly embedded parallel with the PEO surfaces. However, the formation of ‘nano-knife’ structures (particles embedded perpendicularly to the implant surfaces) was also found around the pores of the PEO layers. Enhanced in vitro antibacterial activity against methicillin-resistant Staphylococcus aureus was observed for the rGO+Ag-containing surfaces compared to the PEO surfaces prepared only with AgNPs. This was caused by a significant improvement in the generation of reactive oxygen species, higher levels of Ag+ release, and the presence of rGO ‘nano-knife’ structures. In addition, the implants developed in this study stimulated the metabolic activity and osteogenic differentiation of MC3T3-E1 preosteoblast cells compared to the PEO surfaces without nanoparticles. Therefore, the PEO titanium surfaces incorporating controlled levels of rGO+Ag nanoparticles have high clinical potential as multifunctional surfaces for 3D-printed orthopaedic implants.

Antimicrobial effect of radiant catalytic ionization

The main purpose of micro-organisms elimination from the air and surfaces is to ensure microbiological safety in health care facilities or food production plants. Currently, many disinfection methods are used, both physical, chemical and, increasingly, biological. Scientists seek new solutions with high antimicrobial effectiveness (especially against the drug-resistant strains of bacteria), low production and operating costs, and, above all, the safety of patients and food consumers. The limitation of the methods used so far is primarily the micro-organisms acquire the resistance, mainly to antimicrobial agents. One of the new and alternative methods of disinfection is radiant catalytic ionization (RCI). RCI is an active method of air and surface purification. The technology proved high efficiency against viruses, Gram-positive and -negative bacteria, and fungi, both in the air and on surfaces (planktonic forms and biofilm). RCI has many advantages as well as some minor limitations. This overview summarizes the current knowledge about RCI technology.

A novel strategy of nanosized herbal Plectranthus amboinicus, Phyllanthus niruri and Euphorbia hirta treated TiO2 nanoparticles for antibacterial and anticancer activities

Titanium dioxide nanoparticles exhibit good anticancer and antibacterial activities. They are known to be environmentally friendly, stable, less toxic, and have excellent biocompatibility nature. Due to these properties, they are well suited for biological applications particularly in biomedical applications such as drug delivery and cancer therapy. In this research article, three medicinal herbs namely, Plectranthus amboinicus (Karpooravalli), Phyllanthus niruri (Keezhanelli), and Euphorbia hirta (Amman Pacharisi), were used to modify the surface of the TiO₂ nanoparticles. The synthesized nanoparticles were subjected to various characterization techniques. The samples are then subjected to MTT assay to determine cell viability. KB oral cancer cells are used for the determination of the anticancer nature of the pure and bio modified nanoparticles. It is observed that Plectranthus amboinicus-Phyllanthus niruri modified TiO₂ nanoparticles exhibit excellent anticancer activities among other bio modified and pure samples. The samples are then examined for antibacterial activities against three Gram-negative bacterial strains namely, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and two Gram-positive bacterial strains namely, Staphylococcus aureus and Streptococcus mutans, respectively. Among the modified and pure samples, Plectranthus amboinicus showed good antibacterial activity against Gram-positive and Gram-negative bacteria. In the Flow cytometry analysis, the generation of p53 protein expression from Plectranthus amboinicus-Phyllanthus niruri modified TiO₂ nano herbal particles shows the anti-cancerous nature of the sample. Then to determine the toxic nature of the Plectranthus amboinicus-Phyllanthus niruri modified TiO₂ nano herbal particles against normal cells, the NPs were subjected to MTT assay against normal L929 cells, and it was found to be safer and less toxic towards the normal cells.

Bismuth-Graphene Nanohybrids: Synthesis, Reaction Mechanisms, and Photocatalytic Applications—A Review

Photocatalysis is a classical solution to energy conversion and environmental pollution control problems. In photocatalysis, the development and exploration of new visible light catalysts and their synthesis and modification strategies are crucial. It is also essential to understand the mechanism of these reactions in the various reaction media. Recently, bismuth and graphene’s unique geometrical and electronic properties have attracted considerable attention in photocatalysis. This review summarizes bismuth-graphene nanohybrids’ synthetic processes with various design considerations, fundamental mechanisms of action, heterogeneous photocatalysis, benefits, and challenges. Some key applications in energy conversion and environmental pollution control are discussed, such as CO2 reduction, water splitting, pollutant degradation, disinfection, and organic transformations. The detailed perspective of bismuth-graphene nanohybrids’ applications in various research fields presented herein should be of equal interest to academic and industrial scientists.

Topographical nanostructures for physical sterilization

The development in nanobiotechnology provides an in-depth understanding of cell-surface interactions at the nanoscale level. Particularly, several surface features have shown the ability to interrogate the bacterial behavior and fate. In the past decade, the mechanical and physical sterilization has attracted considerable attention, as paradigms of such do not rely on chemical substances to damage or kill bacteria, whereas it is associated with natural living organisms or synthetic materials. Of note, such antibacterial scenario does not cause bacterial resistance, as the morphology of nanometer can directly cause bacterial death through physical and mechanical interactions. In this review, we provide an overview of recently developed technologies of leveraging topographical nanofeatures for physical sterilization. We mainly discuss the development of various morphologic nanostructures, and colloidal nanostructures show casing the capacity of "mechanical sterilization." Mechanically sterilized nanostructures can penetrate or cut through bacterial membranes. In addition, surface morphology, such as mechanical bactericidal nanoparticles and nanoneedles, can cause damage to the membrane of microorganisms, leading to cell lysis and death. Although the research in the field of mechanical sterilization is still in infancy, the effect of these nanostructure morphologies on sterilization has shown remarkable antibacterial potential, which could provide a new toolkit for anti-infection and antifouling applications. The mechanical and physical sterilization has attracted considerable attention, as paradigms of such do not rely on chemical substances to damage or kill bacteria. Moreover, such antibacterial scenario does not cause bacterial resistance, as the morphology of nanometer can directly cause bacterial death through physical and mechanical interactions. In this review, we focus on the advanced development of various morphologic nanostructures and colloidal nanostructures that show the capacity of "mechanical sterilization."

Eco-Friendly Preparation of Epoxy-Rich Graphene Oxide for Wound Healing

Despite the ever-growing endangerment caused by the multidrug resistance (MDR) of bacteria, the development of effective antibacterial materials still remains a global challenge. Current antibiotic therapies cannot simultaneously inactivate bacteria and accelerate wound healing. This study aimed to originally separate the intercalation of MnO₃⁺ and the oxidation processes to synthesize epoxy-rich graphene oxide (erGO) nanofilms via an eco-friendly synthetic route, which possessed low density and large lamellar distribution and was rich in epoxide. Importantly, the MnO₃⁺ could be separated from the product and recycled for preparing the next generation of erGO nanofilms, which was quite economical and eco-friendly. The erGO nanofilm was capable of successfully inhibiting Gram-negative bacteria and even had excellent growth-inhibitory effects on Gram-positive bacteria including multidrug resistance (MDR) bacteria, as evidenced by antibacterial phenomena. Additionally, the erGO nanofilm with high ^•C density formed from epoxide exerted excellent antibacterial effects through tight membrane wrapping and induction of lipid peroxidation. The wound-healing property of the erGO nanofilm was evaluated via treatments of wounds infected by Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli), which not only killed bacteria but also accelerated wound healing in mice with a skin infection. The novel erGO nanofilm with dual antimicrobial mechanisms might serve as a promising multifunctional antimicrobial agent for medical wound dressing with high biocompatibility.

Bactericidal Activity of TiO2 Nanotube Thin Films on Si by Photocatalytic Generation of Active Oxygen Species

The photocatalytic bactericidal activity of titanium dioxide (TiO₂) thin films has been extensively studied. In this study, we investigated the bactericidal activities of TiO₂ nanotube (NT) thin films using Escherichia coli and Staphylococcus aureus cells as the model bacteria. Metallic titanium (Ti) thin films were anodized on a silicon (Si) wafer substrate to form TiO₂ NT thin films. To evaluate the bactericidal activity of the TiO₂ NT thin films, bacteria on the TiO₂ NT thin films were irradiated with near-ultraviolet light (UV-A) at a wavelength of 365 nm. The bactericidal activity was estimated by the survival rate derived from the number of live cells, which form colonies on the cell culture medium. We demonstrated that the survival rate of the two types of bacteria investigated in this study was significantly reduced by UV light irradiation and that there was a difference in the temporal change in the survival rate between the two types of bacteria. Furthermore, we investigated the generation of reactive oxygen species (ROSs) by UV light irradiation of TiO₂ NT thin films using electron spin resonance spectroscopy and fluorescence analysis. We found that the main ROS generated on the surface of the TiO₂ NT film was the hydroxyl radical, OH^•. In addition, the generation of ROSs increased with an increase in the UV irradiation time. We proposed a kinetic model that reproduces the dependence of bacterial viability on the UV light irradiation time by considering the temporal change in the amount of ROSs generated by UV light irradiation. A comparison of the calculated and experimental results revealed that the bactericidal effect consisted of the direct photolysis of bacteria and the photocatalysis via the generation of hydroxyl radicals, with the latter exhibiting a stronger bactericidal effect than the former.

One-Step and One-Precursor Hydrothermal Synthesis of Carbon Dots with Superior Antibacterial Activity

Discovering efficient antibacterial materials is crucial in the area of increasing drug resistance. Herein, we synthesized carbon dots (C-dots) with superior antibacterial activity through a simple one-step hydrothermal method. In this method, p-phenylenediamine serves as not only the carbon source but also the origin for the functional group anchored on the obtained C-dots. The antibacterial activity of the obtained C-dots was tested against Staphylococcus aureus and Escherichia coli. The minimum bactericidal concentrations of the synthesized C-dots against S. aureus and E. coli were 2 and 30 μg/mL, respectively, which are lower than that of previously reported C-dots. The antibacterial mechanism was investigated, and the results indicated that a large number of -NH₃⁺ groups on the C-dots' surface enhanced their antibacterial activity. Besides, the C-dots exhibited negligible cytotoxicity.

Vis-Responsive Copper-Modified Titania for Decomposition of Organic Compounds and Microorganisms

Seven commercial titania (titanium(IV) oxide; TiO2) powders with different structural properties and crystalline compositions (anatase/rutile) were modified with copper by two variants of a photodeposition method, i.e., methanol dehydrogenation and water oxidation. The samples were characterized by diffuse reflectance spectroscopy (DRS), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Although zero-valent copper was deposited on the surface of titania, oxidized forms of copper, post-formed in ambient conditions, were also detected in dried samples. All samples could absorb visible light (vis), due to localized surface plasmon resonance (LSPR) of zero-valent copper and by other copper species, including Cu2O, CuO and CuxO (x:1-2). The photocatalytic activities of samples were investigated under both ultraviolet (UV) and visible light irradiation (>450 nm) for oxidative decomposition of acetic acid. It was found that titania modification with copper significantly enhanced the photocatalytic activity, especially for anatase samples. The prolonged irradiation (from 1 to 5 h) during samples’ preparation resulted in aggregation of copper deposits, thus being detrimental for vis activity. It is proposed that oxidized forms of copper are more active under vis irradiation than plasmonic one. Antimicrobial properties against bacteria (Escherichia coli) and fungi (Aspergillus niger) under vis irradiation and in the dark confirmed that Cu/TiO2 exhibits a high antibacterial effect, mainly due to the intrinsic activity of copper species.

Metal Oxide Nanoparticles Against Bacterial Biofilms: Perspectives and Limitations

At present, there is an urgent need in medicine and industry to develop new approaches to eliminate bacterial biofilms. Considering the low efficiency of classical approaches to biofilm eradication and the growing problem of antibiotic resistance, the introduction of nanomaterials may be a promising solution. Outstanding antimicrobial properties have been demonstrated by nanoparticles (NPs) of metal oxides and their nanocomposites. The review presents a comparative analysis of antibiofilm properties of various metal oxide NPs (primarily, CuO, Fe3O4, TiO2, ZnO, MgO, and Al2O3 NPs) and nanocomposites, as well as mechanisms of their effect on plankton bacteria cells and biofilms. The potential mutagenicity of metal oxide NPs and safety problems of their wide application are also discussed.

Role of Nanofluids in Drug Delivery and Biomedical Technology: Methods and Applications

Recently, suspensions of several nanoparticles or nanocomposites have attained a vast field of application in biomedical research works in some specified conditions and clinical trials. These valuable suspensions, which allow the nanoparticles to disperse and act in homogenous and stable media, are named as nanofluids. Several studies have introduced the advantages of nanofluids in biomedical approaches in different fields. Few review articles have been reported for presenting an overview of the wide biomedical applications of nanofluids, such as diagnosis and therapy. The review is focused on nanosuspensions, as the nanofluids with solid particles. Major applications are focused on nanosuspension, which is the main type of nanofluids. So, concise content about major biomedical applications of nanofluids in drug delivery systems, imaging, and antibacterial activities is presented in this paper. For example, applying magnetic nanofluid systems is an important route for targeted drug delivery, hyperthermia, and differential diagnosis. Also, nanofluids could be used as a potential antibacterial agent to overcome antibiotic resistance. This study could be useful for presenting the novel and applicable methods for success in current medical practice.

TiO2 Nanoparticles and Commensal Bacteria Alter Mucus Layer Thickness and Composition in a Gastrointestinal Tract Model

Nanoparticles (NPs) are used in food packaging and processing and have become an integral part of many commonly ingested products. There are few studies that have focused on the interaction between ingested NPs, gut function, the mucus layer, and the gut microbiota. In this work, an in vitro model of gastrointestinal (GI) tract is used to determine whether, and how, the mucus layer is affected by the presence of Gram-positive, commensal Lactobacillus rhamnosus; Gram-negative, opportunistic Escherichia coli; and/or exposure to physiologically relevant doses of pristine or digested TiO2 NPs. Caco-2/HT29-MTX-E12 cell monolayers are exposed to physiological concentrations of bacteria (expressing fluorescent proteins) and/or TiO2 nanoparticles for a period of 4 h. To determine mucus thickness and composition, cell monolayers are stained with alcian blue, periodic acid schiff, or an Alexa Fluor 488 conjugate of wheat germ agglutinin. It is found that the presence of both bacteria and nanoparticles alter the thickness and composition of the mucus layer. Changes in the distribution or pattern of mucins can be indicative of pathological conditions, and this model provides a platform for understanding how bacteria and/or NPs may interact with and alter the mucus layer.

Structural, luminescent and antimicrobial properties of ZnS and CdSe/ZnS quantum dot structures originated by precursors

ZnS quantum dots (QDs) and their core/shell (CdSe/ZnS) structures were studied for Zn based precursor reactivities. ZnS and CdSe/ZnS QDs were prepared selecting aqueous route and then characterized via XRD, TEM, EDX, PL, RAMAN and FTIR practices. Core/shell nanostructures were synthesized by taking dissimilar precursors for the shell formation. Photoluminescence spectra of prepared QDs corroborate the effectual luminescence. Prepared QDs have large surface area that make them useful alternative as organic antimicrobial agent which are highly irritant and unstable. Study of antimicrobial behavior of QD structures was carried out by disk diffusion method. Antimicrobial study of QDs and their core/shell structures was performed against gram negative and gram positive bacteria, E. coli, A. baumanni and Bacillus subtilis respectively. It is found that elemental composition and size of QDs plays important role in antimicrobial behavior. Prepared QDs are fluorescent and have a key role in complex microbial population studies and identification of bacteria.

Nanomaterials for removal of waterborne pathogens

As the nanotechnological applications have taken over in different fields, their applications for water and wastewater treatment is also surfacing as a fast-developing and very promising area. Recent advancements in nanotechnological science and engineering advise that many of the waterborne pathogens could be culminated or debilitated using nanobiosorbents, nanocatalysts, bioactive nanoparticles, nanostructured catalytic membranes, nanobioreactors, nanoparticle-enhanced filtration among other products, and processes resulting from the development of nanotechnology. A detailed insight has been provided for advanced techniques such as photochemical (photocatalytic and advanced oxidation processes) applications of metal oxide nanoparticles, nanomembrane technology, bioinspired nanomaterials, and nanotechnological innovations (nano-Ag, fullerenes, nanotubes, and molecularly imprinted polymers, etc.), which prove to be highly potential as well as promising and cost-effective. However, there are still some shortcomings and challenges that must be overcome which will be looked upon in this chapter.

Bio-modified TiO2 nanoparticles with Withania somnifera, Eclipta prostrata and Glycyrrhiza glabra for anticancer and antibacterial applications

Titanium dioxide nanoparticles exhibit good anticancer and antibacterial activities. They are known to be environmentally friendly and stable, less toxic and excellent biocompatibility nature. In this paper we report the biological properties of pure TiO₂ nanoparticles modified with Withania somnifera (Ashwagandha), Eclipta prostrata (Karisalankanni) and Glycyrrhiza glabra (Athimathuram) for biological applications. X-ray diffraction results revealed the anatase nature of the samples. From the TEM analyses, it is observed that there is an increase in the particle size of the bio modified samples. UV results show the red shift for the bio modified samples when compared with the pure samples. The samples are then subjected to MTT assay to determine the cell viability. KB oral cancer cells are used for the determination of anticancer nature of the pure and bio modified nanoparticles. It is observed that Withania somnifera - Eclipta prostrate modified TiO₂ nanoparticles exhibit excellent anticancer activities among other bio modified and pure samples. The samples are then examined for their antibacterial activities against three Gram-negative bacterial strains namely, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa and two Gram-positive bacterial strains namely, Staphylococcus aureus and Streptococcus mutans. Among the modified and pure samples, Withania somnifera - Eclipta prostrata showed good antibacterial nature against Gram-positive and Gram-negative bacteria.

Decontamination of ubiquitous harmful microbial lineages in water using an innovative Zn2Ti0.8Fe0.2O4 nanostructure: dielectric and terahertz properties

Many ubiquitous dangerous microbial lines could originate in different sources of polluted water and be distributed to tap water, which could cause multiple types of illnesses to humans and livestock. Despite enormous attempts to guarantee safety of potable water, these species are still regarded to be threated prevalent health issues and concerns. However, these species need a powerful disinfectant to be removed from contaminated water for receiving clean and healthy water. This study was therefore conducted to produce magnificent magnetic iron titanate zinc nano-particles (Zn₂Ti_0.8Fe_0.2O₄ MNPs) as a sophisticated approach for drinking water (DW) and wastewater purification. The identification of crystalline phase, dielectric and terahertz spectroscopy of iron zinc titanate nanostructure prepared via acidic sol-gel process and calcined at 800 °C. Results show that the formation of cubic structure for Zn₂TiO₄ phase, and the dielectric constant (ε') decreased with the higher frequency, tan (δ) has higher values at lower frequency and the conductivity increases relatively with frequency that attributes to the high resistive grain boundaries. Absorption coefficient, refractive index and dielectric properties of iron zinc titanate nano-particles was estimated via time domain-terahertz spectrometer and adjusted via the applied electric field. In particular, the Gram-negative bacteria were more prone than other microbes tested to the Magnetic Nano-Particles (MNPs). Results also was ascertained that the minimum inhibitory concentration (MIC) was 25 ppm at 30 min for E. coli and Salmonella enterica, 45 min for Listeria monocyteogens, Staphylococcus aureus, and Candida albicans and 60 min for Aspergillus niger with a noticeable bactericidal impact. Results exhibit that the MNPs explored are non-toxic and protected for individuals and the environment. MNPs can, therefore, be proposed as an expedient and impressive nano-scale applicant for inactivation during the drinking water and wastewater conservation of the prevailing dangerous microbes.

Hollow, Rough, and Nitric Oxide-Releasing Cerium Oxide Nanoparticles for Promoting Multiple Stages of Wound Healing

Wound healing is a complex and sequential biological process that involves multiple stages. Although various nanomaterials are applied to accelerate the wound healing process, only a single stage is promoted during the process, lacking hierarchical stimulation. Herein, hollow CeO₂ nanoparticles (NPs) with rough surface and l-arginine inside (_Ah CeO₂ NPs) are developed as a compact and programmable nanosystem for sequentially promoting the hemostasis, inflammation, and proliferation stages. The rough surface of _Ah CeO₂ NPs works as a nanobridge to rapidly closure the wounds, promoting the hemostasis stage. The hollow structure of _Ah CeO₂ NPs enables the multireflection of light inside particles, significantly enhancing the light harvest efficiency and electron-hole pair abundance. Simultaneously, the porous shell of _Ah CeO₂ NPs facilitates the electron-hole separation and reactive oxygen species production, preventing wound infection and promotion wound healing during the inflammation stage. The enzyme mimicking property of _Ah CeO₂ NPs can alleviate the oxidative injury in the wound, and the released l-arginine can be converted into nitric oxide (NO) under the catalysis of inducible NO synthase, both of which promote the proliferation stage. A series of in vitro and in vitro biological assessments corroborate the effectiveness of _Ah CeO₂ NPs in the wound healing process.

Antibacterial Properties of Graphene-Based Nanomaterials

Bacteria mediated infections may cause various acute or chronic illnesses and antibiotic resistance in pathogenic bacteria has become a serious health problem around the world due to their excessive use or misuse. Replacement of existing antibacterial agents with a novel and efficient alternative is the immediate demand to alleviate this problem. Graphene-based materials have been exquisitely studied because of their remarkable bactericidal activity on a wide range of bacteria. Graphene-based materials provide advantages of easy preparation, renewable, unique catalytic properties, and exceptional physical properties such as a large specific surface area and mechanical strength. However, several queries related to the mechanism of action, significance of size and composition toward bacterial activity, toxicity criteria, and other issues are needed to be addressed. This review summarizes the recent efforts that have been made so far toward the development of graphene-based antibacterial materials to face current challenges to combat against the bacterial targets. This review describes the inherent antibacterial activity of graphene-family and recent advances that have been made on graphene-based antibacterial materials covering the functionalization with silver nanoparticles, other metal ions/oxides nanoparticles, polymers, antibiotics, and enzymes along with their multicomponent functionalization. Furthermore, the review describes the biosafety of the graphene-based antibacterial materials. It is hoped that this review will provide valuable current insight and excite new ideas for the further development of safe and efficient graphene-based antibacterial materials.

Effect of dissolved silica on photocatalytic water purification with a TiO2 ceramic catalyst

If photocatalytic water purification technologies will find practical applications, the impact of total dissolved solids in the source water on the activity of the photocatalyst must be evaluated. In this study, we evaluated the effects of SiO₃^2- in water on a TiO₂ ceramic photocatalyst; specifically, we determined the effects of SiO₃^2- on the rate of photocatalytic degradation of formic acid (as a model contaminant) and on the rate of photocatalytic inactivation of Escherichia coli in an aqueous solution. Both the rate of formic acid degradation and the sterilization rate decreased with increasing SiO₃^2- concentration. On the other hand, at a given SiO₃^2- concentration, the activity of the photocatalyst did not decrease over the course of 120 h, and the surface structure of the photocatalyst did not change (i.e., no precipitate formed on the surface). The decreases in photocatalytic activity due to the presence of SiO₃^2- could be recovered by flushing the experimental apparatus with distilled water. These results show that the reason for the lower photocatalytic activity in the presence of SiO₃^2- than in its absence was due to adsorption of SiO₃^2- onto the surface of the TiO₂ photocatalyst and that SiO₃^2- adsorption was an equilibrium process in water.

Research progress of photocatalytic sterilization over semiconductors

With increasingly serious environmental issues, practical applications of semiconductor photocatalysts for environmental purification have attracted broad attention. Semiconductor photocatalysts for the disinfection of soil surfaces, air and water are of great interest.

Heterostructured d-Ti3 C2 /TiO2/ g-C3 N4 Nanocomposites with Enhanced Visible-Light Photocatalytic Hydrogen Production Activity

The construction of a 2D-2D heterostructured composite is an efficient method to improve the photocatalytic hydrogen generation capability under visible light. In this work, simple heat treatment of a mixture of g-C₃ N₄ and delaminated Ti₃ C₂ was used to prepare a series of d-Ti₃ C₂ /TiO₂ /g-C₃ N₄ nanocomposites. The d-Ti₃ C₂ not only acted as the support layer and resource to glue the anatase TiO₂ particles and g-C₃ N₄ layers together but also served as the fast electron transfer channel to improve the photogenerated charge carriers' separation efficiency. By tuning the g-C₃ N₄ /d-Ti₃ C₂ mass ratio, heating temperature and soaking time, the d-Ti₃ C₂ /TiO₂ /g-C₃ N₄ nanocomposite 4-1-350-1 achieved an excellent H₂ evolution rate of 1.62 mmol h^-1  g^-1 driven by a 300 W Xe lamp with a 420 nm cutoff filter. The heterostructured composite photocatalyst was stable even after 3 cycles, representing excellent potential for the practical application in solar energy conversion.

Nanocomposites: suitable alternatives as antimicrobial agents

The exploration of nanocomposites has gained a strong research following over the last decade. These materials have been heavily exploited in several fields, with applications ranging from biosensors to biomedicine. Among these applications, great advances have been made in the field of microbiology, specifically as antimicrobial agents. This review aims to provide a comprehensive account of various nanocomposites that elucidate promising antimicrobial activity. The composition, physical and chemical properties, as well as the antimicrobial performance of these nanocomposites, are discussed in detail.

Antiviral activity of multifunctional composite based on TiO2-modified hydroxyapatite

An antiviral activity of TiO₂-modified hydroxyapatite composite (HA/TiO₂) had been investigated. The HA/TiO₂ composite (HA50:Ti50) was prepared by a solid state reaction method followed by calcination at 650 °C for 2 h. Phase formations and morphologies of the obtained HA/TiO₂ composite powders were determined using XRD and SEM. XRD result confirmed that HA/TiO₂ composite was successfully prepared. SEM revealed small crystals of anatase TiO₂ embedded in larger HA crystals. A strong antiviral activity against H1N1 Influenza A Virus was observed at 0.5 mg/ml concentration of the composite under the UV irradiation for 60 min. It showed the highest rate of reducing virus titer approximately more than 2 log/h. Results obtained from this study indicated that HA/TiO₂ composite could be a promising material to be used as antimicrobial filtration applications such as in face masks.

Evaluation of antibacterial activity and toxic metal removal of chemically synthesized magnetic iron oxide titanium coated nanoparticles and application in bacterial treatment

Co-precipitation method was used for preparation of two types of iron oxide nanoparticles coated by titanium dioxide according to divalent salts used. The average size of iron oxide nanoparticles coated by titanium dioxide measured by particle size analyzer, ranged approximately between 20 nm and 100 nm with mean particle size of 60 nm. Characterization of the prepared nanoparticles was done by X-ray diffraction analysis and scanning electron microscope indicating the sole existence of inverse cubic spinel phase of magnetic iron oxide nanoparticles. Further, the antibacterial activity of two prepared iron oxide nanoparticles was evaluated against four pathogenic bacteria where both preparations showed promising antibacterial activities against Gram positive and Gram negative strains which offers a potential application in pharmaceutical and biomedical industries. The antibacterial activity showed high reduction percent after 30 min by 150 μg mL^-1 of nanoparticles prepared. Also, high reduction percent was achieved for removal of iron and manganese ions from polluted water and good effect on decreasing chemical oxygen demand and biochemical oxygen demand concentrations with decreased percent of total nitrogen concentration.

Synthesis of multifunctional activated carbon nanocomposite comprising biocompatible flake nano hydroxyapatite and natural turmeric extract for the removal of bacteria and lead ions from aqueous solution

Clean water, which is free from pathogens and toxic chemicals, is vital to human health. The blue planet is encountering remarkable challenges in meeting the ever-increasing demands of clean water. The intention of this research study was to develop a water filter material that is capable of removing bacterial contaminants and heavy metals from fresh water using cost effective and easily fabricated biocompatible filter material. For this purpose, granular activated carbon (GAC) was coated with both hydroxyapatite (HAP) nanoflakes and turmeric extract (TE) (HAP/TE/GAC) which had been extracted from natural turmeric powder. In addition, GAC was coated only with HAP nanoflakes to synthesize HAP coated GAC (HAP/GAC) composite. Prepared HAP/GAC and HAP/TE/GAC were characterized using Fourier-transform infrared spectroscopy, X-ray diffractometry, scanning electron microscopy and UV–visible spectrophotometry. Antibacterial effect of the prepared nanocomposites, HAP/GAC and HAP/TE/GAC was compared with neat GAC using Gram-negative bacteria Escherichia coli. Results showed that antibacterial studies of the synthesized nanocomposites exhibit effective antibacterial activity against E. coli compared with neat GAC alone. However, the composite HAP/TE/GAC revealed better activity than HAP/GAC. Heavy metal adsorption ability of the synthesized composites was carried out using Pb²⁺ ions at room temperature at different time intervals and different pH levels. The equilibrium adsorption data were assessed via Langmuir and Freundlich adsorption isotherm models for neat GAC, HAP/GAC and HAP/TE/GAC at pH 6. The equilibrium adsorption data for GAC, HAP/GAC and HAP/TE/GAC were well fitted with both Freundlich and Langmuir isotherm models in the given Pb²⁺ concentrations. The HAP/TE/GAC composite is capable of maintaining the natural function of GAC in addition to removal of bacterial contaminants and heavy metals, which can be used as a point-of-use water filter material.

Controllable synthesis of graphitic carbon nitride nanomaterials for solar energy conversion and environmental remediation: the road travelled and the way forward

This review discusses advances in the synthesis and design of g-C₃N₄-based nanomaterials and their various photocatalytic and photoredox applications.