Synthesis and evaluation of α-Ag 2 WO 4 as novel antifungal agent

Modulation of cell death mechanisms via α-Ag2WO4 morphology-dependent factors

The cytotoxic of α-Ag2WO4 synthesized in different morphologies (cuboidal (AW-C), hexagonal rod-like (AW-HRL) and nanometric rod-like (AW-NRL) was analyzed to understand the impact of morphological modulation on the toxicity of 3 T3 cell lines in the dark and when photoactivated by visible light. Pathways of toxicity were examined, such as parameters and electrostatic interaction, uptake, ion release and ROS production. Cytotoxicity was observed for all samples after reaching concentrations exceeding 7.8 μg/mL. Uptake tests demonstrated that the samples were not internalized by cells, likely due to their negative surface charge. AW-NRL exhibited autophagy in the absence of light and during photoactivation, primarily attributed to its ability to generate singlet oxygen. Analyzing intercellular ROS and RNS production, AW-HRL induced an increase in NO through exposure to photo-generated hydroxyl radicals, while AW-NRL showed increases only at non-photoactivated concentrations and AW-C did not exhibit increases. Interestingly, in the dark, these cells showed a low propensity for apoptosis, with late apoptosis and necrosis being more pronounced. When photoactivated, this behavior changed, revealing predominantly apoptotic and late apoptotic cell death. There is a need for an understanding of how morphology can alter the biological properties of α-Ag2WO4 to predict and optimize its effects on cellular responses.

Biocompatibility and inflammatory response of silver tungstate, silver molybdate, and silver vanadate microcrystals

Silver tungstate (α-Ag2WO4), silver molybdate (β-Ag2MoO4), and silver vanadate (α-AgVO3) microcrystals have shown interesting antimicrobial properties. However, their biocompatibility is not yet fully understood. Cytotoxicity and the inflammatory response of silver-containing microcrystals were analyzed in THP-1 and THP-1 differentiated as macrophage-like cells, with the alamarBlue™ assay, flow cytometry, confocal microscopy, and ELISA. The present investigation also evaluated redox signaling and the production of cytokines (TNFα, IL-1β, IL-6, and IL-8) and matrix metalloproteinases (MMP-8 and -9). The results showed that α-AgVO3 (3.9 μg/mL) did not affect cell viability (p > 0.05). α-Ag2WO4 (7.81 μg/mL), β-Ag2MoO4 (15.62 μg/mL), and α-AgVO3 (15.62 μg/mL) slightly decreased cell viability (p ≤ 0.003). All silver-containing microcrystals induced the production of O2 - and this effect was mitigated by Reactive Oxygen Species (ROS) scavenger and N-acetylcysteine (NAC). TNFα, IL-6 and IL-1β were not detected in THP-1 cells, while their production was either lower (p ≤ 0.0321) or similar to the control group (p ≥ 0.1048) for macrophage-like cells. The production of IL-8 by both cellular phenotypes was similar to the control group (p ≥ 0.3570). The release of MMP-8 was not detected in any condition in THP-1 cells. Although MMP-9 was released by THP-1 cells exposed to α-AgVO3 (3.9 μg/mL), no significant difference was found with control (p = 0.7). Regarding macrophage-like cells, the release of MMP-8 and -9 decreased in the presence of all microcrystals (p ≤ 0.010). Overall, the present work shows a promising biocompatibility profile of, α-Ag2WO4, β-Ag2MoO4, and α-AgVO3 microcrystals.

Polypropylene Modified with Ag-Based Semiconductors as a Potential Material against SARS-CoV-2 and Other Pathogens

The worldwide outbreak of the coronavirus pandemic (COVID-19) and other emerging infections are difficult and sometimes impossible to treat, making them one of the major public health problems of our time. It is noteworthy that Ag-based semiconductors can help orchestrate several strategies to fight this serious societal issue. In this work, we present the synthesis of α-Ag₂WO₄, β-Ag₂MoO₄, and Ag₂CrO₄ and their immobilization in polypropylene in the amounts of 0.5, 1.0, and 3.0 wt %, respectively. The antimicrobial activity of the composites was investigated against the Gram-negative bacterium Escherichia coli, the Gram-positive bacterium Staphylococcus aureus, and the fungus Candida albicans. The best antimicrobial efficiency was achieved by the composite with α-Ag₂WO₄, which completely eliminated the microorganisms in up to 4 h of exposure. The composites were also tested for the inhibition of SARS-CoV-2 virus, showing antiviral efficiency higher than 98% in just 10 min. Additionally, we evaluated the stability of the antimicrobial activity, resulting in constant inhibition, even after material aging. The antimicrobial activity of the compounds was attributed to the production of reactive oxygen species by the semiconductors, which can induce high local oxidative stress, causing the death of these microorganisms.

Disclosing the Biocide Activity of α-Ag2−2xCuxWO4 (0 ≤ x ≤ 0.16) Solid Solutions

In this work, α-Ag2−2xCuxWO4 (0 ≤ x ≤ 0.16) solid solutions with enhanced antibacterial (against methicillin-resistant Staphylococcus aureus) and antifungal (against Candida albicans) activities are reported. A plethora of techniques (X-ray diffraction with Rietveld refinements, inductively coupled plasma atomic emission spectrometry, micro-Raman spectroscopy, attenuated total reflectance–Fourier transform infrared spectroscopy, field emission scanning electron microscopy, ultraviolet–visible spectroscopy, photoluminescence emissions, and X-ray photoelectron spectroscopy) were employed to characterize the as-synthetized samples and determine the local coordination geometry of Cu2+ cations at the orthorhombic lattice. To find a correlation between morphology and biocide activity, the experimental results were sustained by first-principles calculations at the density functional theory level to decipher the cluster coordinations and electronic properties of the exposed surfaces. Based on the analysis of the under-coordinated Ag and Cu clusters at the (010) and (101) exposed surfaces, we propose a mechanism to explain the biocide activity of these solid solutions.

Silver Trimolybdate (Ag2Mo3O10.2H2O) Nanorods: Synthesis, Characterization, and Photo-Induced Antibacterial Activity under Visible-Light Irradiation

The present study reports the synthesis, characterization, and antibacterial properties of silver trimolybdate (Ag2Mo3O10.2H2O) nanorods. The synthesis was performed using a conventional hydrothermal method. The sample was characterised by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, UV-Vis-NIR diffuse reflectance, thermogravimetric analysis (TGA), and differential scanning calorimeter (DSC). The direct antibacterial activity was evaluated using the microdilution method to determine the minimum inhibitory concentration (MIC). To assess the ability of Ag2Mo3O10.2H2O nanorods to modulate antibacterial resistance, the MIC of aminoglycosides was established in the presence of a subinhibitory concentration of this substance alone and associated with LED light exposure. The characterization of the sample indicated that the synthesis of silver trimolybdate generated nanometric crystals with rod-like morphology, without secondary phases. The treatment with Ag2Mo3O10.2H2O nanorods alone or combined with visible LED lights exhibited clinically relevant antibacterial activity against both Gram-negative and Gram-positive bacteria. This nanostructure presented a variable antibiotic-modulating action, which was not improved by visible LED light exposure. Nevertheless, LED lights showed promising antibiotic-enhancing activities in the absence of Ag2Mo3O10.2H2O nanorods. In conclusion, silver trimolybdate dihydrate nanorods have antibacterial properties that can be photocatalysed by visible-light exposure. While showing the potential use to combat antibacterial resistance, the simultaneous combination of silver trimolybdate, visible LED lights, and antibacterial drugs should be carefully analysed to avoid antagonist effects that could impair the effectiveness of antibiotic therapy.

Modified Titanium Dioxide as a Potential Visible-Light-Activated Photosensitizer for Bladder Cancer Treatment

Low oxygen concentration inside the tumor microenvironment represents a major barrier for photodynamic therapy of many malignant tumors, especially urothelial bladder cancer. In this context, titanium dioxide, which has a low cost and can generate high ROS levels regardless of local O₂ concentrations, could be a potential type of photosensitizer for treating this type of cancer. However, the use of UV can be a major disadvantage, since it promotes breakage of the chemical bonds of the DNA molecule on normal tissues. In the present study, we focused on the cytotoxic activities of a new material (Ti(OH)₄) capable of absorbing visible light and producing high amounts of ROS. We used the malignant bladder cell line MB49 to evaluate the effects of multiple concentrations of Ti(OH)₄ on the cytotoxicity, proliferation, migration, and production of ROS. In addition, the mechanisms of cell death were investigated using FACS, accumulation of lysosomal acid vacuoles, caspase-3 activity, and mitochondrial electrical potential assays. The results showed that exposure of Ti(OH)₄ to visible light stimulates the production of ROS and causes dose-dependent necrosis in tumor cells. Also, Ti(OH)₄ was capable of inhibiting the proliferation and migration of MB49 in low concentrations. An increase in the mitochondrial membrane potential associated with the accumulation of acid lysosomes and low caspase-3 activity suggests that type II cell death could be initiated by autophagic dysfunction mechanisms associated with high ROS production. In conclusion, the characteristics of Ti(OH)₄ make it a potential photosensitizer against bladder cancer.

Inactivation of SARS-CoV-2 by a chitosan/α-Ag2WO4 composite generated by femtosecond laser irradiation

In the current COVID-19 pandemic, the next generation of innovative materials with enhanced anti-SARS-CoV-2 activity is urgently needed to prevent the spread of this virus within the community. Herein, we report the synthesis of chitosan/α-Ag₂WO₄ composites synthetized by femtosecond laser irradiation. The antimicrobial activity against Escherichia coli, Methicilin-susceptible Staphylococcus aureus (MSSA), and Candida albicans was determined by estimating the minimum inhibitory concentration (MIC) and minimal bactericidal/fungicidal concentration (MBC/MFC). To assess the biocompatibility of chitosan/α-Ag₂WO₄ composites in a range involving MIC and MBC/MFC on keratinocytes cells (NOK-si), an alamarBlue™ assay and an MTT assay were carried out. The SARS-CoV-2 virucidal effects was analyzed in Vero E6 cells through viral titer quantified in cell culture supernatant by PFU/mL assay. Our results showed a very similar antimicrobial activity of chitosan/α-Ag₂WO₄ 3.3 and 6.6, with the last one demonstrating a slightly better action against MSSA. The chitosan/α-Ag₂WO₄ 9.9 showed a wide range of antimicrobial activity (0.49-31.25 µg/mL). The cytotoxicity outcomes by alamarBlue™ revealed that the concentrations of interest (MIC and MBC/MFC) were considered non-cytotoxic to all composites after 72 h of exposure. The Chitosan/α-Ag₂WO₄ (CS6.6/α-Ag₂WO₄) composite reduced the SARS-CoV-2 viral titer quantification up to 80% of the controls. Then, our results suggest that these composites are highly efficient materials to kill bacteria (Escherichia coli, Methicillin-susceptible Staphylococcus aureus, and the yeast strain Candida albicans), in addition to inactivating SARS-CoV-2 by contact, through ROS production.

Antifungal Activity and Biocompatibility of α-AgVO3, α-Ag2WO4, and β-Ag2MoO4 Using a Three-Dimensional Coculture Model of the Oral Mucosa

Fungal infections have become a major concern in the medical community, especially those caused by Candida spp. Within this species, Candida albicans stands out for being an opportunistic commensal fungus that can cause superficial and invasive infections. Current antifungal therapy involves the local and/or systemic use of drugs such as azoles, polyenes, and echinocandins. These antifungals are based on highly specific target sites, and the development of resistance may occur with changes in the enzymatic pathways that serve as the drug targets. Thus, the development of new antifungal drugs is highly recommended to prevent drug resistance. The present investigation evaluated the antifungal activity of silver-containing microcrystals such as silver vanadate (α-AgVO₃), silver tungstate (α-Ag₂WO₄), and silver molybdate (β-Ag₂MoO₄). In addition to having antimicrobial activity, such compounds should not cause damage to underlying tissues. Thus, to better assess the biocompatibility of new compounds, a new three-dimensional (3D) coculture model involving three cell lines was developed. The validation of the model was based on fluorescent markers and confocal laser microscopy. The biocompatibility of silver-containing microcrystals was evaluated by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. 3D coculture was infected with C. albicans biofilm and challenged with α-AgVO₃, α-Ag₂WO₄, and β-Ag₂MoO₄. The action of microcrystals on C. albicans biofilm was evaluated by colony-forming units (CFU/ml) and LIVE/DEAD staining. In addition, production of proinflammatory cytokines interleukin 6 (IL-6), IL-8, IL-1β, and tumor necrosis factor α (TNF-α) was measured by cytometric bead array kit using flow cytometry. The 3D coculture model described here proved to be adequate to assess both the biocompatibility of the new materials and the infectious processes. Regarding the biocompatibility of the microcrystals, only α-AgVO₃ (15.62 µg/ml) showed a decrease in cell viability. The antibiofilm activity of α-Ag₂WO₄ was similar to that of the standard drug (fluconazole). Although α-Ag₂WO₄ was able to induce the production of IL-6, IL-8, and IL-1β, no differences in cytokine production were observed between noninfected and infected models treated with this microcrystal. β-Ag₂MoO₄ inhibits the production of TNF-α in the infected model; however, it showed no antibiofilm activity. Based on the biocompatibility and antifungal findings, α-Ag₂WO₄ is a promising material for treating C. albicans infection.

Toxicity of α-Ag2WO4 microcrystals to freshwater microalga Raphidocelis subcapitata at cellular and population levels

Silver-based materials have microbicidal action, photocatalytic activity and electronic properties. The increase in manufacturing and consumption of these compounds, given their wide functionality and application, is a source of contamination to freshwater ecosystems and causes toxicity to aquatic biota. Therefore, for the first time, we evaluated the toxicity of the silver tungstate (α-Ag₂WO₄), in different morphologies (cube and rod), for the microalga Raphidocelis subcapitata. To investigate the toxicity, we evaluated the growth rate, cell complexity and size, reactive oxygen species (ROS) production and chlorophyll a (Chl a) fluorescence. The α-Ag₂WO₄ - R (rod) was 1.7 times more toxic than α-Ag₂WO₄-C (cube), with IC₁₀ and IC₅₀ values of, respectively, 8.68 ± 0.91 μg L^-1 and 13.72 ± 1.48 μg L^-1 for α-Ag₂WO₄ - R and 18.60 ± 1.61 μg L^-1 and 23.47 ± 1.16 μg L^-1 for α-Ag₂WO₄-C. The release of silver ions was quantified and indicated that the silver ions dissolution from the α-Ag₂WO₄ - R ranged from 34 to 71%, while the Ag ions from the α-Ag₂WO₄-C varied from 35 to 97%. The α-Ag₂WO₄-C induced, after 24 h exposure, the increase of ROS at the lowest concentrations (8.81 and 19.32 μg L^-1), whereas the α-Ag₂WO₄ - R significantly induced ROS production at 96 h at the highest concentration (31.76 μg L^-1). Both microcrystal shapes significantly altered the cellular complexity and decreased the Chl a fluorescence at all tested concentrations. We conclude that the different morphologies of α-Ag₂WO₄ negatively affect the microalga and are important sources of silver ions leading to harmful consequences to the aquatic ecosystem.

Bioactive Ag3PO4/Polypropylene Composites for Inactivation of SARS-CoV-2 and Other Important Public Health Pathogens

The current unprecedented coronavirus pandemic (COVID-19) is increasingly demanding advanced materials and new technologies to protect us and inactivate SARS-CoV-2. In this research work, we report the manufacture of Ag3PO4 (AP)/polypropylene (PP) composites using a simple method and also reveal their long-term anti-SARS-CoV-2 activity. This composite shows superior antibacterial (against Staphylococcus aureus and Escherichia coli) and antifungal activity (against Candida albicans), thus having potential for a variety of technological applications. The as-manufactured materials were characterized by XRD, Raman spectroscopy, FTIR spectroscopy, AFM, UV-vis spectroscopy, rheology, SEM, and contact angle to confirm their structural integrity. Based on the results of first-principles calculations at the density functional level, a plausible reaction mechanism for the initial events associated with the generation of both hydroxyl radical •OH and superoxide radical anion •O2- in the most reactive (110) surface of AP was proposed. AP/PP composites proved to be an attractive avenue to provide human beings with a broad spectrum of biocide activity.

Structure, Photoluminescence Emissions, and Photocatalytic Activity of Ag2SeO3: A Joint Experimental and Theoretical Investigation

In this paper, we report the synthesis of silver selenite (Ag₂SeO₃) by different methods [sonochemistry, ultrasonic probe, coprecipitation, and microwave-assisted hydrothermal methods]. These microcrystals presented a structural long-range order as confirmed by X-ray diffraction (XRD) and Rietveld refinements and a structural short-range order as confirmed by Fourier transform infrared (FTIR) and Raman spectroscopies. X-ray photoelectron spectroscopy (XPS) provided information about the surface of the samples indicating that they were pure. The microcrystals presented different morphologies and sizes due to the synthesis method as observed by field emission scanning electron microscopy (FE-SEM). The optical properties of these microcrystals were evaluated by ultraviolet-visible (UV-vis) spectroscopy and photoluminescence (PL) measurements. Thermal analysis confirmed the temperature stability of the as-synthetized samples. Further trapping experiments prove that the holes and hydroxyl radicals, to a minor extent, are responsible for the photocatalytic reactions. The experimental results are sustained by first-principles calculations, at the density functional theory (DFT) level, to decipher the structural parameters, electronic properties of the bulk, and surfaces of Ag₂SeO₃. By matching the experimental FE-SEM images and theoretical morphologies, we are capable of finding a correlation between the morphology and photocatalytic activity, along with photodegradation of the Rhodamine B dye under UV light, based on the different numbers of unsaturated superficial Ag and Se cations (local coordination, i.e., clusters) of each surface.

Rational Design of W-Doped Ag3PO4 as an Efficient Antibacterial Agent and Photocatalyst for Organic Pollutant Degradation

Bacterial and organic pollutants are major problems with potential adverse impacts on human health and the environment. A promising strategy to alleviate these impacts consists in designing innovative photocatalysts with a wider spectrum of application. In this paper, we report the improved photocatalytic and antibacterial activities of chemically precipitated Ag3PO4 microcrystals by the incorporation of W at doping levels 0.5, 1, and 2 mol %. The presence of W directly influences the crystallization of Ag3PO4, affecting the morphology, particle size, and surface area of the microcrystals. Also, the characterization via experimental and theoretical approaches evidenced a high density of disordered [AgO4], [PO4], and [WO4] structural clusters due to the substitution of P5+ by W6+ into the Ag3PO4 lattice. This leads to new defect-related energy states, which decreases the band gap energy of the materials (from 2.27 to 2.04 eV) and delays the recombination of e'-h• pairs, leading to an enhanced degradation process. As a result of such behaviors, W-doped Ag3PO4 (Ag3PO4:W) is a better visible-light photocatalyst than Ag3PO4, demonstrated here by the photodegradation of potential environmental pollutants. The degradation of rhodamine B dye was 100% in 4 min for Ag3PO4:W 1%, and for Ag3PO4, the obtained result was 90% of degradation in 15 min of reaction. Ag3PO4:W 1% allowed the total degradation of cephalexin antibiotic in only 4 min, whereas pure Ag3PO4 took 20 min to achieve the same result. For the degradation of imidacloprid insecticide, Ag3PO4:W 1% allowed 90% of degradation, whereas Ag3PO4 allowed 40%, both in 20 min of reaction. Moreover, the presence of W-dopant results in a 16-fold improvement of bactericidal performance against methicillin-resistant Staphylococcus aureus. The outstanding results using the Ag3PO4:W material demonstrated its potential multifunctionality for the control of organic pollutants and bacteria in environmental applications.

Ag Nanoparticles/α-Ag2WO4 Composite Formed by Electron Beam and Femtosecond Irradiation as Potent Antifungal and Antitumor Agents

The ability to manipulate the structure and function of promising systems via external stimuli is emerging with the development of reconfigurable and programmable multifunctional materials. Increasing antifungal and antitumor activity requires novel, effective treatments to be diligently sought. In this work, the synthesis, characterization, and in vitro biological screening of pure α-Ag₂WO₄, irradiated with electrons and with non-focused and focused femtosecond laser beams are reported. We demonstrate, for the first time, that Ag nanoparticles/α-Ag₂WO₄ composite displays potent antifungal and antitumor activity. This composite had an extreme low inhibition concentration against Candida albicans, cause the modulation of α-Ag₂WO₄ perform the fungicidal activity more efficient. For tumor activity, it was found that the composite showed a high selectivity against the cancer cells (MB49), thus depleting the populations of cancer cells by necrosis and apoptosis, without the healthy cells (BALB/3T3) being affected.