Controlling the Geometry of Silver Nanostructures for Biological Applications

Antibacterial Activity and Mechanisms of Action of Inorganic Nanoparticles against Foodborne Bacterial Pathogens: A Systematic Review

Foodborne disease outbreaks due to bacterial pathogens and their toxins have become a serious concern for global public health and security. Finding novel antibacterial agents with unique mechanisms of action against the current spoilage and foodborne bacterial pathogens is a central strategy to overcome antibiotic resistance. This study examined the antibacterial activities and mechanisms of action of inorganic nanoparticles (NPs) against foodborne bacterial pathogens. The articles written in English were recovered from registers and databases (PubMed, ScienceDirect, Web of Science, Google Scholar, and Directory of Open Access Journals) and other sources (websites, organizations, and citation searching). "Nanoparticles," "Inorganic Nanoparticles," "Metal Nanoparticles," "Metal-Oxide Nanoparticles," "Antimicrobial Activity," "Antibacterial Activity," "Foodborne Bacterial Pathogens," "Mechanisms of Action," and "Foodborne Diseases" were the search terms used to retrieve the articles. The PRISMA-2020 checklist was applied for the article search strategy, article selection, data extraction, and result reporting for the review process. A total of 27 original research articles were included from a total of 3,575 articles obtained from the different search strategies. All studies demonstrated the antibacterial effectiveness of inorganic NPs and highlighted their different mechanisms of action against foodborne bacterial pathogens. In the present study, small-sized, spherical-shaped, engineered, capped, low-dissolution with water, high-concentration NPs, and in Gram-negative bacterial types had high antibacterial activity as compared to their counterparts. Cell wall interaction and membrane penetration, reactive oxygen species production, DNA damage, and protein synthesis inhibition were some of the generalized mechanisms recognized in the current study. Therefore, this study recommends the proper use of nontoxic inorganic nanoparticle products for food processing industries to ensure the quality and safety of food while minimizing antibiotic resistance among foodborne bacterial pathogens.

Particle-Driven Effects at the Bacteria Interface: A Nanosilver Investigation of Particle Shape and Dose Metric

Design criteria for controlling engineered nanomaterial (ENM) antimicrobial performance will enable advances in medical, food production, processing and preservation, and water treatment applications. In pursuit of this goal, better resolution of how specific ENM properties, such as nanoparticle shape, influence antimicrobial activity is needed. This study probes the antimicrobial activity toward a model Gram-negative bacterium, Escherichia coli (E. coli), that results from interfacial interactions with differently shaped silver nanoparticles (AgNPs): cube-, disc-, and pseudospherical-AgNPs. The EC50 value (i.e., the concentration of AgNPs that inactivates 50% of the microbial population) for each shape is identified and presented as a function of mass, surface area, and particle number. Further, shifts in relative potency are identified from the associated dose-response curves (e.g., shifts left, to lower concentrations, indicate greater potency). When using a mass-based dose metric, the disc-AgNPs present the highest antimicrobial activity of the three shapes (EC50: 2.39 ± 0.26 μg/mL for discs, 2.99 ± 0.96 μg/mL for cubes, 116.33 ± 6.43 μg/mL for pseudospheres). When surface area and particle number are used as dose metrics, the cube-AgNPs possess the highest antimicrobial activity (EC50-surface area: 4.70 × 10-5 ± 1.51 × 10-5 m2/mL, EC50-particle: 5.97 × 109 ± 1.92 × 109 particles/mL), such that the relative trend in potency becomes cubes > discs > pseudospheres and cubes ≫ discs ⩾ pseudospheres, respectively. The results reveal that the antimicrobial potency of disc-AgNPs is sensitive to the dose metric, significantly decreasing in potency (∼5-30×) upon conversion from a mass-based concentration to surface area and particle number and influencing the conclusions drawn. The shift in relative particle potency highlights the importance of investigating various dose metrics within the experimental design and signals different particle parameters influencing shape-based antimicrobial activity. To probe shape-dependent behavior, we use a unique empirical approach where the physical and chemical properties (ligand chemistry, surface charge) of the AgNP shapes are carefully controlled, and total available surface area is equivalent across shapes as made through modifications to particle size and concentration. The results herein suggest that surface area alone does not drive antimicrobial activity as the different AgNP shapes at equivalent particle surface area yield significantly different magnitudes of antimicrobial activity (i.e., 100% inactivation for cube-AgNPs, <25% inactivation for disc- and pseudospherical-AgNPs). Further, the particle shapes studied possess different crystal facets, illuminating their potential influence on differentiating interactions between the particle surface and the microbe. Whereas surface area may partly contribute to antimicrobial activity in certain ENM shapes (i.e., disc-AgNPs in relation to the pseudospherical-AgNPs), the different magnitudes of antimicrobial activity across shape provide insight into the likely role of other particle-specific factors, such as crystal facets, driving the antimicrobial activity of other shapes (i.e., cube-AgNPs).

Green Synthesis of Controlled Shape Silver Nanostructures and Their Peroxidase, Catalytic Degradation, and Antibacterial Activity

Nanoparticles with unique shapes have garnered significant interest due to their enhanced surface area-to-volume ratio, leading to improved potential compared to their spherical counterparts. The present study focuses on a biological approach to producing different silver nanostructures employing Moringa oleifera leaf extract. Phytoextract provides metabolites, serving as reducing and stabilizing agents in the reaction. Two different silver nanostructures, dendritic (AgNDs) and spherical (AgNPs), were successfully formed by adjusting the phytoextract concentration with and without copper ions in the reaction system, resulting in particle sizes of ~300 ± 30 nm (AgNDs) and ~100 ± 30 nm (AgNPs). These nanostructures were characterized by several techniques to ascertain their physicochemical properties; the surface was distinguished by functional groups related to polyphenols due to plant extract that led to critical controlling of the shape of nanoparticles. Nanostructures performance was assessed in terms of peroxidase-like activity, catalytic behavior for dye degradation, and antibacterial activity. Spectroscopic analysis revealed that AgNDs demonstrated significantly higher peroxidase activity compared to AgNPs when evaluated using chromogenic reagent 3,3',5,5'-tetramethylbenzidine. Furthermore, AgNDs exhibited enhanced catalytic degradation activities, achieving degradation percentages of 92.2% and 91.0% for methyl orange and methylene blue dyes, respectively, compared to 66.6% and 58.0% for AgNPs. Additionally, AgNDs exhibited superior antibacterial properties against Gram-negative E. coli compared to Gram-positive S. aureus, as evidenced by the calculated zone of inhibition. These findings highlight the potential of the green synthesis method in generating novel nanoparticle morphologies, such as dendritic shape, compared with the traditionally synthesized spherical shape of silver nanostructures. The synthesis of such unique nanostructures holds promise for various applications and further investigations in diverse sectors, including chemical and biomedical fields.

Impact of Nanomedicine in Women's Metastatic Breast Cancer

Metastatic breast cancer is responsible for 90% of mortalities among women suffering from various types of breast cancers. Traditional cancer treatments such as chemotherapy and radiation therapy can cause significant side effects and may not be effective in many cases. However, recent advances in nanomedicine have shown great promise in the treatment of metastatic breast cancer. For example, nanomedicine demonstrated robust capacity in detection of metastatic cancers at early stages (i.e., before the metastatic cells leave the initial tumor site), which gives clinicians a timely option to change their treatment process (for example, instead of endocrine therapy they may use chemotherapy). Here recent advances in nanomedicine technology in the identification and treatment of metastatic breast cancers are reviewed.

A comparative study of iron nanoflower and nanocube in terms of antibacterial properties

It is known that heavy metal containing nanomaterials can easily prevent the formation of microbial cultures. The emergence of new generation epidemic diseases in the last 2 years has increased the importance of both personal and environmental hygiene. For this reason, in addition to preventing the spread of diseases, studies on alternative disinfectant substances are also carried out. In this study, the antibacterial activity of nanoflower and nanocube, which are easily synthesized and nanoparticle species containing iron, were compared. The antioxidant abilities of new synthesized NF@FeO(OH) and NC@α-Fe2O3 were tested by DPPH scavenging activity assay. The highest DPPH inhibition was achieved with NC@α-Fe2O3 as 71.30% at 200 mg/L. NF@FeO(OH) and NC@α-Fe2O3 demonstrated excellent DNA cleavage ability. The antimicrobial capabilities of NF@FeO(OH) and NC@α-Fe2O3 were analyzed with micro dilution procedure. In 500 mg/L, the antimicrobial activity was 100%. In addition to these, the biofilm inhibition of NF@FeO(OH) and NC@α-Fe2O3 were investigated against S. aureus and P. aeruginosa and it was found that they showed significant antibiofilm inhibition. It is suggested that additional studies can be continued to be developed and used as an antibacterial according to the results of the nanoparticles after various toxicological test systems.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13204-023-02822-5.

What function of nanoparticles is the primary factor for their hyper-toxicity?

Nanomaterials have applications in environmental protection, hygiene, medicine, agriculture, and the food industry due to their enhanced bio-efficacy/toxicity as science and technology have progressed, notably nanotechnology. The extension in the use of nanoparticles in day-to-day products and their excellent efficacy raises worries about safety concerns associated with their use. Therefore, to understand their safety concerns and find the remedy, it is imperative to understand the rationales for their enhanced toxicity at low concentrations to minimize their potential side effects. The worldwide literature quotes different nanoparticle functions responsible for their enhanced bio-efficacy/ toxicity. Since the literature on the comparative toxicity study of nanoparticles of different shapes and sizes having different other physic-chemical properties like surface areas, surface charge, solubility, etc., evident that the nanoparticle's toxicity is not followed the fashion according to their shape, size, surface area, surface charge, solubility, and other Physico-chemical properties. It raises the question then what function of nanoparticle is the primary factor for their hyper toxicity. Why do non-spherical and large-sized nanoparticles show the same or higher toxicity to the same or different cell line or test organism instead of having lower surface area, surface charge, larger size, etc., than their corresponding spherical and smaller-sized nanoparticles? Are these factors a secondary, not primary, factor for nanoparticles hyper-toxicity? If so, what function of nanoparticles is the primary function for their hyper-toxicity? Therefore, in this article, literature related to the comparative toxicity of nanoparticles was thoroughly studied, and a hypothesis is put forth to address the aforesaid question, that the number of atoms/ions/ molecules per nanoparticles is the primary function of nanoparticles toxicity.

Nonspherical Metal-Based Nanoarchitectures: Synthesis and Impact of Size, Shape, and Composition on Their Biological Activity

Metal-based nanoentities, apart from being indispensable research tools, have found extensive use in the industrial and biomedical arena. Because their biological impacts are governed by factors such as size, shape, and composition, such issues must be taken into account when these materials are incorporated into multi-component ensembles for clinical applications. The size and shape (rods, wires, sheets, tubes, and cages) of metallic nanostructures influence cell viability by virtue of their varied geometry and physicochemical interactions with mammalian cell membranes. The anisotropic properties of nonspherical metal-based nanoarchitectures render them exciting candidates for biomedical applications. Here, the size-, shape-, and composition-dependent properties of nonspherical metal-based nanoarchitectures are reviewed in the context of their potential applications in cancer diagnostics and therapeutics, as well as, in regenerative medicine. Strategies for the synthesis of nonspherical metal-based nanoarchitectures and their cytotoxicity and immunological profiles are also comprehensively appraised.

Size- and shape-dependent toxicity of silver nanomaterials in green alga Chlorococcum infusionum

Silver nanomaterials (AgNMs) of different shapes and sizes are potentially toxic to aquatic organisms. However, studies on the toxicity of AgNMs and on their shape-dependent effects on algae are scarce. The present study evaluated the effects of three AgNMs (silver nanospheres, AgNPs; silver nanowires, AgNWs; silver nanoplates, AgPLs) with different shapes coated with polyvinylpyrrolidone on the growth and photosynthetic performance of an alga, Chlorococcum infusionum. We used growth measurements and determined the photosynthetic parameters based on chlorophyll fluorescence transients in the algal cells exposed to different concentrations of the three AgNMs. The effective concentrations at 50% (EC₅₀) of AgNPs, AgNWs, and AgPLs were calculated to be 0.1, 0.045, and 0.021 mg/L, respectively. The results showed that the toxicity of AgNMs in C. infusionum was in the order, AgPLs (40 nm diameter) > AgNWs (21,000 nm length × 42 nm diameter) > AgNPs (57 nm diameter), based on the decrease in growth and three photosynthetic activities. We propose that the toxic potential of AgNMs is primarily dependent on their diameter and secondarily on their shape. Overall, this study provides, for the first time, a comparison of the growth and photosynthetic activities of C. infusionum exposed to AgNMs of three different shapes.

The effects of silver nanomaterial shape and size on toxicity to Caenorhabditis elegans in soil media

Silver nanomaterials (AgNMs) of various shapes and sizes are manufactured for different purposes and used as ingredients in a wide variety of products and applications. Recently, the toxicity of AgNMs has attracted significant attention. However, the effect of the shape of AgNMs (particles, wires, plates) on their toxicity in soil ecosystems remains poorly understood. In this study, we added AgNMs of different shapes and sizes (silver nanoparticles, AgNPs; 10 μm silver nanowires, 10-AgNWs; 20 μm silver nanowires, 20-AgNWs; silver nanoplates, AgPLs) to natural soil and determined their effect on the growth and reproduction of the free-living nematode, Caenorhabditis elegans. AgNPs and AgPLs were found to inhibit the growth and reproduction of C. elegans, whereas AgNWs had a negligible effect. Among these AgNMs, the results of this study suggest AgNPs are the most toxic. This confirms that the shape of AgNPs plays a significant role in their toxicity level. To the best of our knowledge, this is the first comparative analysis of the shape-dependent toxicity of AgNMs in the soil using nematode C. elegans. This study provides a scientific reference for assessing shape-dependent soil nanotoxicity.

Silicone/Ag@SiO2core–shell nanocomposite as a self-cleaning antifouling coating material

The effects of Ag@SiO₂ core–shell nanofiller dispersion and micro-nano binary structure on the self-cleaning and fouling release (FR) in the modelled silicone nano-paints were studied. An ultrahydrophobic polydimethylsiloxane/Ag@SiO₂ core–shell nanocomposite was prepared as an antifouling coating material. Ag@SiO₂ core–shell nanospheres with 60 nm average size and a preferential {111} growth direction were prepared via a facile solvothermal and a modified Stöber methods with a controlled shell thickness. Ag@SiO₂ core–shell nanofillers were inserted in the silicone composite surface via solution casting technique. A simple hydrosilation curing mechanism was used to cure the surface coating. Different concentrations of nanofillers were incorporated in the PDMS matrix for studying the structure–property relationship. Water contact angle (WCA) and surface free energy determinations as well as atomic force microscopy and scanning electron microscope were used to investigate the surface self-cleaning properties of the nanocomposites. Mechanical and physical properties were assessed as durability parameters. A comparable study was carried out between silicone/spherical Ag@SiO₂ core–shell nanocomposites and other commercial FR coatings. Selected micro-foulants were used for biological and antifouling assessments up to 28 days. Well-distributed Ag@SiO₂ core–shell (0.5 wt%) exhibited the preferable self-cleaning with WCA of 156° and surface free energy of 11.15 mN m⁻¹.

The effects of Ag@SiO₂ core–shell nanofiller dispersion and micro-nano binary structure on the fouling release of silicone paints were studied. An ultrahydrophobic PDMS/Ag@SiO₂ core–shell nanocomposite was prepared as an antifouling coating material.

Dimension-dependent toxicity of silver nanomaterials on the cladocerans Daphnia magna and Daphnia galeata

Silver nanomaterials (AgNMs) are widely used in many fields because of their antimicrobial properties. Depending on the shapes and dimensions of the AgNMs, their potential uses and needs vary. Consequently, vast quantities of multi-dimensional AgNMs are being manufactured and released into aquatic ecosystems, where they have toxic effects on aquatic organisms. Therefore, an assessment of the toxicities of each multi-dimensional AgNM on aquatic ecosystems is necessary. In this study, important aquatic model species, Daphnia magna and Daphnia galeata, were used to assess and compare the toxic effects of silver ions (Ag⁺ ions) and multi-dimensional AgNMs, including silver nanoparticles (AgNPs), silver nanowires (AgNWs), and silver nanoplates (AgPLs). The results indicated that Ag⁺ ions were more toxic than AgNMs of different dimensions and sizes, and that AgPLs were the most toxic of the AgNMs. In the case of AgNWs, the longer (20 μm) nanowire was more toxic than the shorter (10 μm) one. In addition, D. galeata was more sensitive than D. magna to both Ag⁺ ions and AgNMs. This study elucidates the dimension-dependent toxicity of and silver ions and nanomaterials in the cladocerans D. magna and D. galeata. Further studies will be necessary to further elucidate the actual risk of multi-dimensional nanomaterials in ecosystems.

Modeling of spherical silver nanoparticles in silicone-based nanocomposites for marine antifouling

A non-toxic foul-release model of silicone/spherical AgNP hybrid nanocomposites with enhanced hydrophobicity, self-cleaning, and marine fouling release performance.

Dissolution of silver nanowires and nanospheres dictates their toxicity to Escherichia coli

Silver nanoparticles are extensively used in antibacterial applications. However, the mechanisms of their antibacterial action are not yet fully explored. We studied the solubility-driven toxicity of 100 × 6100 nm (mean primary diameter × length) silver nanowires (NWs) to recombinant bioluminescent Escherichia coli as a target representative of enteric pathogens. The bacteria were exposed to silver nanostructures in water to exclude the speciation-driven alterations. Spherical silver nanoparticles (83 nm mean primary size) were used as a control for the effect of NPs shape. Toxicity of both Ag NWs and spheres to E. coli was observed at similar nominal concentrations: the 4h EC50 values, calculated on the basis of inhibition of bacterial bioluminescence, were 0.42 ± 0.06 and 0.68 ± 0.01 mg Ag/L, respectively. Dissolution and bioavailability of Ag from NWs and nanospheres, analyzed with AAS or Ag-sensor bacteria, respectively, suggested that the toxic effects were caused by solubilized Ag⁺ ions. Moreover, the antibacterial activities of Ag NWs suspension and its ultracentrifuged particle-free supernatant were equal. The latter indicated that the toxic effects of ~80–100 nm Ag nanostructures to Escherichia coli were solely dependent on their dissolution and no shape-induced/related effects were observed. Yet, additional nanospecific effects could come into play in case of smaller nanosilver particles.