Synthesis Of Metal Nanoparticles Research Articles

Recent advances in synthesis and bio-applications of natural stabilizers for metal nanoparticles

Due to their exceptional physicochemical properties, the synthesis and application of metal nano-particles gained significant traction and a grip in industries and scientific fields or regions. However, the thermodynamic instability of metal nanoparticles poses or leads to challenges in their controlled synthesis and stabilization. To address this stability and the immobilization strategies, natural polymers such as cellulose, starch, alginate, chitosan, and hyaluronic acid have been explored for their non-toxic, biodegradable, and environmentally friendly characteristics. Recent advances in nanotechnology have led to an increased focus on these natural polymer’s utilization as effective stabilizers for diverse metal nanoparticles. This review comprehensively examines recent advances in utilizing these natural polymers as stabilizers for metal nanoparticles. Synthesis methods, stabilization mechanisms, and applications spanning catalysis, sensing, drug delivery, and biomedical imaging are discussed. Challenges such as scalability and reproducibility are addressed, alongside future directions for research and development. In this review, our goal is to encourage continued research and creativity in sustainable nanomaterials. By doing so, we hope to advance the development of adaptable and environmentally friendly nanoparticles that find applications across various industries.

Green Synthesis of Noble Metal Nanoparticles: Nonlinear Optics and Applications

This study presents a green method for synthesising gold nanoparticles (AuNPs) and silver nanoparticles (AgNPs) employing Gum Arabic extract as a reducing and stabilising agent. The synthesised nanoparticles are characterised using UV-Vis absorption spectroscopy and transmission electron microscopy (TEM). The visible colour change and the presence of surface plasmon resonance (SPR) peaks confirmed the formation of silver and gold nanoparticles. The size of the nanoparticles was determined from the UV-Vis spectra data, and the results were compared to sizes measured by TEM. The nonlinear refraction (n2) and nonlinear absorption (b) coefficient of AgNPs and AuNPs at 488 and 514 nm were investigated under continuous wave (CW) mode excitation using the Z-scan technique. By fitting the experimental data to the Z-scan theoretical equations, the nonlinear refraction index and the nonlinear absorption coefficient were found. The origin of the nonlinearities was discussed, and it was proposed to be of thermal effect for the nonlinear refractive index and Reverse Saturation Absorption (RSA) for nonlinear absorption. Optical limiting and switching were demonstrated by taking advantage of the samples' nonlinear optical characteristics.

Potential applications of Bacillus thuringiensis Berliner in agriculture, medicine and environment

Bacillus thuringiensis (Bt) is renowned for its insecticidal activity against a wide range of target pests. Bt formulations offer safe alternatives to chemical insecticides, effectively eliminating insects using toxins and enzymes such as chitinases and metalloproteases. This bacterium has transformed pest management through the development of genetically modified insect-resistant crops, providing targeted protection. Beyond pest control, Bt serves as an alternative to antibiotics, fertilizers, bioremediation agents and for nanomaterial synthesis. While its effectiveness in insect control contributes to sustainable farming practices, Bt further promotes plant growth as a biofertilizer and growth enhancer. Additionally, it plays various roles in medicine and environmental applications. Bacteriocins, proteins produced by Bt, exhibit high efficacy against pathogenic bacteria and demonstrate some fungicidal activity, offering potential applications in medicine and food preservation. Bt’s influence extends to environmental bioremediation, where it targets heavy metals and dyes. It is also involved in the synthesis of metal nanoparticles and exhibits anti-cancer activity by targeting various cancerous cells. Overall, Bt showcases a broad spectrum of activity across agriculture, medicine and environmental sectors, highlighting its potential to enhance crop productivity, improve human health and reduce environmental pollution.

An Overview of Metallic Nanoparticles: Classification, Synthesis, Applications, and their Patents.

Nanotechnology has gained enormous attention in pharmaceutical research. Nanotechnology is used in the development of nanoparticles with sizes ranging from 1-100 nm, with several extraordinary features. Metallic nanoparticles (MNPs) are used in various areas, such as molecular biology, biosensors, bio imaging, biomedical devices, diagnosis, pharmaceuticals, etc., for their specific applications. For this study, we have performed a systematic search and screening of the literature and identified the articles and patents focusing on various physical, chemical, and biological methods for the synthesis of metal nanoparticles and their pharmaceutical applications. A total of 174 references have been included in this present review, of which 23 references for recent patents were included. Then, 29 papers were shortlisted to describe the advantages, disadvantages, and physical and chemical methods for their synthesis, and 28 articles were selected to provide the data for biological methods for the formulation of metal NPs from bacteria, algae, fungi, and plants with their extensive synthetic procedures. Moreover, 27 articles outlined various clinical applications of metal NPs due to their antimicrobial and anticancer activities and their use in drug delivery. Several reviews are available on the synthesis of metal nanoparticles and their pharmaceutical applications. However, this review provides updated research data along with the various methods employed for their development. It also summarizes their various advantages and clinical applications (anticancer, antimicrobial drug delivery, and many others) for various phytoconstituents. The overview of earlier patents by several scientists in the arena of metallic nanoparticle preparation and formulation is also presented. This review will be helpful in increasing the current knowledge and will also inspire to innovation of nanoparticles for the precise and targeted delivery of phytoconstituents for the treatment of several diseases.

Extracellular Biosynthesis, Characterization and Antimicrobial Activity of Silver Nanoparticles Synthesized by Filamentous Fungi.

The green synthesis of metal nanoparticles has received substantial attention due to their applications in various domains. The aim of the study was to obtain silver nanoparticles (AgNPs) by green synthesis with filamentous fungi, such as Cladosporium cladosporoides, Penicillium chrysogenum, and Purpureocillium lilacinum. Fungal species were grown on nutrient media and aqueous mycelium extracts were used to reduce Ag+ to Ag (0). The silver nanoparticles were analyzed by various techniques, such as UV-Visible spectroscopy (UV-Vis), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), dynamic light scattering (DLS), and Zeta potential. The formation of silver nanoparticles was confirmed by UV-Vis spectroscopy and the color change of the mixture containing metal precursor and aqueous mycelium extract. FTIR displayed different functional groups as capping and reducing agents for the biosynthesis of AgNPs. SEM and TEM provided information on the particles' morphology. DLS diagrams indicated mean particle diameters in the 124-168 nm region. All biosynthesized AgNPs had negative zeta values, which is a sign of good stability. Silver nanoparticles were evaluated for antimicrobial activity, and the most active were those synthesized with metabolites from Cladosporium, leading to 93.75% inhibition of Staphylococcus aureus, 67.20% of Escherichia coli, and 69.56% of Candida albicans. With the highest microbial inhibition percentage and a very good Poly Dispersion Index (Pd I), Cladosporium cladosporoides was selected as an environmentally friendly source of silver nanoparticles that could be used as a potential antimicrobial agent.

Bioleaching of Printed Circuit Board Waste to Obtain Metallic Nanoparticles

In this work, a biological recovery of metals (copper and gold) from computer printed circuit board (PCB) waste was carried out by bioleaching using Aspergillus niger. Three bioleaching methods comprising one or two steps or using spent medium were tested in an incubator shaker at 30 °C and 160 rpm with different PCB waste concentrations (2.5 to 10 g/L). Glucose was used as the carbon source. The best condition evaluated was carried out in a stirred tank reactor. The FTIR spectrum confirmed the presence of oxalic, citric, and gluconic acids. A. niger showed an efficiency of bioleaching of up to 100% and 42.5% for copper and gold, respectively, using the two-step method with 2.5 g/L PCB waste after 14 days of the process. The efficiency of bioleaching in a stirred tank reactor was 83% for copper and 24% for gold. The mean metallic particle size obtained after bioleaching varied according to the PCB waste concentration (2.5–10 g/L) added in the experiments. A transmission electron microscope analysis confirmed the synthesis of metallic nanoparticles with spherical morphology. The results indicated that the PCBs bioleaching process with A. niger can be an environmentally friendly alternative to current mechanical and metallurgical processes for metal leaching.

Thermal stability and coalescence dynamics of exsolved metal nanoparticles at charged perovskite surfaces

Exsolution reactions enable the synthesis of oxide-supported metal nanoparticles, which are desirable as catalysts in green energy conversion technologies. It is crucial to precisely tailor the nanoparticle characteristics to optimize the catalysts’ functionality, and to maintain the catalytic performance under operation conditions. We use chemical (co)-doping to modify the defect chemistry of exsolution-active perovskite oxides and examine its influence on the mass transfer kinetics of Ni dopants towards the oxide surface and on the subsequent coalescence behavior of the exsolved nanoparticles during a continuous thermal reduction treatment. Nanoparticles that exsolve at the surface of the acceptor-type fast-oxygen-ion-conductor SrTi0.95Ni0.05O3−δ (STNi) show a high surface mobility leading to a very low thermal stability compared to nanoparticles that exsolve at the surface of donor-type SrTi0.9Nb0.05Ni0.05O3−δ (STNNi). Our analysis indicates that the low thermal stability of exsolved nanoparticles at the acceptor-doped perovskite surface is linked to a high oxygen vacancy concentration at the nanoparticle-oxide interface. For catalysts that require fast oxygen exchange kinetics, exsolution synthesis routes in dry hydrogen conditions may hence lead to accelerated degradation, while humid reaction conditions may mitigate this failure mechanism.

Characterization of Zinc Nanoparticles Synthesized Using the Mushroom, Pleurotus sajor-caju

Fungi including mushrooms contain various enzymes and biomolecules, making them an effective agent for synthesizing various nanoparticles. This study aimed to synthesize and characterize zinc nanoparticles using the zinc sulphate salt at the concentration of 1mM and the mushroom Pleurotus sajor-caju. The P. sajor-caju synthesized zinc nanoparticles were characterized using UV-Visible spectral analysis, Field Emission Scanning Electron Microscopy, and Fourier Transform Infrared Spectroscopy. They did not change the color and showed a characteristic surface plasmon resonance band peaking at 300nm. They were spherical and the particle size was found in the range of 7.29 nm to 13.27 nm. They showed ten bands at different stretching with wave numbers ranging between 675.17cm-1 and 3675.56cm-1. The presence of advantageous features in the zinc nanoparticles synthesized from P. sajor-caju revealed the usefulness of the synthesis of other metal nanoparticles from P. sajor-caju.

Exploring the Complex Chemistry and Degradation of Ascorbic Acid in Aqueous Nanoparticle Synthesis.

Ascorbic acid (AA) is the most widely used reductant for noble metal nanoparticle (NP) synthesis. Despite the synthetic relevance, its aqueous chemistry remains misunderstood, due in part to various assumptions about its reduction pathway which are insufficiently supported by experimental evidence. This study aims to provide an understanding of the complex chemistry associated with AA under aqueous conditions. We demonstrate that (i) AA undergoes appreciable degradation in alkaline solution on a timescale relevant to NP synthesis, (ii) contrary to popular belief, AA does not degrade into dehydroascorbic acid (DHA), nor is DHA the oxidized product of AA under noble metal NP synthetic conditions, (iii) DHA, which readily degrades under alkaline conditions, can also effectively reduce metal salt precursors to metal NPs, (iv) neither ascorbate nor dehydroascorbate act as surface capping agents post-synthetically on the NPs (v) AA degradation time greatly affects the morphology and polydispersity of the resultant NP. Results from our mechanistic investigation enabled us to utilize purposefully-aged reductants to achieve control over shape yield and monodispersity in the seed-mediated synthesis of Au nanorods. Our findings have important implications for achieving monodispersed products in the many metal NP synthesis reactions that make use of AA as a reducing agent.

Exploring the Complex Chemistry and Degradation of Ascorbic Acid in Aqueous Nanoparticle Synthesis

AbstractAscorbic acid (AA) is the most widely used reductant for noble metal nanoparticle (NP) synthesis. Despite the synthetic relevance, its aqueous chemistry remains misunderstood, due in part to various assumptions about its reduction pathway which are insufficiently supported by experimental evidence. This study aims to provide an understanding of the complex chemistry associated with AA under aqueous conditions. We demonstrate that (i) AA undergoes appreciable degradation in alkaline solution on a timescale relevant to NP synthesis, (ii) contrary to popular belief, AA does not degrade into dehydroascorbic acid (DHA), nor is DHA the oxidized product of AA under noble metal NP synthetic conditions, (iii) DHA, which readily degrades under alkaline conditions, can also effectively reduce metal salt precursors to metal NPs, (iv) neither ascorbate nor dehydroascorbate act as surface capping agents post‐synthetically on the NPs (v) AA degradation time greatly affects the morphology and polydispersity of the resultant NP. Results from our mechanistic investigation enabled us to utilize purposefully‐aged reductants to achieve control over shape yield and monodispersity in the seed‐mediated synthesis of Au nanorods. Our findings have important implications for achieving monodispersed products in the many metal NP synthesis reactions that make use of AA as a reducing agent.

Recent advancements in the plant-based synthesis and mechanistic insights of noble metal nanoparticles and their therapeutic applications

Recent advancements in the plant-based synthesis and mechanistic insights of noble metal nanoparticles and their therapeutic applications

Green synthesis of metal nanoparticles using plant growth promoting rhizobacteria and application in agriculture

Green synthesis of metal nanoparticles using plant growth promoting rhizobacteria and application in agriculture

Bio-Inspired Synthesis of Gold Nanoparticles Using Leaf Extract of Jamun and Research on Its Biomedical Potential.

Bio-based synthesis of metallic nanoparticles has garnered much attention in recent times owing to their non-toxic, environmentally friendly, and cost-effective nature. In this study, gold nanoparticles (S4-GoNPs) were synthesized by a simple and environmentally friendly technique using an aqueous extract of jamun leaves (JLE) as an effective capping, stabilizer, and reducing agent. JLE was screened for the presence of phytochemicals followed by synthesis, characterization, and evaluation of their antibacterial, antidiabetic, antioxidant, and photocatalytic degradation potentials using standard established procedures. The phytochemical profile of JLE was found to be rich in flavonoids, tannins, terpenoid phenols, anthraquinones, and cardiac glycosides. Its GC-MS analysis revealed the presence of compounds majorly of them as the (1R)-2,6,6-Trimethylbicyclo[3.1.1]hept-2-ene (5.141%), 2(10)-pinene (4.119%), α-cyclopene (5.274%) α,α-muurolene (7.525%), naphthalene, 1,2,3,4,4a,5,6,8a-octahydro-7-methyl-4-methylene-1-(1-methylethyl)-(1.alpha.,4a.beta.,8a.alpha) (8.470%), delta-cadinene (23.246), α-guajene (3.451%), and gamma-muurolene (4.379%). The visual morphology and UV-Vis spectral surface plasmon resonance at 538 nm confirmed the successful synthesis of S4-GoNPs. The average particle size was determined as 120.5 nm with Pdi = 0.152, and -27.6 mV zeta potential. Using the Scherrer equation, the average crystallite size was calculated as 35.69 nm. S4-GoNPs displayed significant antidiabetic properties, with 40.67% of α-amylase and 91.33% of α-glucosidase inhibition activity. It also exhibited promising antioxidant potential in terms of the DPPH (91.56%) ABTS (76.59%) scavenging. It displayed 31.04% tyrosinase inhibition at 0.1 mg/mL. Moreover, it also demonstrated encouraging antibacterial effects with zones of inhibition ranging from 11.02 - 14.12 mm as compared to 10.55-16.24 mm by the reference streptomycin (at 0.01 mg/disc). In addition, S4-GoNPs also showed potential for the photocatalytic degradation of the industrial dye, methylene blue. In conclusion, these results suggest the promising applicability of green-synthesized S4-GoNPs in various sectors, including the biomedical, cosmetic, food, and environmental waste management industries.

A review on the green metal nanotechnology in monogastric animal health: current trends and future prospects.

Green nanotechnology is the emerging field of research in recent decades with growing interest rapidly. This integrates green chemistry with green engineering to avoid using toxic chemicals in the synthesis of organic nanomaterials. Green nanotechnology would create a huge potential for the use of nanoparticles for more sustainable utilization in improving animal health. Nanoparticles can be synthesised by physical, chemical and biological processes. Traditional methods for physical and chemical synthesis of nanoparticles are toxic to humans, animals and environmental health, which limits their usefulness. Green synthesis of nanoparticles via biological processes and their application in animal health could maximize the benefits of nanotechnology in terms of enhancing food animal health and production as well as minimize the undesirable impacts on Planetary Health. Recent advances in nanotechnology have meant different nanomaterials, especially those from metal sources, are now available for use in nanomedicine. Metal nanoparticles are one of the most widely researched in green nanotechnology, and the number of articles on this subject in food animal production is growing nowadays. Therefore, research on metal nanoparticles using green technologies have utmost importance. In this review, we report the recent advancement of green synthesized metal nanoparticles in terms of their utilization in monogastric animal health, elucidate the research gap in this field and provide recommendations for future prospects.

Biogenic synthesis and physicochemical characterization of metal nanoparticles based on Calotropis procera as promising sustainable materials against skin cancer

The UAE harbors a rich diversity of wild medicinal plants, such as Calotropis procera (CP), that are renowned for their extensive use in traditional medicine due to their abundance of bioactive phytochemicals. Zinc and iron metals possess significant pharmacological effects including antioxidant and anticancer properties. In this study, nanoparticles (NPs) containing zinc and iron were green synthesized utilizing ethanolic and aqueous extracts of CP aerial parts. UV-Vis spectra revealed absorption peaks around 270–275 nm, while FT-IR analysis confirmed successful coating of the NPs with plant’s phytochemicals. SEM/EDX analysis indicated a more potent reducing effect of the aqueous extract, whereas the alcoholic extract demonstrated more effective coating of the NPs. DLS showed monodispersed NPs with average sizes of 32.67–202 nm. The alcoholic extract-based zinc and iron NPs exhibited the highest phenolic and flavonoid contents (51.06 ± 2.82 µg of GAE/mg of DW and 66.26 ± 1.12 µg of Qu/mg of DW, respectively) and the strongest antioxidant effect against ABTS and DPPH radicals (IC50 = 52.81 and 148.46 µg/mL, respectively). The aqueous extract-based zinc NPs demonstrated the greatest cytotoxicity against A-431 cell lines (IC50 = 188.97 µg/mL). The findings highlight promising potential of these sustainable materials for therapeutic applications, indicating a need for continued research and development in this area.

A Review on Green Synthesized Metal Nanoparticles Applications

Nanotechnology pertains to the manipulation of materials at exceedingly small scales, specifically between 1 and 100 nanometers. Materials at this scale exhibit significantly different properties compared to the same materials at larger scales. An emerging trend is the utilization of nanoparticles (NPs) to address environmental issues. Metallic nanoparticles are among the several nanoparticles that are extensively utilized in environmentally sustainable endeavors. A sustainable, economical, and enduring approach is to synthesize nanoparticles through a more ecologically friendly procedure instead of a physical or chemical method. Plant components primarily function as reducing and capping agents in eco-friendly synthesis. Diverse metallic nanoparticles of various sizes and shapes have been created utilizing extracts from plant materials, including leaves, bark, fruits, and flowers. The synthesis of Nobel laureate metal nanoparticles is essential to the medical sector. A diverse array of glycosides and phenolic compounds constitutes numerous organic constituents in plants, facilitating the synthesis of metal nanoparticles. The absence of detrimental by-products in metal nanoparticle synthesis is the primary significance of green synthesis. The nanoparticles generated by an eco-friendly approach demonstrate several significant biological activity. A substantial body of literature demonstrates that the synthesized nanoparticles are efficacious against both gram-positive and gram-negative bacteria, including E. coli, Bacillus subtilis, Klebsiella pneumoniae, and Pseudomonas fluorescens. The synthesized nanoparticles not only display antifungal efficacy against several cancer cell lines, including those of breast cancer, but also demonstrate antifungal activity against Trichophyton simii, Trichophyton mentagrophytes, and Trichophyton rubrum. Moreover, they exhibit potent antioxidant properties. The dimensions and morphology of these metal nanoparticles substantially influence their functionalities. Particles characterized by a large surface area and diminutive size provide significant potential for medical applications. This paper aims to provide a comprehensive summary of current advancements in the synthesis of nanoparticles utilizing biological entities and their numerous potential applications.

Optical Study of Desmodium Elegan Mediated Silver Nanoparticles Using Tauc’s Equation

Green synthesis of metallic nanoparticles is more eco-friendly, simpler, and nontoxic as compared to chemical synthesis. Due to their thermal stability and good electrical conduction silver nanoparticles have significant importance these days. In the present work, the stable silver nanoparticles were prepared from the aqueous solution of AgNO3 by green synthesis technique in which the Desmodium elegan plant extract was used as a reducing and capping agent to convert Ag+ to Ag0. A UV-visible spectrometer is used in the range of 200 nm to 800 nm with a scanning speed of 200 nm per minute, the absorption band is found at a 450 nm peak that indicates the synthesis of silver nanoparticles. The particle size of the nanoparticles was in the range of 11 nm to 70 nm with an average of 45 nm and a spherical shape. Further confirmation of nano size, scanning electron microscopy (SEM) was also utilized for the size distribution and shape of the synthesized nanoparticles. The synthesized nanoparticles SEM studies show irregular spherical morphology with polydispersed trend and the average particle size was found at 45 nm. The absorption band for the synthesized sample was found at 450 nm peak. The bandgap energy was 2.84 eV estimated by Tauc’s equation. This indicates that the synthesized nanoparticles electrically lie in the range of semiconductors and can be used as a biosensor. This synthesis technique is a nontoxic technique so these particles may be used for water treatment.

Design, Synthesis, and Evaluation of Noble Metal Nanoparticles and In Situ-Decorated Carbon-Supported Nanoparticle Electrocatalysts Using Hypergolic Reactions

Design, Synthesis, and Evaluation of Noble Metal Nanoparticles and In Situ-Decorated Carbon-Supported Nanoparticle Electrocatalysts Using Hypergolic Reactions

Plant‐Based Biosynthesis of Metal and Metal Oxide Nanoparticles: An Update on Antimicrobial and Anticancer Activity

AbstractNanotechnology has changed and developed all the sectors and working fields. Nanoparticles are one of the important evolutionary materials that have application in almost all the working areas such as catalysis, bioengineering, photoelectricity, antibacterial, anticancer, and medical imaging due to their unique physical and chemical properties. Traditionally used chemical and physical method of synthesis of nanoparticles have several disadvantages like using different chemicals, high cost, and most importantly they are hazardous to the environment. Counter to these disadvantages, a more eco‐friendly, easy, and cost‐effective green synthesis method is widely employed nowadays. Various parts of a plant are used as a fuel for reducing the metal ion salt. Plant extracts act as reducing, stabilizing, and capping agents. Besides these advantages, photosynthesized nanoparticles are nontoxic, more stable, and more uniform in size than their counterparts prepared by the traditional method. In this present review, the synthesis of various plant extract‐mediated metal and metal oxide nanoparticles is discussed along with their different applications. This review provides a comprehensive overview of key findings in green synthesis of metal and metal oxide nanoparticles and attempts to determine their possible synthesis mechanism. This article also focuses on factors affecting their synthesis, characterization, potential applications, and prospects.

Synthesis of metal nanoparticles on graphene oxide and antibacterial properties.

Pathogen-induced infections and the rise of antibiotic-resistant bacteria, such as Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), pose significant global health challenges, emphasizing the need for new antimicrobial strategies. In this study, we synthesized graphene oxide (GO)-based composites functionalized with silver nanoparticles (AgNPs) and copper nanoparticles (CuNPs) as potential alternatives to traditional antibiotics. The objective is to assess the antibacterial properties of these composites and explore their efficacy against E. coli and S. aureus, two common bacterial pathogens. The composites are prepared using eco-friendly and conventional methods to ensure effective nanoparticle attachment to the GO surface. Structural and morphological characteristics are confirmed through SEM, AFM, EDS, XRD, UV-vis, FTIR, and Raman spectroscopy. The antibacterial efficacy of the composites is tested through disk diffusion assays, colony-forming unit (CFU) counts, and turbidimetry analysis, with an emphasis on understanding the effects of different nanoparticle concentrations. The results demonstrated a dose-dependent antibacterial effect, with GO/AgNP-1 showing superior antibacterial activity over GO/AgNP-2, particularly at lower concentrations (32.0μg/mL and 62.5μg/mL). The GO/CuNP composite also exhibited significant antibacterial properties, with optimal performance at 62.5μg/mL for both bacterial strains. Turbidimetry analysis confirmed the inhibition of bacterial growth, especially at moderate concentrations, although slight nanoparticle aggregation at higher doses reduced efficacy. Lastly, both GO/AgNP and GO/CuNP composites demonstrated significant antibacterial potential. The results emphasize the need to fine-tune nanoparticle concentration and refine synthesis techniques to improve their efficacy, positioning these composites as strong contenders for antimicrobial use.