A Review on The Biogenic Synthesis of Silver Nanoparticles and Nanotechnology

Abstract

The biogenic synthesis of silver nanoparticles (AgNPs) has emerged as a sustainable and eco-friendly alternative to conventional physical and chemical methods. This review explores various biological entities, including plants, bacteria, fungi, and algae, as sources for synthesizing AgNPs. The biogenic process offers several advantages, such as low toxicity, cost-effectiveness, and enhanced biocompatibility, making it highly suitable for medical, pharmaceutical, agricultural, and environmental applications. The mechanism of AgNP biosynthesis involves the reduction of silver ions (Ag?) to metallic silver (Ag?) through bioactive compounds, followed by nanoparticle nucleation and stabilization. Characterization techniques such as UV-Vis spectroscopy, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and electron microscopy help confirm the successful synthesis and properties of AgNPs. Due to their unique physicochemical properties, AgNPs have been widely applied in antimicrobial coatings, drug delivery systems, biosensors, water purification, and catalysis. However, challenges such as variability in nanoparticle size, large-scale production limitations, and potential cytotoxic effects necessitate further research. Future studies should focus on optimizing synthesis methods, improving nanoparticle stability, and assessing environmental and health risks to ensure their safe and effective use. This review highlights recent advancements in biogenic AgNP synthesis, its applications in nanotechnology, and potential future directions for enhancing its practical applications.

Keywords

Silver nanoparticles, Biogenic synthesis, Nanotechnology, Green chemistry, Antimicrobial, Drug delivery, Environmental applications

Introduction

Nanotechnology has revolutionized various scientific and industrial fields, offering innovative solutions for medicine, agriculture, environmental management, and material science. Among different types of nanoparticles, silver nanoparticles (AgNPs) are particularly significant due to their unique physical, chemical, and biological properties, including antimicrobial, anticancer, and catalytic activities. Traditional synthesis methods of AgNPs involve physical and chemical processes that often require toxic reagents, high energy, and complex procedures. To address these challenges, biogenic synthesis has emerged as a sustainable and eco-friendly alternative, utilizing plants, bacteria, fungi, and algae for nanoparticle production. “Nanotechnology” is the newest and one of the most promising and active areas of modern research. The technology deals with the design, synthesis, and manipulation of particles size ranging from 1–1000 nm. Within this size range, the chemical, physical, and biological properties change in the fundamental way of both individual atoms and their corresponding bulk material.

A Nanoparticle or ultrafine particle is a particle of matter 1 to 100 nanometres (nm) in diameter. The term is sometimes used for larger particles, up to 500 nm, or fibers and tubes that are less than 100 nm in only two directions. ^? At the lowest range, metal particles smaller than 1 nm are usually called atom clusters instead. Nanoparticles are distinguished from microparticles (1-1000 μm), "fine particles" (sized between 100 and 2500 nm), and "coarse particles" (ranging from 2500 to 10,000 nm), because their smaller size drives very different physical or chemical properties, like colloidal properties and ultrafast optical effects or electric properties.

BIOGENIC SYNTHESIS OF SILVER NANOPARTICLES

Biogenic synthesis, also known as green synthesis, is a cost-effective and environmentally friendly method for producing AgNPs. This approach harnesses biological entities that naturally contain reducing and stabilizing agents capable of converting silver ions (Ag?) into silver nanoparticles (Ag?). AgNPs are among the most promising items in the nanotechnology business among the different metallic nanoparticles. The creation of reliable procedures for AgNP synthesis is a key area of contemporary nanotechnology research. AgNPs' special optical, electrical, and magnetic properties make them useful in a variety of applications, including antibacterial, antiviral, and antifungal ones; they can also be used in composite fibers, biosensor materials, cosmetics, the food industry, and electronic components.AgNPs have also been identified as pharmaceutical and medicinal substances that have come into direct contact with human tissue in products like toothpaste, shampoos, detergents, soaps, and cosmetics.

1. BIOLOGICAL SOURCES FOR BIOGENIC SYNTHESIS

Different biological sources are used in the synthesis of AgNPs, each offering unique advantages:

Plants: Plant extracts are rich in bioactive compounds such as flavonoids, polyphenols, tannins, alkaloids, and proteins, which serve as reducing and stabilizing agents. Examples of plants used include:

Azadirachta indica (Neem) – Known for its strong antioxidant properties.

Ocimum sanctum (Tulsi) – Contains phenolic compounds that aid in nanoparticle synthesis.

Aloe vera – Contains enzymes and polysaccharides beneficial for stabilization.

Bacteria: Several bacterial strains have been explored for AgNP biosynthesis, including:

Pseudomonas aeruginosa – Produces extracellular enzymes that facilitate silver ion reduction.

Bacillus subtilis – Known for its high efficiency in AgNP production.

Fungi: Fungi offer a high yield of extracellular enzymes and proteins for AgNP stabilization. Notable examples include:

Aspergillus niger – Produces AgNPs with strong antimicrobial activity.

Fusarium oxysporum – Generates well-dispersed nanoparticles.

Algae: Algae-based synthesis is gaining interest due to their high bioaccumulation potential. Examples include:

Chlorella vulgaris – A green algae species capable of synthesizing nanoparticles under mild conditions.

Sargassum sp. – A marine algae known for its ability to reduce metal ions.

2. MECHANISM OF BIOGENIC SYNTHESIS

The synthesis of AgNPs follows three primary steps:

1. Reduction of Silver Ions (Ag? to Ag?): Biomolecules in the biological medium donate electrons to Ag?, reducing them to metallic silver (Ag?).

2. Nucleation and Growth: Reduced silver atoms aggregate to form small nuclei, which then grow into stable nanoparticles.

3. Capping and Stabilization: Organic compounds such as proteins, polysaccharides, and secondary metabolites act as stabilizers, preventing agglomeration.

CHARACTERIZATION OF SILVER NANOPARTICLES

To confirm successful synthesis, various characterization techniques are used:

UV-Vis Spectroscopy: Measures surface plasmon resonance (SPR), indicating nanoparticle formation.

X-ray Diffraction (XRD): Determines crystalline structure.

Fourier Transform Infrared Spectroscopy (FTIR): Identifies functional groups responsible for stabilization.

Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM): Examine morphology and size distribution.

Dynamic Light Scattering (DLS): Assesses nanoparticle size and stability.

APPLICATIONS OF SILVER NANOPARTICLES IN NANOTECHNOLOGY

The unique properties of AgNPs enable their use in various fields:

1. Medical and Pharmaceutical Applications

Antimicrobial agents: Effective against bacteria (E. coli, S. aureus), fungi, and viruses.

Wound healing and dressings: Silver-impregnated dressings prevent infections.

Cancer therapy: AgNPs induce cytotoxic effects in cancer cells.

Drug delivery: Functionalized AgNPs improve targeted drug delivery.

2. Environmental Applications

Water purification: AgNP-based filters remove pathogens and pollutants.

Bioremediation: Helps degrade toxic heavy metals and dyes.

3. Agricultural Applications

Nano-fertilizers and nano-pesticides: Enhance crop yield and pest resistance.

Antimicrobial coatings for food packaging: Extends shelf life by preventing microbial contamination.

4. Industrial Applications

Catalysis: Used in chemical reactions for efficient synthesis of organic compounds.

Textile coatings: Antibacterial fabrics with AgNPs prevent microbial growth.

CHALLENGES AND FUTURE PERSPECTIVES

Despite the promising benefits, some challenges need to be addressed:

Variability in Synthesis: Differences in biological sources lead to variations in nanoparticle size and stability.

Scalability: Large-scale production requires process optimization.

Toxicity Concerns: Potential cytotoxic and genotoxic effects of AgNPs need thorough investigation.

Regulatory Issues: Standardization and safety assessments are essential for commercialization.

Future research should focus on optimizing synthesis parameters, exploring novel biological sources, and conducting in-depth toxicological studies to enhance the safety and efficiency of AgNPs.

CONCLUSION

Biogenic synthesis of silver nanoparticles is a sustainable and efficient method in nanotechnology. The use of plant extracts, microbes, and algae offers a green alternative to conventional synthesis methods. AgNPs exhibit remarkable properties suitable for applications in medicine, environment, agriculture, and industry. However, further research is required to overcome synthesis challenges and ensure the safe and effective application of AgNPs in various fields.

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