The growing interest in eco-friendly methods has led to the use of natural sources like bacteria, fungi, algae, and plants to make silver nanoparticles (AgNPs). This “green synthesis” approach is safer, more sustainable, and allows large-scale production with fewer impurities. In this process, natural substances—such as plant extracts, yeast, or bacteria—often act as stabilizers or capping agents. These help control the size of the nanoparticles and prevent them from clumping together.

Synthesis using plant extract

Green synthesis with plant extracts means using parts of plants (like leaves, roots, fruits, or seeds) to make nanoparticles in an eco-friendly way. The natural chemicals in plants act as both reducing agents (they help convert metal ions into nanoparticles) and stabilizers (they prevent the particles from clumping together). This method is safe, cost-effective, and avoids harmful chemicals, making it a popular choice for producing silver nanoparticles.

Researchers have used many different plants and plant parts to make silver nanoparticles (AgNPs) in an eco-friendly way. For example, Eugenia jambolana leaf extract helps form AgNPs and shows the presence of alkaloids, flavonoids, saponins, and sugars. The bark extract of Saraca asoca containes hydroxylamine and carboxyl groups that contributes to nanoparticle formation. Leaves of Rhynchotechum ellipticum produces AgNPs with compounds like polyphenols, flavonoids, alkaloids, terpenoids, carbohydrates, and steroids. Similarly, hesperidin generates AgNPs of 20–40 nm, while phenolic compounds such as pyrogallol and oleic acid also acts as effective reducing agents. Other plant extracts, like pepper leaves, formed nanoparticles sized between 5–60 nm, while fruit extracts from apple (Malus domestica), grape (Vitis vinifera), Andean blackberry, baobab (Adansonia digitata), Solanum nigrum, and Nitraria schoberi can also be used. In addition, multiple fruit peels and even combinations of different plant extracts can to aid AgNP synthesis. Beyond fruits and leaves, many natural substances has a role, including polysaccharides, soluble starch, natural rubber, tarmac, cinnamon, apple stem callus, egg white, lemongrass, coffee, black tea, and okra juice. Almost every part of a plant—peel, seed, fruit, bark, flower, stem, or root—can be applied in such nanoformulations. Overall, green synthesis is not only cost-effective but also safe for the environment.

Figure 14.1 Plant Mediated Synthesis Of AgNPS. (Adapted from Dikshit PK, Kumar J, Das AK, Sadhu S, Sharma S, Singh S, Gupta PK, Kim BS. Green synthesis of metallic nanoparticles: applications and limitations. Catalysts. 2021)

Alga-mediated synthesis of AgNPs

Algae, a diverse group of aquatic microorganisms, have been widely used for the green synthesis of silver nanoparticles (AgNPs). They range in size from tiny microscopic forms like picoplankton to larger macroscopic species such as red algae (Rhodophyta). For example, AgNPs is synthesized using microalgae like Chaetoceros calcitrans, C. salina, Isochrysis galbana, and Tetraselmis gracilis. Also, the marine alga Cystophora moniliformis acts as both a reducing and stabilizing agent in AgNP formation.

Fungus-mediated synthesis of AgNPs

Fungi can also be used for extracellular synthesis of silver nanoparticles (AgNPs), offering a cost-effective option for large-scale production. They are often preferred over bacteria because they tolerate metals better and can accumulate them more efficiently.

Wound dressing

Nanotechnology plays an important role in wound healing, mainly due to the strong antimicrobial and anti-inflammatory properties of nanoparticles. For instance, cotton fabric treated with silver nanoparticles (22 nm in size) shows remarkable healing ability. Another breakthrough came with bacterial cellulose wound dressings infused with AgNPs. Produced by Acetobacter xylinum (strain TISTR 975) and soaked in silver nitrate, this dressing proved effective against both Gram-positive and Gram-negative bacteria. Similarly, polymers have been enhanced with nanoparticles for better healing performance. In one example, polyurethane containing silver ions is electrospun and reduced with dimethylformamide, while collagen is added to improve hydrophilicity. The resulting collagen sponge with AgNPs accelerated wound healing in animal studies. More recently, a nanoengineered tissue embedded with AgNPs is developed that successfully prevented bacterial growth on its surface, showing promise for reducing healthcare-related infections.

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Nanotechnology In Orthodontics

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