UNIT-III: NANOBIOTECHNOLOGY

Nanoparticle Synthesis Using Plants, Bacteria, Fungi, and Viruses

1. Green Synthesis of Nanoparticles

Green synthesis means producing nanoparticles using natural biological materials instead of chemicals. It is eco-friendly, low-cost, and safe. Biological organisms contain proteins, enzymes, metabolites, or biomolecules that can reduce metal ions into nanoparticles.

2. Plant-Mediated Nanoparticle Synthesis

Plants contain phytochemicals like flavonoids, alkaloids, terpenoids, phenolics, sugars, and proteins. These act as reducing and stabilizing agents.

Process

• Prepare plant extract (leaf, stem, bark, fruit).
• Mix extract with metal salt solution (e.g., AgNO₃ for silver).
• Phytochemicals convert metal ions into nanoparticles.
• Colour change confirms formation (e.g., silver turns brown/yellowish).

Advantages

• Very simple process
• No need for microbes
• Fast reaction

Examples

• Silver nanoparticles from neem, tulsi, aloe vera
• Gold nanoparticles from tea extract or turmeric
• Copper nanoparticles from plant leaves

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3. Bacteria-Mediated Nanoparticle Synthesis

Bacteria can reduce metals due to their enzymes. They can synthesize nanoparticles either inside the cell (intracellular) or outside the cell (extracellular).

Mechanism

• Metal ions enter the bacterial cell
• Enzymes convert metal ions to metal atoms
• Atoms group together to form nanoparticles

Examples

• Bacillus sp. produces silver and gold nanoparticles
• Pseudomonas sp. produces iron oxide nanoparticles

Advantages

• Good control over particle shape
• Scalable production

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4. Fungi-Mediated Nanoparticle Synthesis

Fungi produce a large amount of enzymes and proteins. They are considered the best microbial factories for nanoparticle synthesis.

Process

• Metal salts are added to fungal biomass or extract
• Enzymes reduce metal ions
• Nanoparticles form inside or outside the cells

Examples

• Aspergillus, Fusarium, Penicillium
• Silver, gold, titanium oxide nanoparticles

Advantages

• High yield
• More stable nanoparticles
• Easy to grow fungi in large scale

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5. Virus-Mediated Nanoparticle Synthesis

Viruses can act as templates (molds) because they have regular shapes.

Mechanism

• Virus capsid proteins bind to metal ions
• Metal ions get arranged along virus structure
• Reduction forms nanoparticles in specific shapes

Examples

• Tobacco Mosaic Virus (TMV) used for metal nanowires
• Cowpea Mosaic Virus used for gold nanoparticles

Applications

• Drug delivery
• Biosensors
• Imaging

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Metal Nanoparticle Synthesis and Mechanisms

1. Silver Nanoparticles (AgNPs)

Synthesis

• Chemical reduction (using NaBH₄, citrate)
• Biological synthesis (plants, bacteria, fungi)

Mechanism

Ag⁺ ions get reduced to Ag⁰ atoms → atoms aggregate → nanoparticles form.

Applications

• Antibacterial coating
• Wound healing
• Water purification
• Sensors

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2. Gold Nanoparticles (AuNPs)

Synthesis

• Turkevich method (citrate reduction)
• Biological methods

Mechanism

Au³⁺ → Au⁰ reduction forms small nuclei → grows into nanoparticles.

Applications

• Drug delivery
• Cancer therapy
• Diagnostic kits (pregnancy tests, LFAs)
• Biosensors

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3. Copper Nanoparticles (CuNPs)

Synthesis

• Chemical reduction
• Green synthesis

Mechanism

Cu²⁺ ions are reduced to Cu⁰; stabilizers prevent oxidation.

Applications

• Antimicrobial surfaces
• Conductive inks
• Catalysis
• Wastewater treatment

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4. Zinc Nanoparticles (Zn/ZnO NPs)

Synthesis

• Sol-gel method
• Precipitation
• Biological methods

Mechanism

Zn²⁺ ions react with hydroxide → Zn(OH)₂ → on heating → ZnO nanoparticles.

Applications

• Sunscreens
• Antibacterial creams
• Food packaging
• Photocatalysis

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Magnetic Nanoparticles – Synthesis and Applications

What Are Magnetic Nanoparticles?

These nanoparticles respond to a magnetic field. The most common ones are iron oxide nanoparticles like Fe₃O₄ (magnetite) and γ-Fe₂O₃ (maghemite).

Synthesis Methods

1. Co-precipitation

Mix Fe²⁺ and Fe³⁺ ions in alkaline solution → black magnetic nanoparticles form.
(Fe²⁺ + 2Fe³⁺ + 8OH⁻ → Fe₃O₄ + 4H₂O)

2. Thermal decomposition

Organic iron precursors heated in high-boiling solvents → uniform nanoparticles.

3. Hydrothermal / Solvothermal

Reactions performed in sealed high-pressure chambers → highly crystalline particles.

4. Green synthesis

Using plant extracts, bacteria, or fungi to reduce iron salts.

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Applications of Magnetic Nanoparticles

• Drug delivery – magnetic field guides nanoparticles to the target organ
• MRI contrast agents – improves imaging
• Cancer therapy (magnetic hyperthermia) – nanoparticles heat up and kill tumor cells
• Water purification – remove heavy metals and dyes; easy magnetic separation
• Biosensors – detect DNA, proteins, bacteria
• Catalysis – can be recovered easily using magnet.