Detailed Explanation:

Answer: Option 3 — 1, 3 and 4 only

Carbon nanotubes (CNTs) are cylindrical nanostructures with unique properties that make them suitable for biomedical applications including drug delivery, biosensing, and under certain conditions, biodegradation. Statement 2 is incorrect as CNTs cannot be reliably made into functional artificial blood capillaries—this application remains experimental and lacks validated clinical use.

✅ Statement 1 – Correct: CNTs can be functionalized with drugs and antigens, making them effective carriers for targeted delivery in the human body due to their ability to cross biological membranes.

❌ Statement 2 – Incorrect: While CNTs have been explored in tissue engineering scaffolds, they cannot be made into functional artificial blood capillaries as these require precise biological compatibility, flexibility, and permeability that CNTs alone cannot replicate.

✅ Statement 3 – Correct: CNTs possess high surface-to-volume ratio and unique electrical properties, making them ideal for biochemical sensors that detect biomolecules like glucose, proteins, and DNA with high sensitivity.

✅ Statement 4 – Correct: Research has shown that CNTs can be biodegraded by oxidative enzymes such as myeloperoxidase (MPO) found in human neutrophils, though biodegradability depends on CNT type, structure, and surface functionalization.

📝 Short Notes: Carbon Nanotubes

• Structure: Cylindrical nanostructures composed of rolled-up sheets of graphene, with diameters in nanometers and lengths up to micrometers.
• Types: Single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs).
• Properties: Exceptional mechanical strength, high electrical and thermal conductivity, high surface area, and ability to be functionalized.
• Biomedical Applications: Drug delivery systems, gene therapy carriers, biosensors, tissue engineering scaffolds, and imaging contrast agents.
• Drug Delivery: Can be functionalized to carry therapeutic agents and target specific cells, improving drug efficacy and reducing side effects.
• Biosensors: Used in electrochemical and optical sensors for detecting glucose, cholesterol, DNA, proteins, and pathogens with high sensitivity.
• Biodegradability Debate: Some studies show enzymatic degradation by peroxidases, but biodegradability varies with CNT structure, functionalization, and environmental conditions; persistence in biological systems remains a concern.
• Challenges: Potential toxicity, biocompatibility issues, aggregation in biological fluids, and lack of standardized methods for large-scale production and functionalization.