With reference to carbon nanotubes, consider the following statements: 1) They can be used as carriers of drugs and antigens in the human body. 2) They can be made into artificial blood capillaries for an injured part of human body. 3) They can be used in biochemical sensors. 4) Carbon nanotubes are biodegradable. Which of the statements given above are correct?

The correct option is D, all four statements. The core concept is that carbon nanotubes (CNTs) are cylindrical allotropes of carbon with high surface area, strength and electrical conductivity, which makes them useful in biomedicine and nano-sensing.

• Statement 1 is correct. Functionalised CNTs can carry drugs, vaccine antigens and biomolecules into cells, which is the basis of drug-delivery research.
• Statement 2 is correct. CNT-based scaffolds and composites are being studied for tissue engineering, including vascular and capillary-like structures for damaged tissue.
• Statement 3 is correct. CNTs are used in biosensors because their electrical properties respond to binding of glucose, DNA or proteins.
• Statement 4 is correct, with a caveat. CNTs were long believed to be persistent, but studies showed enzymes such as myeloperoxidase can degrade them, so they are considered partly biodegradable. Their long-term environmental persistence is still a concern.

For Mains, link this to nanotechnology in health and the environmental and toxicity questions it raises.

Trap: Rejecting statement 4 just because CNTs are 'persistent' or 'non-biodegradable' in general.