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?

Answer: C. Statements 1, 3 and 4 are correct; Statement 2 is wrong. CARBON NANOTUBES (CNTs) are cylindrical NANOSTRUCTURES of carbon atoms arranged in a hexagonal lattice (essentially rolled-up sheets of graphene). They come in single-walled (SWCNT) and multi-walled (MWCNT) varieties. Their properties: exceptional tensile strength (about 100 times stronger than steel for the same weight), high electrical conductivity, and high thermal conductivity. Statement 1 is CORRECT. Carbon nanotubes have been investigated as CARRIERS FOR DRUGS, ANTIGENS, GENES, AND IMAGING AGENTS in nanomedicine. CNTs can be FUNCTIONALISED (with carboxyl, amine or polyethylene glycol groups) to attach drug molecules, antibodies, or DNA, and they can penetrate cellular membranes for targeted delivery. Research has explored CNT-based cancer drug delivery (doxorubicin), vaccine antigen delivery, and gene therapy vectors. Statement 2 is WRONG. While CNTs are explored in tissue engineering scaffolds, the claim that they 'can be made into artificial blood capillaries' is NOT a validated clinical reality. CNTs raise concerns about biocompatibility, immunogenicity, and clearance in the bloodstream. Artificial blood vessels are made of polymeric materials (PTFE, polyester, polyurethane) for large vessels, and self-assembling biomaterial scaffolds for smaller ones. CNT-based capillaries are not in clinical use. Statement 3 is CORRECT. CNTs are widely used in BIOCHEMICAL SENSORS. Their high surface area, electrical conductivity, and easy functionalisation allow CNT-based sensors to detect proteins, DNA, glucose, biomarkers of disease, and environmental pollutants at very low concentrations. Glucose biosensors and electrochemical immunosensors are well-established applications. Statement 4 is CORRECT (with nuance). Recent research demonstrates that certain CNTs (especially functionalised, short, and SWCNT varieties) CAN BE BIODEGRADED enzymatically by myeloperoxidase, eosinophil peroxidase, and other oxidative enzymes inside cells. This was a major finding (Star et al., Kotchey et al., Bhattacharya et al. studies). Earlier views that CNTs are entirely biopersistent have been revised. UPSC marks this as correct in the official key. So 1, 3, 4 are correct; 2 overstates current clinical reality. Source: NCERT Class 12 Chemistry 'Surface Chemistry' references; ACS Nano publications on carbon nanotube biomedical applications; PNAS Bhattacharya et al. on CNT biodegradation.