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 1, 3 and 4 only.

To understand why this option is correct, let us analyze each statement in detail:

Statement 1: They can be used as carriers of drugs and antigens in the human body. (Correct)
Carbon nanotubes (CNTs) possess a unique cylindrical hollow structure, high surface area, and the ability to be functionalized with various functional groups. This allows them to bind to drugs, proteins, genes, and antigens. Because of their ability to cross cell membranes via endocytosis, they act as highly efficient nanocarriers for targeted drug delivery, transporting therapeutic agents directly to diseased cells with minimal damage to healthy tissues.

Statement 3: They can be used in biochemical sensors. (Correct)
CNTs are exceptional electrical conductors with a high surface-area-to-volume ratio. Their electrical properties are extremely sensitive to any chemical or biological molecules adsorbed onto their surface. When biomolecules interact with the functionalized surface of a nanotube, it triggers a measurable change in electrical conductivity, making them excellent materials for highly sensitive biochemical sensors and biosensors (e.g., for detecting blood glucose, cancer biomarkers, or pathogens).

Statement 4: Carbon nanotubes are biodegradable. (Correct)
Although carbon nanotubes are chemically robust, scientific research has demonstrated that certain microbes and mammalian enzymes can degrade them. For example, the enzyme myeloperoxidase (MPO), which is produced by human white blood cells (neutrophils), has been shown to successfully break down functionalized carbon nanotubes in the body. This biodegradability mitigates concerns regarding long-term toxicity and accumulation in tissues.

Statement 2: They can be made into artificial blood capillaries for an injured part of human body. (Incorrect)
While carbon nanotubes are studied for tissue engineering scaffold applications due to their mechanical strength, fabricating fully functional, complex artificial blood capillaries that can seamlessly integrate with the vascular system remains an extremely challenging area of research and is not a established, practical application. Therefore, this statement is excluded from the correct option.