Carbon nanotubes (CNTs) can act as non-covalent, non-specific protein transporters, enabling the intracellular delivery of various proteins, including those with molecular weights up to 80 kD. This study demonstrates that acid-oxidized single-walled carbon nanotubes (SWNTs) can transport proteins such as streptavidin (SA), protein A (SpA), bovine serum albumin (BSA), and cytochrome c (cyt-c) into mammalian cells via endocytosis. Once inside the cells, the proteins are released from endosomes and can perform biological functions, as evidenced by the induction of apoptosis by transported cytochrome c. The proteins are non-covalently bound to the nanotube sidewalls, and the transport process is energy-dependent. The study also shows that chloroquine can be used to release the protein-nanotube conjugates from endosomes into the cytoplasm, allowing the proteins to exert their biological functions. The results indicate that SWNTs can serve as a new class of molecular transporters for in vitro and in vivo protein delivery applications. The study highlights the potential of SWNTs for delivering functional proteins into cells, with the ability to induce apoptosis, suggesting their potential in biomedical applications. However, the study also notes that the transport efficiency may be limited for larger proteins, such as human immunoglobulin G (hIgG), due to size mismatch and inefficient endocytosis. The biocompatibility of SWNTs was assessed using cell proliferation assays, which showed no significant toxicity to cells. The study concludes that SWNTs are generic intracellular protein transporters, capable of delivering various proteins into cells and performing biological functions, opening up new possibilities for their use in biomedical applications.Carbon nanotubes (CNTs) can act as non-covalent, non-specific protein transporters, enabling the intracellular delivery of various proteins, including those with molecular weights up to 80 kD. This study demonstrates that acid-oxidized single-walled carbon nanotubes (SWNTs) can transport proteins such as streptavidin (SA), protein A (SpA), bovine serum albumin (BSA), and cytochrome c (cyt-c) into mammalian cells via endocytosis. Once inside the cells, the proteins are released from endosomes and can perform biological functions, as evidenced by the induction of apoptosis by transported cytochrome c. The proteins are non-covalently bound to the nanotube sidewalls, and the transport process is energy-dependent. The study also shows that chloroquine can be used to release the protein-nanotube conjugates from endosomes into the cytoplasm, allowing the proteins to exert their biological functions. The results indicate that SWNTs can serve as a new class of molecular transporters for in vitro and in vivo protein delivery applications. The study highlights the potential of SWNTs for delivering functional proteins into cells, with the ability to induce apoptosis, suggesting their potential in biomedical applications. However, the study also notes that the transport efficiency may be limited for larger proteins, such as human immunoglobulin G (hIgG), due to size mismatch and inefficient endocytosis. The biocompatibility of SWNTs was assessed using cell proliferation assays, which showed no significant toxicity to cells. The study concludes that SWNTs are generic intracellular protein transporters, capable of delivering various proteins into cells and performing biological functions, opening up new possibilities for their use in biomedical applications.