Conjugation of quantum dots on carbon nanotubes for medical diagnosis and treatment

Abstract

Cancer is one of the leading causes of death worldwide and early detection provides the best possible prognosis for cancer patients. Nanotechnology is the branch of engineering that deals with the manipulation of individual atoms and molecules. This area of science has the potential to help identify cancerous cells and to destroy them by various methods such as drug delivery or thermal treatment of cancer. Carbon nanotubes (CNT) and quantum dots (QDs) are the two nanoparticles, which have received considerable interest in view of their application for diagnosis and treatment of cancer. Fluorescent nanoparticles known as QDs are gaining momentum as imaging molecules with life science and clinical applications. Clinically they can be used for localization of cancer cells due to their nano size and ability to penetrate individual cancer cells and high-resolution imaging derived from their narrow emission bands compared with organic dyes. CNTs are of interest to the medical community due to their unique properties such as the ability to deliver drugs to a site of action or convert optical energy into thermal energy. By attaching antibodies that bind specifically to tumor cells, CNTs can navigate to malignant tumors. Once at the tumor site, the CNTs enter into the cancer cells by penetration or endocytosis, allowing drug release, and resulting in specific cancer cell death. Alternatively, CNTs can be exposed to near-infrared light in order to thermally destroy the cancer cells. The amphiphilic nature of CNTs allows them to penetrate the cell membrane and their large surface area (in the order of 2600 m(2)/g) allows drugs to be loaded into the tube and released once inside the cancer cell. Many research laboratories, including our own, are investigating the conjugation of QDs to CNTs to allow localization of the cancer cells in the patient, by imaging with QDs, and subsequent cell killing, via drug release or thermal treatment. This is an area of huge interest and future research and therapy will focus on the multimodality of nanoparticles. In this review, we seek to explore the biomedical applications of QDs conjugated to CNTs, with a particular emphasis on their use as therapeutic platforms in oncology.

Keywords: cancer; carbon nanotubes; cytotoxicity; drug delivery; near-infrared light; photothermal therapy; quantum dots.

Figure 1

QDs synthesis in our laboratory. Abbreviation: QDs, quantum dots.

Figure 2

Schematic diagram of QD structure; QDs consist of an inorganic core, an inorganic shell, and aqueous organic coating. Abbreviation: QDs, quantum dots.

Figure 3

Schematic diagram showing the interaction between CD3 receptors on the Jurkat T leukemia cell membranes and a CNT-QD nanoassembly. Note: A biotinylated anti-CD3 monoclonal antibody was used to link CD3 to the nanoassembly. Abbreviations: CNT, carbon nanotube; QDs, quantum dots.

Figure 4

Schematic diagram, showing the conjugation of both QDs to CNT and QDs to CNT coated with SiO₂. Abbreviations: CNT, carbon nanotube; QDs, quantum dots.

Figure 5

Formation of ZnO QD–MWCNT composites. Note: Sodium dodecyl benzene sulfonate (SDBS) was used as a linker for conjugation of QDs (in this case ZnO) to CNTs in a polar solvent. Abbreviations: CNTs, carbon nanotubes; MWCNT, multiwalled carbon nanotubes; QDs, quantum dots.

Figure 6

Transmission electron micrographs (TEM) illustrating (A) MWCNT-NH₂; (B) 2.8–4.6 nm CdSe QDs; (C) mixture of MWCNT-COCl and QDs-COOH; (D) QDs/MWCNT = 1:10; (E) QDs/MWCNT = 1:1; (F) QDs/MWCNT = 10:1; (G) high-resolution TEM image of QDs-MWCNT (QDs/MWCNT = 1:1). Note: Copyright © 2006. Reprinted with permission from Elsevier. Pan B, Cui D, He R, Gao F, Zhang Y. Covalent attachment of quantum dot on carbon nanotubes. Chem Phys Lett. 2006;417(4–6):419–424. Abbreviations: Cdse, cadmium selenide; MWCNT, multiwalled carbon nanotubes; QDs, quantum dots.