PDT involves the localization of photosensitizers in target tissue. Upon irradiation with light of an appropriate wavelength (usually visible light), a complex photochemical reaction is initiated to generate reactive oxygen species and trigger a cascade of molecular events that lead to cell death. PTT is an experimental use of electromagnetic radiation (most often in the form of infrared light) to generate significant local hyperthermia for the destruction of cells or tissues. Unlike photodynamic therapy, photothermal therapy does not require oxygen to interact with the target cells or tissues.

Phycocyanin (PC) is a photoharvesting pigment that provides the intense blue colour in blue-green algae. The water-soluble protein is frequently used as a colouring agent in food and cosmetics. Most importantly, PC is also a cytotoxic photosensitizer capable of killing cells via singlet oxygen production upon visible light radiation. As a result, PC could be an attractive candidate for PDT due to its solubility, non-carcinogenicity and non-toxicity.

Carbon nanotubes (CNTs) have been considered potential biomedical materials because of their interesting physicochemical properties, such as high surface area, high electrical and thermal conductivity. Compared with single-walled carbon nanotubes (SWNTs), multi-walled carbon nanotubes (MWNTs) can be expected to absorb significantly more near-infrared (NIR) radiation. MWNTs hold a particular interest for the development of PTT.

Conjugation strategy

CNTs tend to form bundles that disperse poorly in aqueous solutions, which would be unsuitable for pharmacological use. The inclusion of water-soluble chitosan (CS) on the one hand improves the water solubility of MWNTs, and on the other hand links MWNTs (the PTT agent) and PC (the PDT agent) together. CS possesses attractive characteristics. The material is non-toxic, easy to modify and low cost.

In their study, the researchers from South China University of Technology prepared and characterized nanoparticles comprising MWNT-CS-PC. The team tested the formulation on two human cancer cells (breast cancer cell line MCF-7 and liver cancer cell line HepG2) and one human normal cell (liver cell line L-o2) with and without laser irradiation.

The results showed that photoinduced cytotoxicity was indeed enhanced with irradiation of either NIR light (808 nm) or visible light (532 nm), suggesting that MWNT-CS-PC may potentially serve a biomedical material for future photodynamic and photothermal cancer therapy.

More information can be found in the journal Nanotechnology.