Optical Interaction in Plasmonic Photothermal Therapeutics

Cancer is a disease in which biological cells grow uncontrollably and spread to other organs of a patient. Cancer disease comprises of abnormal cells, which can develop in any part of the human body. Normally, cells grow and multiply in a controlled manner, and when these become old or damaged, then cells die i.e., known as programmed cell death or apoptosis. Sometimes this controlled process of cell growth or death breaks down and there is abnormal growth of cells which form tumors in the body. The tumor cells grow slowly and do not spread in the body are known as benign (noncancerous) tumors. When tumor cells grow rapidly, these spread throughout the body and are called malignant tumors (cancerous). While there is no one specific cause of cancer, factors such as smoking, excessive UV exposure from the sun or tanning beds, being overweight or obese, and excessive alcohol use can all contribute to the formation of cancerous cells in the body.

A few emerging techniques such as immunotherapy, radio-frequency ablation, thermal ablation, cryotherapy, photodynamic therapy and plasmonic photothermal therapy, show higher efficacy and long survival rates as compared to the conventional methods.

Nanoparticles (1-100 nm in size) offer a biocompatible and biodegradable platform for cancer diagnosis as a contrast agent and as a cancer treatment through nanoparticle based thermal ablation or delivery of conventional chemotherapeutic drugs. The light interaction of biological tissue provides a basis for a wide variety of biomedical applications, like non-invasive diagnosis (tumor detection, contrast microscopy, optical coherence tomography, etc.), treatment (laser surgery, photodynamic therapy, photothermal therapy, etc.), and monitoring of bio-parameters (pulse oximetry, glucose monitoring, etc.). The thermal ablation of the tumor by using light interaction of metallic nanoparticles is known as plasmonic photothermal interaction. This allows for tumor treatment with minimal side effects on nearby healthy tissue. This technique is critically governed by the optical characteristics of tissue as well as the variations in the properties during the interaction of light with the nanoparticles or tissue. For example, the efficacy of cancer treatment by plasmonic photothermal therapy mainly depends upon the light absorption by tumor cells and/or nanoparticles. Therefore, it is important to characterize the optical characteristics of tissue, especially in the presence of nanoparticles and at different stages of photothermal therapy for pre-treatment planning as well as improving the efficacy of the therapy.