The "Nano" World in Photodynamic Therapy


Austin J Nanomed Nanotechnol. 2014;2(3): 1020.

The “Nano” World in Photodynamic Therapy

Huang-Chiao Huang1 and Tayyaba Hasan1,2*

1Harvard Medical School, Massachusetts General Hospital, USA

2Division of Health Sciences and Technology, Harvard- MIT, USA

*Corresponding author: Tayyaba Hasan, Division of Health Sciences and Technology, Harvard Medical School, Massachusetts, USA

Received: May 22, 2014; Accepted: May 27, 2014; Published: May 29, 2014


Photodynamic Therapy (PDT) is an externally activated, photochemistrybased approach that generates cytotoxic reactive molecular species (RMS), which kill or modulate biological targets. PDT provides unique opportunities for applications of nanotechnology where light activation can trigger both direct RMS–mediated cytotoxic activity and the release of contents within the nanoconstructs (Figure 1). This process allows several species, working via different mechanisms and molecular targets to be activated or released in the right place and time, thus providing a distinctive approach to combination therapy. With advances in the development of miniaturized, even–biodegradable light sources and delivery systems, exciting possibilities of anatomical reach with PDT are being made possible. This brief article introduces aspects of interfaces of PDT and nanotechnology but, due to space constraints, makes no attempt to be a comprehensive review.


The concept of combining light and chemicals for therapy is thousands of years old [1,2]. PDT, in its present form, can be dated back to Raab's accidental discovery in 1900 that Paramecia combined with acridine orange and exposed to sunlight resulted in cytotoxicityto the organism [3]. Contemporary PDT was developed by contributions from many investigators, notably of Lipson, Schwartz and Dougherty [4–8] and is approved for several cancer and noncancer applications [2]. PDT involves the light activation of certainchemicals called photosensitizers (PS) to elicit photochemistry that is cytotoxic or deleterious to biologic targets. Inherent to PDT is thedual selectivity imparted by preferential accumulation of the typical photosensitizing agents and by the confinement of light to defined volumes. This photochemistry–based approach is distinct from the more frequently reported laser–activated photothermal approaches where high intensity, often using pulse lasers, is required to generatethermal effects. PDT typically requires low irradiances in the mW⁄ cm2 ranges and does not depend on thermally induced “burning” oftissues but rather on the induced photochemistry. It is thus a “kinder,gentler” approach to phototoxicity allowing biological effects tocontinue after the light trigger has been switched off. Combined withnanotechnology, PDT–Nano provides exceptional opportunities for delivery of therapeutic reagents and newer approaches tocombination treatments grounded in cellular mechanisms [9–13] andother advances in photomedicine [14,15]. In addition to enhancedPS delivery, it allows modification of PS physiochemical properties, development of novel, even resorbable light sources, establishment of personalized predictive dosimetry, and the evolution of novel combinatorial therapeutic approaches.

Citation: Huang HC and Hasan T. The "Nano" World in Photodynamic Therapy. Austin J Nanomed Nanotechnol. 2014;2(3): 1020. ISSN:2381-8956