Measuring fluorescent photodynamic cancer therapy agents using Dynamic Light Scattering

In simple terms, for photodynamic tumor therapy (PDT) to be successful all it takes is a photosensitizer (PS) at the right place, light and sufficient oxygen. It is the action of the PS on oxygen that is key here, as it converts oxygen into singlet oxygen (1O2). 

In contrast to oxygen in the triplet ground state, 1O2 is highly reactive, especially in a biological environment. Mainly proteins, but also lipids and DNA can react with 1O2, which will lead to cell death. Due to its high reactivity, the lifetime of 1Oin a biological environment was found to be shorter than 400 ns [1]. This means that the toxic effect of PDT treatment is limited to the cell, where the 1Ois generated and hence has the ability to be a very specific and targeted treatment.

However, PS are usually small, low molecular weight molecules which have the disadvantage of not showing active accumulation in the target tissue, this can lead to inducing sensitization of other tissues. 

According to the so-called EPR effect, enhanced permeability and retention, which was discovered more than 30 years ago, molecules with a molecular weight above ~40 kDa are preferentially accumulated in solid tumors due to differences in the structure of tumor capillaries versus those in normal tissues and on the limited lymphatic drainage in solid tumors [2,3]. There is common agreement that it takes a carrier system to exploit this effect and improve accumulation in the target tissue. Nanoparticle-based formulations are a promising option.

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