Skip to main content
. 2016 Oct 23;6(13):2458–2487. doi: 10.7150/thno.16183

Figure 5.

Figure 5

A. Three different ways to excite PSs for PDT using NIR radiation. Method 1 relies on direct two-photon excitation of the PS that, once excited, can undergo type I or type II photodynamic processes involving reactive molecular species and singlet oxygen. Methods 2 and 3 involve a nanotransducer. In the second scenario, the nanotransducer absorbs the NIR radiation through two-photon processes and transfers part of the energy to excite the PS either through a radiative or a non-radiative mechanism. The nanotransducers involved may be either organic chromophores that have a high TP-absorption cross-section, or optically active nanoparticulate entities such as Gold Nanorods (GNR), quantum dots (QD) or carbon quantum dots (CQD). Method 3 illustrates the use of up-converting nanoparticles that successively absorb two NIR photons through a metastable energy state and transfer part of this energy to the PS. B. This figure illustrates three ways to activate the PS using ionizing radiation such as X-rays. Because X-rays are used for radiation therapy, each of these activation routes could be combined with radiotherapy to enhance the overall efficiency of the tumor treatment. Method 1 involves direct excitation of the PS using ionizing radiation such as X-rays. In this case, the PSs are called radiosensitizers. Method 2 involves a local generation of light using the broad spectrum Cerenkov emission process, when a charged particle travels faster than light in a given matter and emits Cerenkov radiation. This emission presents a strong overlap with the absorption spectra of many PS and can subsequently be used to excite them. Method 3 shows the use of nanoscintillators that act as nanotransducers to locally convert ionizing radiation into visible light to excite PSs. The transfer from the nanoscintillator to the PS can either be radiative or non-radiative (FRET), and leads to activation of the PS. Abbreviations: NIR: Near Infrared, FL: Fluorescence, PH: Phosphorescence, ISC: Inter-System Crossing, MS: Metastable State, NRD: Non Radiative Decay, NER: Non-Elastic Relaxation and T: Thermalisation.