Singlet Oxygen Production by OLED Irradiation in Photodynamic Therapy Assay Using Metallic Nanoparticles

Nanotechnology is considered one of the key technologies for the future. One of the most strategic subjects of the century is the research on nanostructured materials for the development of new electronic devices towards to a more advanced society. Nanostructured materials can present both physics and chemical properties completely different from either solids or microscopic materials. Therefore, the capability of manipulation and control of such materials represents an actual challenge to the scientific and technological community. Furthermore, in the last few years, phototherapy have been calling attention due to recent development in scientific research that involves interactions of an incident photon over a chromophore present in a biological environment. Here stands out the photodynamic therapy (PDT) mechanism as a growing field of application of phototherapies with high relevance. Noble metal nanoparticles (NPs), such as AuNPs and AgNPs, plays an important role in the future of photomedicine experiments based on PDT, due to the concentration of light caused by the Localized Surface Plasmon Resonance (LSPR), and low citotoxicity. In particular, some metal oxide NPs synthesized by pulsed laser ablation (PLA) in water, can also produce via <i>water splitting</i> H₂ and O₂gas phase that could enhance the free oxygen content. The PDT mechanism is non-invasive treatment for surface lesions, such as human skin, which uses visible light to excite a photosensitizer (PS), which is a photosensitive drug. The PS molecule in its ground state (S0) can absorb a photon and pass to its excited state (Sn) and, through vibrational and internal conversion processes, pass to the singlet excited state (S1). Furthermore, the PS molecule can go from the S1 state to the triplet excited state, via intersystem crossing. This triplet state has at least two reaction mechanisms known as type I and type II. Both mechanisms generate ROS and the production of singlet oxygen (type II mechanism) is the most relevant in treatments involving photodynamic therapy. In the absence of the irradiation light, the photosensitizer is non-toxic. The oxygen produced is reactive and can destroy nearby cells such as bacteria, fungi, and tumor cells. In a PDT treatment, the incident light must be within the therapeutic window, approximately between 600 nm and 1000 nm, which allows penetration of human tissue into deeper regions, between 5 mm and 20 mm, avoiding invasive treatments. In this work, we investigate the production of singlet oxygen using a PDT assay platform based on organic light-emitting diode (OLEDs), as light source with emission in the therapeutic windows, seeking applications in biological environments. The PDT assay consists of monitoring, as a function of time, the absorption spectra of a solution (phosphate buffer) with a photosensitizer, NPs, and a probe molecule. With the incidence of light in the range of the therapeutic window, PS can produce singlet oxygen modifying the probe while NPs can increase this effect. The influence of <i>water splitting </i>mechanism in the singlet oxygen consumed by the probe molecule is also investigated. Thus, it’s possible to indirectly access information on the amount of singlet oxygen produced by OLED irradiation as well as on the efficiency of the PDT assay. Here we investigate the production of singlet oxygen dependence on: (i) the concentrations of different PS used; (ii) concentration and size of AuNPs and AgNPs and other metal-oxide NPs; (iii) the concentration of probe molecule; and (iv) the emitted light (wavelength and light power) of the OLEDs with different emissions.