An illumination system for screening the light and oxygen dependence in photodynamic therapy

Photodynamic therapy (PDT) involves three interdependent parameters, including photosensitizer (PS), light, and oxygen (O2). Obtaining an appropriate PDT dosimetry remains a highly challenging and labor-intensive work. In this paper, we described the design and assembly of a low-cost dual-wavelength illumination system for the in vitro PDT experimentation. A light-emitting diode (LED) array was designed to irradiate cells at 625 nm and 408 nm, respectively. An optical filtering layer with a printed pattern of five gradient pixel grey values was inserted between the LED panel and 96-well plate to achieve spatial light intensity control. The device was further integrated with an air-permeable aerogel monolith apparatus allowing for gas diffusion and delivery. The system performance was confirmed by testing the efficacy of 5-aminolevulinic acid (5-ALA)-assisted PDT on human breast cancer cell MCF-7. Cell viability results suggested that the high-energy violet light irradiation at 408 nm resulted in a more pronounced 5-ALA phototoxic effect at a much lower light dose. The gradient increase of the light dose for either red or violet light was followed by decreased cell viability. Regardless of irradiation conditions, the hypoxic environment significantly reduced the efficacy of 5-ALA-PDT. In conclusion, the illumination system can be used for reproducible and convenient in vitro PDT testing on the presentation of appropriate dosimetry of different light doses and wavelengths.