One of the significant advantages of the PDT

One of the significant advantages of the PDT method is the fact that the photochemical reaction is accompanied by the fluorescence of both the photosensitizer and the singlet oxygen produced as a result of the reaction. The fluorescence analysis allows to perform in situ diagnostics, i.e., directly during photodynamic therapy; additionally, this offers opportunities for early cancer detection. Primary imaging of the photochemical reaction proceeding is possible from the analysis of the singlet oxygen photoluminescence intensity and its spatial distribution. However, its fluorescence spectrum is located in the near-infrared range with the maximum at a wavelength of 1270 nm [5,6]. The systems previously developed for imaging the photoluminescence of oxygen used near-infrared sensitive cameras based on InGaAs and spectrally selective filters [5,6]. However, these systems are rather expensive and are used mainly in fundamental studies. In XMU-MP-1 to the luminescence spectrum of singlet oxygen, the spectral features of Photoditazin\'s fluorescence lie in the visible region where photosensitive Si-based CCD and CMOS arrays can be successfully used for imaging; these are considerably cheaper than the InGaAs-based devices. The studies carried out using a two-channel imaging system for the visible and the infrared regions [5] have revealed a correlation between the photoluminescence intensities of singlet oxygen and of the photosensitizer, which allows performing photoluminescence diagnostics of the photosensitizer in the visible area. This system includes a monochrome silicon camera, a diode illuminator, and software for imaging and analyzing the spatial distribution of Photoditazin\'s photoluminescence; it has already been devised [7,8], has successfully passed clinical trials as a means of diagnosing malignant tumors presenting externally, and is authorized for use in the Russian Federation [9]. Even though the PDT method was initially developed to treat malignant tumors presenting externally, recently it has found application in other areas of medicine, e.g., in dentistry, as an anti-aging therapy in aesthetic medicine, etc. The type of PDT used in dentistry is antibacterial photodynamic therapy (APT) that allows to combat pathogenic bacterial flora in the oral cavity. Lately, a number of studies reported having successfully used APT for treating inflammatory periodontal diseases [10], and for photoactivated decontamination in endodontics and periodontology [11]. However, no data could be found in literature on using the main advantage of photodynamics, i.e., the fluorescent diagnostics for control during APT, since the currently existing imaging systems for PDT [5–7] cannot be used in dentistry due to their large sizes.
The optical properties of Photoditazin Photoditazin was chosen as a photosensitizer for the system of fluorescent diagnostics during APT in dentistry that we have developed on the strength of the compound\'s overall properties. Its optical characteristics, and, in particular its optical absorption spectrum, are well-known. Photoditazin has an absorption line at a wavelength of 653 nm, a number of weak features in the 500- and 600-nm regions, and a strong absorption line with a maximum at 403 nm. The fluorescence spectra of Photoditazin when excited by radiation of various wavelengths were measured and discussed in detail earlier in Ref. [12]. The results of this study are shown in Fig. 1 as the absorption spectrum of a Photoditazin solution and the spectra of its photoluminescence when excited by light at 650- and 405-nm wavelengths. It can be seen from the absorption spectra shown in Fig. 1 that the absorption coefficient at the 403-nm wavelength is at least 5 times higher than that at the 653-nm wavelength. This could result in more efficient excitation of the photosensitizer by shortwave radiation; however, radiation in the 400-nm region is virtually never used in oncology due to its low penetration depth.