## 2 Materials and Methods  
### Photosensitizers and Laser Sources  
For these experiments, the examined photosensizers and their respective concentrations are based on ones that have been clinically explored [11; 26]. The analysed photosensizers with their respective concentrations and mixing procedures are indicated below:  
* Methylene blue (Methylene Blue, Sigma-Aldrich Merck KGaA, Darmstadt, Germany) at 0.05, 0.10 and 10.00 mg/mL (\(w/v\)), respectively, in sterile distilled water.
* Toluidine blue gel (ready to use syringe) (BluLase PDT Gel, Schneider-Dental, Pilsach, Germany). Information regarding the concentration present and the preparation is not provided by the manufacturer.
* Indocyanine green (Emundo(r), A.R.C. laser GmbH, Nurnberg, Germany) at 1.00 mg/mL and 0.10 mg/mL (\(w/v\)) in sterile distilled water.
* For the higher concentration, a single tablet containing 1.00 mg was dissolved in a 1.00 mL volume of sterile distilled water, according to the manufacturer's instructions. For the lower concentration, one tablet of 1.00 mg was dissolved in 10.00 mL of sterile distilled water.
* Curcumin (UltraCur+Pro(r), Weber Medical GmbH, Lauenforde, Germany) at 5.00 mg/mL; according to the manufacturer, this product is water-soluble, which resolves the obstacle of low water solubility [8]. For this purpose, one tablet of 60 mg was dissolved in 12.00 mL of sterile distilled water.
* A methylene blue derivative (ready to use syringe) (Photolase(r) Europe Ltd., Hamburg, Germany). Information concerning the concentration present and the preparation of this solution was not provided by the manufacturer.  
Regarding the laser devices and parameters, the following systems and parameters were used:  
* a 445 nm wavelength device (SiroLaser Blue, Sirona Dental Systems GmbH, Bensheim, Germany), at 150 mW of power output and with an applicator tip of a 6 mm diameter.
* a 635 nm wavelength device (Klas-DX/LX162, Konftec Corporation, New Taipei City, Taiwan), at 150 mW of power output and with an applicator tip of a 6 mm diameter.
* a 660 nm wavelength device (Klas-DX/LX161, Konftec Corporation, New Taipei City, Taiwan), at 150 mW of power output and with an applicator tip of a 6 mm diameter.
* a 808 nm wavelength device (Klas-DX/LX182, Konftec Corporation, New Taipei City, Taiwan), at 150 mW of power output and with an applicator tip of a 6 mm diameter.  
The power output of each laser was calibrated before use with a power meter (Thorlabs PM160T-HP Thorlabs GmbH, Bergkirchen, Germany). The specific power of 150 mW was selected for all lasers, since this was the lowest value attainable by the SiroLaser Blue laser device. Moreover, this value is within the range of 100-200 mW, which is usually applied clinically as well as in in vitro investigations [11].  
To perform the experiments, the following combinations of photosensitizers and laser wavelengths were implemented; these were based on the absorption maxima of each photosensitizer [27] and the laser wavelengths available:  
* Curcumin + 445 nm;* Methylene blue + 660 nm;
* Toluidine blue + 635 nm;
* Toluidine blue + 808 nm (as declared by the manufacturer) [28];
* Indocyanine green + 808 nm;
* Methylene blue derivative + 660 nm;
* Methylene blue derivative + 808 nm (as declared by the manufacturer) [29].  
All the information regarding the photosensitizers and their respective manufacturers, concentrations and laser parameters applied in the experiment are provided in Table 1.