## 3 Results and Discussion  
The physicochemical properties of RB and Ce6 were evaluated. Firstly, the stability under sonication (1 MHz, 3 W) of the sensitizers was assessed, and no changes were noticed in the UV-Vis spectra. Therefore, it was concluded that the studied sensitizers are stable under ultrasounds used in the measurements. Next, the reactive oxygen species (ROS) production by ultrasound-excited sensitizers was estimated via the decomposition process of DPBF and TTF by monitoring the disappearing characteristic absorption bands, at 417 nm (Figure 2) and 317 nm, respectively. DPBF and TTF are well-known ROS chemical traps for singlet oxygen and other ROS [24; 25]. To avoid overlapping the trap and sensitizer bands, the RB with the DPBF and the Ce6 with the TTF were mixed. There were also performed studies of singlet oxygen trap stability under sonication. It was concluded that TTF reveals high stability, whereas DPBF, as a very reactive molecule, is less stable (Table 1). \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **DPBF** & **RB** & \
\begin{tabular}{c} **DPBF in the** \\ **Presence of RB** \\ \end{tabular} & **TTF** & **Ce6** &
\begin{tabular}{c} **TTF in the** \\ **Presence of Ce6** \\ \end{tabular} \\ \hline \(k\) (min\({}^{-1}\)) & 0.021 & 0.039 & 0.036 & 0.008 & 0.009 & 0.007 \\ t\({}_{0.5}\) (min) & 33.2 & 18.0 & 19.3 & 88.9 & 74.6 & 97.6 \\ In(A) & \(-\)0.0035 & 0.076 & \(-\)0.0073 & 0.0046 & 0.0094 & 0.0035 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Kinetic parameters of DPBF and TTF decomposition upon sonication in DMF solution alone and in the presence of Ce6 and RB. The stability parameters of RB and Ce6 upon sonication were also shown. Figure 2: Spectra changes in the RB and DPBF mixture in DMF under sonication with 1 MHz, 3 W and duty cycle 40% during the experiment. Due to the complexity of the interaction between the sonosensitizer and the surrounding molecules of the sample including the molecular oxygen, solvent, and sonosensitizer itself [21; 26], the calculation of the quantum yields of formation singlet oxygen was abandoned. However, the kinetic parameters of the decomposition of DPBF and TTF in the presence of sensisitizer and ultrasounds were calculated (Table 1). According to the studies reported before, the reaction between singlet oxygen and traps follows first-order kinetics [27] (Figure 3). The first-order kinetic equation (1) was applied for the calculations. \[\ln[A_{0}]=kt+\ln[A] \tag{1}\]  
As shown in Table 1 the improvement in trap decomposition induced by ultrasounds in the presence of RB compared to DPBF alone was noticed. It was concluded that the generated singlet oxygen by RB ultrasound excitation accelerates DPBF decomposition by about 1.8-fold. It enables us to consider RB as an efficient singlet oxygen generator. Interestingly, under sonication of the mixture of Ce6 and TTF solution, the presence of SS did not significantly improve the decomposition of the singlet oxygen chemical quencher (TTF) (Table 1). This observation enables us to conclude that Ce6 is a much weaker SS in comparison to RB (Figure 3). The potential interaction between RB and Ce6 in the solution was analyzed by [PERSON]'s method. As shown in Figure 4, interactions were excluded and it was confirmed that each sensitizer existed as a separate molecule in the solution. Figure 3: Effect of mixtures RB + DPBF and Ce6 + TTF sonication with 1 MHz, 3 W (40% duty cycle) vs. time: (**A**) % DPBF decomposed in the presence of RB; (**B**) kinetic curve of DPBF decomposition by RB (red); (**C**) % TTF decomposed in the presence of Ce6; (**D**) kinetic curve of TTF decomposition by Ce6 (pink). The synergy study between PDT and SDT is currently poorly developed [21]. Several experiments evaluating synergism against cancer have emerged in recent years, but in the case of microorganisms, studies are deficient [28; 29; 30]. [PERSON] et al.