Photodynamic therapy (PDT), which has been used so far just as a cancer treatment method, was applied in combination with laser radiation and evaluated for biofilm disinfecting method. The PDT is a binary therapy, which combines the application of light and light-activated dyes. It involves the uptake of the photoactive sensitizer into the target cell, and the generation of toxic oxygen species through direct activation of the photosensitizer with light. Phthalocyanines molecules are second-generation photosensitizers with enhanced photophysical and photochemical properties, one of which is chloroaluminum phthalocyanine (ALPc).
In the present study, we investigated the phototoxic potential of the combination of unsulphonated ALPc and laser irradiation towards P.aeruginosa biofilm.
After preincubation of the biofilm with ALPc we used laser irradiation as the light energy source in order to do both - activate the photosensitizer inside the biofilm cells and to enhance the remain phthalocyanine transport into the biofilm matrix by damaging its structure. We studied the synergistic effect of using both methods (PDT and laser irradiation), with different ALPc dilutions and different light energy doses, most effective killing was achieved with ALPc concentration of 20x10-6 mg/ml, however when different light doses were used upon irradiation, no significant change in the biofilm survival was found. Another experiment was conducted with ALPc sulphonated derivative - tetra sulphonated phthalocyanine (ALPcS4) that had shown lower toxicity levels towards the biofilm matrix.
The results showed that phthalocyanines are extremely powerful and aggressive towards bacterial biofilms and the combination of both methods (ALPc and laser) is even more effective. This good efficacy suggests that the proposed technique is a potential disinfecting method towards bacterial biofilms.