Antimicrobial Photodynamic Therapy (aPDT)

Chemical / physical background

The chemical/physical process is carried out in 3 steps:

Step 1: Staining of the microorganisms

  • This is a diffusion-determining step,
  • with migration and attachment of the dye molecules,
  • on the wall of the microorganisms. (charge attraction)

Step 2: Exposure and activation of the photosensitiser

  • This is an energy-controlled step,
  • determined by physical-optical properties,
  • with excitation of the sensitizer molecules,
  • from singlet state to triplet state.

Step 3: Oxygen radical formation and destruction of the microorganisms

  • Exposure and activation of the photosensitiser leads to the build-up of singlet-oxygen and
  • An oxidative destruction of membrane lipids and enzymes.

The decisive factor is a question of which biological target molecules are reached by the radical reactions:

  • In principle, all molecules are affected by singlet-oxygen.


  • Unsaturated fatty acids in the bacterial membranes are particularly susceptible to damage.

The body's own healthy cells have cellular defences against the attack of radicals - so-called catalase or superoxide dismutase.

It is thus specifically the pathogenic bacteria that are destroyed by antimicrobial photodynamic therapy. Healthy cells are at no risk!

Further information about "Photodynamic Therapy"?

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