A method to quantify the potency of photosensitizers that modify cell membranes

The numerical assessment of sensitizing potency of different species of photosensitizer molecules has historically been impracticable because of the difficulty of measuring all of the factors that must be taken into account. This paper describes a new method for quantifying relative sensitizer potency that obviates most of the past difficulties. The physical data needed to assess photosensitizing potency are the absorption spectrum of a sample of medium containing sensitizer, the illumination spectrum impinging on the preparation, the duration of illumination, and the amount of light-induced modification. The measurement of these quantities is relatively straightforward, but it is easy to overlook a number of artifacts that can distort the values for potency. Avoiding error requires careful attention to the optical properties of the system, particularly in the light path through the medium containing sensitizer.