An equal volume of either 20 μM methylene blue (S+) or PBS (S-) was added to S. aureus α-haemolysin and samples were either exposed to laser light doses of 1.93 J/cm2, 3.86 J/cm2 and 9.65 J/cm2 (L+) or kept in the dark (L). After irradiation/dark incubation, samples were serially diluted and an equal volume of 4% rabbit erythrocytes was added. Following incubation in the dark at 37°C for one hour, the haemolytic titre was recorded. The haemolytic titre is the highest dilution giving rise to haemolysis. Experiments were performed twice in triplicate and a representative experiment is shown.