Apoptosis and necrosis assays for mechanisms of in vitro PDT

Cells cultured in 96-well plate after PDT were immediately washed with the HEPES buffer (10 mM HEPES, pH 7.4, 140 mM saline, 2.5 mM CaCl₂), stained with 1:20 Annexin V-FITC (Invitrogen), for phosphastidylserine, and 1 μg/ml of propidium iodide (PI), for DNA, in the HEPES buffer for 15 min at room temperature, and then washed and refilled with in 1× DPBS. The cells were visualized and photographed immediately under a fluorescent microscope.